MELAS Syndrome
MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes) is a maternally inherited multisystem mitochondrial disease caused most often by the m.3243A>G point mutation in the MT-TL1 gene, which encodes the mitochondrial tRNA-Leu(UUR). The mutation impairs mitochondrial tRNA aminoacylation and translation, producing a respiratory chain (oxidative phosphorylation) deficiency that manifests above a heteroplasmy threshold. Energy failure in brain, muscle, and small blood vessels drives the cardinal stroke-like episodes (often in non-vascular territories), lactic acidosis, seizures, myopathy, sensorineural hearing loss, and diabetes mellitus. Other MT-TL1 variants and variants in additional mitochondrial genes (notably MT-ND5) cause a minority of cases. Two points shape how the entry should be read. First, the mechanism of the stroke-like episode itself is genuinely unsettled: the classical ischemic "mitochondrial angiopathy" account and the non-ischemic neuronal hyperexcitability account make different predictions and imply different treatments, and the pathograph here wires both, with the causal edges tagged by hypothesis group. Second, MELAS is a clinical syndrome carved out of a much larger m.3243A>G carrier population: only about a tenth of carriers in a systematically phenotyped cohort met classical MELAS criteria, so organ-specific frequencies drawn from carrier cohorts and from MELAS cohorts are not interchangeable.
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Classifications
Harrison's Part
Mechanistic Nosology
ICIMD (Inherited Metabolic Disorders)
Mappings
MONDO
MIDD is the other major clinical syndrome produced by m.3243A>G, and the two are repeatedly contrasted in this entry - MIDD accounts for roughly 30% of carriers in a systematically phenotyped cohort against 10% for classical MELAS, and the MELAS-versus-MIDD divergence is what the genotype-phenotype gap turns on. The predicate is deliberately relatedMatch, not narrowMatch: MONDO does not place MIDD under MELAS, subsuming it instead under diabetes mellitus and mitochondrial oxidative phosphorylation disorder, so the two are distinct classes sharing a causal variant rather than a parent and a subtype. relatedMatch also correctly leaves MIDD in the curation queue as a disease still owed its own entry.
NCIT
NCIT:C84885
MELAS Syndrome
NCI Thesaurus carries MELAS Syndrome as a disease concept with the same scope as this entry.
ICD-10-CM
ICD10CM:E88.41
MELAS syndrome
ICD-10-CM carries a dedicated code for MELAS syndrome under E88.4 (mitochondrial metabolism disorders), with the same name and scope as this entry.
ICD-11 Foundation
icd11f:1369657886
Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes
The ICD-11 Foundation entity spells out the acronym this entry is named for and denotes the same syndrome. Note that ICD-11 additionally carries two separate cardiomyopathy-due-to-MELAS entities, which are manifestation codes rather than alternative names for the syndrome and are therefore not mapped here.
NCIT
NCIT:C84885
MELAS Syndrome
NCI Thesaurus carries MELAS Syndrome as a disease concept with the same scope as this entry.
Inheritance
1
Mitochondrial inheritance
HP:0001427
MELAS is maternally inherited through the mitochondrial genome. Clinical expression depends on the heteroplasmy level of mutant mtDNA, with a threshold effect.
Show evidence (5 references)
"Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most frequent maternally inherited mitochondrial disorders."
Establishes MELAS as a maternally inherited mitochondrial disorder.
"Southern blot analysis confirmed that the mutant DNA always coexists with the wild-type DNA"
Documents heteroplasmy (coexistence of mutant and wild-type mtDNA), the basis for the threshold effect in MELAS.
"A man with a mtDNA pathogenic variant cannot transmit the variant to any of his offspring."
GeneReviews genetic counseling: paternal mtDNA is not transmitted, so an affected father carries no recurrence risk for his children. This is the asymmetry that distinguishes mitochondrial from autosomal inheritance.
+ 2 more references
Subtypes
10
MT-TL1 tRNA-Leu(UUR), including m.3243A>G
MONDO:0800032
The majority form, caused by pathogenic variants in MT-TL1 (mitochondrial tRNA-Leu(UUR)). The m.3243A>G transition accounts for roughly 80% of MELAS. Non-3243 MT-TL1 variants, most notably m.3271T>C, cause a minority of cases and impair tRNA-Leu(UUR) function through the same loss of the wobble taurine modification.
Show evidence (2 references)
"The m.3243A>G pathogenic variant in the mitochondrial gene MT-TL1 is present in approximately 80% of individuals with MELAS."
Establishes m.3243A>G as the majority genotype defining this subtype.
"mt tRNA(Leu(UUR)) with either the MELAS 3243 or 3271 mutation"
Confirms that the 3271 variant shares the wobble-modification defect of the common 3243 variant.
MT-TQ tRNA-Gln
MONDO:0800033
MELAS-spectrum disease attributed to a heteroplasmic m.4332G>A variant in MT-TQ (mitochondrial tRNA-Gln). The reported presentation combined deafness, a stroke-like episode, leukoencephalopathy and basal ganglia calcification, with a late onset and neuroradiological pattern the authors judged atypical for MELAS.
Show evidence (3 references)
"A heteroplasmic G to A transition at nucleotide 4332 in the tRNA glutamine gene was identified in the patient's muscle mitochondrial DNA."
Identifies the MT-TQ variant reported in a patient given a MELAS-spectrum diagnosis.
"The pathogenicity of the mutation was shown in single muscle fibers by the correlation between high mutation load and cytochrome c oxidase defect."
Single-fibre correlation of mutation load with a respiratory-chain defect is the pathogenicity argument for this variant, and it is the standard heteroplasmy-threshold argument rather than a zygosity claim.
"The authors studied a 47-year-old patient who presented with an association of deafness, acute cerebral stroke-like episode, leukoencephalopathy, and extensive basal ganglia calcifications. Late onset and neuroradiologic findings were atypical for MELAS syndrome"
Supports the reported presentation and the authors' judgement that onset and imaging were atypical for MELAS.
MT-TH tRNA-His
MONDO:0800034
MELAS-spectrum disease caused by variants in MT-TH (mitochondrial tRNA-His). The reported family carried m.12146A>G and showed varying degrees of lactic acidosis and stroke-like episodes; transmitochondrial cybrids established that the tRNA-His variant, rather than the nuclear background, produced the respiratory-chain enzyme deficiency.
Show evidence (2 references)
"We report a new mutation in m.12146 A>G in the mt-tRNA(His) in a family with a remarkable clinical history having different degrees of lactic acidosis and stroke-like episodes."
Ties an MT-TH variant to the lactic acidosis and stroke-like episodes that define MELAS.
"Transmitochondrial cybrid analysis proved that this tRNA(His) mutation causes the enzymatic deficiency."
Cybrid transfer separates the mtDNA variant's effect from the patient's nuclear background.
MT-TK tRNA-Lys
MONDO:0800035
MELAS-spectrum disease attributed to m.8296A>G in MT-TK (mitochondrial tRNA-Lys). The reported patient had optic atrophy, cardiomyopathy and bilateral striatal necrosis before stroke-like episodes appeared, with ragged-red fibres on muscle biopsy. The same variant had previously been reported in patients with diabetes mellitus or with myoclonus epilepsy with ragged-red fibres rather than MELAS, so this genotype is not MELAS-specific.
Show evidence (4 references)
"Skeletal muscle total mitochondrial DNA analysis identified a heteroplasmic A to G point mutation in the tRNA(Lys) gene at position 8296."
Identifies the MT-TK variant in a patient diagnosed with MELAS.
"We conclude that the 8296 mutation is likely to be pathogenic"
The authors' own pathogenicity assessment for this MT-TK variant.
"We report on a unique patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) presenting optic atrophy, cardiomyopathy, and bilateral striatal necrosis before stoke-like episodes became apparent."
Supports the reported presentation preceding the stroke-like episodes.
+ 1 more reference
MT-TC tRNA-Cys
MONDO:0800036
MELAS-spectrum disease attributed to m.5783G>A in MT-TC (mitochondrial tRNA-Cys). In the reported case genetic analysis of blood lymphocyte DNA was negative and the variant was found only on sequencing mtDNA from urinary sediment, so a negative blood result did not exclude the diagnosis.
Show evidence (3 references)
"the patient was eventually diagnosed with MELAS with the mtDNA 5783G>A mutation in the MT-TC gene with a urinary sediment genetic test"
Names MT-TC as the gene carrying the variant in a patient diagnosed with MELAS.
"This case report expands the genetic repertoire associated with MELAS syndrome"
The authors present this genotype as an addition to the MELAS gene spectrum rather than an established cause.
"Although genetic analysis of blood lymphocyte DNA was negative, brain imaging, including magnetic resonance imaging, magnetic resonance spectroscopy, and clinical and laboratory findings, were all suggestive of MELAS."
Supports the negative blood-lymphocyte result that preceded the urinary-sediment diagnosis.
MT-TS1 tRNA-Ser(UCN)
MONDO:0800037
MELAS-spectrum disease caused by variants in MT-TS1 (mitochondrial tRNA-Ser(UCN)). The reported family carried a heteroplasmic m.7512T>C variant disrupting a conserved acceptor-stem base pair and presented as a MERRF/MELAS overlap syndrome rather than as classical MELAS.
Show evidence (2 references)
"We found a new point mutation in the mitochondrial tRNA(Ser(UCN)) gene in a family with MERRF/MELAS overlap syndrome by screening for heteroplasmy"
Links MT-TS1 to a MELAS-overlap phenotype rather than to MELAS alone.
"revealed a heteroplasmic mutation at nt 7512 in the tRNA(Ser(UCN)) gene"
Gives the specific heteroplasmic MT-TS1 variant behind this subtype.
MT-TS2 tRNA-Ser(AGY)
MONDO:0800041
MELAS-spectrum disease caused by variants in MT-TS2 (mitochondrial tRNA-Ser(AGY)). A m.12244G>A variant has been reported with a classical MELAS phenotype together with functional evidence of impaired mitochondrial translation and oxidative phosphorylation. Across the reported MT-TS2 variants the phenotype is variable, spanning encephalopathy, myopathy, deafness, diabetes and retinopathy.
Show evidence (2 references)
"We identified a rare m.12244G > A variant in the tRNASer(AGY) gene associated with classical MELAS phenotype."
Ties an MT-TS2 variant to a classical MELAS presentation.
"Literature review showed that MT-TS2 variants are associated with variable phenotypes including encephalopathy, myopathy, deafness, diabetes, and retinopathy."
Records that MT-TS2 genotypes are not MELAS-specific, which is why this row is a spectrum rather than a distinct disease.
MT-ND1 complex I subunit
MONDO:0800038
MELAS-spectrum disease caused by variants in the complex I subunit gene MT-ND1. This genotype class attacks complex I directly rather than through a mitochondrial translation defect. Two novel missense variants, m.3959G>A and m.3995A>G, were reported in probands with MELAS features and reduced complex I activity.
Show evidence (3 references)
"Sequencing of the mitochondrial DNA revealed two novel MT-ND1 gene missense mutations, m.3959G>A and m.3995A>G, which are highly conserved among species."
Names the MT-ND1 variants reported in probands with MELAS features.
"A respiratory chain function study showed decreased activity of mitochondrial respiratory chain complex I in both probands."
Confirms that the biochemical lesion in this genotype class is at complex I.
"whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
Independent cohort confirmation that MT-ND1 is among the complex I subunit genes reported in MELAS.
MT-ND5 complex I subunit
MONDO:0800039
MELAS-spectrum disease caused by variants in the complex I subunit gene MT-ND5, the commonest non-MT-TL1 cause named by GeneReviews. In a MELAS/Leigh overlap cohort, m.13513G>A was the commonest variant among the thirteen patients carrying complex I subunit gene variants.
Show evidence (2 references)
"Pathogenic variants in MT-TL1 or other mtDNA genes, particularly MT-ND5, can also cause this disorder."
GeneReviews names MT-ND5 as the leading non-MT-TL1 cause of MELAS.
"Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
Identifies MT-ND5 m.13513G>A as the leading variant in MELAS/Leigh overlap.
MT-ND6 complex I subunit
MONDO:0800040
MELAS-spectrum disease caused by variants in the complex I subunit gene MT-ND6. m.14453G>A has been reported in MELAS, including a late-onset presentation initially taken for acute encephalitis.
Show evidence (2 references)
"broadens the phenotypic spectrum of MELAS syndrome associated with ND6 gene mutation"
The authors place this case within the MELAS phenotypic spectrum attributed to MT-ND6.
"whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
Independent cohort confirmation that MT-ND6 is among the complex I subunit genes reported in MELAS.
Mechanistic Hypotheses
3Canonical wobble-modification and mitochondrial translation-failure model
Evidence balance
2 support
The molecular half of MELAS pathogenesis is not in dispute. Pathogenic MT-TL1 variants strip the taurine-containing modification from the wobble uridine of tRNA-Leu(UUR), degrading codon-anticodon pairing (UUG more than UUA) and impairing synthesis of the mtDNA-encoded respiratory-chain subunits. Complex I is the most affected, and clinical expression requires mutant heteroplasmy above a tissue threshold. Everything downstream of the resulting energy failure - specifically, how it produces a discrete stroke-like episode - is where the competing accounts below begin.
Show evidence (2 references)
"Crucial molecular mechanism includes the lack of taurine modification at the wobble uridine of mutant transfer RNAsLeu(UUR) resulting in defective translation of cognate codons due to a defect in codon-anticodon interaction."
States the molecular mechanism that both competing stroke-like-episode hypotheses take as their shared starting point.
"Multi-system disease risk and penetrance of diabetes, deafness and heart failure greatly increased with m.3243A>G level ≥ 10%."
Population-scale support for the heteroplasmy-threshold component of the canonical model.
Ischemic vascular ("mitochondrial angiopathy") model of stroke-like episodes
Evidence balance
2 support
1 refute
The older account holds that stroke-like episodes are ischemic events caused by mitochondrial angiopathy: proliferation of mitochondria in the smooth muscle and endothelium of cerebral small vessels, compounded by reduced nitric oxide availability, impairs microvascular perfusion. The model is what motivates L-arginine and L-citrulline therapy and the newer soluble guanylate cyclase stimulators, and the muscle-biopsy finding of strongly SDH-reactive vessels is real. Its difficulty is that acute lesions show focal hyperperfusion and elevated apparent diffusion coefficient rather than the hypoperfusion and restricted diffusion of ischemia, and they cross vascular territories.
Pathograph links
Cellular energy failure and lactic acidosis
->
Mitochondrial angiopathy and NO deficiency
Energy failure in cerebral small-vessel endothelium and smooth muscle drives mitochondrial angiopathy and impaired nitric oxide availability.
Mitochondrial angiopathy and NO deficiency
->
Stroke-like episodes
Mitochondrial angiopathy and NO deficiency, together with neuronal energy failure, converge to produce stroke-like episodes that do not respect classic vascular territories.
Mitochondrial angiopathy and NO deficiency
->
Increased cerebral capillary permeability and vasogenic edema
Mitochondrial dysfunction in capillary endothelium leaves the cortical microvasculature primed to leak, which is the substrate on which epileptic activity produces vasogenic edema.
Show evidence (3 references)
"The pathogenesis of stroke-like episodes in mitochondrial encephalopathy, myopathy, lactic acidosis and stroke-like episodes (MELAS) is not fully understood although two main theories have been proposed; ischemic vascular hypothesis caused by "mitochondrial angiopathy" and generalized cytopathic..."
Names the ischemic vascular hypothesis as one of the two standing accounts and records that neither is settled.
"Energy deficiency can also stimulate mitochondrial proliferation in the smooth muscle and endothelial cells of small blood vessels leading to angiopathy and impaired blood perfusion in the microvasculature of several organs."
States the angiopathy mechanism on which the vascular model rests.
"In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
Focal hyperperfusion over the acute lesion is the opposite of what a primarily ischemic mechanism predicts.
Non-ischemic neuronal-hyperexcitability model of stroke-like episodes
Evidence balance
3 support
The competing account treats the stroke-like episode as a non-ischemic neurovascular event. Focal neuronal hyperexcitability develops where energy supply cannot meet demand; the resulting epileptic activity depolarizes adjacent neurons and propagates the lesion into contiguous cortex, while increased capillary permeability - on a background of mitochondrial angiopathy - produces the characteristic cortical vasogenic edema and, ultimately, laminar necrosis. It accounts for the EEG discharges, hyperperfusion, elevated ADC, contiguous spread, and posterior predilection that the vascular model does not, and it implies that aggressive seizure control, rather than vasodilation, is the therapeutic priority. Note that the two models are not mutually exclusive: this one still requires the capillary angiopathy of the vascular model as its substrate.
Pathograph links
Cellular energy failure and lactic acidosis
->
Neuronal hyperexcitability and propagating epileptic activity
In the non-ischemic model, a mismatch between the energy demanded by an active cortical neuronal population and the ATP that a defective respiratory chain can supply renders those neurons hyperexcitable. What converts this chronic vulnerability into a discrete episode is not known.
Mitochondrial angiopathy and NO deficiency
->
Increased cerebral capillary permeability and vasogenic edema
Mitochondrial dysfunction in capillary endothelium leaves the cortical microvasculature primed to leak, which is the substrate on which epileptic activity produces vasogenic edema.
Neuronal hyperexcitability and propagating epileptic activity
->
Increased cerebral capillary permeability and vasogenic edema
Prolonged epileptic activity increases capillary permeability in cortex whose microvasculature is already compromised by mitochondrial angiopathy.
Neuronal hyperexcitability and propagating epileptic activity
->
Cortical laminar necrosis and progressive lesion spread
Depolarization of adjacent neurons propagates the epileptic focus into surrounding cortex, and the most vulnerable cortical layers are lost.
Neuronal hyperexcitability and propagating epileptic activity
->
Seizures
Lowering neuronal seizure thresholds contributes to the overall epileptic phenotype, including focal and generalized events.
Neuronal hyperexcitability and propagating epileptic activity
->
Focal-onset seizures
Localized cortical hyperexcitability underlies focal epileptic activity during stroke-like episodes; this specifies the focal presentation within the broader seizure phenotype.
Cortical laminar necrosis and progressive lesion spread
->
Stroke-like episodes
The evolving cortical lesion is what produces the acute focal deficit and its imaging correlate.
Show evidence (3 references)
"Based on the clinical observations, we speculate that stroke-like episodes appear to be non-ischemic neurovascular events; once neuronal hyperexcitability developed in a localized brain region as a result from either mitochondrial dysfunction in the capillary endothelial cells, or in neurons or..."
The primary statement of the non-ischemic neurovascular model, including its initiating step and propagation mechanism.
"The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
Shows the therapeutic consequence that follows from adopting the hyperexcitability model over the vascular one.
"Although the precise pathophysiology is still unclear, one possible hypothesis for these episodes is a neuronal hyperexcitability theory, including neuron-astrocyte uncoupling."
A recent review presenting hyperexcitability as a leading but still unproven hypothesis, and adding neuron-astrocyte uncoupling as a proposed variant.
Discussions and Knowledge Gaps
9Is the stroke-like episode an ischemic event caused by mitochondrial angiopathy, or a non-ischemic neurovascular event initiated by neuronal hyperexcitability?
Attached to
pathophysiology#Mitochondrial angiopathy and NO deficiency
pathophysiology#Neuronal hyperexcitability and propagating epileptic activity
mechanistic_hypotheses#ischemic_vascular_angiopathy
mechanistic_hypotheses#neuronal_hyperexcitability
datasets#geo:GSE127478
datasets#geo:GSE154825
datasets#geo:GSE165953
datasets#geo:GSE202747
This is the central unresolved question in MELAS and it is not academic: the two models point at different treatments. The vascular model motivates nitric-oxide repletion (arginine, citrulline, soluble guanylate cyclase stimulators); the hyperexcitability model makes aggressive seizure control the priority. The imaging and electrophysiology favour the non-ischemic account - lesions cross vascular territories, ADC is typically elevated, perfusion is focally increased rather than decreased, and epileptiform discharges are recorded over the acute lesion. But the vascular findings are not artefacts either: strongly SDH-reactive vessels are present on muscle biopsy in about 70% of patients, plasma arginine, NO and cGMP are reduced, and diffusion restriction does occur inside some lesions. One proposed synthesis is that capillary angiopathy supplies a leaky substrate on which epileptic activity produces cortical vasogenic edema. This remains a hypothesis; neither the necessity of both components nor their causal order is established.
Public data now let both arms be interrogated in isogenic human cells, which is new. On the vascular side GSE127478 shows m.3243A>G endothelium is cell-autonomously dysfunctional, pro-inflammatory, and pro-atherogenic. On the neuronal side GSE154825 records network-level electrical activity alongside transcriptome and finds reduced presynaptic gene expression plus non-cell-autonomous changes in co-cultured astrocytes, which is the neuron-astrocyte uncoupling variant made measurable; GSE165953 supplies a heteroplasmy-scaled glutamate mechanism confirmed in MELAS post-mortem brain. One dataset cuts against the vascular arm: in GSE202747 the choroidal vasculature of a MELAS eye was near-homoplasmic wild-type while the neural lineages carried a high mutant fraction. That is one donor and one tissue, and retina is not cortex, so it is a lead rather than a refutation - but a vascular hypothesis does need the vessels to carry the mutation.
Show evidence (2 references)
"The pathogenesis of stroke-like episodes in mitochondrial encephalopathy, myopathy, lactic acidosis and stroke-like episodes (MELAS) is not fully understood although two main theories have been proposed; ischemic vascular hypothesis caused by "mitochondrial angiopathy" and generalized cytopathic..."
States the controversy in the terms in which the field frames it.
"Although the precise pathophysiology is still unclear, one possible hypothesis for these episodes is a neuronal hyperexcitability theory, including neuron-astrocyte uncoupling."
Confirms that as of recent review the mechanism remains unsettled.
What converts the chronic, constant energy deficit of MELAS into a discrete stroke-like episode at a particular time and a particular cortical site?
Attached to
The heteroplasmy load and the respiratory-chain defect are present continuously, yet stroke-like episodes are paroxysmal, recur at unpredictable intervals, and favour posterior cortex. Nothing in the current models explains the timing or the site selection. The 2002 study that established the hyperexcitability mechanism said so explicitly and the gap has not closed since. Until it does, prophylaxis cannot be targeted at the trigger, only at the substrate, and trials are forced to use episode counts over long windows as their endpoint.
A survey of public repositories found no dataset that addresses the timing question, and that absence is structural rather than an oversight: every public MELAS dataset is a cross-sectional snapshot of cells or post-mortem tissue, and an episode is a transition in a living cortex. The closest available is GSE27545, which proposes a self-aggravating RXRA-ROS-JNK-PGC1alpha retrograde loop - a candidate account of why a fixed mtDNA lesion produces progressive rather than static dysfunction, though not of why deterioration is punctuated by discrete episodes. Closing this gap needs prospective human monitoring, not another omics deposit.
Proposed experiments
Prospective multimodal monitoring across the transition into a stroke-like episode
melas_prospective_prodrome_monitoring
Follow a cohort of m.3243A>G carriers with recurrent episodes using longitudinal EEG, MR spectroscopy and perfusion imaging at fixed intervals and at symptom onset, to determine whether measurable hyperexcitability, lactate accumulation, or perfusion change precedes the clinical episode and by how long.
Supporting outcome
- Epileptiform activity or a rising regional lactate signal appears in the subsequently affected cortex before the clinical deficit, identifying a prodromal window and a treatable initiating step.
Refuting outcome
- No electrophysiological or metabolic change precedes the deficit, placing the initiating event outside cortical excitability and outside current monitoring reach.
Show evidence (1 reference)
"The episodic nature of stroke-like episodes is unexplained."
The authors of the founding hyperexcitability study state this gap directly.
Why does one variant, m.3243A>G, produce MELAS in some carriers, MIDD or isolated deafness in others, and nothing at all in a further group?
Attached to
Only about 10% of m.3243A>G carriers in a systematically phenotyped cohort had classical MELAS, while 30% had MIDD, 28% had a combination fitting no recognized syndrome, and 9% were asymptomatic. Heteroplasmy level is the conventional explanation, but measured heteroplasmy explains far less than it is credited with: it did not correlate with disease severity in leukocytes or urinary epithelial cells, and it did not correlate with the grade of retinal dystrophy either. Tissue-specific segregation, nuclear genetic background, mtDNA copy number, and age are all candidate modifiers, and none has been shown to account for the variance. This is what makes genetic counselling and prognosis in m.3243A>G families so weak.
Four public datasets attached here attack the gap from different angles and are worth reading against each other. GSE202747 measures heteroplasmy per cell in a human MELAS tissue and finds it partitions by developmental lineage rather than randomly, which would make any single bulk measurement a poor proxy. GSE56158 varies heteroplasmy experimentally in one nuclear background and finds sharp transcriptional transitions rather than a gradient, offering a mechanism by which a continuous variable yields named syndromes. GSE129091 compares low against high load directly on the MELAS-versus-MIDD axis and reports that the two look alike transcriptionally while differing functionally. GSE85549 moves the question from heteroplasmy to allele, comparing the MELAS m.3243A>G lesion against the myopathy-causing m.3302A>G in the same gene. MSV000088237 extends the allele question outside MT-TL1 entirely, profiling fibroblasts from a patient with the complex I subunit variant m.14453G>A. GSE1462 is the only one that holds genotype constant and varies phenotype in patients - four PEO against four MELAS, all m.3243A>G, all muscle - and its authors read the difference as support for nuclear background as the modifier. That is the right experimental design for this gap, at a sample size and on a 2005 platform that cannot settle it.
Show evidence (2 references)
"28% of patients demonstrated a panoply of clinical features, which were not consistent with any of the classical syndromes associated with the m.3243A>G mutation. 9% of individuals harbouring the mutation were clinically asymptomatic."
Quantifies how poorly the classical syndrome labels partition the m.3243A>G carrier population.
"No significant correlations were found between disease severity and the heteroplasmy percentage determined in urinary epithelial cells or the heteroplasmy percentage determined in leukocytes."
Shows that accessible-tissue heteroplasmy does not explain severity, leaving the modifier question open.
Is there any accessible biomarker that predicts the course of m.3243A>G disease in an individual patient?
Attached to
The two obvious candidates both fail. Urinary epithelial cell heteroplasmy, widely used in cohort studies to index genotype against severity, varies by more than 20 percentage points between samples taken from the same patient within a fortnight, so it should not be used prognostically at all. FGF-21 correlates only moderately with cross-sectional severity and not at all with progression over two years. What is left is crude and non-specific: severe lactate elevation and anemia predict mortality. A trial-ready surrogate endpoint for MELAS therefore does not currently exist, which is part of why efficacy trials must run for a year on clinical outcomes.
The attached datasets are the accessible-tissue starting points, and their limits are as informative as their content. GSE14882 is whole blood from ten MELAS patients with expression changes correlated to mutant load and clinical features - the right design, at a sample size and on an array platform that cannot support validation. GSE165953 nominates glutamate as a biomarker and, unusually, confirms the dysregulation in MELAS post-mortem brain. GSE113300 profiles miRNAs, the class most likely to survive in plasma, but does so in a homoplasmic cybrid rather than in patients. GSE89066 is the closest to a proper biomarker study - 20 patients against 20 controls, independent validation, and a serum miRNA benchmarked against lactate - but its endpoint is diagnosis, not prognosis. No public MELAS dataset currently pairs a candidate marker with longitudinal clinical outcome, which is precisely the study FGF-21 failed.
Show evidence (2 references)
"Heteroplasmy levels of UEC in carriers of the m.3243A>G mutation have a significant day-to-day variation. The interpretation of a correlation between heteroplasmy levels in urine and disease severity is therefore not reliable."
Disqualifies urinary heteroplasmy as a prognostic measure on reproducibility grounds.
"Measuring FGF21 concentration had little added value in monitoring and predicting the disease course in this specific patient group."
Disqualifies FGF-21 as a monitoring biomarker in m.3243A>G carriers.
Does L-arginine actually prevent or shorten stroke-like episodes, or is its widespread use resting on uncontrolled data?
Attached to
L-arginine is standard practice in many centres for both acute and prophylactic use, and the supporting data are real but uncontrolled: the efficacy studies were unblinded, and the survival comparison was against natural history rather than a randomized control arm. A 2023 review states flatly that there is no robust evidence of efficacy in either setting. This matters more than a generic call for better trials, because the newer soluble guanylate cyclase stimulators target the same NO-cGMP axis: if the axis is not the operative mechanism of the stroke-like episode, a whole therapeutic programme is aimed at the wrong node. Contrast taurine, whose prevention claim rests on a prospective multicentre phase III trial.
One public dataset speaks to the rationale rather than the efficacy question, and is worth separating from it. MSV000088237 reports downregulated arginine biosynthesis via blocked argininosuccinate synthase in MELAS patient fibroblasts - a cell-intrinsic route to arginine deficiency, not merely the reduced plasma arginine the therapy was built on. That strengthens the mechanistic case for supplying arginine while leaving the clinical question exactly where it was: no dataset can substitute for the randomized trial that has never been run.
Show evidence (2 references)
"There is no robust evidence to prove the efficacy of l-arginine for both acute and prophylactic settings."
Explicit statement that the evidence base for the most widely used MELAS therapy is inadequate.
"Unblinded studies showed that l-arginine therapy improves stroke-like episode symptoms and decreases the frequency and severity of these episodes."
The supporting evidence, with its uncontrolled design stated in the source itself.
Can any available model system reproduce a stroke-like episode, or is the defining feature of MELAS accessible only in patients?
Attached to
MELAS has no faithful animal model, and the reason is structural rather than incidental: the mitochondrial genome cannot be edited with transgenic technology, so a targeted m.3243A>G animal cannot be made the way a nuclear knock-in can. The nearest attempt reached mouse ES cells carrying an orthologous tRNA-Leu(UUR) mutation with respiration defects, explicitly framed as a step toward a future model rather than a model itself. Patient iPSC-derived neurons are the best available human system and do reproduce the complex I-predominant deficiency, but they cannot produce a stroke-like episode, which needs cortex, vasculature, and seizure activity together; and heteroplasmy segregates toward homoplasmy during reprogramming, so clonal mutant load is not patient tissue load. Cultured patient cells often fail to manifest a phenotype at all. Consequently every mechanistic claim about the stroke-like episode itself rests on human imaging, electrophysiology, and autopsy - which is precisely why the controversy above has stayed open for two decades.
The public model datasets attached here show the workaround maturing rather than the gap closing. GSE324301 is a cerebral organoid slice model with cortical architecture, generated explicitly because no animal carries the mutation, and its deep-layer neuron degeneration was checked against MELAS brain autopsy - a real advance on neuron monoculture. PXD058785 extends the approach to skeletal muscle with graded heteroplasmy. GSE61390 turns the reprogramming bottleneck into an asset by deriving isogenic corrected lines. What none has is vasculature plus network seizure activity plus cortex in one system, so the stroke-like episode itself remains unmodelled.
Show evidence (3 references)
"Targeted modification of the mitochondrial genome has not succeeded with the current transgenic technologies. Furthermore, readily available cultured patient cells often do not manifest the disease phenotype."
States both halves of the modelling problem for mtDNA disease - no transgenic route, and weak phenotypes in patient cells.
"the ES cells harboring A2748G mtDNA may be useful for generation of transmitochondrial mice harboring A2748G mtDNA as potential disease models of MELAS"
The nearest available rodent work is framed as a precursor to a future model, confirming that no such mouse yet exists.
"During reprogramming, heteroplasmic mtDNA showed bimodal segregation toward homoplasmy, with concomitant changes in mtDNA organization, mimicking mtDNA bottleneck during epiblast specification."
Documents the heteroplasmy shift during reprogramming that limits how directly iPSC clones represent patient tissue.
How much of the MELAS phenotype outside the nervous system is genuinely absent versus simply not looked for?
Attached to
Three organ systems are described in their own literatures as under-recognized in m.3243A>G disease. Renal involvement is called probably underestimated; oligosymptomatic and kidney-limited m.3243A>G presentations can be difficult to recognize. Intestinal pseudo-obstruction is under-recognized and can be the presenting problem. Cardiac involvement has rarely been studied prospectively, which the reviewers themselves offer as the reason its reported incidence looks lower than expected. GeneReviews provides syndrome-level frequency intervals for cardiomyopathy, conduction abnormalities, and nephropathy. The 2025 cardiac study supplies a right-bundle-branch-block denominator among 11 clinical MELAS participants, but participation from 30 contacted patients was limited by severity and deaths. Neither those results nor the GeneReviews intervals close the separate ascertainment gap in unselected m.3243A>G carriers. This is the one gap in the entry that omics deposits cannot close, because it is a sampling problem rather than a mechanistic one - and a survey of public repositories bore that out, returning no dataset that changes the denominator. The relevant public resources are instead the two natural-history efforts attached here: NCT01532791, which recruits through maternal relatives of known carriers regardless of their own carrier status and uses paternal relatives as controls, and NCT05554835, which harmonizes national registries into a global cohort. A related class-level resource, Metabolomics Workbench study ST003924, profiles urinary metabolites in genetically confirmed paediatric primary mitochondrial disorders with an explicitly renal framing, but its sample factors record only the disease-class label, so MELAS cases cannot be identified within it and it is deliberately not curated as a MELAS dataset here.
Show evidence (2 references)
"Cardiac involvement in m.3243A>G carriers has been only rarely systematically studied, which is perhaps why the incidence of cardiac diseases in MELAS is lower than would be expected."
The reviewers attribute the low reported cardiac incidence to ascertainment rather than to biology.
"Not frequently reported, renal involvement in these diseases is probably underestimated, yet it increases morbidity."
States the same ascertainment problem for the kidney.
Which tissue-specific mechanisms explain the remaining clinical manifestations in clinically defined MELAS?
Attached to
phenotypes#Migraine-like headaches
phenotypes#Short stature
phenotypes#Learning disability
phenotypes#Progressive external ophthalmoplegia
phenotypes#Ptosis
phenotypes#Wolff-Parkinson-White syndrome
phenotypes#Anemia
phenotypes#Cerebellar atrophy
phenotypes#Basal ganglia calcification
phenotypes#Cardiac conduction abnormality
phenotypes#Ataxia
phenotypes#Right bundle branch block
The remaining clinical gaps have distinct evidence limitations. GeneReviews supports migraine as a possible trigger of stroke-like episodes, now represented in that direction; it does not establish the cause of migraine or a reverse cortical-injury-to-migraine relation. Short stature and learning disability are documented clinically, but the reviewed sources do not identify a phenotype-specific causal relation from the curated mechanisms; learning disability is not interchangeable with acquired dementia. The m.3243A>G cohort documents MELAS/PEO overlap without establishing the causal sequence from generalized myopathy to extraocular dysfunction. The ptosis case provides occurrence evidence, including a prior myasthenia diagnosis, without establishing eyelid-muscle pathogenesis. Broad conduction abnormalities, right bundle branch block, and Wolff-Parkinson-White syndrome are documented, but the reviewed sources do not establish their causal route from the curated myocardial remodeling mechanism or explain how mitochondrial dysfunction produces an accessory conduction pathway. The anemia cohort explicitly leaves dietary and other contributors unresolved. The imaging study documents cerebellar atrophy and basal ganglia calcification but does not establish their causal route from the cortical stroke-like lesion mechanism. Its suggestion of dystrophic calcification does not identify the initiating injury. Lactate, ragged-red fibers, and focal epileptiform EEG discharges are linked separately as observational readouts. GeneReviews documents ataxia without assigning it to the cortical injury mechanism or establishing that the imaged cerebellar atrophy causes it. The cardiac review supports a qualified remodeling-to-arrhythmia relation, now represented, but the right bundle branch block case is not causally assigned to that remodeling route by the observational cohort. These gaps concern causal attribution, not a requirement to identify every intermediate step.
Show evidence (5 references)
"Our study found that 30.8% of patients exhibited anemia, a slightly higher proportion than expected, potentially influenced by patient selection criteria, though dietary or other factors affecting hemoglobin levels could not be ruled out."
The authors explicitly leave the causes of anemia unresolved.
"10% of patients exhibited a classical MELAS phenotype, 30% had MIDD, 6% MELAS/MIDD, 2% MELAS/chronic PEO (CPEO) and 5% MIDD/CPEO overlap syndromes."
Quantifies the MELAS/CPEO overlap within the m.3243A>G phenotypic spectrum.
"Her clinical status included multiple medical problems related to her MELAS diagnosis: sensorineural hearing loss, myopathy, bilateral ophthalmoplegia, ptosis, seizures and stroke-like episodes with concern for dementia."
Extraocular involvement is one of the manifestations this entry records clinically without modelling a tissue-specific mechanism for it, which is the gap this discussion names.
+ 2 more references
Which cardiac findings reported across m.3243A>G carriers can be assigned specifically to clinically defined MELAS?
Attached to
The systematic cardiac review pools m.3243A>G carriers with MELAS, MIDD, MERRF, Leigh syndrome, and MELAS/KSS overlap. It reports left and right bundle branch block, supraventricular and ventricular arrhythmias, sinus tachycardia, atrial fibrillation, nonsustained ventricular tachycardia, and sudden cardiac death. Its myocardial spectrum includes thickening, hypertrophic and dilated cardiomyopathy, noncompaction, fibrosis, systolic dysfunction, heart failure, and arterial hypertension; myocardial abnormalities are reported more often than arrhythmias or conduction defects. These observations remain relevant to cardiac assessment, but the review abstract does not assign each manifestation or its frequency to a MELAS subgroup. GeneReviews independently supports MELAS cardiomyopathy, broad conduction abnormalities, and WPW, and recommends ECG and echocardiographic surveillance. Independent clinical MELAS evidence does establish right bundle branch block in a selected 11-patient cohort and non-sustained atrial tachycardia in a case report; these are now represented using those sources. The clinical review also describes atrial fibrillation and ventricular tachycardia and proposes conduction-pathway mitochondrial dysfunction, while the cardiac cohort review describes a remodeling-to-rhythm-disorder route. Sudden cardiac death and left bundle branch block remain carrier-spectrum observations here because the reviewed primary reports do not establish those outcomes in their MELAS patients. Prophylactic device recommendations are not evidence that a sudden-death event occurred.
Show evidence (8 references)
"The m.3243A>G variant may manifest phenotypically as mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), maternally inherited diabetes and deafness (MIDD), myoclonic epilepsy with ragged red fiber (MERRF), Leigh syndrome, or MELAS/KSS (Kearns-Sayre syndrome) overlap."
Defines the pooled syndromic scope of the carrier review.
"Myocardial abnormalities include myocardial thickening, hypertrophic cardiomyopathy, dilated cardiomyopathy, noncompaction, myocardial fibrosis, systolic dysfunction, heart failure, or arterial hypertension."
Preserves the reported myocardial spectrum at carrier-population scope.
"Arrhythmias reported in m.3243A>G carriers include paroxysmal supraventricular or ventricular arrhythmias, including sinus tachycardia, atrial fibrillation and nonsustained ventricular tachycardia, and sudden cardiac death."
Preserves clinically relevant arrhythmia and sudden-death reports without transferring them to a MELAS subgroup that the abstract does not identify.
+ 5 more references
Pathophysiology
21Taurine wobble-modification deficiency of tRNA-Leu(UUR)
The pathogenic MT-TL1 variants abolish the normal taurine-containing modification (5-taurinomethyluridine) at the anticodon wobble position of mitochondrial tRNA-Leu(UUR). This is the proximal molecular lesion: the unmodified anticodon can no longer form a correct codon-anticodon pair, and the resulting decoding failure is codon-specific rather than a uniform loss of leucine incorporation. The same defect is the rationale for taurine supplementation.
Downstream
Loss of the wobble taurine modification degrades codon-anticodon pairing, with UUG decoding affected more severely than UUA, so mitochondrial translation fails in a codon-biased way.
Show evidence (2 references)
"mt tRNA(Leu(UUR)) with a MELAS A3243G mutation and mt tRNA(Lys) with a MERRF A8344G mutation derived from HeLa background cybrid cells are deficient in normal taurine-containing modifications"
Identifies the specific chemical modification that is absent from mutant tRNA-Leu(UUR) in MELAS.
"We report here wobble modification deficiencies of mutant mt tRNAs from cybrid cells with different nuclear backgrounds, as well as from patient tissues."
Shows the modification defect is not an artefact of one cybrid nuclear background and is present in patient tissue.
Mitochondrial tRNA-Leu(UUR) translation defect
The m.3243A>G variant in MT-TL1 disrupts the structure and aminoacylation of mitochondrial tRNA-Leu(UUR), impairing mitochondrial protein synthesis (translation) of the mtDNA-encoded respiratory chain subunits.
Downstream
Defective synthesis of mtDNA-encoded subunits reduces assembly and activity of the respiratory chain complexes, especially complex I.
Show evidence (2 references)
"Here we report an A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNA(Leu)(UUR) that is specific to patients with MELAS."
The foundational paper identifying the m.3243A>G transition in mitochondrial tRNA-Leu(UUR) (MT-TL1) as the MELAS-specific lesion.
"These mutations reduce both the aminoacylation of tRNA(Leu(UUR)) and a posttranslational modification in the wobble position of tRNA(Leu(UUR)). Both changes result in reduced transcription of mitochondria-encoded proteins"
Directly supports the mechanism that MT-TL1 mutations impair tRNA aminoacylation and wobble modification, reducing mitochondrial protein synthesis.
Non-MT-TL1 mitochondrial tRNA dysfunction
MELAS is primarily linked to variants in mitochondrial tRNA genes, and the reported set extends beyond MT-TL1 to MT-TQ, MT-TH, MT-TK, MT-TC, MT-TS1, MT-TS2, MT-TV, MT-TW and MT-TM. These variants impair mitochondrial translation of the mtDNA-encoded respiratory chain subunits, the same lesion MT-TL1 variants produce, while acting on different tRNAs. Cybrid transfer for MT-TH places the resulting enzyme deficiency in the tRNA rather than in the nuclear background, and functional assays for MT-TS2 and MT-TW measure the translation defect directly.
Downstream
Impaired mitochondrial translation reduces synthesis of the mtDNA-encoded respiratory chain subunits, lowering respiratory chain activity.
Show evidence (4 references)
"A common subtype, MELAS ... is primarily linked to variants in mitochondrial transfer RNA (mt-tRNA) genes"
Establishes that the mitochondrial tRNA genes as a class, not MT-TL1 alone, are the principal MELAS genotypes. Graded as background because the sentence states the field's position rather than this paper's own result.
"Functional analysis demonstrated impaired mitochondrial translation and OXPHOS dysfunction."
Direct functional evidence that a non-MT-TL1 mt-tRNA variant impairs mitochondrial translation.
"Transmitochondrial cybrid analysis proved that this tRNA(His) mutation causes the enzymatic deficiency."
Cybrid transfer places the respiratory-chain deficiency in the tRNA variant rather than the nuclear background.
+ 1 more reference
Complex I structural subunit defect
Variants in the mtDNA-encoded complex I subunit genes MT-ND1, MT-ND5 and MT-ND6 lower complex I activity by altering a structural subunit directly, rather than by impairing mitochondrial translation. In a MELAS/Leigh overlap cohort, thirteen patients carried MTND variants, with m.13513G>A in MT-ND5 the commonest.
Downstream
Reduced complex I activity lowers electron entry into the respiratory chain and so reduces oxidative phosphorylation.
Show evidence (3 references)
"A respiratory chain function study showed decreased activity of mitochondrial respiratory chain complex I in both probands."
Measures reduced complex I activity in patients carrying MT-ND1 variants, the biochemical claim this node makes.
"whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
Names the three complex I subunit genes bound on this node.
"Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
Gives the cohort counts behind the statement that MT-ND5 m.13513G>A leads this genotype class.
Oxidative phosphorylation deficiency
Impaired mitochondrial translation reduces the abundance and activity of respiratory chain complexes, lowering ATP synthesis through oxidative phosphorylation. The defect becomes clinically apparent above a heteroplasmy threshold of mutant mtDNA.
Downstream
Reduced ATP synthesis forces a shift to anaerobic glycolysis, raising lactate, and starves high-energy-demand tissues (brain, muscle, vascular endothelium and smooth muscle).
The respiratory-chain deficit is not distributed evenly across the complexes or across cell types; complex I is disproportionately affected, and in neurons the deficient complex is actively cleared by mitophagy.
Oxidative phosphorylation failure in retinal pigment epithelium may disrupt metabolic cooperation with photoreceptors and contribute to retinal dystrophy. Human donor-eye observations support this proposed sequence but do not prove causal order.
Show evidence (1 reference)
"The pathogenesis of this syndrome is not fully understood and believed to result from several interacting mechanisms including impaired mitochondrial energy production, microvasculature angiopathy, and nitric oxide (NO) deficiency."
Establishes impaired mitochondrial energy production (OXPHOS deficiency) as a core pathogenic mechanism of MELAS.
Complex I-predominant deficiency and neuronal mitophagy
The respiratory-chain deficit produced by defective mitochondrial translation is not uniform. Complex I deficiency predominates, as in MELAS patient tissues, and the pattern of deficiency differs between cell types derived from the same patient. In differentiated neurons, complex I specifically is sequestered into PINK1/Parkin-positive autophagosomes, suggesting that active mitophagy - not only failed assembly - contributes to the neuronal deficit. This is a proposed, iPSC-derived explanation for why one heteroplasmic variant can produce a neuron-weighted, rather than uniformly systemic, disease.
Experimental models
m.3243A>G patient iPSC-derived neurons
Reproduces the complex I-predominant respiratory-chain defect seen in MELAS patient tissue and adds the neuron-specific mitophagic clearance step.
Downstream
Selective loss of complex I lowers NADH oxidation and ATP output most severely in the neuronal populations that can least tolerate it.
Show evidence (2 references)
"Induced pluripotent stem cell-derived neurons and various tissues derived from teratomas manifested cell-type specific respiratory chain (RC) deficiency patterns. Similar to MELAS patient tissues, complex I defect predominated."
Shows the complex I predominance and its cell-type dependence in a patient-derived m.3243A>G model, matching patient tissue.
"Upon neuronal differentiation, complex I specifically was sequestered in perinuclear PTEN-induced putative kinase 1 (PINK1) and Parkin-positive autophagosomes, suggesting active degradation through mitophagy."
Direct evidence for selective mitophagic clearance of complex I in neurons as a component of the neuronal deficit.
Cellular energy failure and lactic acidosis
OXPHOS deficiency drives a compensatory increase in anaerobic glycolysis, producing elevated blood and CSF lactate. Energy failure preferentially affects metabolically demanding tissues, underlying encephalopathy, myopathy, and endocrine dysfunction.
Downstream
Energy failure in cerebral small-vessel endothelium and smooth muscle drives mitochondrial angiopathy and impaired nitric oxide availability.
In the non-ischemic model, a mismatch between the energy demanded by an active cortical neuronal population and the ATP that a defective respiratory chain can supply renders those neurons hyperexcitable. What converts this chronic vulnerability into a discrete episode is not known.
Energy deficiency can stimulate mitochondrial proliferation.
Failure of mitochondrial energy production contributes to skeletal muscle weakness.
Energy failure in skeletal muscle contributes to mitochondrial myopathy.
Impaired mitochondrial energy production may compromise intestinal smooth muscle and enteric neural function.
Respiratory-chain failure increases glycolytic lactate production and can produce lactic acidosis.
Mitochondrial dysfunction may impair energy-dependent cochlear and auditory neural processes, producing sensorineural hearing loss.
Mitochondrial dysfunction in pancreatic beta cells impairs insulin secretion and contributes to diabetes mellitus.
Myocardial energy deficits may stimulate compensatory hypertrophy, providing a proposed route to hypertrophic cardiomyopathy.
Glomerular mitochondrial dysfunction can impair renal protein retention and produce proteinuria. The cell-specific injury sequence is unresolved in the reviewed clinical synthesis.
Mitochondrial dysfunction compromises energy-dependent peripheral nerve function and contributes to chronic sensory and motor neuropathy.
Show evidence (1 reference)
"The inability of dysfunctional mitochondria to generate sufficient energy to meet the needs of various organs results in the multi-organ dysfunction observed in MELAS syndrome."
Supports cellular energy failure in high-demand tissues as the link between OXPHOS deficiency and the multisystem phenotype.
Mitochondrial angiopathy and NO deficiency
Mitochondrial proliferation in the smooth muscle and endothelial cells of small blood vessels (mitochondrial angiopathy) and impaired nitric oxide availability produce endothelial dysfunction and impaired microvascular perfusion. This NO-deficient endothelial dysfunction is the target of L-arginine therapy.
Downstream
Mitochondrial angiopathy and NO deficiency, together with neuronal energy failure, converge to produce stroke-like episodes that do not respect classic vascular territories.
Mitochondrial dysfunction in capillary endothelium leaves the cortical microvasculature primed to leak, which is the substrate on which epileptic activity produces vasogenic edema.
Show evidence (2 references)
"Energy deficiency can also stimulate mitochondrial proliferation in the smooth muscle and endothelial cells of small blood vessels leading to angiopathy and impaired blood perfusion in the microvasculature of several organs."
Directly supports the mitochondrial angiopathy mechanism in cerebral small vessels underlying stroke-like episodes.
"MELAS is associated with endothelial dysfunction by decreased plasma L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate."
Supports impaired nitric oxide availability and endothelial dysfunction as a contributor to stroke-like episodes.
Neuronal hyperexcitability and propagating epileptic activity
In the non-ischemic model of the stroke-like episode, focal neuronal hyperexcitability arises in a cortical region where mitochondrial dysfunction - in neurons, astrocytes, or capillary endothelium - has left energy supply unable to meet demand. The resulting epileptic activity depolarizes adjacent neurons, which is how a stroke-like lesion spreads into contiguous cortex over days to weeks instead of appearing at once in a fixed arterial territory. Focal epileptiform discharges and focal cortical hyperperfusion, not hypoperfusion, are recorded over the acute lesion.
Downstream
Prolonged epileptic activity increases capillary permeability in cortex whose microvasculature is already compromised by mitochondrial angiopathy.
Depolarization of adjacent neurons propagates the epileptic focus into surrounding cortex, and the most vulnerable cortical layers are lost.
Lowering neuronal seizure thresholds contributes to the overall epileptic phenotype, including focal and generalized events.
Localized cortical hyperexcitability underlies focal epileptic activity during stroke-like episodes; this specifies the focal presentation within the broader seizure phenotype.
Show evidence (3 references)
"In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the acute brain lesion. In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
Electrophysiological and perfusion findings that are hard to reconcile with a primarily ischemic lesion and that anchor the hyperexcitability model.
"The stroke-like episodes in MELAS may reflect neuronal hyperexcitability, which increases energy demand and creates energy imbalance between energy requirement and adequate availability of adenosine triphosphate due to oxidative phosphorylation defect particularly in the susceptible neuronal..."
States the demand-supply mismatch mechanism linking hyperexcitability to cortical necrosis.
"several lines of evidence supporting neuronal hyper-excitability as the key mechanism of stroke-like episodes are discussed"
A recent review treating neuronal hyperexcitability as the leading mechanistic account.
Increased cerebral capillary permeability and vasogenic edema
Cortical stroke-like lesions in MELAS are characteristically edematous with elevated apparent diffusion coefficient and focal hyperperfusion, the signature of vasogenic rather than purely cytotoxic edema. The picture is not clean: diffusion restriction consistent with a cytotoxic component is also reported within the same lesions, so both processes appear to coexist.
Downstream
Sustained edema in cortex that is simultaneously hyperexcitable and energy-starved converts reversible signal change into tissue loss.
Show evidence (2 references)
"These results suggest that the stroke-like episodes is related to vasogenic edema, hyperperfusion, and neuronal damage."
Serial multimodal imaging supporting vasogenic edema with hyperperfusion as the lesion physiology.
"Stroke-like episodes are characterized by neuronal hyperexcitability, neuronal vulnerability, increased capillary permeability, and focal hyperaemia."
Lists increased capillary permeability and focal hyperaemia as defining features of the lesion.
Cortical laminar necrosis and progressive lesion spread
The lesion of a stroke-like episode is an edematous lesion predominantly involving the cerebral cortex, spreads into surrounding cortex over weeks, and is proposed to leave neuronal loss in a laminar or pseudo-laminar distribution. Cortical laminar necrosis is visible as subacute T1 hyperintense cortical signal, and intracortical gyral microhemorrhage has been confirmed pathologically.
Downstream
The evolving cortical lesion is what produces the acute focal deficit and its imaging correlate.
Accumulating cortical injury contributes to cognitive encephalopathy.
Show evidence (5 references)
"In 6 of 11 episodes T1-weighted hyperintense cortical signal compatible with cortical laminar necrosis was seen during subacute stage of the episode."
Documents cortical laminar necrosis as the subacute tissue outcome of a stroke-like episode.
"Repeated MRI performed in two episodes revealed progressive spread of the cortical lesion to the surrounding cortex for a few weeks after the onset of symptoms."
Documents the contiguous spread over weeks that distinguishes the MELAS lesion from an arterial infarct.
"susceptible neuronal population in the cortex may result in neuronal loss with a laminar or pseudo-laminar distribution"
Describes the laminar pattern of neuronal loss that gives the lesion its characteristic appearance; the review states it as a proposal.
+ 2 more references
Stroke-like episodes
Acute neurological deficits with neuroimaging lesions that do not conform to classic vascular territories are the defining clinical manifestation of MELAS. Proposed contributors include neuronal energy failure and hyperexcitability, mitochondrial angiopathy, and nitric oxide deficiency; their relative causal roles remain contested.
Downstream
Repeated stroke-like episodes accumulate cortical tissue loss; brain atrophy and cognitive decline are the residue left in survivors.
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
A posterior cortical stroke-like lesion can produce visual field loss.
Show evidence (2 references)
"During the stroke-like episodes neuroimaging shows increased T2-weighted signal areas that do not correspond to the classic vascular distribution (hence the term "stroke-like")."
GeneReviews documents stroke-like episodes with non-vascular-territory neuroimaging lesions as the defining MELAS feature, the clinical outcome of the angiopathy and energy-failure mechanisms.
"(3) lesion distribution is inconsistent with vascular territory; (4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months; (6) neurological symptoms and stroke-like lesions tend to be reversible, as presented on..."
Enumerates the defining features that separate a stroke-like episode from an ischemic stroke, including posterior predilection, contiguous spread, and reversibility.
Progressive brain atrophy and dementia
Beyond any single episode, MELAS is slowly progressive: brain dysfunction and atrophy advance between episodes, and recurrent stroke-like episodes leave progressive brain atrophy and dementia as their long-term sequel.
Downstream
Clinical manifestation of accumulated cerebral injury after recurrent stroke-like episodes.
Clinical manifestation of accumulated cerebral injury after recurrent stroke-like episodes.
Show evidence (2 references)
"Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
Identifies brain atrophy and dementia as the accumulated outcome of recurrent episodes.
"(8) brain dysfunction and atrophy are slowly progressive"
Confirms the slowly progressive interictal course, distinct from the episodic lesions themselves.
Skeletal muscle mitochondrial proliferation
Accumulation of mitochondria within skeletal muscle fibers produces the characteristic histological pattern of mitochondrial myopathy.
Show evidence (1 reference)
"Modified Gomori Trichrome stain (40X) showing a typical Ragged Red muscle fiber (RRF) containing mitochondrial hyperproliferation."
The ragged-red fiber reflects mitochondrial proliferation in muscle.
Enteric neuromuscular dysfunction
Mitochondrial dysfunction may impair intestinal propulsion through visceral smooth-muscle disease and/or myenteric neuropathy. The relative contributions remain unresolved in MELAS.
Downstream
Failure of intestinal neuromuscular propulsion can produce pseudo-obstruction.
Show evidence (2 references)
"The pathophysiological mechanisms underlying gastrointestinal dysmotility in mitochondrial disorders are not completely understood and most likely involve myenteric plexus neuropathy and visceral myopathy."
The MELAS case review proposes enteric neuropathy and visceral myopathy, without resolving their relative contribution.
"These findings suggest that mitochondrial dysfunction and energy production impairment may be the basis for the gastrointestinal symptoms in these patients, similar to the effects in the brain during stroke-like episodes."
The review cautiously links mitochondrial dysfunction to bowel symptoms after discussing MELAS gastrointestinal tissue findings.
Cochlear and auditory neural energy dysfunction
Mitochondrial dysfunction may impair energy-dependent cochlear and auditory neural processes, producing sensorineural hearing loss.
Downstream
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
Show evidence (1 reference)
"This symptom may be caused by mitochondrial dysfunction within the cochlea and the auditory neural pathways, disrupting the energy-dependent processes of sound transmission and auditory perception [37]."
The preceding sentence identifies sensorineural hearing loss in MELAS. The review presents cochlear and auditory neural dysfunction as a proposed cause.
Impaired pancreatic beta-cell insulin secretion
Mitochondrial dysfunction in pancreatic beta cells impairs insulin secretion and contributes to diabetes mellitus.
Downstream
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
Show evidence (1 reference)
"The pathophysiology of diabetes in patients with MELAS is primarily due to mitochondrial dysfunction in pancreatic beta cells, which impairs insulin secretion [42]."
The review links pancreatic beta-cell mitochondrial dysfunction to impaired insulin secretion and diabetes; the specific cellular intermediates are not resolved here.
Myocardial energy deficit and hypertrophic remodeling
Myocardial energy deficits may stimulate compensatory hypertrophy, providing a proposed route to hypertrophic cardiomyopathy.
Downstream
Hypertrophic remodeling provides a proposed mechanism for the hypertrophic subset of the broader cardiomyopathy phenotype; it does not explain every dilated or other myocardial presentation.
Compensatory myocardial hypertrophy is proposed to produce the specifically hypertrophic cardiomyopathy phenotype.
Myocardial remodeling can contribute to cardiac rhythm disorders in MELAS; the electrical intermediates and contributions of primary conduction-pathway dysfunction remain unresolved.
Show evidence (1 reference)
"Hypertrophic changes in the myocardium are likely a result of energy deficits due to impaired oxidative phosphorylation, leading to myocardial hypertrophy as the heart attempts to compensate for the loss of efficient energy production [1,2,39]."
The review proposes compensatory myocardial hypertrophy in response to oxidative phosphorylation failure; this is retained as a provisional causal model.
Glomerular mitochondrial dysfunction
Glomerular mitochondrial dysfunction can impair renal protein retention and produce proteinuria. The cell-specific injury sequence is unresolved in the reviewed clinical synthesis.
Downstream
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
Show evidence (1 reference)
"Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44]."
The MELAS renal section assigns proteinuria to glomerular mitochondrial defects; podocyte-specific intermediates are not established by this passage.
Peripheral nerve mitochondrial dysfunction
Mitochondrial dysfunction compromises energy-dependent peripheral nerve function and contributes to chronic sensory and motor neuropathy.
Downstream
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
Show evidence (1 reference)
"Furthermore, patients with MELAS often experience peripheral neuropathy, which presents as chronic sensory and motor deficits in the extremities. Peripheral nerves, which are energy-intensive tissues, are especially vulnerable to mitochondrial dysfunction, leading to symptoms such as muscle..."
The review identifies mitochondrial dysfunction in peripheral nerves as the basis of the described sensory and motor neuropathy.
Retinal pigment epithelium metabolic dysfunction
Oxidative phosphorylation failure in retinal pigment epithelium may disrupt metabolic cooperation with photoreceptors and contribute to retinal dystrophy. Human donor-eye observations support this proposed sequence but do not prove causal order.
Downstream
RPE dysfunction is a proposed early step leading to outer retinal degeneration.
Show evidence (1 reference)
"However, a high proportion of m.3243G in the RPE, as seen in the current study, likely causes decreased electron transport chain function and leads to derangement of the RPE-photoreceptor cells cooperative metabolic ecosystem, eventually causing photoreceptor cell dysfunction and vision loss."
Human MELAS donor-eye analyses support a proposed RPE metabolic mechanism; the causal sequence is inferred rather than established by an intervention.
Histopathology
3
Ragged-red fibers on modified Gomori trichrome
FREQUENT
Subsarcolemmal aggregates of proliferating abnormal mitochondria in skeletal muscle, the classic morphological signature of a mitochondrial myopathy. Present in about three quarters of biopsied MELAS patients, so a negative biopsy does not exclude the diagnosis.
Show evidence (1 reference)
"Ragged-red fibers (RRF) were observed in 29 patients (74.4%), and SDH strongly reactive blood vessels (SSV) were observed in 28 patients (71.8%)."
Quantifies ragged-red fiber yield (74.4%, within the FREQUENT 30-79% band) in a cohort where every patient underwent muscle biopsy.
Strongly SDH-reactive blood vessels with preserved cytochrome c oxidase activity
FREQUENT
Intramuscular arterioles stain darkly for succinate dehydrogenase, reflecting the mitochondrial proliferation in vascular smooth muscle that gives the "mitochondrial angiopathy" hypothesis its histological footing. The discriminating detail is the COX result: SSV in MELAS retain normal cytochrome c oxidase activity, whereas the morphologically identical vessels in MERRF are COX-negative. The same lesion therefore carries a different enzymatic meaning in the two diseases, and SSV alone should not be read as a MELAS-specific finding.
Show evidence (3 references)
"On the other hand, SSV in muscle biopsies from patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) had normal CCO activity as shown by light and electron microscopy."
Establishes the MELAS half of the distinction, COX-normal SSV.
"More than half of the intramuscular blood vessels in muscle biopsies from five patients with myoclonus epilepsy with ragged-fibers (MERRF) who had a point mutation in mitochondrial DNA at the tRNALys region were darkly stained with succinate dehydrogenase (SDH) stain, showing the morphologic..."
Establishes the MERRF half of the distinction, morphologically similar SSV lacking COX activity.
"SDH strongly reactive blood vessels (SSV) were observed in 28 patients (71.8%)"
Quantifies SSV yield on muscle biopsy in a MELAS cohort; 71.8% falls in the FREQUENT (30-79%) band.
Cortical laminar necrosis with intracortical gyral microhemorrhage
The neuropathological correlate of the stroke-like lesion: neuronal loss in a laminar or pseudo-laminar cortical distribution, with petechial gyral microhemorrhages confirmed at autopsy and matched in life by subacute T1-hyperintense cortical signal.
Show evidence (1 reference)
"Fat-suppression MRI confirmed intracortical gyral hemorrhage in one episode. Petechial gyral microhemorrhages were also pathologically confirmed in the autopsy of another patient."
Pathological confirmation of intracortical microhemorrhage within a stroke-like lesion.
Pathograph
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Phenotypes
40Blood 1
Anemia
HP:0001903
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Anemia (HP:0001903). HP:0001903 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
"Blood hemoglobin tests indicated anemia, defined as hemoglobin levels below the normal range, in 30.8% of patients."
Directly documents anemia in the 39-patient clinical MELAS cohort.
"In contrast, hemoglobin levels were negatively correlated with MRS scores (r = -0.375, p = 0.015)."
Links lower hemoglobin to greater disability on the modified Rankin Scale.
"Patients without anemia had a lower risk of death compared to those with anemia (OR = 0.175, 95% CI 0.033–0.921, p = 0.040)."
The body of the article identifies absence of anemia as the lower-risk comparator; the association does not establish causation.
Cardiovascular 7
Stroke-like episodes
VERY_FREQUENT
HP:0002401
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Stroke-like episode (HP:0002401). HP:0002401 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"During the stroke-like episodes neuroimaging shows increased T2-weighted signal areas that do not correspond to the classic vascular distribution (hence the term "stroke-like")."
GeneReviews documents stroke-like episodes with non-vascular-territory neuroimaging lesions as the defining MELAS feature.
Cardiomyopathy
<25%
HP:0001638
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Cardiomyopathy (HP:0001638). HP:0001638 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Both dilated and hypertrophic cardiomyopathy have been observed, however, the more typical is a non-obstructive concentric hypertrophy"
Documents myocardial phenotypes observed in MELAS.
"<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo"
The complete <25% row of GeneReviews Table 3 includes cardiomyopathy. The exact source interval is retained because it crosses HPO frequency bands.
Hypertrophic cardiomyopathy
HP:0001639
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Hypertrophic cardiomyopathy (HP:0001639). HP:0001639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Both dilated and hypertrophic cardiomyopathy have been observed, however, the more typical is a non-obstructive concentric hypertrophy"
Documents myocardial phenotypes observed in MELAS.
Wolff-Parkinson-White syndrome
HP:0001716
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Wolff-Parkinson-White syndrome (HP:0001716). HP:0001716 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Cardiac conduction abnormalities including Wolff-Parkinson-White syndrome has been reported occasionally"
Documents this specific conduction phenotype in MELAS; other arrhythmias and bundle branch block are distinct findings.
Cardiac conduction abnormality
<25%
HP:0031546
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Cardiac conduction abnormality (HP:0031546). HP:0031546 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Cardiac conduction abnormalities including Wolff-Parkinson-White syndrome has been reported occasionally"
Supports the broad conduction phenotype in MELAS and the separately represented WPW subtype.
"<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo"
The complete <25% row of GeneReviews Table 3 includes cardiac conduction abnormality. The exact source interval is retained because it crosses HPO frequency bands.
Arrhythmia
HP:0011675
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Arrhythmia (HP:0011675). HP:0011675 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"A Holter monitor demonstrated episodes of non-sustained atrial tachycardia, a finding not been previously described in this population."
The report documents arrhythmia in a 44-year-old woman with clinically defined MELAS, stroke-like episodes, and m.3243A>G; it is occurrence evidence rather than a prevalence estimate.
"Patients with MELAS are also at an increased risk for arrhythmias, including atrial fibrillation and ventricular tachycardia, because of the involvement of mitochondrial dysfunction in the conduction pathways of the heart [40]."
The MELAS review describes additional rhythm phenotypes and proposes mitochondrial dysfunction in cardiac conduction pathways as a contributor. The review does not quantify subtype-specific risks.
Right bundle branch block
OCCASIONAL
HP:0011710
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Right bundle branch block, completeness unspecified, annotated with Bundle branch block (HP:0011710). HP:0011710 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"ECG was performed in all patients. Surprisingly, right branch bundle block was only found in one (1/11, 9.1%)."
Directly documents right bundle branch block; 1/11 falls in OCCASIONAL (5-29%) within this selected clinical cohort. The reported right-sided finding does not establish complete block.
"Clinically, all patients reported stroke-like episodes and lactic acidosis."
Establishes the clinical MELAS manifestations in this cohort, distinguishing it from a genotype-only carrier series.
Digestive 2
Recurrent vomiting
FREQUENT
HP:0002013
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Recurrent vomiting, annotated with Vomiting (HP:0002013), qualified as temporality recurrent. HP:0002013 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"muscle weakness and exercise intolerance, normal early psychomotor development, recurrent headaches, recurrent vomiting, hearing impairment, peripheral neuropathy, learning disability, and short stature"
GeneReviews lists recurrent vomiting among the common manifestations of MELAS.
"50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature"
The complete 50%-74% row of GeneReviews Table 3 includes recurrent vomiting. The entire interval lies within FREQUENT (30-79%).
Intestinal pseudo-obstruction
HP:0004389
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Intestinal pseudo-obstruction (HP:0004389). HP:0004389 is a phenotype from the Human Phenotype Ontology.
Show evidence (5 references)
"Intestinal pseudo-obstruction (IPO) is most commonly observed in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), although this symptom can also affect patients with MELAS syndrome (5), particularly those with the m.3243A>G mutation; however, IPO remains an underrecognized condition."
Documents intestinal pseudo-obstruction as an under-recognized m.3243A>G MELAS manifestation.
"The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
Places pseudo-obstruction inside stroke-like-episode management rather than treating it as a separate problem.
"IPO is a rare and severe condition that is characterized by abdominal distension, nausea, vomiting, and pain due to impaired propulsive activity in the gastrointestinal tract and resembles mechanical intestinal obstruction (6)."
Defines the clinical obstruction syndrome and the failure of propulsion.
+ 2 more references
Ear 1
Sensorineural hearing loss
Sensorineural hearing impairment
HP:0000407
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"In addition to SLEs and seizures, sensorineural hearing loss is a frequent and progressive manifestation in MELAS."
Specifies the sensorineural and progressive nature of hearing impairment in MELAS.
Endocrine 1
Diabetes mellitus
25%-49%
HP:0000819
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Diabetes mellitus (HP:0000819). HP:0000819 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
"MELAS syndrome is a multi-organ disease with broad manifestations including stroke-like episodes, dementia, epilepsy, lactic acidemia, myopathy, recurrent headaches, hearing impairment, diabetes, and short stature."
The El-Hattab review lists diabetes among the broad manifestations of MELAS, reflecting the endocrine involvement of the m.3243A>G mutation.
"There was a trend toward higher rates of diabetes in symptomatic non-MELAS patients compared to MELAS (56.7% vs. 33.3, p = 0.058)."
Separates diabetes in clinically defined MELAS from the broader variant-associated disease spectrum.
"25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)"
The complete 25%-49% row of GeneReviews Table 3 includes diabetes mellitus. The exact source interval is retained because it crosses HPO frequency bands.
Eye 5
Hemianopia
HP:0012377
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Hemianopia (HP:0012377). HP:0012377 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"The neurological evaluation revealed left hemianopia, temporal, and spatial disorientation and moderate psychic and motion slowness."
Documents hemianopia during a genetically confirmed MELAS stroke-like presentation.
Cortical (cerebral) visual impairment
HP:0100704
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Cerebral visual impairment (HP:0100704). HP:0100704 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"hearing loss, cortical blindness and diabetes mellitus were significantly more frequent in the adult form"
Nationwide cohort data placing cortical blindness in the adult-onset MELAS phenotype.
"Focal-onset seizures, encephalopathy, and visual disturbances are prominent findings associated with stroke-like episodes, with a predilection for the posterior cerebral cortex."
Links the visual deficits to the posterior-cortex predilection of stroke-like lesions.
Mitochondrial retinal dystrophy
HP:0000556
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Mitochondrial retinal dystrophy (pigmentary macular pattern dystrophy), annotated with Retinal dystrophy (HP:0000556). HP:0000556 is a phenotype from the Human Phenotype Ontology.
Show evidence (4 references)
"Twenty-five of the 29 mutation carriers (86%) had retinal abnormalities that could be classified into 4 grades."
Quantifies retinal involvement in a systematically examined m.3243A>G carrier cohort.
"The grade of mitochondrial retinal dystrophy correlated significantly with both age (r = -0.483, P = 0.008) and visual acuity (r = -0.614, P < 0.001), whereas no correlation was observed with heteroplasmy level or overall disease involvement."
Shows retinal severity is uncoupled from heteroplasmy and from systemic disease burden.
"Six patients (21%) had grade 1 retinal dystrophy with fine pigment abnormalities that were clearly visible with FAF and fluorescein angiography. Eleven patients (38%) had grade 2 abnormalities that were characterized by yellowish or mildly pigmented deposits in the early stage; in advanced grade..."
Defines the four anatomical grades in the carrier cohort, without transferring its frequency to clinically defined MELAS.
+ 1 more reference
Progressive external ophthalmoplegia
<25%
HP:0000590
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Progressive external ophthalmoplegia (HP:0000590). HP:0000590 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"10% of patients exhibited a classical MELAS phenotype, 30% had MIDD, 6% MELAS/MIDD, 2% MELAS/chronic PEO (CPEO) and 5% MIDD/CPEO overlap syndromes."
Quantifies the MELAS/CPEO overlap within the m.3243A>G phenotypic spectrum.
"<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo"
The complete <25% row of GeneReviews Table 3 includes progressive external ophthalmoplegia. The exact source interval is retained because it crosses HPO frequency bands.
Ptosis
HP:0000508
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Ptosis (HP:0000508). HP:0000508 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Her clinical status included multiple medical problems related to her MELAS diagnosis: sensorineural hearing loss, myopathy, bilateral ophthalmoplegia, ptosis, seizures and stroke-like episodes with concern for dementia."
Reports ptosis together with ophthalmoplegia as part of one patient's MELAS phenotype. A single case supports occurrence, not a frequency or an eyelid-muscle mechanism.
"Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
GeneReviews names ptosis among the manifestations of MELAS that require management, which is why the phenotype is recorded at disease level rather than as a single-case observation.
Genitourinary 1
Proteinuria
HP:0000093
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Proteinuria (HP:0000093). HP:0000093 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
"Not frequently reported, renal involvement in these diseases is probably underestimated, yet it increases morbidity. It generally manifests as subnephrotic proteinuria and progressive deterioration of kidney function."
Characterizes the renal phenotype of m.3243A>G disease and notes it is probably under-ascertained.
"Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44]."
The review specifically identifies proteinuria in its MELAS renal-involvement section.
"that may include Fanconi proximal tubulopathy, proteinuria, and focal segmental glomerulosclerosis"
Places proteinuria within the renal spectrum of MELAS. Focal segmental glomerulosclerosis is a possible renal lesion; this passage does not establish a treatment response or an immunosuppression error rate.
Metabolism 2
Elevated blood lactate
VERY_FREQUENT
Increased circulating lactate concentration
HP:0002151
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Increased circulating lactate concentration (HP:0002151). HP:0002151 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Lactic acidemia is very common and muscle biopsies typically show ragged red fibers."
GeneReviews documents lactic acidemia as a very common feature of MELAS.
Lactic acidosis
HP:0003128
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"The m.3243A>G mutation compromises the function of the electron transport chain (ETC), which forces cells to rely on anaerobic glycolysis, thereby leading to the accumulation of lactate and lactic acidosis, a hallmark of MELAS [16,17]."
Describes lactic acidosis as a consequence of respiratory-chain dysfunction.
Musculoskeletal 4
Mitochondrial myopathy
HP:0003737
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Mitochondrial myopathy (HP:0003737). HP:0003737 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Common clinical manifestations include stroke-like episodes, encephalopathy with seizures and/or dementia, muscle weakness and exercise intolerance"
GeneReviews lists muscle weakness and exercise intolerance, the clinical expression of mitochondrial myopathy, among common manifestations.
"To confirm this hypothesis, the patient underwent MR spectroscopy (MRS) and demonstrated elevation of the lactate peak within the abnormal lesion (Figure 2D), a muscle biopsy that was consistent with mitochondrial myopathy (Figures 2E–H) and genetic testing, which revealed the presence of a..."
Muscle biopsy documented mitochondrial myopathy in genetically confirmed MELAS.
Ragged-red fibers
Ragged-red muscle fibers
HP:0003200
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Ragged-red muscle fibers (HP:0003200). HP:0003200 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Lactic acidemia is very common and muscle biopsies typically show ragged red fibers."
GeneReviews documents ragged-red fibers as a typical muscle biopsy finding in MELAS.
Muscle weakness
HP:0001324
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Muscle weakness (HP:0001324). HP:0001324 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"presents clinically as muscle weakness and exercise intolerance."
Identifies weakness and exercise intolerance as clinical expressions of MELAS myopathy.
Basal ganglia calcification
25%-49%
HP:0002135
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Basal ganglia calcification (HP:0002135). HP:0002135 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Bilateral basal ganglia calcifications were found in 6 of 9 (67%) patients who underwent CT."
Documents calcification in the selected CT subgroup, not an unselected MELAS population.
"25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)"
The complete 25%-49% row of GeneReviews Table 3 includes basal ganglia calcification. The exact source interval is retained because it crosses HPO frequency bands.
Nervous System 14
Seizures
VERY_FREQUENT
HP:0001250
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"MELAS had higher prevalence of seizures (88.1% vs. 16.7%, p < 0.05) and shorter survival from onset to death (50% mortality at 25 years vs. 10%, p < 0.05)."
The 88.1% estimate is from 42 clinically defined MELAS patients; the comparator is symptomatic non-MELAS mitochondrial disease.
Encephalopathy
HP:0001298
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Encephalopathy (HP:0001298). HP:0001298 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Common clinical manifestations include stroke-like episodes, encephalopathy with seizures and/or dementia, muscle weakness and exercise intolerance"
GeneReviews lists encephalopathy with seizures and/or dementia among the common manifestations of MELAS.
Migraine-like headaches
HP:0002076
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Migraine (HP:0002076). HP:0002076 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
GeneReviews names migraine headache among the manifestations of MELAS that require management. The claim follows from the management recommendation rather than from a counted frequency, hence INDIRECT.
"in the form of recurrent attacks of severe pulsatile headaches with frequent vomiting are typical in individuals with MELAS and can precipitate stroke-like episodes."
GeneReviews describes the migraine phenotype and identifies it as a possible precipitant of stroke-like episodes.
Peripheral neuropathy
FREQUENT
HP:0009830
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Peripheral neuropathy (HP:0009830). HP:0009830 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"muscle weakness and exercise intolerance, normal early psychomotor development, recurrent headaches, recurrent vomiting, hearing impairment, peripheral neuropathy, learning disability, and short stature"
GeneReviews lists peripheral neuropathy among the common manifestations of MELAS.
"50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature"
The complete 50%-74% row of GeneReviews Table 3 includes peripheral neuropathy. The entire interval lies within FREQUENT (30-79%).
Learning disability
FREQUENT
Specific learning disability
HP:0001328
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Learning disability, annotated with Specific learning disability (HP:0001328). HP:0001328 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"muscle weakness and exercise intolerance, normal early psychomotor development, recurrent headaches, recurrent vomiting, hearing impairment, peripheral neuropathy, learning disability, and short stature"
GeneReviews lists learning disability among the common manifestations of MELAS.
"50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature"
The complete 50%-74% row of GeneReviews Table 3 includes learning disability. The entire interval lies within FREQUENT (30-79%).
Focal-onset seizures
VERY_FREQUENT
HP:0007359
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Focal-onset seizure (HP:0007359). HP:0007359 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
"Focal seizures occurred in 21 of 22 subjects (95.5%), whereas generalized seizures developed in seven of 22 subjects (31.8%)."
Quantifies focal versus generalized seizure frequency in a pediatric m.3243A>G MELAS cohort with epilepsy.
"The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group"
Establishes earlier seizure onset as a predictor of drug resistance.
"Seizure semiology and electroencephalography abnormalities showed no syndrome-specific findings."
The pediatric MELAS epilepsy cohort found no diagnostic seizure or EEG signature; its focal-seizure frequency remains conditional on epilepsy.
Status epilepticus
HP:0002133
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Status epilepticus (HP:0002133). HP:0002133 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
"An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%)."
Identifies status epilepticus as a leading cause of death in a followed MELAS cohort.
"Six patients died from stroke-like episodes, with status epilepticus being the clinical manifestation prior to death."
Independent cohort confirming status epilepticus as the terminal manifestation in most MELAS deaths.
"The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
The clinical review identifies aggressive seizure management as a priority; the cohort evidence above identifies status epilepticus among predominant proximate causes of death.
Dementia and progressive cognitive decline
HP:0000726
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Dementia (HP:0000726). HP:0000726 is a phenotype from the Human Phenotype Ontology.
Show evidence (4 references)
"Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
Establishes dementia as the long-term neurological outcome of recurrent stroke-like episodes.
"It is a multi-system disorder with a wide range of manifestations, characterized by recurrent stroke-like episodes, progressive intellectual decline, and dementia"
Lists progressive intellectual decline and dementia among the defining manifestations.
"Both the underlying neurologic dysfunction and the accumulating cortical injuries due to stroke-like episodes contribute to dementia."
GeneReviews separates the underlying neurological dysfunction from the cumulative effects of stroke-like cortical injury.
+ 1 more reference
Cerebral atrophy
HP:0002059
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Cerebral atrophy (HP:0002059), qualified as course progressive. HP:0002059 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"(8) brain dysfunction and atrophy are slowly progressive"
Documents progressive brain atrophy as a listed feature of the MELAS course.
"For all 59 imaging studies, cerebral atrophy occurred in 38 (64%), and cerebellar atrophy occurred in 40 (68%)."
Documents cerebral atrophy; these denominators count imaging studies, not distinct patients.
Hemiparesis
HP:0001269
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Hemiparesis (HP:0001269). HP:0001269 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6]."
Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
Aphasia
HP:0002381
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Aphasia (HP:0002381). HP:0002381 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6]."
Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
Cerebellar atrophy
HP:0001272
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Cerebellar atrophy (HP:0001272). HP:0001272 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"For all 59 imaging studies, cerebral atrophy occurred in 38 (64%), and cerebellar atrophy occurred in 40 (68%)."
The 24-patient pediatric series documents cerebellar atrophy in 40 imaging studies; it does not provide a 40-patient numerator.
Focal epileptiform EEG discharges
EEG with focal epileptiform discharges
HP:0011185
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is EEG with focal epileptiform discharges (HP:0011185). HP:0011185 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the acute brain lesion."
Episode-level EEG findings in six MELAS patients support focal epileptic activity during acute lesions.
Ataxia
25%-49%
HP:0001251
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)"
The complete 25%-49% row of GeneReviews Table 3 includes ataxia. The exact source interval is retained because it crosses HPO frequency bands.
Constitutional 1
Exercise intolerance
HP:0003546
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Exercise intolerance (HP:0003546). HP:0003546 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
"Common clinical manifestations include stroke-like episodes, encephalopathy with seizures and/or dementia, muscle weakness and exercise intolerance"
GeneReviews lists exercise intolerance among the common manifestations of MELAS.
Growth 1
Short stature
FREQUENT
HP:0004322
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
"muscle weakness and exercise intolerance, normal early psychomotor development, recurrent headaches, recurrent vomiting, hearing impairment, peripheral neuropathy, learning disability, and short stature"
GeneReviews lists short stature among the common manifestations of MELAS.
"50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature"
The complete 50%-74% row of GeneReviews Table 3 includes short stature. The entire interval lies within FREQUENT (30-79%).
Genetic Associations
13
MT-TL1 m.3243A>G
(The m.3243A>G point mutation in MT-TL1 (mitochondrial tRNA-Leu(UUR)) is the most common cause of MELAS, found in roughly 80% of patients. Disease expression depends on the heteroplasmy level of mutant mtDNA.)
Show evidence (4 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"The m.3243A>G pathogenic variant in the mitochondrial gene MT-TL1 is present in approximately 80% of individuals with MELAS."
GeneReviews establishes m.3243A>G in MT-TL1 as the most common cause of MELAS (~80% of cases).
"The mutation was present in 26 out of 31 independent MELAS patients and 1 out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested."
Original genotyping data establishing the m.3243A>G variant as MELAS-specific.
+ 1 more reference
MT-ND5
(MT-ND5 is the leading non-MT-TL1 cause of MELAS named by GeneReviews. Unlike the tRNA genotypes, it encodes a complex I structural subunit rather than a component of the translation apparatus. In a MELAS/Leigh overlap cohort, MT-ND gene variants predominated and m.13513G>A in MT-ND5 was the commonest single variant, so genotype may partly indicate where a patient sits on the MELAS-Leigh spectrum; the cited cohort does not test this prediction directly.)
Show evidence (4 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"Pathogenic variants in MT-TL1 or other mtDNA genes, particularly MT-ND5, can also cause this disorder."
GeneReviews documents MT-ND5 and other mtDNA genes as additional causes of MELAS beyond the common MT-TL1 m.3243A>G variant.
"Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
Identifies MT-ND5 m.13513G>A as the leading variant in MELAS/Leigh overlap, the presentation most enriched for complex I subunit genotypes.
+ 1 more reference
MT-ND1
(Variants in the complex I subunit gene MT-ND1 are reported in MELAS. Unlike the mitochondrial tRNA genotypes, MT-ND1 variants lower complex I activity by altering a structural subunit rather than by impairing mitochondrial translation.)
Show evidence (4 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"Sequencing of the mitochondrial DNA revealed two novel MT-ND1 gene missense mutations, m.3959G>A and m.3995A>G, which are highly conserved among species."
Reports MT-ND1 missense variants in probands presenting with MELAS features.
"A respiratory chain function study showed decreased activity of mitochondrial respiratory chain complex I in both probands."
Establishes reduced complex I activity as the biochemical consequence in these MT-ND1 patients.
+ 1 more reference
MT-ND6
(Variants in the complex I subunit gene MT-ND6 are reported in MELAS, including m.14453G>A. As with MT-ND1 and MT-ND5, the lesion is in a complex I structural subunit rather than in the translation apparatus.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"broadens the phenotypic spectrum of MELAS syndrome associated with ND6 gene mutation"
The authors attribute a MELAS presentation to an MT-ND6 variant and treat it as extending that gene's MELAS spectrum.
"whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
Independent cohort listing MT-ND6 among the complex I subunit genes reported in MELAS.
MT-TQ
(A heteroplasmic m.4332G>A variant in MT-TQ (mitochondrial tRNA-Gln) was reported in a patient given a MELAS-spectrum diagnosis, with pathogenicity argued from the correlation between mutation load and a respiratory-chain defect in single muscle fibres.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"A heteroplasmic G to A transition at nucleotide 4332 in the tRNA glutamine gene was identified in the patient's muscle mitochondrial DNA."
Identifies the MT-TQ variant in the reported MELAS-spectrum patient.
"The pathogenicity of the mutation was shown in single muscle fibers by the correlation between high mutation load and cytochrome c oxidase defect."
The mutation-load-to-defect correlation is the pathogenicity argument offered for this variant.
MT-TH
(Variants in MT-TH (mitochondrial tRNA-His) are reported with lactic acidosis and stroke-like episodes. For m.12146A>G, transmitochondrial cybrids showed that the tRNA-His variant itself, not the nuclear background, produced the respiratory-chain enzyme deficiency.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"We report a new mutation in m.12146 A>G in the mt-tRNA(His) in a family with a remarkable clinical history having different degrees of lactic acidosis and stroke-like episodes."
Ties an MT-TH variant to the MELAS-defining combination of lactic acidosis and stroke-like episodes in one family.
"Transmitochondrial cybrid analysis proved that this tRNA(His) mutation causes the enzymatic deficiency."
Cybrid transfer isolates the mtDNA variant as the cause of the enzyme deficiency.
MT-TK
(m.8296A>G in MT-TK (mitochondrial tRNA-Lys) was reported in a patient with optic atrophy, cardiomyopathy and bilateral striatal necrosis who later developed stroke-like episodes. The same variant had been reported earlier in patients with diabetes mellitus or with myoclonus epilepsy with ragged-red fibres, so the genotype does not predict a MELAS phenotype.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"Skeletal muscle total mitochondrial DNA analysis identified a heteroplasmic A to G point mutation in the tRNA(Lys) gene at position 8296."
Identifies the MT-TK variant in the reported MELAS patient.
"We conclude that the 8296 mutation is likely to be pathogenic"
The authors' pathogenicity assessment for this MT-TK variant.
MT-TC
(m.5783G>A in MT-TC (mitochondrial tRNA-Cys) was reported in a late-onset MELAS patient in whom blood lymphocyte DNA testing was negative and the variant was found only by sequencing mtDNA from urinary sediment.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"the patient was eventually diagnosed with MELAS with the mtDNA 5783G>A mutation in the MT-TC gene with a urinary sediment genetic test"
Names MT-TC as the gene carrying the variant in a patient diagnosed with MELAS.
"This case report expands the genetic repertoire associated with MELAS syndrome"
The authors present the genotype as an addition to the MELAS gene spectrum rather than an established cause.
MT-TS1
(A heteroplasmic m.7512T>C variant in MT-TS1 (mitochondrial tRNA-Ser(UCN)), disrupting a conserved acceptor-stem base pair, was reported in a family presenting as MERRF/MELAS overlap syndrome rather than as classical MELAS.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"We found a new point mutation in the mitochondrial tRNA(Ser(UCN)) gene in a family with MERRF/MELAS overlap syndrome by screening for heteroplasmy"
Links MT-TS1 to a MELAS-overlap phenotype in one family.
"revealed a heteroplasmic mutation at nt 7512 in the tRNA(Ser(UCN)) gene"
Gives the specific heteroplasmic MT-TS1 variant.
MT-TS2
(Variants in MT-TS2 (mitochondrial tRNA-Ser(AGY)) are reported in MELAS. For m.12244G>A the presentation was a classical MELAS phenotype, with functional work showing impaired mitochondrial translation and oxidative phosphorylation. Across reported MT-TS2 variants the phenotype is variable.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"We identified a rare m.12244G > A variant in the tRNASer(AGY) gene associated with classical MELAS phenotype."
Ties an MT-TS2 variant to a classical MELAS presentation.
"Literature review showed that MT-TS2 variants are associated with variable phenotypes including encephalopathy, myopathy, deafness, diabetes, and retinopathy."
Records that MT-TS2 genotypes are not MELAS-specific.
MT-TV
(A heteroplasmic m.1616A>G variant in MT-TV (mitochondrial tRNA-Val) was reported in a man with MELAS whose course was dominated by rapidly progressive cardiomyopathy and severe heart failure. The authors present the respiratory-chain consequence as a possibility rather than a measurement.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"He had a mitochondrial transfer RNA (tRNA) mutation (m.1616A>G) of the (tRNA-Val) gene, and it was not found in MELAS syndrome ever before."
Identifies the MT-TV variant in a patient diagnosed with MELAS.
"The presence of this newly observed tRNA-Val mutation (m.1616A>G) may induce multiple respiratory chain enzyme deficiencies and contribute to MELAS syndrome symptoms that are associated with mitochondrial DNA (mtDNA) mutations."
The respiratory-chain link is stated by the authors as a possibility, which is why this gene is recorded without a claim of established pathogenicity.
MT-TW
(A heteroplasmic m.5541C>T variant in MT-TW (mitochondrial tRNA-Trp) was reported in a patient with MELAS and multiple organ involvement. Functional work put the translation defect first and the respiratory dysfunction after it, which places this genotype in the same mechanism class as the other mitochondrial tRNA variants. Patient-derived induced pluripotent stem cells carrying near-homoplasmic mutant mtDNA were used separately to show cell-type-specific phenotypes.)
Show evidence (3 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"We found a disease-causative mutation, m.5541C>T heteroplasmy in MT-TW gene, in a patient exhibiting mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) with multiple organ involvement."
Names MT-TW as the gene carrying the variant in a patient diagnosed with MELAS.
"This mutation firstly disturbed the translation machinery of mitochondrial tRNA(Trp) and induced mitochondrial respiratory dysfunction, followed by severely injured mitochondrial homeostasis."
Places the primary lesion in mitochondrial translation rather than in the respiratory chain, which is the mechanism this entry models for mt-tRNA genotypes.
MT-TM
(A heteroplasmic m.4450G>A variant in MT-TM (mitochondrial tRNA-Met) was reported in a girl who met the clinical criteria for MELAS. Heteroplasmy was measured in six tissues and ranged from 20% in blood to 59% in urinary sediment, and patient fibroblasts showed reduced oxygen consumption with decreased complex I and IV activities.)
Show evidence (4 references)
"MELAS is caused by pathogenic variants in mtDNA and is transmitted by maternal inheritance."
GeneReviews states that the mtDNA variants causing MELAS are maternally transmitted, i.e. constitutional (germline) rather than somatically acquired, which supports variant_origin GERMLINE for this genetic record.
"Mitochondrial gene analysis revealed a heteroplasmic m.4450G > A mutation in the mitochondrial tRNAMet."
Identifies the MT-TM variant and records that it is heteroplasmic.
"Stroke-like episodes, lactic acidosis, encephalopathy with brain magnetic resonance imaging findings, and declined mitochondrial function were consistent with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome."
The authors' basis for calling this presentation MELAS rather than an isolated myopathy.
+ 1 more reference
Medical Actions
6
L-arginine therapy
Intravenous L-arginine in the acute phase and oral supplementation for prophylaxis aims to restore nitric oxide availability and improve endothelial function, reducing the frequency and severity of stroke-like episodes.
Show evidence (2 references)
"Unblinded studies showed that l-arginine therapy improves stroke-like episode symptoms and decreases the frequency and severity of these episodes."
Supports L-arginine as a therapy that reduces stroke-like episode frequency and severity in MELAS.
"the systematic administration of L-arginine to patients with MELAS significantly improved the survival curve of patients compared with natural history."
Clinical trial follow-up data supporting survival benefit of systematic L-arginine therapy in MELAS.
Taurine supplementation
Oral taurine supplementation aims to restore taurine modification of the wobble uridine of mutant mitochondrial tRNA-Leu(UUR), improving codon decoding and reducing stroke-like episode recurrence. Unusually for MELAS, this is a therapy aimed at the proximal molecular lesion rather than at a downstream consequence.
Show evidence (2 references)
"Taurine reduced the annual relapse rate of stroke-like episodes from 2.22 to 0.72 (P=0.001)."
A multicentre phase III trial showing high-dose taurine significantly reduced stroke-like episode recurrence in MELAS.
"a taurine modification defect at the first anticodon nucleotide of mitochondrial tRNALeu(UUR), resulting in failure to decode codons accurately"
Provides the molecular rationale: taurine restores wobble-uridine modification of mutant tRNA-Leu(UUR), improving codon decoding.
Citrulline supplementation
Oral citrulline, a nitric oxide precursor, increases arginine availability and nitric oxide production. Stable-isotope studies suggest citrulline may be a more effective NO precursor than arginine in MELAS.
Show evidence (1 reference)
"The greater effect of citrulline in increasing NO production is due to its greater ability to increase arginine availability particularly in the intracellular compartment in which NO synthesis takes place."
Stable-isotope study showing citrulline increases NO production more effectively than arginine in children with MELAS, supporting it as a NO precursor therapy.
Supportive mitochondrial disease management
Supportive care including antiseizure medications, management of diabetes and hearing loss, avoidance of mitochondrial toxins, and mitochondrial cofactor supplementation (e.g., coenzyme Q10, L-carnitine). GeneReviews recommends annual ophthalmologic, audiologic, and cardiac assessment, including ECG and echocardiography, plus annual urinalysis and fasting glucose to detect multisystem involvement.
Show evidence (3 references)
"Management is largely symptomatic and should involve a multidisciplinary team."
Supports symptomatic, multidisciplinary supportive management as the mainstay of MELAS care.
"Additionally, carnitine and coenzyme Q10 are commonly used in MELAS syndrome without proven efficacy."
Supports common use of carnitine and coenzyme Q10 cofactors, while noting their efficacy is unproven (hence PARTIAL).
"Annual ophthalmologic, audiology, and cardiologic (electrocardiogram and echocardiogram) evaluations are recommended. Annual urinalysis and fasting blood glucose level are also recommended."
The 2018 GeneReviews surveillance recommendations cover cardiac conduction and myocardial disease as well as hearing, vision, renal, and endocrine involvement.
Aggressive antiseizure therapy
Under the neuronal-hyperexcitability model, seizure control is not merely symptomatic management but treatment aimed at the mechanism that initiates and propagates the stroke-like lesion. Epilepsy in MELAS is typically drug resistant, yet most patients achieve substantial seizure reduction with combinations of two or more antiseizure medications. Valproic acid is specifically avoided as a mitochondrial toxin.
Show evidence (2 references)
"Twenty of 22 subjects (90.9%) achieved partial to complete reduction of clinical seizures for more than one year with a combination of more than two antiepileptic drugs."
Quantifies achievable seizure control with multi-drug antiseizure therapy in MELAS.
"Mitochondrial toxins, including aminoglycoside antibiotics, linezolid, cigarettes, and alcohol; valproic acid for seizure treatment; metformin because of its propensity to cause lactic acidosis; dichloroacetate (DCA) because of increased risk for peripheral neuropathy."
Records the constraint that valproic acid must be avoided when choosing antiseizure medication in MELAS.
Soluble guanylate cyclase stimulation (investigational)
Zagociguat and the earlier IW-6463 are CNS-penetrant stimulators of soluble guanylate cyclase, the receptor for nitric oxide. They act one step downstream of the arginine and citrulline strategy: rather than supplying more NO precursor, they amplify signalling through the NO-cGMP axis whose failure defines the endothelial-dysfunction node. Both have been taken into MELAS-specific trials; neither is approved, and the IW-6463 study was terminated.
Show evidence (2 references)
"PRIZM is a Phase 2b randomized, double-blind, placebo-controlled, 3-treatment, 2-period, crossover study evaluating the efficacy and safety of oral zagociguat 15 and 30 mg vs. placebo when administered daily for 12 weeks in participants with genetically and phenotypically defined MELAS."
A completed randomized placebo-controlled MELAS-specific trial of a soluble guanylate cyclase stimulator.
"This is a single-arm study to evaluate safety and tolerability of oral IW-6463 in adults diagnosed with MELAS."
The earlier single-arm MELAS study of the same mechanism, which was terminated.
Environmental Factors
1Mitochondrial toxins and agents to avoid
Certain drugs and exposures can precipitate or worsen MELAS by impairing mitochondrial function or triggering lactic acidosis, and should be avoided.
Show evidence (1 reference)
"Mitochondrial toxins, including aminoglycoside antibiotics, linezolid, cigarettes, and alcohol; valproic acid for seizure treatment; metformin because of its propensity to cause lactic acidosis; dichloroacetate (DCA) because of increased risk for peripheral neuropathy."
GeneReviews lists agents and circumstances to avoid in MELAS, including aminoglycosides, linezolid, valproic acid, metformin, dichloroacetate, cigarettes, and alcohol.
Biochemical Markers
4
Blood lactate
(Elevated)
Context: The "LA" of the acronym. Beyond diagnosis, the degree of elevation carries prognostic weight: severe hyperlactatemia is an independent predictor of mortality and correlates with disability scores.
Reference Ranges
≤ 2.0 mmol/L
Normal
(< 2.0 mmol/L)
Mild hyperlactatemia
(2.0–4.0 mmol/L)
Severe hyperlactatemia
(≥ 4.0 mmol/L)
Severe hyperlactatemia: Independently associated with mortality in MELAS and correlated with modified Rankin Scale disability.
Show evidence (1 reference)
"Mild hyperlactatemia was defined as a blood lactate level greater than the upper limit of the normal range (>2 mmol/L), while severe hyperlactatemia was defined as a blood lactate level greater than twice the upper limit of the normal range (>4 mmol/L)."
Defines the mild and severe blood-lactate bands used in the prognostic analysis.
Show evidence (3 references)
"Lactic acidemia is very common and muscle biopsies typically show ragged red fibers."
Establishes lactic acidemia as a very common finding in MELAS.
"There was a positive correlation between lactic acid levels and MRS scores (r = 0.460, p = 0.003)."
Links the magnitude of lactate elevation to disability, supporting its prognostic use.
"In multivariate analysis, severe lactate elevation (OR = 7.279, 95% CI 1.102-48.086, p = 0.039) and anemia (OR = 0.137, 95% CI 0.021-0.908, p = 0.039) were identified as independent predictors of mortality."
Supports severe hyperlactatemia as an independent predictor of mortality, as stated in the context.
Cerebrospinal fluid lactate
(Elevated)
Context: CSF lactate can be raised when blood lactate is normal, so a normal serum value does not exclude MELAS. Proton MR spectroscopy detects the same signal non-invasively, including in normal-appearing brain.
Reference Ranges
≤ 2.2 mmol/L
Normal
(< 2.2 mmol/L)
Mild elevation
(2.2–4.4 mmol/L)
Severe elevation
(≥ 4.4 mmol/L)
Show evidence (1 reference)
"Similarly, mild elevation in cerebrospinal fluid (CSF) lactate was defined as a level exceeding the upper normal limit (>2.2 mmol/L), and severe elevation was defined as a level exceeding two times the upper normal limit (>4.4 mmol/L)."
Defines the CSF lactate bands used in the prognostic analysis.
Show evidence (1 reference)
"Proton spectroscopy showed the presence of lactate and reduction of N-acetyl aspartate peak in stroke-like lesion and the presence of lactate in apparently spared brain."
Demonstrates elevated brain lactate detectable by spectroscopy even outside the visible lesion.
Growth differentiation factor 15 (GDF-15)
(Elevated)
Context: A circulating marker of mitochondrial disease rather than of MELAS specifically. In a meta-analysis of diagnostic accuracy for mitochondrial disease, GDF-15 had higher pooled sensitivity, specificity, diagnostic odds ratio, and SROC than FGF-21, and the authors conclude that GDF-15 had the highest diagnostic accuracy of the two. The meta-analysis did not report MELAS-specific accuracy.
Show evidence (2 references)
"Pooled sensitivity, specificity, DOR and SROC of FGF-21 were 0.71 (95% CI 0.53, 0.84), 0.88(95% CI 0.82, 0.93), 18 (95% CI 6, 54), 0.90 (95% CI 0.87, 0.92), respectively, which were lower than GDF-15 values; 0.83 (95% CI 0.65, 0.92), 0.92 (95% CI 0.84, 0.96), 52 (95% CI 13, 205), 0.94 (95% CI..."
Meta-analytic diagnostic performance of GDF-15 against FGF-21 for mitochondrial disease as a class, not MELAS specifically.
"FGF-21 and GDF-15 showed acceptable sensitivity and high specificity. Of the biomarkers, GDF-15 had the highest diagnostic accuracy."
The authors' own conclusion on the comparison.
Fibroblast growth factor 21 (FGF-21)
(Elevated)
Context: Useful for diagnosis but poor for monitoring. In adult m.3243A>G carriers FGF-21 correlates only moderately with cross-sectional disease severity and showed no correlation with disease progression over two years, so it does not substitute for clinical scoring as a longitudinal endpoint.
Show evidence (3 references)
"Our analysis revealed a moderate, significant correlation between FGF21 concentration and disease severity (r = 0.49; p = <0.001)."
Establishes only a moderate cross-sectional relationship with severity in m.3243A>G carriers.
"Repeated measurements following 25 subjects for 2 years revealed no significant correlation between FGF21 concentration and disease progression."
Refutes the use of FGF-21 as a longitudinal progression marker in this population.
"FGF-21 and GDF-15 showed acceptable sensitivity and high specificity."
Supports the diagnostic usefulness of FGF-21 for mitochondrial disease as a class.
Imaging Findings
5
Cortical T2/FLAIR hyperintensity crossing vascular territories
The defining imaging finding. Lesions favour posterior (occipital, parietal, temporal) cortex, do not conform to an arterial territory, extend into contiguous cortex over weeks to months, and are often at least partly reversible - a combination no arterial infarct produces.
Show evidence (2 references)
"During the stroke-like episodes neuroimaging shows increased T2-weighted signal areas that do not correspond to the classic vascular distribution (hence the term "stroke-like")."
The reference statement of the non-vascular-territory imaging pattern.
"(4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months; (6) neurological symptoms and stroke-like lesions tend to be reversible, as presented on magnetic resonance imaging"
Adds the posterior predilection, contiguous extension, and reversibility that complete the imaging signature.
Elevated apparent diffusion coefficient within the acute lesion
Acute stroke-like lesions typically show normal-to-elevated ADC, consistent with vasogenic rather than cytotoxic edema, and this has been used to separate them from ischemic infarcts. The rule is not absolute: diffusion restriction is reported within the same lesions, so restricted diffusion does not exclude MELAS.
Show evidence (2 references)
"In the temporal lobe lesion, the apparent diffusion coefficient (ADC) at 44 days after onset was higher (average: 1.219x10(-3)mm2/s) than that in a normal region (average: 0.796x10(-3)mm2/s)."
Quantitative demonstration of elevated ADC within a stroke-like lesion.
"Both MRI that were performed during those episodes of stroke-like lesion revealed areas of diffusion restriction, coexisting areas of high ADC."
Qualifies the elevated-ADC rule by documenting coexisting restricted diffusion in the same lesions.
Lactate peak on proton MR spectroscopy
A lactate doublet with reduced N-acetylaspartate within the lesion, and frequently a lactate peak in normal-appearing brain as well - which makes MRS informative even where conventional sequences are unremarkable. The lesional peak falls as the lesion resolves.
Show evidence (2 references)
"(1)H-MRS of the left parietal lobe lesion at the same day showed a decrease in N-acetylaspartate/(creatine+phosphocreatine) (NAA/Cr) (0.43) and a peak in lactate. 1H-MRS of the contralateral side at the same day showed NAA/Cr (1.57) and no peak in lactate."
Shows the lesional lactate peak with reduced NAA against an unaffected contralateral control.
"Proton spectroscopy showed the presence of lactate and reduction of N-acetyl aspartate peak in stroke-like lesion and the presence of lactate in apparently spared brain."
Documents lactate in normal-appearing brain as well as within the lesion.
Focal cortical hyperperfusion during the acute episode
Perfusion imaging over an acute stroke-like lesion shows focal hyperperfusion, not the hypoperfusion an ischemic mechanism predicts. This is one of the strongest single arguments against the purely vascular model of the stroke-like episode.
Show evidence (2 references)
"In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
Direct perfusion evidence contradicting an ischemic mechanism for the acute lesion.
"Perfusion imaging at onset showed high intensity in bilateral occipital lobes, which indicated hyperperfusion in stroke-like lesions."
Independent MR perfusion confirmation of lesional hyperperfusion.
Cerebral atrophy
Progressive brain atrophy accumulating across the disease course, the imaging correlate of the interictal cognitive decline.
Cerebral atrophy
HP:0002059
Human Phenotype Ontology (HP)
Show evidence (1 reference)
"(8) brain dysfunction and atrophy are slowly progressive"
Documents progressive atrophy as part of the MELAS imaging course.
Progression
5Juvenile-onset form
Short stature is significantly more frequent in the juvenile form, and juvenile onset carries a substantially higher risk of death than adult onset. The cited cohort abstract does not state the age cutoff separating the juvenile and adult forms. In a separate pediatric cohort, earlier seizure onset predicted drug-resistant epilepsy.
Show evidence (3 references)
"According to a Kaplan-Meier analysis, the juvenile form was associated with a higher risk of death than the adult form (hazard ratio, 3.29; 95%CI, 1.32-8.20; p=0.0105)."
Quantifies the survival difference between the juvenile and adult forms in a nationwide prospective cohort.
"Short stature was significantly more frequent in the juvenile form"
Supports the juvenile-form short-stature difference stated in the notes.
"The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group"
Supports the seizure-onset sentence; this pediatric cohort compares earlier and later seizure onset, not the juvenile and adult forms.
Adult-onset form
Hearing loss, cortical blindness, and diabetes mellitus are significantly more frequent in the adult form than in the juvenile form.
Show evidence (1 reference)
"Short stature was significantly more frequent in the juvenile form, whereas hearing loss, cortical blindness and diabetes mellitus were significantly more frequent in the adult form."
Separates the two natural-history subgroups by their differentiating manifestations.
Late-onset presentation (after age 40)
A small minority present after age 40 and typically follow a less aggressive course, though the late-onset course is not uniformly benign.
Show evidence (1 reference)
"Although childhood is the typical age of onset, a small fraction (1-6%) of individuals manifest the disease after 40 years of age and usually have a less aggressive disease course."
Documents the frequency and general course of late-onset MELAS.
Rapid degenerative decline in the first five years after onset
Disease-rating-scale scores rise steeply within five years of onset in both the juvenile and adult forms, so the early years after the first stroke-like episode carry most of the accumulating disability.
Show evidence (1 reference)
"According to the Japanese mitochondrial disease rating scale, MELAS patients showed rapidly increasing scores (mean±standard deviation, 12.8±8.7) within 5years from onset of the disease."
Quantifies the rate of degenerative progression in the first five years.
Accumulated disability and death
Acute stroke-like episodes and status epilepticus are the leading causes of death, and survival declines mainly in the first dozen years after onset. Progressive brain atrophy and dementia are the sequelae of recurrent stroke-like episodes in survivors.
Show evidence (4 references)
"Of the 121 subjects who successfully completed the follow-up, 28 subjects died (mortality rate 23.1%). An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%)."
Cohort mortality rate and the dominant proximate causes of death.
"The survival rate declined mainly within 12years after the disease onset."
Supports survival declining mainly in the first dozen years after onset.
"Among the surviving patients (n=93), 39.8% (37/93) required assistance in daily life (mRS scores 3-5). The mRS scores were inversely correlated with the age of onset"
Quantifies residual disability among survivors and its inverse relation to age at onset.
+ 1 more reference
Prevalence
3Japan (nationwide prospective cohort, clinically defined MELAS)
Prevalence of clinically defined MELAS (Japanese diagnostic criteria) in the total Japanese population, an order of magnitude below the prevalence of m.3243A>G-related disease as a whole because most carriers never meet full MELAS criteria.
Show evidence (1 reference)
"the prevalence of MELAS was 0.18 (95%CI, 0.02-0.34)/100,000 in the total population"
Nationwide prospective cohort estimate for clinically defined MELAS specifically, rather than for all m.3243A>G carriers.
General population (m.3243A>G carrier frequency)
Carrier frequency of the causal variant, not of MELAS. Most m.3243A>G carriers have MIDD, an oligosymptomatic phenotype, or no symptoms at all; the gap between this figure and the MELAS prevalence above is the measure of incomplete penetrance for the full syndrome.
Show evidence (1 reference)
"Population-based studies suggest the m.3243A>G mutation in MTTL1 is the most common disease-causing mtDNA mutation, with a carrier rate of 1 in 400 people."
Establishes the population carrier rate of the causal variant, which greatly exceeds the prevalence of the MELAS syndrome itself.
Clinical Burden
High
MELAS combines a high mortality rate with severe residual disability among survivors. Roughly a quarter of a followed cohort died, most often from acute stroke-like episodes or status epilepticus, and about 40% of survivors needed help with daily life. Epilepsy was drug-resistant in a pediatric MELAS epilepsy cohort, and recurrent stroke-like episodes leave progressive brain atrophy and dementia. Treatment is generally supportive; no disease-modifying therapy is established.
Show evidence (5 references)
"MELAS had high mortality and morbidity in this cohort of Chinese patients."
Direct statement of the mortality and morbidity burden in a followed cohort.
"Of the 121 subjects who successfully completed the follow-up, 28 subjects died (mortality rate 23.1%). An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%). Among the surviving patients (n=93), 39.8% (37/93) required assistance in daily life (mRS..."
Supplies the mortality, cause-of-death, and survivor-disability figures stated in the rationale.
"Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
Supports the long-term neurological burden of recurrent stroke-like episodes.
+ 2 more references
Differential Diagnoses
3Conditions with similar clinical presentations that must be differentiated from MELAS Syndrome:
Acute ischemic stroke
Overlapping Features
Stroke-like episodes share their onset pattern and focal neurological symptoms with ischemic stroke. Features that favour MELAS are lesion distribution inconsistent with an arterial territory, posterior predilection, contiguous spread into adjacent sites over weeks to months, accompanying seizures, focal hyperperfusion rather than hypoperfusion, and a lactate peak on spectroscopy. Diffusion is a weaker discriminator: lesional ADC is often elevated, but restricted diffusion can coexist in the same lesions.
Distinguishing Features
- Lesion distribution inconsistent with a vascular territory
- Progressive spread into adjacent cortex over weeks to months
- Focal cortical hyperperfusion rather than hypoperfusion
- Lactate peak on proton MR spectroscopy, including in normal-appearing brain
- Frequent accompanying focal-onset seizures
Show evidence (5 references)
"Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a disease that should be considered as a differential diagnosis to acute ischemic stroke taking into account its onset pattern and neurological symptoms, which are similar to those of an ischemic stroke."
States the differential explicitly and the reason the two are confused.
"Stroke-like episodes in MELAS have the following features: (1) symptoms are neurolocalized according to lesion site; (2) epileptic seizures are often present; (3) lesion distribution is inconsistent with vascular territory; (4) lesions are common in the posterior brain regions; (5) lesions..."
Supplies the lesion-distribution, posterior-predilection, contiguous-spread, and seizure features listed as distinguishing.
"In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
Supports focal hyperperfusion, rather than the hypoperfusion of ischemia, during stroke-like episodes.
+ 2 more references
MERRF (myoclonic epilepsy with ragged-red fibers)
Overlapping Features
Shares ragged-red fibers and strongly SDH-reactive vessels on muscle biopsy, so morphology alone does not separate them. The enzyme histochemistry does: SSV are cytochrome c oxidase deficient in MERRF and COX-normal in MELAS. Overlap syndromes carrying both phenotypes are described.
Distinguishing Features
- Cytochrome c oxidase activity absent from SSV in MERRF, preserved in MELAS
- Myoclonus rather than stroke-like episodes as the cardinal feature
- m.8344A>G in MT-TK rather than m.3243A>G in MT-TL1
Show evidence (3 references)
"More than half of the intramuscular blood vessels in muscle biopsies from five patients with myoclonus epilepsy with ragged-fibers (MERRF) who had a point mutation in mitochondrial DNA at the tRNALys region were darkly stained with succinate dehydrogenase (SDH) stain, showing the morphologic..."
Establishes the MERRF half of the COX-activity criterion, in patients with a tRNALys point mutation.
"On the other hand, SSV in muscle biopsies from patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) had normal CCO activity as shown by light and electron microscopy."
Establishes the MELAS half of the criterion, COX-normal SSV.
"Furthermore, a growing number of patients may exhibit overlap syndrome, such as MELAS/LS, MERRF/MELAS, and LHON/MELAS (3)."
Supports the statement that MERRF/MELAS overlap syndromes are described.
Overlapping Features
Bilateral symmetrical basal ganglia, thalamic, and brainstem lesions define Leigh syndrome, whereas MELAS lesions are predominantly cortical. MELAS/Leigh overlap is a recognized entity and is enriched for complex I subunit variants, particularly MT-ND5 m.13513G>A rather than MT-TL1 m.3243A>G.
Distinguishing Features
- Bilateral symmetrical basal ganglia and brainstem lesions rather than predominantly cortical lesions
- Ataxia, spastic paraplegia, and bulbar palsy as leading features
- Enriched for MT-ND (complex I subunit) variants in overlap cases
Show evidence (4 references)
"Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
Shows the genotype shift toward complex I subunit genes in MELAS/Leigh overlap.
"As for the clinical hallmarks of LS, the top three most common symptoms were ataxia, spastic paraplegia, and bulbar palsy."
Names the Leigh-type features most common in the MELAS/LS overlap cohort; it does not address lesion distribution or genotype, which the other items cover.
"LS is defined as an early-onset progressive neurodegenerative MD typically characterized by subacute onset of psychomotor regression and encephalopathy associated with the development of bilateral symmetrical lesions in the basal ganglia, thalami, subthalamic regions, mesencephalon, and..."
Supports bilateral symmetrical deep grey matter and brainstem lesions as the defining Leigh lesion pattern.
+ 1 more reference
Related Datasets
16
Non-random distribution of mitochondrial m.3243A>G heteroplasmy in human retina and its impact on cellular phenotype
geo:GSE202747
Single-cell RNA-seq, mitochondrial single-cell ATAC-seq, and multimodal single-cell sequencing of retina and choroid from a MELAS donor eye and healthy controls, measuring per-cell m.3243A>G heteroplasmy alongside transcriptome and chromatin state. SuperSeries; the scRNA, scATAC, and multiome SubSeries are GSE202735, GSE202746, and GSE202886 and should not be curated separately.
The most directly informative public dataset for the genotype-phenotype gap, because it measures heteroplasmy inside a tissue at single-cell resolution rather than in an accessible surrogate. Also bears on the stroke-like-episode mechanism controversy: in this tissue the neuroectoderm-derived neural cells carried a high mutant fraction while the mesoderm-derived choroidal vasculature was near-homoplasmic wild-type, which is the opposite of what a primarily vascular pathogenesis would predict. One donor eye, and retina is not cortex, so it is a lead rather than a settled answer.
Show evidence (1 reference)
"All neuroectoderm-derived neural cells exhibited a high percentage of the mutant variant. However, a subset of mesoderm-derived lineage, namely the vasculature of the choroid, was near homoplasmic for the WT allele."
Shows heteroplasmy partitions non-randomly by cell lineage within one tissue, which is a candidate explanation for organ-level phenotype variation that bulk heteroplasmy cannot capture.
Transcriptomic analysis of human cybrid cell lines harboring increasing levels of the mitochondrial DNA (mtDNA) 3243A>G mutation
geo:GSE56158
RNA-seq of isogenic somatic-cell cybrids spanning the complete range of m.3243A>G heteroplasmy, with paired cellular phenotyping, designed to test how continuous variation in mutant load maps onto discrete clinical syndromes.
Addresses the genotype-phenotype gap from the opposite direction to the retina data: one nuclear background, heteroplasmy varied experimentally. Its result - that the nucleus has only a few discrete states available - is a mechanistic proposal for why a continuous variable produces named syndromes. Cybrids are an immortalized non-neural cell line, so the thresholds are not directly transferable to patient tissue.
Show evidence (2 references)
"Small increases in mutant mtDNAs caused relatively modest defects in oxidative capacity but resulted in sharp transitions in cellular phenotype and gene expression."
Demonstrates threshold-like transcriptional switching rather than a graded response, which is the shape a mechanism must have to turn continuous heteroplasmy into discrete syndromes.
"a major factor in the phenotypic variation in heteroplasmic mtDNA mutations is the limited number of states that the nucleus can acquire in response to progressive changes in mitochondrial retrograde signaling"
States the proposed explanation for genotype-phenotype discordance that this dataset was generated to test.
Quantitative variation in m.3243A>G mutation produce discrete changes in energy metabolism
geo:GSE129091
Expression profiling of cells carrying low versus high m.3243A>G mutation load against wild type, paired with bioenergetic, biogenesis, and fuel-catabolism assays, framed explicitly around the MELAS-versus-MIDD divergence.
Directly targets the question the entry records as open - why the same variant yields MELAS at high load and MIDD at low load - and reports that the transcriptional signatures are similar while the functional states diverge, which argues against expression profiling alone resolving the gap.
Show evidence (1 reference)
"despite striking similarities in the energy metabolic gene expression signature, the mitochondrial bioenergetics, biogenesis and fuel catabolic functions are distinct in cells harboring low or high levels of the m.3243 A > G mutation compared to wild type cells"
Shows the low-load and high-load states differ functionally while looking alike transcriptionally, a caution for biomarker work that relies on expression signatures.
Expression data from human blood from MELAS patients and controls
geo:GSE14882
Affymetrix whole-blood transcriptomes from ten MELAS patients and controls, analysed with regulatory- and protein-interaction-network methods to look for master regulators and disease-modifying genes.
One of the few MELAS datasets from an accessible tissue, so it is the natural starting point for the prognostic-biomarker gap. It also reports correlations between expression change, mutant load, and clinical characteristics, which is the genotype-phenotype question in a blood sample. Ten patients and a 2011 array platform limit what can be asked of it; treat it as a hypothesis source, not a validation set.
Show evidence (1 reference)
"Correlation analyses of gene alterations and clinico-genetic data detected significant correlations between A3243G-induced nuclear gene expression changes and mutant mtDNA load as well as disease characteristics."
Establishes that an accessible-tissue transcriptome tracks both mutant load and clinical features, the property a prognostic biomarker would need.
Mitochondrial DNA heteroplasmy drives cortical neuronal disturbances in human organoids harbouring the common m.3243A>G mutation
geo:GSE324301
Single-cell RNA-seq of human iPSC-derived cerebral organoid slices carrying m.3243A>G at varying heteroplasmy, generated as a cortical model because no animal carries the mutation. Reports heteroplasmy-dependent transcriptional shifts and preferential impairment of deep-layer neurons with axonal degeneration and apoptosis, compared against MELAS brain autopsy.
The most direct public response to the human-model-mismatch gap recorded in this entry: a model with cortical architecture, which iPSC-derived neuron monocultures lack, validated against patient brain tissue. It still cannot produce a stroke-like episode - organoid slices have no vasculature and no seizure activity - so it addresses neuronal vulnerability rather than the episode itself. Deposited 2026 with no linked publication at the time of curation, so nothing here is attributed to a peer-reviewed report.
Metabolic remodelling in hiPSC-derived myofibres carrying the m.3243A>G mutation
pride:PXD058785
Proteomic, phosphoproteomic, and metabolomic profiling of hiPSC-derived muscle fibres carrying variable m.3243A>G heteroplasmy, with membrane potential and oxygen consumption measured against mutant load.
Extends the model set beyond neurons to the tissue that produces the myopathy, and is heteroplasmy-graded, so it speaks to both the human-model-mismatch and genotype-phenotype gaps. No linked publication in the repository record at the time of curation.
Genetic Correction and Metabolic Rescue of Pluripotent Cells from Patients with mtDNA
geo:GSE61390
Transcriptomes from iPSC lines derived from a MELAS patient with heteroplasmic m.3243A>G and from a Leigh syndrome patient, used to evaluate generating genetically corrected pluripotent cells as a therapeutic strategy.
Relevant to the human-model-mismatch gap for a specific reason: it exploits the bimodal segregation of heteroplasmy during reprogramming that is otherwise the main limitation of iPSC models, turning it into a source of isogenic mutant and corrected lines.
Mitochondrial 3243A > G mutation confers pro-atherogenic and pro-inflammatory properties in MELAS iPS derived endothelial cells
geo:GSE127478
RNA-seq of endothelial cells differentiated from MELAS patient iPSCs and an isogenic control, characterising reactive oxygen species, oxidised LDL, VCAM-1 expression, and monocyte adhesion.
The vascular arm of the stroke-like-episode controversy in an isogenic human system. Note what it does and does not show: it establishes that m.3243A>G endothelium is intrinsically dysfunctional and inflammatory, which the vascular hypothesis requires, but endothelial dysfunction in a dish is not an ischemic stroke-like episode in cortex.
Show evidence (1 reference)
"in addition to endothelial dysfunction, diseased endothelial cells (ECs) were found to be pro-atherogenic and pro-inflammation due to high levels of ROS and Ox-LDLs, and high basal expressions of VCAM-1"
Provides a cell-autonomous mechanism for the vascular arm of the controversy in isogenic human endothelium.
Sonlicromanol improves neuronal network dysfunction and transcriptome changes linked to m.3243A>G heteroplasmy in iPSC-derived neurons
geo:GSE154825
Combined micro-electrode array recording and RNA-seq (MEA-seq) of excitatory neurons differentiated from MELAS patient iPSCs at low and high m.3243A>G heteroplasmy, co-cultured with astrocytes, with and without sonlicromanol.
The neuronal arm of the same controversy, and the only public MELAS dataset that measures network-level electrical activity rather than inferring it. It reports reduced presynaptic gene expression and non-cell-autonomous changes in co-cultured astrocytes, which is directly relevant to the neuron-astrocyte uncoupling variant of the hyperexcitability model. It also provides the transcriptomic readout for a drug now in a phase III trial in this entry.
Show evidence (1 reference)
"We combined micro-electrode array (MEA) measurements with RNA sequencing (MEA-seq) and found reduced expression of genes involved in mitochondrial respiration and presynaptic function, as well as non-cell autonomous processes in co-cultured astrocytes."
Couples network electrophysiology to transcriptome in m.3243A>G neurons and implicates astrocytes, the two elements the neuron-astrocyte uncoupling hypothesis requires.
Glutamate pathway dysfunction in MELAS syndrome is alleviated by ketogenic diet
geo:GSE165953
Multi-omic profiling of neuronal cybrids carrying graded m.3243A>G loads, reporting glutamate accumulation proportional to heteroplasmy, altered glutamate, GABA, and TCA-cycle gene clusters, confirmation in MELAS post-mortem brain, and reversal by ketone-body exposure.
Sits across three of the gaps at once. Glutamate accumulation scaled to heteroplasmy is a candidate mechanism for the cortical hyperexcitability the non-ischemic model requires; the authors propose glutamate as a disease biomarker; and the ketone-body rescue is the preclinical rationale for the ketogenic-diet trial recorded in this entry. The post-mortem brain confirmation is what lifts it above a cell-line result.
Show evidence (2 references)
"These results were supported by post-mortem brain tissue analysis from a MELAS patient, confirming the glutamate dysregulation."
Anchors the cell-model glutamate finding in human MELAS brain, which is what makes it usable for the cortical hyperexcitability question.
"a multi-omic integrated approach to MELAS cells revealed glutamate as a promising disease biomarker, while also indicating that a ketogenic diet should be tested in MELAS patients"
States both the biomarker candidacy and the therapeutic hypothesis that this dataset generated.
Differential expression of miRNAs in a cellular model of MELAS.
geo:GSE113300
Small-RNA sequencing of a transmitochondrial cybrid model homoplasmic for m.3243A>G, identifying 246 differentially expressed miRNAs whose predicted targets fall in muscle, nervous-system, and cardiac developmental pathways.
A candidate source for circulating-biomarker work, since miRNAs survive in plasma where transcriptomes do not. Two limits are worth stating: the model is 100% mutant cybrid rather than patient tissue, and the target pathways are computationally predicted. No linked publication in the repository record.
Defects in mitochondrial RNA processing in disease
geo:GSE85549
Parallel analysis of RNA ends (PARE) comparing m.3243A>G against m.3302A>G in mt-tRNA-Leu(UUR), mapping the 5' ends of mitochondrial RNAs to localise where each mutation disrupts tRNA processing.
Bears on a narrower but real question: two mutations in the same gene give different diseases (MELAS versus mitochondrial myopathy), and this dataset asks whether their RNA-processing defects differ. Relevant to the genotype-phenotype gap at the level of allele rather than heteroplasmy.
Show evidence (1 reference)
"identified common internal cleavage sites and new sites unique to the m.3243A>G mutants that do not correspond to transcript ends"
Identifies processing defects specific to the MELAS allele rather than shared with the myopathy allele, a candidate basis for allele-level phenotype divergence.
A Systems Approach for Decoding Mitochondrial Retrograde Signaling Pathways
geo:GSE27545
Expression profiling of cells engineered to carry varying amounts of m.3243A>G, used to infer the transcription factors mediating mitochondrial retrograde signalling; identifies an RXRA-ROS-JNK-PGC1alpha loop that further suppresses nuclear-encoded OXPHOS genes.
Supplies a candidate feed-forward mechanism by which a fixed mtDNA lesion progressively worsens nuclear OXPHOS gene expression, which is one of the few published proposals for why MELAS is progressive rather than static.
Show evidence (1 reference)
"This RXR pathway contributed to the decrease in mRNA abundances of oxidative phosphorylation enzymes encoded in the nuclear genome, thereby aggravating the dysfunction in oxidative phosphorylation caused by the reduced abundance of mitochondria-encoded enzymes of oxidative phosphorylation."
Describes a self-aggravating retrograde loop, a candidate mechanism for progression from a non-progressive genetic lesion.
Identification of miRNA, lncRNA and mRNA-associated ceRNA networks and potential biomarker for MELAS with mitochondrial DNA A3243G mutation
geo:GSE89066
Non-coding RNA profiling of muscle from 20 MELAS patients with m.3243A>G and 20 controls, with selected transcripts validated by qRT-PCR in muscle and serum in independent cohorts and assessed by ROC analysis against lactate. The GEO deposit itself holds four samples, so the 20-versus-20 cohort describes the study rather than the deposited profiles. SuperSeries; SubSeries GSE89065 and GSE89059 should not be curated separately.
The only public MELAS dataset built as a biomarker study proper - patient cohort, discovery and training phases, independent validation, and a circulating readout benchmarked against the incumbent marker. Read the claim precisely: serum miR-27b-3p outperformed lactate on *diagnostic* discrimination, which is not the same as predicting an individual's course, and the gap recorded in this entry is about prognosis. It is nonetheless the closest existing template for the longitudinal study that gap needs.
Show evidence (2 references)
"ROC curve analysis indicated reduced serum miR-27b-3p had the better diagnosis value than lactate and might serve as a novel, noninvasive biomarker for MELAS."
A circulating candidate benchmarked against lactate in patients, the design the prognostic-biomarker gap calls for even though the endpoint here is diagnosis.
"we found that the dysregulated muscle miRNAs and lncRNAs between 20 MELAS patients with mtDNA A3243G mutation and 20 controls formed complex regulation networks"
Establishes the patient-cohort basis and sample size of the discovery phase.
Integrated proteomic and metabolomic analyses of the mitochondrial neurodegenerative disease MELAS
massive:MSV000088237
Paired global proteomics (data-dependent acquisition verified by data-independent acquisition) and polar plus nonpolar metabolomics of patient-derived dermal fibroblasts carrying the ultra-rare MELAS variant m.14453G>A in MT-ND6, a complex I structural subunit, against control.
Two things make this worth more than its single-patient design. It is the only public patient-tissue multi-omics deposit found for a non-m.3243A>G MELAS genotype, so it speaks to the allele arm of the genotype-phenotype gap and to the complex I subunit subtype curated in this entry. And it reports downregulated arginine biosynthesis through blocked argininosuccinate synthase - a cell-intrinsic route to arginine deficiency, which is a different claim from the reduced plasma arginine that the existing therapeutic rationale rests on. One patient and one ultra-rare variant; the authors call it proof-of-principle and say validation in a larger cohort is still needed.
Show evidence (2 references)
"The most clinically relevant discovery is the downregulation of the arginine biosynthesis pathway, likely due to blocked argininosuccinate synthase, which is congruent with the MELAS cardinal symptom of stroke-like episodes and its current treatment by arginine infusion."
Supplies a cell-intrinsic biosynthetic mechanism for arginine deficiency, distinct from the plasma-level observations the arginine rationale currently rests on.
"The pathogenic mechanism of MELAS remains enigmatic due to the exceptional clinical heterogeneity and the obscure genotype-phenotype correlation among MELAS patients."
The authors frame the study against the same genotype-phenotype gap this entry records.
Mitochondrial disorders
geo:GSE1462
Affymetrix expression profiling of skeletal-muscle biopsies from twelve patients with mitochondrial encephalomyopathy - four with the common 4977 bp mtDNA deletion and eight carrying m.3243A>G, the latter split evenly between progressive external ophthalmoplegia and MELAS phenotypes - against age-matched controls.
The only dataset in this entry that holds genotype constant and varies clinical phenotype in patient tissue: four PEO and four MELAS patients, all m.3243A>G, all muscle. That design isolates the modifier question the genotype-phenotype gap turns on, and the authors read their result as support for nuclear background as the modifier. Four patients per arm on a 2005 array platform, so it is a hypothesis, not a demonstration - but it is the right experiment. Note this record is easy to mis-triage: its GEO title is the uninformative "Mitochondrial disorders" and summary-level screening reads it as a mixed-genotype cohort rather than a matched-genotype phenotype contrast.
Show evidence (2 references)
"the differential expression profile of MELAS(A3243G) vs. PEO(A3243G) may support a role of nuclear background in contributing to these different clinical phenotypes"
A patient-tissue contrast with the mtDNA genotype held fixed, nominating nuclear background as the modifier behind divergent m.3243A>G phenotypes.
"the clinical phenotype is not simply a direct consequence of the relative abundance of mutated mtDNA. Other factors, such as nuclear background, can contribute to the disease process, resulting in a wide range of phenotypes caused by the same mutation"
States the premise of the genotype-phenotype gap and the modifier hypothesis this dataset was built to test.
Clinical Trials
9
NCT06402123
PHASE_II
COMPLETED
PRIZM: randomized, double-blind, placebo-controlled crossover trial of oral zagociguat, a soluble guanylate cyclase stimulator, in genetically and phenotypically defined MELAS. Tests the NO-cGMP arm of the vascular hypothesis one step downstream of arginine and citrulline.
Show evidence (1 reference)
"PRIZM is a Phase 2b randomized, double-blind, placebo-controlled, 3-treatment, 2-period, crossover study evaluating the efficacy and safety of oral zagociguat 15 and 30 mg vs. placebo when administered daily for 12 weeks in participants with genetically and phenotypically defined MELAS."
Registration record establishing design, comparator, and MELAS-specific population.
NCT04475549
PHASE_II
TERMINATED
Single-arm safety, tolerability, pharmacokinetic and pharmacodynamic study of the CNS-penetrant soluble guanylate cyclase stimulator IW-6463 in adults with MELAS. Terminated.
Show evidence (1 reference)
"This is a single-arm study to evaluate safety and tolerability of oral IW-6463 in adults diagnosed with MELAS."
Registration record for the earlier, uncontrolled trial of the same mechanism.
NCT03952234
PHASE_I
COMPLETED
Dose-finding and safety study of L-citrulline in adults with MELAS, intended to establish a dose for a later efficacy trial of nitric oxide repletion.
Show evidence (1 reference)
"The main purpose of this study is to determine the safest maximum dose of an amino acid, citrulline, which will be used as potential treatment for adult patients with a disorder of energy metabolism called Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS)."
Establishes that citrulline dosing in MELAS was still at the dose-finding stage, before any efficacy trial.
NCT01339494
COMPLETED
Stable-isotope study of arginine flux and nitric oxide production in MELAS, with arginine and citrulline supplementation. The mechanistic study behind the finding that citrulline raises NO production more effectively than arginine.
Show evidence (1 reference)
"The purpose of this study is to measure nitric oxide in individuals with MELAS and see if giving arginine or citrulline will increase the formation of nitric oxide."
Registration record for the NO-flux study underpinning arginine and citrulline therapy in MELAS.
NCT04165239
PHASE_II
COMPLETED
KHENERGYZE: double-blind, randomized, placebo-controlled three-way crossover study of two doses of sonlicromanol (KH176) in m.3243A>G carriers, with attention-domain cognitive function as the primary endpoint. Notable as one of the few MELAS-relevant trials to use a cognitive rather than an episode-count endpoint.
Show evidence (1 reference)
"The primary objective is an evaluation of KH176 in the attention domain of cognitive functioning, as assessed by the visual identification test score of the Cogstate computerised cognitive testing battery."
Registration record establishing the cognitive primary endpoint of the randomized sonlicromanol crossover trial in m.3243A>G carriers.
NCT06451757
PHASE_III
RECRUITING
KHENERFIN: randomized, double-blind, placebo-controlled pivotal trial of sonlicromanol over 52 weeks in adults with a genetically confirmed m.3243A>G variant, with fatigue and physical function as primary outcomes. Enrolls by genotype rather than by MELAS syndrome label.
Show evidence (1 reference)
"The KHENERFIN study aims to determine whether the study medicine, sonlicromanol, is able to reduce symptoms of fatigue and the impact of fatigue on daily life, and whether sonlicromanol is able to improve physical abilities of people like balance control and lower limb skeletal muscle strength..."
Registration record for the pivotal sonlicromanol trial in m.3243A>G carriers.
NCT06013397
NOT_APPLICABLE
NOT_RECRUITING
Trial of a ketogenic diet in MELAS, testing an alternative-fuel strategy rather than a vascular or translational one.
Show evidence (1 reference)
"The goal of this clinical trial is to evaluate the effectiveness of ketogenic diet in patients with MELAS syndrome."
Registration record establishing that ketogenic-diet efficacy in MELAS remains an open, untested question.
NCT01532791
RECRUITING
Natural-history study of known m.3243A>G carriers together with their maternal relatives, enrolled regardless of carrier status, with paternal relatives as controls. The design is what makes it relevant here: it ascertains through the family rather than through a neurology clinic, so it can in principle measure organ involvement in carriers who would never present to a mitochondrial-disease service.
Show evidence (1 reference)
"and their maternal relatives (carrier status not a requirement for participation). Paternal relatives will serve as controls."
Family-based rather than clinic-based ascertainment, the sampling frame needed to estimate organ involvement without neurology-referral bias.
NCT05554835
RECRUITING
Global mitochondrial disease registry harmonizing prior national registries, intended to support natural-history description, outcome-measure definition, and trial readiness.
Show evidence (1 reference)
"provision of a global registry for mitochondrial disorders to harmonize previous national registries, enable world-wide participation and facilitate natural history studies, definition of outcome measures and conduction of clinical trials"
The registry infrastructure that both the ascertainment gap and the absent trial-ready outcome measure depend on.
Experimental Models
1
m.3243A>G patient iPSC-derived neurons
IPSC_DERIVED_MODEL
Induced pluripotent stem cells reprogrammed from m.3243A>G patients, then differentiated to neurons and to teratoma-derived tissues. The model exists because the mitochondrial genome cannot be edited by transgenic methods, so patient cells are the only route to a human m.3243A>G system. Its distinctive result is that respiratory-chain deficiency is cell-type specific from one shared genotype, with complex I predominating as it does in patient tissue, and that neurons additionally clear complex I by mitophagy.
Organism
human
NCBITaxon:9606
NCBI Taxonomy (NCBITaxon)
Relation: this experimental model is built in this organism
This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
Pathograph links
Complex I-predominant deficiency and neuronal mitophagy
Reproduces the complex I-predominant respiratory-chain defect seen in MELAS patient tissue and adds the neuron-specific mitophagic clearance step.
Limitations: Heteroplasmy segregates bimodally toward homoplasmy during reprogramming, so the clone's mutant load is not the patient's tissue load; the model is a cultured neuron rather than cortex, and it cannot reproduce a stroke-like episode, which requires vasculature, seizure activity, and an intact cortical network.
Readouts
Respiratory chain complex I deficiency
Direction: DECREASED
Interpretation: Matches the complex I predominance observed in MELAS patient tissues.
Show evidence (1 reference)
"Induced pluripotent stem cell-derived neurons and various tissues derived from teratomas manifested cell-type specific respiratory chain (RC) deficiency patterns. Similar to MELAS patient tissues, complex I defect predominated."
The measurement establishing complex I predominance in the model and its correspondence to patient tissue.
Perinuclear PINK1/Parkin-positive autophagosomal sequestration of complex I
Direction: INCREASED
Interpretation: Indicates active mitophagic degradation of complex I on neuronal differentiation.
Show evidence (1 reference)
"Upon neuronal differentiation, complex I specifically was sequestered in perinuclear PTEN-induced putative kinase 1 (PINK1) and Parkin-positive autophagosomes, suggesting active degradation through mitophagy."
The imaging readout supporting selective mitophagy of complex I in neurons.
Show evidence (1 reference)
"Our data show that cellular context actively modifies RC deficiency manifestation in MELAS and that autophagy is a significant component of neuronal MELAS pathogenesis."
The authors' own statement that the model is informative for neuronal MELAS pathogenesis.
A second use of MELAS iPSC-derived neurons is as a recipient in mitochondrial-transfer experiments, where donated mitochondria from purified mesenchymal stem cells restored membrane potential, ATP and ROS production, calcium storage, and oxygen consumption rate.
Show evidence (1 reference)
"Here, utilizing induced pluripotent stem cells (iPSC), we differentiated neurons with impaired mitochondrial function from patients with MELAS."
Independent derivation of MELAS iPSC neurons with an impaired-mitochondrial-function phenotype, used as a therapeutic testbed.
Source YAML
click to showname: MELAS Syndrome
creation_date: "2026-06-08T00:00:00Z"
description: >-
MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and
Stroke-like episodes) is a maternally inherited multisystem mitochondrial
disease caused most often by the m.3243A>G point mutation in the MT-TL1 gene,
which encodes the mitochondrial tRNA-Leu(UUR). The mutation impairs
mitochondrial tRNA aminoacylation and translation, producing a respiratory
chain (oxidative phosphorylation) deficiency that manifests above a
heteroplasmy threshold. Energy failure in brain, muscle, and small blood
vessels drives the cardinal stroke-like episodes (often in non-vascular
territories), lactic acidosis, seizures, myopathy, sensorineural hearing
loss, and diabetes mellitus. Other MT-TL1 variants and variants in additional
mitochondrial genes (notably MT-ND5) cause a minority of cases.
Two points shape how the entry should be read. First, the mechanism of the
stroke-like episode itself is genuinely unsettled: the classical ischemic
"mitochondrial angiopathy" account and the non-ischemic neuronal
hyperexcitability account make different predictions and imply different
treatments, and the pathograph here wires both, with the causal edges tagged
by hypothesis group. Second, MELAS is a clinical syndrome carved out of a much
larger m.3243A>G carrier population: only about a tenth of carriers in a
systematically phenotyped cohort met classical MELAS criteria, so
organ-specific frequencies drawn from carrier cohorts and from MELAS cohorts
are not interchangeable.
references:
- reference: PMID:20301411
title: MELAS.
tags:
- GeneReviews
category: Mendelian
parents:
- hereditary disease
- mitochondrial disease
disease_term:
preferred_term: MELAS syndrome
term:
id: MONDO:0010789
label: MELAS syndrome
notes: >-
Lump/split ruling for the gene-defined MELAS children in MONDO. All ten
(MONDO:0800032 through MONDO:0800041) are curated as has_subtypes rows on this
entry rather than as separate Disease entries: they share one mechanism chain
and one management approach, and differ only in which mtDNA gene carries the
variant. The evidence behind them is very uneven, which the per-row and
per-gene notes record. MT-TL1 and MT-ND5 are named by GeneReviews and appear in
cohorts; MT-TQ, MT-TK and MT-TC rest on one reported patient each; MT-TS1 was
reported in a MERRF/MELAS overlap family rather than in classical MELAS.
MONDO's gene list is narrower than the published one. Enumerating the
hierarchical children of MONDO:0010789 in OLS on 2026-09-24 returns exactly
those ten terms, with no child for MT-TV, MT-TW or MT-TM, although MELAS has
been attributed to variants in all three. Those three genes are curated here as
genetic records with no subtype anchor, and bound to the non-MT-TL1 mt-tRNA
pathophysiology node, since a subtype row needs a MONDO term and a genetic
record does not.
has_subtypes:
- name: MT-TL1
display_name: MT-TL1 tRNA-Leu(UUR), including m.3243A>G
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TL1
term:
id: MONDO:0800032
label: MELAS syndrome caused by mutation in MTTL1
description: >-
The majority form, caused by pathogenic variants in MT-TL1 (mitochondrial
tRNA-Leu(UUR)). The m.3243A>G transition accounts for roughly 80% of MELAS.
Non-3243 MT-TL1 variants, most notably m.3271T>C, cause a minority of cases
and impair tRNA-Leu(UUR) function through the same loss of the wobble
taurine modification.
genes:
- preferred_term: MT-TL1
term:
id: hgnc:7490
label: MT-TL1
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The m.3243A>G pathogenic variant in the mitochondrial gene MT-TL1 is
present in approximately 80% of individuals with MELAS.
explanation: Establishes m.3243A>G as the majority genotype defining this subtype.
- reference: PMID:17132941
reference_title: Human mitochondrial diseases associated with tRNA wobble modification deficiency.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "mt tRNA(Leu(UUR)) with either the MELAS 3243 or 3271 mutation"
explanation: Confirms that the 3271 variant shares the wobble-modification defect of the common 3243 variant.
- name: MT-TQ
display_name: MT-TQ tRNA-Gln
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TQ
term:
id: MONDO:0800033
label: MELAS syndrome caused by mutation in MTTQ
description: >-
MELAS-spectrum disease attributed to a heteroplasmic m.4332G>A variant in
MT-TQ (mitochondrial tRNA-Gln). The reported presentation combined deafness,
a stroke-like episode, leukoencephalopathy and basal ganglia calcification,
with a late onset and neuroradiological pattern the authors judged atypical
for MELAS.
genes:
- preferred_term: MT-TQ
term:
id: hgnc:7495
label: MT-TQ
evidence:
- reference: PMID:11171912
reference_title: Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A heteroplasmic G to A transition at nucleotide 4332 in the tRNA glutamine
gene was identified in the patient's muscle mitochondrial DNA.
explanation: Identifies the MT-TQ variant reported in a patient given a MELAS-spectrum diagnosis.
- reference: PMID:11171912
reference_title: Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The pathogenicity of the mutation was shown in single muscle fibers by the
correlation between high mutation load and cytochrome c oxidase defect.
explanation: >-
Single-fibre correlation of mutation load with a respiratory-chain defect
is the pathogenicity argument for this variant, and it is the standard
heteroplasmy-threshold argument rather than a zygosity claim.
- reference: PMID:11171912
reference_title: Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The authors studied a 47-year-old patient who presented with an association of deafness, acute cerebral stroke-like episode, leukoencephalopathy, and extensive basal ganglia calcifications. Late onset and neuroradiologic findings were atypical for MELAS syndrome"
explanation: Supports the reported presentation and the authors' judgement that onset and imaging were atypical for MELAS.
- name: MT-TH
display_name: MT-TH tRNA-His
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TH
term:
id: MONDO:0800034
label: MELAS syndrome caused by mutation in MTTH
description: >-
MELAS-spectrum disease caused by variants in MT-TH (mitochondrial tRNA-His).
The reported family carried m.12146A>G and showed varying degrees of lactic
acidosis and stroke-like episodes; transmitochondrial cybrids established
that the tRNA-His variant, rather than the nuclear background, produced the
respiratory-chain enzyme deficiency.
genes:
- preferred_term: MT-TH
term:
id: hgnc:7487
label: MT-TH
evidence:
- reference: PMID:21704194
reference_title: New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We report a new mutation in m.12146 A>G in the mt-tRNA(His) in a family
with a remarkable clinical history having different degrees of lactic
acidosis and stroke-like episodes.
explanation: Ties an MT-TH variant to the lactic acidosis and stroke-like episodes that define MELAS.
- reference: PMID:21704194
reference_title: New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Transmitochondrial cybrid analysis proved that this tRNA(His) mutation
causes the enzymatic deficiency.
explanation: Cybrid transfer separates the mtDNA variant's effect from the patient's nuclear background.
- name: MT-TK
display_name: MT-TK tRNA-Lys
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TK
term:
id: MONDO:0800035
label: MELAS syndrome caused by mutation in MTTK
description: >-
MELAS-spectrum disease attributed to m.8296A>G in MT-TK (mitochondrial
tRNA-Lys). The reported patient had optic atrophy, cardiomyopathy and
bilateral striatal necrosis before stroke-like episodes appeared, with
ragged-red fibres on muscle biopsy. The same variant had previously been
reported in patients with diabetes mellitus or with myoclonus epilepsy with
ragged-red fibres rather than MELAS, so this genotype is not MELAS-specific.
genes:
- preferred_term: MT-TK
term:
id: hgnc:7489
label: MT-TK
evidence:
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Skeletal muscle total mitochondrial DNA analysis identified a
heteroplasmic A to G point mutation in the tRNA(Lys) gene at position
8296.
explanation: Identifies the MT-TK variant in a patient diagnosed with MELAS.
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We conclude that the 8296 mutation is likely to be pathogenic"
explanation: The authors' own pathogenicity assessment for this MT-TK variant.
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We report on a unique patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) presenting optic atrophy, cardiomyopathy, and bilateral striatal necrosis before stoke-like episodes became apparent."
explanation: Supports the reported presentation preceding the stroke-like episodes.
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Recent reports describe the 8296 mutation identified in patients with diabetes mellitus or myoclonus epilepsy with ragged-red fibers, not MELAS."
explanation: Supports the statement that this genotype is not MELAS-specific.
- name: MT-TC
display_name: MT-TC tRNA-Cys
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TC
term:
id: MONDO:0800036
label: MELAS syndrome caused by mutation in MTTC
description: >-
MELAS-spectrum disease attributed to m.5783G>A in MT-TC (mitochondrial
tRNA-Cys). In the reported case genetic analysis of blood
lymphocyte DNA was negative and the variant was found only on sequencing
mtDNA from urinary sediment, so a negative blood result did not exclude the
diagnosis.
genes:
- preferred_term: MT-TC
term:
id: hgnc:7477
label: MT-TC
evidence:
- reference: PMID:38881794
reference_title: "Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the patient was eventually diagnosed with MELAS with the mtDNA 5783G>A
mutation in the MT-TC gene with a urinary sediment genetic test
explanation: Names MT-TC as the gene carrying the variant in a patient diagnosed with MELAS.
- reference: PMID:38881794
reference_title: "Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This case report expands the genetic repertoire associated with MELAS syndrome"
explanation: The authors present this genotype as an addition to the MELAS gene spectrum rather than an established cause.
- reference: PMID:38881794
reference_title: "Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Although genetic analysis of blood lymphocyte DNA was negative, brain imaging, including magnetic resonance imaging, magnetic resonance spectroscopy, and clinical and laboratory findings, were all suggestive of MELAS."
explanation: Supports the negative blood-lymphocyte result that preceded the urinary-sediment diagnosis.
- name: MT-TS1
display_name: MT-TS1 tRNA-Ser(UCN)
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TS1
term:
id: MONDO:0800037
label: MELAS syndrome caused by mutation in MTTS1
description: >-
MELAS-spectrum disease caused by variants in MT-TS1 (mitochondrial
tRNA-Ser(UCN)). The reported family carried a heteroplasmic m.7512T>C
variant disrupting a conserved acceptor-stem base pair and presented as a
MERRF/MELAS overlap syndrome rather than as classical MELAS.
genes:
- preferred_term: MT-TS1
term:
id: hgnc:7497
label: MT-TS1
evidence:
- reference: PMID:7669057
reference_title: A novel point mutation in the mitochondrial tRNA(Ser(UCN)) gene detected in a family with MERRF/MELAS overlap syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We found a new point mutation in the mitochondrial tRNA(Ser(UCN)) gene in
a family with MERRF/MELAS overlap syndrome by screening for heteroplasmy
explanation: Links MT-TS1 to a MELAS-overlap phenotype rather than to MELAS alone.
- reference: PMID:7669057
reference_title: A novel point mutation in the mitochondrial tRNA(Ser(UCN)) gene detected in a family with MERRF/MELAS overlap syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "revealed a heteroplasmic mutation at nt 7512 in the tRNA(Ser(UCN)) gene"
explanation: Gives the specific heteroplasmic MT-TS1 variant behind this subtype.
- name: MT-TS2
display_name: MT-TS2 tRNA-Ser(AGY)
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-TS2
term:
id: MONDO:0800041
label: MELAS syndrome caused by mutation in MTTS2
description: >-
MELAS-spectrum disease caused by variants in MT-TS2 (mitochondrial
tRNA-Ser(AGY)). A m.12244G>A variant has been reported with a classical
MELAS phenotype together with functional evidence of impaired mitochondrial
translation and oxidative phosphorylation. Across the reported MT-TS2
variants the phenotype is variable, spanning encephalopathy, myopathy,
deafness, diabetes and retinopathy.
genes:
- preferred_term: MT-TS2
term:
id: hgnc:7498
label: MT-TS2
evidence:
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We identified a rare m.12244G > A variant in the tRNASer(AGY) gene
associated with classical MELAS phenotype.
explanation: Ties an MT-TS2 variant to a classical MELAS presentation.
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Literature review showed that MT-TS2 variants are associated with variable
phenotypes including encephalopathy, myopathy, deafness, diabetes, and
retinopathy.
explanation: Records that MT-TS2 genotypes are not MELAS-specific, which is why this row is a spectrum rather than a distinct disease.
- name: MT-ND1
display_name: MT-ND1 complex I subunit
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-ND1
term:
id: MONDO:0800038
label: MELAS syndrome caused by mutation in MTND1
description: >-
MELAS-spectrum disease caused by variants in the complex I subunit gene
MT-ND1. This genotype class attacks complex I directly rather than through a
mitochondrial translation defect. Two novel missense variants, m.3959G>A and
m.3995A>G, were reported in probands with MELAS features and reduced complex
I activity.
genes:
- preferred_term: MT-ND1
term:
id: hgnc:7455
label: MT-ND1
evidence:
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sequencing of the mitochondrial DNA revealed two novel MT-ND1 gene
missense mutations, m.3959G>A and m.3995A>G, which are highly conserved
among species.
explanation: Names the MT-ND1 variants reported in probands with MELAS features.
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A respiratory chain function study showed decreased activity of
mitochondrial respiratory chain complex I in both probands.
explanation: Confirms that the biochemical lesion in this genotype class is at complex I.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Independent cohort confirmation that MT-ND1 is among the complex I subunit genes reported in MELAS.
- name: MT-ND5
display_name: MT-ND5 complex I subunit
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-ND5
term:
id: MONDO:0800039
label: MELAS syndrome caused by mutation in MTND5
description: >-
MELAS-spectrum disease caused by variants in the complex I subunit gene
MT-ND5, the commonest non-MT-TL1 cause named by GeneReviews. In a MELAS/Leigh
overlap cohort, m.13513G>A was the commonest variant among the thirteen
patients carrying complex I subunit gene variants.
genes:
- preferred_term: MT-ND5
term:
id: hgnc:7461
label: MT-ND5
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Pathogenic variants in MT-TL1 or other mtDNA genes, particularly MT-ND5,
can also cause this disorder.
explanation: GeneReviews names MT-ND5 as the leading non-MT-TL1 cause of MELAS.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
explanation: Identifies MT-ND5 m.13513G>A as the leading variant in MELAS/Leigh overlap.
- name: MT-ND6
display_name: MT-ND6 complex I subunit
subtype_term:
preferred_term: MELAS syndrome caused by mutation in MT-ND6
term:
id: MONDO:0800040
label: MELAS syndrome caused by mutation in MTND6
description: >-
MELAS-spectrum disease caused by variants in the complex I subunit gene
MT-ND6. m.14453G>A has been reported in MELAS, including a late-onset
presentation initially taken for acute encephalitis.
genes:
- preferred_term: MT-ND6
term:
id: hgnc:7462
label: MT-ND6
evidence:
- reference: PMID:32552696
reference_title: "Late-onset MELAS syndrome with mtDNA 14453G→A mutation masquerading as an acute encephalitis: a case report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "broadens the phenotypic spectrum of MELAS syndrome associated with ND6 gene mutation"
explanation: The authors place this case within the MELAS phenotypic spectrum attributed to MT-ND6.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Independent cohort confirmation that MT-ND6 is among the complex I subunit genes reported in MELAS.
prevalence:
- population: Adults in Southwest Finland (2022, m.3243A>G-related disease)
measure_type: POINT_PREVALENCE
prevalence_class: BAND_1_9_PER_100000
rate_per_100000: 4.2
percentage: 4.2/100,000
evidence:
- reference: PMID:38361968
reference_title: "Incidence and prevalence of mtDNA-related adult mitochondrial disease in Southwest Finland, 2009-2022: an observational, population-based study."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The prevalence of adult mtDNA disease associated with m.3243A>G was
4.2/100 000 (95% CI, 2.5 to 6.7)
explanation: >-
Population-based prevalence of adult m.3243A>G-related mitochondrial
disease, the genotype underlying most MELAS.
notes: >-
m.3243A>G underlies multiple overlapping clinical syndromes (MELAS, MIDD),
so this figure reflects the broader m.3243A>G disease population rather than
classic MELAS specifically.
- population: Japan (nationwide prospective cohort, clinically defined MELAS)
measure_type: POINT_PREVALENCE
prevalence_class: BAND_1_9_PER_1000000
rate_per_100000: 0.18
rate_low: 0.02
rate_high: 0.34
notes: >-
Prevalence of clinically defined MELAS (Japanese diagnostic criteria) in the
total Japanese population, an order of magnitude below the prevalence of
m.3243A>G-related disease as a whole because most carriers never meet full
MELAS criteria.
evidence:
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the prevalence of MELAS was 0.18 (95%CI, 0.02-0.34)/100,000 in the total population"
explanation: Nationwide prospective cohort estimate for clinically defined MELAS specifically, rather than for all m.3243A>G carriers.
- population: General population (m.3243A>G carrier frequency)
measure_type: CARRIER_FREQUENCY
prevalence_class: ABOVE_1_IN_1000
rate_per_100000: 250.0
notes: >-
Carrier frequency of the causal variant, not of MELAS. Most m.3243A>G
carriers have MIDD, an oligosymptomatic phenotype, or no symptoms at all;
the gap between this figure and the MELAS prevalence above is the measure of
incomplete penetrance for the full syndrome.
evidence:
- reference: PMID:23355809
reference_title: "The UK MRC Mitochondrial Disease Patient Cohort Study: clinical phenotypes associated with the m.3243A>G mutation--implications for diagnosis and management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Population-based studies suggest the m.3243A>G mutation in MTTL1 is the most common disease-causing mtDNA mutation, with a carrier rate of 1 in 400 people."
explanation: Establishes the population carrier rate of the causal variant, which greatly exceeds the prevalence of the MELAS syndrome itself.
progression:
- phase: Juvenile-onset form
age_range: Juvenile onset
notes: >-
Short stature is significantly more frequent in the juvenile form, and
juvenile onset carries a substantially higher risk of death than adult
onset. The cited cohort abstract does not state the age cutoff separating
the juvenile and adult forms. In a separate pediatric cohort, earlier
seizure onset predicted drug-resistant epilepsy.
evidence:
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "According to a Kaplan-Meier analysis, the juvenile form was associated with a higher risk of death than the adult form (hazard ratio, 3.29; 95%CI, 1.32-8.20; p=0.0105)."
explanation: Quantifies the survival difference between the juvenile and adult forms in a nationwide prospective cohort.
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Short stature was significantly more frequent in the juvenile form"
explanation: Supports the juvenile-form short-stature difference stated in the notes.
- reference: PMID:27671241
reference_title: "Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group"
explanation: Supports the seizure-onset sentence; this pediatric cohort compares earlier and later seizure onset, not the juvenile and adult forms.
- phase: Adult-onset form
age_range: Onset in adulthood
notes: >-
Hearing loss, cortical blindness, and diabetes mellitus are significantly
more frequent in the adult form than in the juvenile form.
evidence:
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Short stature was significantly more frequent in the juvenile form, whereas hearing loss, cortical blindness and diabetes mellitus were significantly more frequent in the adult form."
explanation: Separates the two natural-history subgroups by their differentiating manifestations.
- phase: Late-onset presentation (after age 40)
age_range: Onset after 40 years
notes: >-
A small minority present after age 40 and typically follow a less aggressive
course, though the late-onset course is not uniformly benign.
evidence:
- reference: PMID:30766507
reference_title: "Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Although childhood is the typical age of onset, a small fraction (1-6%) of individuals manifest the disease after 40 years of age and usually have a less aggressive disease course."
explanation: Documents the frequency and general course of late-onset MELAS.
- phase: Rapid degenerative decline in the first five years after onset
duration: 5 years from onset
notes: >-
Disease-rating-scale scores rise steeply within five years of onset in both
the juvenile and adult forms, so the early years after the first
stroke-like episode carry most of the accumulating disability.
evidence:
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "According to the Japanese mitochondrial disease rating scale, MELAS patients showed rapidly increasing scores (mean±standard deviation, 12.8±8.7) within 5years from onset of the disease."
explanation: Quantifies the rate of degenerative progression in the first five years.
- phase: Accumulated disability and death
notes: >-
Acute stroke-like episodes and status epilepticus are the leading causes of
death, and survival declines mainly in the first dozen years after onset.
Progressive brain atrophy and dementia are the sequelae of recurrent
stroke-like episodes in survivors.
evidence:
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Of the 121 subjects who successfully completed the follow-up, 28 subjects died (mortality rate 23.1%). An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%)."
explanation: Cohort mortality rate and the dominant proximate causes of death.
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The survival rate declined mainly within 12years after the disease onset."
explanation: Supports survival declining mainly in the first dozen years after onset.
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Among the surviving patients (n=93), 39.8% (37/93) required assistance in daily life (mRS scores 3-5). The mRS scores were inversely correlated with the age of onset"
explanation: Quantifies residual disability among survivors and its inverse relation to age at onset.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
explanation: Identifies the long-term neurological endpoint of recurrent stroke-like episodes.
clinical_burden:
burden_level: HIGH
rationale: >-
MELAS combines a high mortality rate with severe residual disability among
survivors. Roughly a quarter of a followed cohort died, most often from
acute stroke-like episodes or status epilepticus, and about 40% of
survivors needed help with daily life. Epilepsy was drug-resistant in a
pediatric MELAS epilepsy cohort, and recurrent stroke-like episodes leave
progressive brain atrophy and dementia. Treatment is generally supportive;
no disease-modifying therapy is established.
evidence:
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "MELAS had high mortality and morbidity in this cohort of Chinese patients."
explanation: Direct statement of the mortality and morbidity burden in a followed cohort.
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Of the 121 subjects who successfully completed the follow-up, 28 subjects died (mortality rate 23.1%). An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%). Among the surviving patients (n=93), 39.8% (37/93) required assistance in daily life (mRS scores 3-5)."
explanation: Supplies the mortality, cause-of-death, and survivor-disability figures stated in the rationale.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
explanation: Supports the long-term neurological burden of recurrent stroke-like episodes.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Treatment for MELAS is generally supportive."
explanation: Supports the absence of an established disease-modifying therapy.
- reference: PMID:27671241
reference_title: "Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Epilepsy in this population is drug resistant, but a certain degree of clinical seizure reduction was achievable with antiepileptic drugs, with more favorable outcomes than historically expected."
explanation: Establishes drug-resistant epilepsy as a contributor to burden in a pediatric MELAS cohort, while noting partial treatability. It supports the epilepsy sentence of the rationale only; the mortality and disability figures rest on the survival cohort.
pathophysiology:
- name: Taurine wobble-modification deficiency of tRNA-Leu(UUR)
biological_scale: MOLECULAR
description: >-
The pathogenic MT-TL1 variants abolish the normal taurine-containing
modification (5-taurinomethyluridine) at the anticodon wobble position of
mitochondrial tRNA-Leu(UUR). This is the proximal molecular lesion: the
unmodified anticodon can no longer form a correct codon-anticodon pair,
and the resulting decoding failure is codon-specific rather than a uniform
loss of leucine incorporation. The same defect is the rationale for taurine
supplementation.
genes:
- preferred_term: MT-TL1
term:
id: hgnc:7490
label: MT-TL1
biological_processes:
- preferred_term: tRNA wobble uridine modification
modifier: DECREASED
term:
id: GO:0002098
label: tRNA wobble uridine modification
evidence:
- reference: PMID:15893315
reference_title: Wobble modification deficiency in mutant tRNAs in patients with mitochondrial diseases.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "mt tRNA(Leu(UUR)) with a MELAS A3243G mutation and mt tRNA(Lys) with a MERRF A8344G mutation derived from HeLa background cybrid cells are deficient in normal taurine-containing modifications"
explanation: Identifies the specific chemical modification that is absent from mutant tRNA-Leu(UUR) in MELAS.
- reference: PMID:15893315
reference_title: Wobble modification deficiency in mutant tRNAs in patients with mitochondrial diseases.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "We report here wobble modification deficiencies of mutant mt tRNAs from cybrid cells with different nuclear backgrounds, as well as from patient tissues."
explanation: Shows the modification defect is not an artefact of one cybrid nuclear background and is present in patient tissue.
downstream:
- target: Mitochondrial tRNA-Leu(UUR) translation defect
causal_link_type: DIRECT
description: >-
Loss of the wobble taurine modification degrades codon-anticodon pairing,
with UUG decoding affected more severely than UUA, so mitochondrial
translation fails in a codon-biased way.
evidence:
- reference: PMID:17132941
reference_title: Human mitochondrial diseases associated with tRNA wobble modification deficiency.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "the translational activity of MELAS mt tRNA(Leu(UUR)) lacking wobble modification is more depressed in decoding of UUG codon than UUA codon"
explanation: Establishes that the decoding defect is codon-specific, which is what distinguishes MELAS from a generic translation failure.
- name: Mitochondrial tRNA-Leu(UUR) translation defect
biological_scale: MOLECULAR
description: >-
The m.3243A>G variant in MT-TL1 disrupts the structure and aminoacylation
of mitochondrial tRNA-Leu(UUR), impairing mitochondrial protein synthesis
(translation) of the mtDNA-encoded respiratory chain subunits.
genes:
- preferred_term: MT-TL1
term:
id: hgnc:7490
label: MT-TL1
biological_processes:
- preferred_term: tRNA aminoacylation for protein translation
modifier: DECREASED
term:
id: GO:0006418
label: tRNA aminoacylation for protein translation
- preferred_term: mitochondrial translation
modifier: DECREASED
term:
id: GO:0032543
label: mitochondrial translation
evidence:
- reference: PMID:2102678
reference_title: A mutation in the tRNA(Leu)(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Here we report an A-to-G transition mutation at nucleotide pair 3,243 in
the dihydrouridine loop of mitochondrial tRNA(Leu)(UUR) that is specific
to patients with MELAS.
explanation: >-
The foundational paper identifying the m.3243A>G transition in
mitochondrial tRNA-Leu(UUR) (MT-TL1) as the MELAS-specific lesion.
- reference: PMID:23392880
reference_title: Taurine deficiency and MELAS are closely related syndromes.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
These mutations reduce both the aminoacylation of tRNA(Leu(UUR)) and a
posttranslational modification in the wobble position of tRNA(Leu(UUR)).
Both changes result in reduced transcription of mitochondria-encoded
proteins
explanation: >-
Directly supports the mechanism that MT-TL1 mutations impair tRNA
aminoacylation and wobble modification, reducing mitochondrial protein
synthesis.
downstream:
- target: Oxidative phosphorylation deficiency
causal_link_type: DIRECT
description: >-
Defective synthesis of mtDNA-encoded subunits reduces assembly and
activity of the respiratory chain complexes, especially complex I.
evidence:
- reference: PMID:23392880
reference_title: Taurine deficiency and MELAS are closely related syndromes.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Both changes result in reduced transcription of mitochondria-encoded
proteins
explanation: Links the tRNA defect to reduced production of the mtDNA-encoded respiratory chain subunits.
- name: Non-MT-TL1 mitochondrial tRNA dysfunction
biological_scale: MOLECULAR
description: >-
MELAS is primarily linked to variants in mitochondrial tRNA genes, and the
reported set extends beyond MT-TL1 to MT-TQ, MT-TH, MT-TK, MT-TC, MT-TS1,
MT-TS2, MT-TV, MT-TW and MT-TM. These variants impair mitochondrial
translation of the mtDNA-encoded respiratory chain subunits, the same lesion
MT-TL1 variants produce, while acting on different tRNAs. Cybrid transfer for
MT-TH places the resulting enzyme deficiency in the tRNA rather than in the
nuclear background, and functional assays for MT-TS2 and MT-TW measure the
translation defect directly.
genes:
- preferred_term: MT-TQ
term:
id: hgnc:7495
label: MT-TQ
- preferred_term: MT-TH
term:
id: hgnc:7487
label: MT-TH
- preferred_term: MT-TK
term:
id: hgnc:7489
label: MT-TK
- preferred_term: MT-TC
term:
id: hgnc:7477
label: MT-TC
- preferred_term: MT-TS1
term:
id: hgnc:7497
label: MT-TS1
- preferred_term: MT-TS2
term:
id: hgnc:7498
label: MT-TS2
- preferred_term: MT-TV
term:
id: hgnc:7500
label: MT-TV
- preferred_term: MT-TW
term:
id: hgnc:7501
label: MT-TW
- preferred_term: MT-TM
term:
id: hgnc:7492
label: MT-TM
biological_processes:
- preferred_term: mitochondrial translation
modifier: DECREASED
term:
id: GO:0032543
label: mitochondrial translation
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
A common subtype, MELAS ... is primarily linked to variants in
mitochondrial transfer RNA (mt-tRNA) genes
explanation: >-
Establishes that the mitochondrial tRNA genes as a class, not MT-TL1 alone,
are the principal MELAS genotypes. Graded as background because the
sentence states the field's position rather than this paper's own result.
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Functional analysis demonstrated impaired mitochondrial translation and OXPHOS dysfunction."
explanation: Direct functional evidence that a non-MT-TL1 mt-tRNA variant impairs mitochondrial translation.
- reference: PMID:21704194
reference_title: New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Transmitochondrial cybrid analysis proved that this tRNA(His) mutation
causes the enzymatic deficiency.
explanation: Cybrid transfer places the respiratory-chain deficiency in the tRNA variant rather than the nuclear background.
- reference: PMID:26297375
reference_title: Molecular pathomechanisms and cell-type-specific disease phenotypes of MELAS caused by mutant mitochondrial tRNA(Trp).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
This mutation firstly disturbed the translation machinery of mitochondrial
tRNA(Trp) and induced mitochondrial respiratory dysfunction, followed by
severely injured mitochondrial homeostasis.
explanation: >-
Orders the two lesions for a second mt-tRNA gene: the translation defect
comes first and the respiratory dysfunction follows, which is the claim the
decreased mitochondrial translation annotation on this node makes.
downstream:
- target: Oxidative phosphorylation deficiency
causal_link_type: DIRECT
description: >-
Impaired mitochondrial translation reduces synthesis of the mtDNA-encoded
respiratory chain subunits, lowering respiratory chain activity.
evidence:
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Functional analysis demonstrated impaired mitochondrial translation and OXPHOS dysfunction."
explanation: Reports the translation defect and the oxidative phosphorylation defect together in the same variant.
- name: Complex I structural subunit defect
biological_scale: MOLECULAR
description: >-
Variants in the mtDNA-encoded complex I subunit genes MT-ND1, MT-ND5 and
MT-ND6 lower complex I activity by altering a structural subunit directly,
rather than by impairing mitochondrial translation. In a MELAS/Leigh overlap
cohort, thirteen patients carried MTND variants, with m.13513G>A in MT-ND5
the commonest.
genes:
- preferred_term: MT-ND1
term:
id: hgnc:7455
label: MT-ND1
- preferred_term: MT-ND5
term:
id: hgnc:7461
label: MT-ND5
- preferred_term: MT-ND6
term:
id: hgnc:7462
label: MT-ND6
molecular_functions:
- preferred_term: NADH dehydrogenase (ubiquinone) activity
modifier: DECREASED
term:
id: GO:0008137
label: NADH dehydrogenase (ubiquinone) activity
evidence:
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A respiratory chain function study showed decreased activity of
mitochondrial respiratory chain complex I in both probands.
explanation: Measures reduced complex I activity in patients carrying MT-ND1 variants, the biochemical claim this node makes.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Names the three complex I subunit genes bound on this node.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
explanation: Gives the cohort counts behind the statement that MT-ND5 m.13513G>A leads this genotype class.
downstream:
- target: Oxidative phosphorylation deficiency
causal_link_type: DIRECT
description: >-
Reduced complex I activity lowers electron entry into the respiratory chain
and so reduces oxidative phosphorylation.
evidence:
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A respiratory chain function study showed decreased activity of
mitochondrial respiratory chain complex I in both probands.
explanation: The measured complex I deficit is the respiratory-chain lesion this edge asserts.
- name: Oxidative phosphorylation deficiency
biological_scale: MOLECULAR
conforms_to: "mitochondrial_dysfunction#Bioenergetic Decline and Oxidative Stress"
description: >-
Impaired mitochondrial translation reduces the abundance and activity of
respiratory chain complexes, lowering ATP synthesis through oxidative
phosphorylation. The defect becomes clinically apparent above a heteroplasmy
threshold of mutant mtDNA.
biological_processes:
- preferred_term: oxidative phosphorylation
modifier: DECREASED
term:
id: GO:0006119
label: oxidative phosphorylation
- preferred_term: aerobic respiration
modifier: DECREASED
term:
id: GO:0009060
label: aerobic respiration
evidence:
- reference: PMID:26851065
reference_title: Impaired nitric oxide production in children with MELAS syndrome and the effect of arginine and citrulline supplementation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The pathogenesis of this syndrome is not fully understood and believed to
result from several interacting mechanisms including impaired
mitochondrial energy production, microvasculature angiopathy, and nitric
oxide (NO) deficiency.
explanation: >-
Establishes impaired mitochondrial energy production (OXPHOS deficiency)
as a core pathogenic mechanism of MELAS.
downstream:
- target: Cellular energy failure and lactic acidosis
causal_link_type: DIRECT
description: >-
Reduced ATP synthesis forces a shift to anaerobic glycolysis, raising
lactate, and starves high-energy-demand tissues (brain, muscle, vascular
endothelium and smooth muscle).
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The inability of dysfunctional mitochondria to generate sufficient energy
to meet the needs of various organs results in the multi-organ
dysfunction observed in MELAS syndrome.
explanation: States the link from respiratory-chain failure to energy shortfall in high-demand organs.
- target: Complex I-predominant deficiency and neuronal mitophagy
causal_link_type: DIRECT
description: >-
The respiratory-chain deficit is not distributed evenly across the
complexes or across cell types; complex I is disproportionately affected,
and in neurons the deficient complex is actively cleared by mitophagy.
- target: Retinal pigment epithelium metabolic dysfunction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Oxidative phosphorylation failure in retinal pigment epithelium may disrupt metabolic cooperation with photoreceptors and contribute to retinal dystrophy. Human donor-eye observations support this proposed sequence but do not prove causal order.
evidence:
- reference: PMID:37289546
reference_title: Multimodal single-cell analysis of nonrandom heteroplasmy distribution in human retinal mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: However, a high proportion of m.3243G in the RPE, as seen in the current study, likely causes decreased electron transport chain function and leads to derangement of the RPE-photoreceptor cells cooperative metabolic ecosystem, eventually causing photoreceptor cell dysfunction and vision loss.
explanation: Human MELAS donor-eye analyses support a proposed RPE metabolic mechanism; the causal sequence is inferred rather than established by an intervention.
- name: Complex I-predominant deficiency and neuronal mitophagy
biological_scale: CELLULAR
description: >-
The respiratory-chain deficit produced by defective mitochondrial
translation is not uniform. Complex I deficiency predominates, as in MELAS
patient tissues, and the pattern of deficiency differs between cell types
derived from the same patient. In differentiated neurons, complex I
specifically is sequestered into PINK1/Parkin-positive autophagosomes,
suggesting that active mitophagy - not only failed assembly - contributes
to the neuronal deficit. This is a proposed, iPSC-derived explanation for
why one heteroplasmic variant can produce a neuron-weighted, rather than
uniformly systemic, disease.
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
molecular_functions:
- preferred_term: NADH dehydrogenase (ubiquinone) activity
modifier: DECREASED
term:
id: GO:0008137
label: NADH dehydrogenase (ubiquinone) activity
biological_processes:
- preferred_term: autophagy of mitochondrion
modifier: INCREASED
term:
id: GO:0000422
label: autophagy of mitochondrion
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Induced pluripotent stem cell-derived neurons and various tissues derived from teratomas manifested cell-type specific respiratory chain (RC) deficiency patterns. Similar to MELAS patient tissues, complex I defect predominated."
explanation: Shows the complex I predominance and its cell-type dependence in a patient-derived m.3243A>G model, matching patient tissue.
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Upon neuronal differentiation, complex I specifically was sequestered in perinuclear PTEN-induced putative kinase 1 (PINK1) and Parkin-positive autophagosomes, suggesting active degradation through mitophagy."
explanation: Direct evidence for selective mitophagic clearance of complex I in neurons as a component of the neuronal deficit.
downstream:
- target: Cellular energy failure and lactic acidosis
causal_link_type: DIRECT
description: >-
Selective loss of complex I lowers NADH oxidation and ATP output most
severely in the neuronal populations that can least tolerate it.
- name: Cellular energy failure and lactic acidosis
biological_scale: CELLULAR
description: >-
OXPHOS deficiency drives a compensatory increase in anaerobic glycolysis,
producing elevated blood and CSF lactate. Energy failure preferentially
affects metabolically demanding tissues, underlying encephalopathy,
myopathy, and endocrine dysfunction.
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
- preferred_term: skeletal muscle fiber
term:
id: CL:0008002
label: skeletal muscle fiber
biological_processes:
- preferred_term: generation of precursor metabolites and energy
modifier: DECREASED
term:
id: GO:0006091
label: generation of precursor metabolites and energy
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The inability of dysfunctional mitochondria to generate sufficient energy
to meet the needs of various organs results in the multi-organ
dysfunction observed in MELAS syndrome.
explanation: >-
Supports cellular energy failure in high-demand tissues as the link
between OXPHOS deficiency and the multisystem phenotype.
downstream:
- target: Mitochondrial angiopathy and NO deficiency
causal_link_type: DIRECT
description: >-
Energy failure in cerebral small-vessel endothelium and smooth muscle
drives mitochondrial angiopathy and impaired nitric oxide availability.
hypothesis_groups:
- ischemic_vascular_angiopathy
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Energy deficiency can also stimulate mitochondrial proliferation in the
smooth muscle and endothelial cells of small blood vessels leading to
angiopathy and impaired blood perfusion in the microvasculature of
several organs.
explanation: Direct statement of the causal step from energy deficiency to small-vessel angiopathy.
- target: Neuronal hyperexcitability and propagating epileptic activity
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
In the non-ischemic model, a mismatch between the energy demanded by an
active cortical neuronal population and the ATP that a defective
respiratory chain can supply renders those neurons hyperexcitable. What
converts this chronic vulnerability into a discrete episode is not known.
hypothesis_groups:
- neuronal_hyperexcitability
- target: Skeletal muscle mitochondrial proliferation
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Energy deficiency can stimulate mitochondrial proliferation.
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Energy deficiency can also stimulate mitochondrial proliferation.
explanation: GeneReviews identifies proliferation as a response to energy deficiency.
- target: Muscle weakness
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Failure of mitochondrial energy production contributes to skeletal muscle weakness.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These mutations impair mitochondrial oxidative phosphorylation, leading to systemic manifestations, including stroke-like episodes, lactic acidosis, seizures, muscle weakness, and progressive neurodegeneration [3].
explanation: The MELAS review links oxidative phosphorylation failure to muscle weakness.
- target: Mitochondrial myopathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Energy failure in skeletal muscle contributes to mitochondrial myopathy.
evidence:
- reference: PMID:26095523
reference_title: 'MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The inability of dysfunctional mitochondria to generate sufficient energy to meet the needs of various organs results in the multi-organ dysfunction observed in MELAS syndrome.
explanation: The review describes energy failure as the basis of organ dysfunction, including its described myopathy.
directness: INDIRECT
- target: Enteric neuromuscular dysfunction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Impaired mitochondrial energy production may compromise intestinal smooth muscle and enteric neural function.
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These findings suggest that mitochondrial dysfunction and energy production impairment may be the basis for the gastrointestinal symptoms in these patients, similar to the effects in the brain during stroke-like episodes.
explanation: The review cautiously links mitochondrial dysfunction to bowel symptoms after discussing MELAS gastrointestinal tissue findings.
- target: Lactic acidosis
causal_link_type: DIRECT
description: >-
Respiratory-chain failure increases glycolytic lactate production and can produce lactic acidosis.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The m.3243A>G mutation compromises the function of the electron transport chain (ETC), which forces cells to rely on anaerobic glycolysis, thereby leading to the accumulation of lactate and lactic acidosis, a hallmark of MELAS [16,17].
explanation: Describes lactic acidosis as a consequence of respiratory-chain dysfunction.
- target: Cochlear and auditory neural energy dysfunction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Mitochondrial dysfunction may impair energy-dependent cochlear and auditory neural processes, producing sensorineural hearing loss.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This symptom may be caused by mitochondrial dysfunction within the cochlea and the auditory neural pathways, disrupting the energy-dependent processes of sound transmission and auditory perception [37].
explanation: The preceding sentence identifies sensorineural hearing loss in MELAS. The review presents cochlear and auditory neural dysfunction as a proposed cause.
- target: Impaired pancreatic beta-cell insulin secretion
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Mitochondrial dysfunction in pancreatic beta cells impairs insulin secretion and contributes to diabetes mellitus.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The pathophysiology of diabetes in patients with MELAS is primarily due to mitochondrial dysfunction in pancreatic beta cells, which impairs insulin secretion [42].
explanation: The review links pancreatic beta-cell mitochondrial dysfunction to impaired insulin secretion and diabetes; the specific cellular intermediates are not resolved here.
- target: Myocardial energy deficit and hypertrophic remodeling
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Myocardial energy deficits may stimulate compensatory hypertrophy, providing a proposed route to hypertrophic cardiomyopathy.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Hypertrophic changes in the myocardium are likely a result of energy deficits due to impaired oxidative phosphorylation, leading to myocardial hypertrophy as the heart attempts to compensate for the loss of efficient energy production [1,2,39].
explanation: The review proposes compensatory myocardial hypertrophy in response to oxidative phosphorylation failure; this is retained as a provisional causal model.
- target: Glomerular mitochondrial dysfunction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Glomerular mitochondrial dysfunction can impair renal protein retention and produce proteinuria. The cell-specific injury sequence is unresolved in the reviewed clinical synthesis.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44].
explanation: The MELAS renal section assigns proteinuria to glomerular mitochondrial defects; podocyte-specific intermediates are not established by this passage.
- target: Peripheral nerve mitochondrial dysfunction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Mitochondrial dysfunction compromises energy-dependent peripheral nerve function and contributes to chronic sensory and motor neuropathy.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Furthermore, patients with MELAS often experience peripheral neuropathy, which presents as chronic sensory and motor deficits in the extremities. Peripheral nerves, which are energy-intensive tissues, are especially vulnerable to mitochondrial dysfunction, leading to symptoms such as muscle weakness, numbness, and tingling [38].
explanation: The review identifies mitochondrial dysfunction in peripheral nerves as the basis of the described sensory and motor neuropathy.
- name: Mitochondrial angiopathy and NO deficiency
biological_scale: TISSUE
description: >-
Mitochondrial proliferation in the smooth muscle and endothelial cells of
small blood vessels (mitochondrial angiopathy) and impaired nitric oxide
availability produce endothelial dysfunction and impaired microvascular
perfusion. This NO-deficient endothelial dysfunction is the target of
L-arginine therapy.
cell_types:
- preferred_term: smooth muscle cell
term:
id: CL:0000192
label: smooth muscle cell
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: nitric oxide biosynthetic process
modifier: DECREASED
term:
id: GO:0006809
label: nitric oxide biosynthetic process
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Energy deficiency can also stimulate mitochondrial proliferation in the
smooth muscle and endothelial cells of small blood vessels leading to
angiopathy and impaired blood perfusion in the microvasculature of
several organs.
explanation: >-
Directly supports the mitochondrial angiopathy mechanism in cerebral
small vessels underlying stroke-like episodes.
- reference: PMID:31693521
reference_title: Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is associated with endothelial dysfunction by decreased plasma
L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate.
explanation: >-
Supports impaired nitric oxide availability and endothelial dysfunction
as a contributor to stroke-like episodes.
downstream:
- target: Stroke-like episodes
causal_link_type: DIRECT
description: >-
Mitochondrial angiopathy and NO deficiency, together with neuronal energy
failure, converge to produce stroke-like episodes that do not respect
classic vascular territories.
hypothesis_groups:
- ischemic_vascular_angiopathy
evidence:
- reference: PMID:31693521
reference_title: Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is associated with endothelial dysfunction by decreased plasma
L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate.
explanation: Supports endothelial dysfunction as a proposed contributor to stroke-like episodes; the ischemic causal step remains contested.
directness: INDIRECT
- target: Increased cerebral capillary permeability and vasogenic edema
causal_link_type: DIRECT
description: >-
Mitochondrial dysfunction in capillary endothelium leaves the cortical
microvasculature primed to leak, which is the substrate on which
epileptic activity produces vasogenic edema.
hypothesis_groups:
- neuronal_hyperexcitability
- ischemic_vascular_angiopathy
- name: Neuronal hyperexcitability and propagating epileptic activity
biological_scale: CELLULAR
description: >-
In the non-ischemic model of the stroke-like episode, focal neuronal
hyperexcitability arises in a cortical region where mitochondrial
dysfunction - in neurons, astrocytes, or capillary endothelium - has left
energy supply unable to meet demand. The resulting epileptic activity
depolarizes adjacent neurons, which is how a stroke-like lesion spreads
into contiguous cortex over days to weeks instead of appearing at once in a
fixed arterial territory. Focal epileptiform discharges and focal cortical
hyperperfusion, not hypoperfusion, are recorded over the acute lesion.
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
- preferred_term: astrocyte
term:
id: CL:0000127
label: astrocyte
biological_processes:
- preferred_term: membrane depolarization
modifier: INCREASED
term:
id: GO:0051899
label: membrane depolarization
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the acute brain lesion. In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
explanation: Electrophysiological and perfusion findings that are hard to reconcile with a primarily ischemic lesion and that anchor the hyperexcitability model.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The stroke-like episodes in MELAS may reflect neuronal hyperexcitability, which increases energy demand and creates energy imbalance between energy requirement and adequate availability of adenosine triphosphate due to oxidative phosphorylation defect particularly in the susceptible neuronal population, causing cortical necrosis."
explanation: States the demand-supply mismatch mechanism linking hyperexcitability to cortical necrosis.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "several lines of evidence supporting neuronal hyper-excitability as the key mechanism of stroke-like episodes are discussed"
explanation: A recent review treating neuronal hyperexcitability as the leading mechanistic account.
downstream:
- target: Increased cerebral capillary permeability and vasogenic edema
causal_link_type: DIRECT
description: >-
Prolonged epileptic activity increases capillary permeability in cortex
whose microvasculature is already compromised by mitochondrial
angiopathy.
hypothesis_groups:
- neuronal_hyperexcitability
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Increased capillary permeability provoked by epileptic activities in the presence of mitochondrial capillary angiopathy may cause unique edematous brain lesions predominantly involving the cortex."
explanation: States the proposed causal link from epileptic activity to capillary leak in the presence of angiopathy.
- target: Cortical laminar necrosis and progressive lesion spread
causal_link_type: DIRECT
description: >-
Depolarization of adjacent neurons propagates the epileptic focus into
surrounding cortex, and the most vulnerable cortical layers are lost.
hypothesis_groups:
- neuronal_hyperexcitability
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "epileptic activities may depolarize the adjacent neurons leading to propagation of epileptic activities in the surrounding cortex"
explanation: Describes the propagation step that accounts for the contiguous spread of stroke-like lesions.
- target: Seizures
causal_link_type: DIRECT
description: >-
Lowering neuronal seizure thresholds contributes to the overall epileptic
phenotype, including focal and generalized events.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The impaired energy metabolism in neurons caused by mitochondrial defects increases excitability, thereby leading to lower seizure thresholds and frequent severe epileptic events [32,35].
explanation: >-
Supports the broad seizure category without claiming a specific onset
pattern.
hypothesis_groups:
- neuronal_hyperexcitability
- target: Focal-onset seizures
causal_link_type: DIRECT
description: >-
Localized cortical hyperexcitability underlies focal epileptic activity
during stroke-like episodes; this specifies the focal presentation within the
broader seizure phenotype.
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the
acute brain lesion.
explanation: >-
Localizes epileptic activity to the acute cortical lesion in the human
observations supporting the hyperexcitability model; it does not characterize
every MELAS seizure.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The stroke-like episodes in MELAS may reflect neuronal hyperexcitability,
which increases energy demand and creates energy imbalance between energy
requirement and adequate availability of adenosine triphosphate due to
oxidative phosphorylation defect particularly in the susceptible neuronal
population, causing cortical necrosis.
explanation: >-
The authors propose localized neuronal hyperexcitability as the mechanism of
these epileptic stroke-like events; this remains the provisional model
specified by the parent node.
hypothesis_groups:
- neuronal_hyperexcitability
- name: Increased cerebral capillary permeability and vasogenic edema
biological_scale: TISSUE
description: >-
Cortical stroke-like lesions in MELAS are characteristically edematous with
elevated apparent diffusion coefficient and focal hyperperfusion, the
signature of vasogenic rather than purely cytotoxic edema. The picture is
not clean: diffusion restriction consistent with a cytotoxic component is
also reported within the same lesions, so both processes appear to coexist.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:18289816
reference_title: Serial brain imaging analysis of stroke-like episodes in MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "These results suggest that the stroke-like episodes is related to vasogenic edema, hyperperfusion, and neuronal damage."
explanation: Serial multimodal imaging supporting vasogenic edema with hyperperfusion as the lesion physiology.
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Stroke-like episodes are characterized by neuronal hyperexcitability, neuronal vulnerability, increased capillary permeability, and focal hyperaemia."
explanation: Lists increased capillary permeability and focal hyperaemia as defining features of the lesion.
downstream:
- target: Cortical laminar necrosis and progressive lesion spread
causal_link_type: DIRECT
description: >-
Sustained edema in cortex that is simultaneously hyperexcitable and
energy-starved converts reversible signal change into tissue loss.
- name: Cortical laminar necrosis and progressive lesion spread
biological_scale: TISSUE
description: >-
The lesion of a stroke-like episode is an edematous lesion predominantly
involving the cerebral cortex, spreads into surrounding cortex over weeks,
and is proposed to leave neuronal loss in a laminar or pseudo-laminar
distribution. Cortical laminar necrosis is visible as subacute T1
hyperintense cortical signal, and intracortical gyral microhemorrhage has
been confirmed pathologically.
locations:
- preferred_term: cerebral cortex
term:
id: UBERON:0000956
label: cerebral cortex
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In 6 of 11 episodes T1-weighted hyperintense cortical signal compatible with cortical laminar necrosis was seen during subacute stage of the episode."
explanation: Documents cortical laminar necrosis as the subacute tissue outcome of a stroke-like episode.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Repeated MRI performed in two episodes revealed progressive spread of the cortical lesion to the surrounding cortex for a few weeks after the onset of symptoms."
explanation: Documents the contiguous spread over weeks that distinguishes the MELAS lesion from an arterial infarct.
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "susceptible neuronal population in the cortex may result in neuronal loss with a laminar or pseudo-laminar distribution"
explanation: Describes the laminar pattern of neuronal loss that gives the lesion its characteristic appearance; the review states it as a proposal.
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Increased capillary permeability provoked by epileptic activities in the presence of mitochondrial capillary angiopathy may cause unique edematous brain lesions predominantly involving the cortex."
explanation: Supports the cortical predominance and edematous character of the lesion.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fat-suppression MRI confirmed intracortical gyral hemorrhage in one episode. Petechial gyral microhemorrhages were also pathologically confirmed in the autopsy of another patient."
explanation: Supports the pathologically confirmed intracortical gyral microhemorrhage stated in the description.
downstream:
- target: Stroke-like episodes
causal_link_type: DIRECT
description: >-
The evolving cortical lesion is what produces the acute focal deficit and
its imaging correlate.
hypothesis_groups:
- neuronal_hyperexcitability
evidence:
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Stroke-like episodes in MELAS have the following features: (1) symptoms are neurolocalized according to lesion site"
explanation: Establishes that the clinical deficit follows the evolving cortical lesion.
- target: Encephalopathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Accumulating cortical injury contributes to cognitive encephalopathy.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Cognitive impairment is common and manifests as memory loss, decreased executive functioning, and diminished attention, stemming from mitochondrial dysfunction and from damage induced by recurrent SLEs [2,28,32].
explanation: The review connects neurological dysfunction and accumulated stroke-like injury to cognitive impairment, the clinical encephalopathy described here.
- name: Stroke-like episodes
biological_scale: ORGANISM
description: >-
Acute neurological deficits with neuroimaging lesions that do not conform to classic vascular territories are the defining clinical manifestation of MELAS. Proposed contributors include neuronal energy failure and hyperexcitability, mitochondrial angiopathy, and nitric oxide deficiency; their relative causal roles remain contested.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
During the stroke-like episodes neuroimaging shows increased T2-weighted
signal areas that do not correspond to the classic vascular distribution
(hence the term "stroke-like").
explanation: >-
GeneReviews documents stroke-like episodes with non-vascular-territory
neuroimaging lesions as the defining MELAS feature, the clinical outcome
of the angiopathy and energy-failure mechanisms.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(3) lesion distribution is inconsistent with vascular territory; (4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months; (6) neurological symptoms and stroke-like lesions tend to be reversible, as presented on magnetic resonance imaging; (7) the rate of recurrence is high"
explanation: Enumerates the defining features that separate a stroke-like episode from an ischemic stroke, including posterior predilection, contiguous spread, and reversibility.
downstream:
- target: Progressive brain atrophy and dementia
causal_link_type: DIRECT
description: >-
Repeated stroke-like episodes accumulate cortical tissue loss; brain
atrophy and cognitive decline are the residue left in survivors.
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
explanation: States the causal relation from recurrent episodes to atrophy and dementia.
- target: Hemiparesis
causal_link_type: DIRECT
description: >-
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6].
explanation: Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
- target: Aphasia
causal_link_type: DIRECT
description: >-
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6].
explanation: Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
- target: Cortical (cerebral) visual impairment
causal_link_type: DIRECT
description: >-
Focal cortical dysfunction during a stroke-like episode produces this neurological deficit.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6].
explanation: Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
- target: Hemianopia
causal_link_type: DIRECT
description: >-
A posterior cortical stroke-like lesion can produce visual field loss.
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The neurological evaluation revealed left hemianopia, temporal, and spatial disorientation and moderate psychic and motion slowness.
explanation: Documents hemianopia during a genetically confirmed MELAS stroke-like presentation.
- name: Progressive brain atrophy and dementia
biological_scale: ORGANISM
description: >-
Beyond any single episode, MELAS is slowly progressive: brain dysfunction
and atrophy advance between episodes, and recurrent stroke-like episodes
leave progressive brain atrophy and dementia as their long-term sequel.
locations:
- preferred_term: brain
term:
id: UBERON:0000955
label: brain
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
explanation: Identifies brain atrophy and dementia as the accumulated outcome of recurrent episodes.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(8) brain dysfunction and atrophy are slowly progressive"
explanation: Confirms the slowly progressive interictal course, distinct from the episodic lesions themselves.
downstream:
- target: Dementia and progressive cognitive decline
causal_link_type: DIRECT
description: >-
Clinical manifestation of accumulated cerebral injury after recurrent stroke-like episodes.
- target: Cerebral atrophy
causal_link_type: DIRECT
description: >-
Clinical manifestation of accumulated cerebral injury after recurrent stroke-like episodes.
- name: Skeletal muscle mitochondrial proliferation
biological_scale: CELLULAR
description: >-
Accumulation of mitochondria within skeletal muscle fibers produces the characteristic histological pattern of mitochondrial myopathy.
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Modified Gomori Trichrome stain (40X) showing a typical Ragged Red muscle fiber (RRF) containing mitochondrial hyperproliferation.
explanation: The ragged-red fiber reflects mitochondrial proliferation in muscle.
- name: Enteric neuromuscular dysfunction
biological_scale: TISSUE
description: >-
Mitochondrial dysfunction may impair intestinal propulsion through visceral smooth-muscle disease and/or myenteric neuropathy. The relative contributions remain unresolved in MELAS.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The pathophysiological mechanisms underlying gastrointestinal dysmotility in mitochondrial disorders are not completely understood and most likely involve myenteric plexus neuropathy and visceral myopathy.
explanation: The MELAS case review proposes enteric neuropathy and visceral myopathy, without resolving their relative contribution.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These findings suggest that mitochondrial dysfunction and energy production impairment may be the basis for the gastrointestinal symptoms in these patients, similar to the effects in the brain during stroke-like episodes.
explanation: The review cautiously links mitochondrial dysfunction to bowel symptoms after discussing MELAS gastrointestinal tissue findings.
downstream:
- target: Intestinal pseudo-obstruction
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: Failure of intestinal neuromuscular propulsion can produce pseudo-obstruction.
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The pathophysiological mechanisms underlying gastrointestinal dysmotility in mitochondrial disorders are not completely understood and most likely involve myenteric plexus neuropathy and visceral myopathy.
explanation: The MELAS case review proposes enteric neuropathy and visceral myopathy, without resolving their relative contribution.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These findings suggest that mitochondrial dysfunction and energy production impairment may be the basis for the gastrointestinal symptoms in these patients, similar to the effects in the brain during stroke-like episodes.
explanation: The review cautiously links mitochondrial dysfunction to bowel symptoms after discussing MELAS gastrointestinal tissue findings.
- name: Cochlear and auditory neural energy dysfunction
biological_scale: TISSUE
description: >-
Mitochondrial dysfunction may impair energy-dependent cochlear and auditory neural processes, producing sensorineural hearing loss.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This symptom may be caused by mitochondrial dysfunction within the cochlea and the auditory neural pathways, disrupting the energy-dependent processes of sound transmission and auditory perception [37].
explanation: The preceding sentence identifies sensorineural hearing loss in MELAS. The review presents cochlear and auditory neural dysfunction as a proposed cause.
downstream:
- target: Sensorineural hearing loss
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This symptom may be caused by mitochondrial dysfunction within the cochlea and the auditory neural pathways, disrupting the energy-dependent processes of sound transmission and auditory perception [37].
explanation: The preceding sentence identifies sensorineural hearing loss in MELAS. The review presents cochlear and auditory neural dysfunction as a proposed cause.
- name: Impaired pancreatic beta-cell insulin secretion
biological_scale: TISSUE
description: >-
Mitochondrial dysfunction in pancreatic beta cells impairs insulin secretion and contributes to diabetes mellitus.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The pathophysiology of diabetes in patients with MELAS is primarily due to mitochondrial dysfunction in pancreatic beta cells, which impairs insulin secretion [42].
explanation: The review links pancreatic beta-cell mitochondrial dysfunction to impaired insulin secretion and diabetes; the specific cellular intermediates are not resolved here.
downstream:
- target: Diabetes mellitus
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The pathophysiology of diabetes in patients with MELAS is primarily due to mitochondrial dysfunction in pancreatic beta cells, which impairs insulin secretion [42].
explanation: The review links pancreatic beta-cell mitochondrial dysfunction to impaired insulin secretion and diabetes; the specific cellular intermediates are not resolved here.
- name: Myocardial energy deficit and hypertrophic remodeling
biological_scale: TISSUE
description: >-
Myocardial energy deficits may stimulate compensatory hypertrophy, providing a proposed route to hypertrophic cardiomyopathy.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Hypertrophic changes in the myocardium are likely a result of energy deficits due to impaired oxidative phosphorylation, leading to myocardial hypertrophy as the heart attempts to compensate for the loss of efficient energy production [1,2,39].
explanation: The review proposes compensatory myocardial hypertrophy in response to oxidative phosphorylation failure; this is retained as a provisional causal model.
downstream:
- target: Cardiomyopathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Hypertrophic remodeling provides a proposed mechanism for the hypertrophic
subset of the broader cardiomyopathy phenotype; it does not explain every
dilated or other myocardial presentation.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Hypertrophic changes in the myocardium are likely a result of energy deficits due to impaired oxidative phosphorylation, leading to myocardial hypertrophy as the heart attempts to compensate for the loss of efficient energy production [1,2,39].
explanation: >-
Supports the hypertrophic component of this broad clinical class. The
parallel subtype edge makes the narrower anatomical claim explicit.
- target: Hypertrophic cardiomyopathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Compensatory myocardial hypertrophy is proposed to produce the specifically
hypertrophic cardiomyopathy phenotype.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Hypertrophic changes in the myocardium are likely a result of energy deficits due to impaired oxidative phosphorylation, leading to myocardial hypertrophy as the heart attempts to compensate for the loss of efficient energy production [1,2,39].
explanation: >-
The cited passage directly addresses hypertrophic remodeling; its proposed
energy-deficit cause remains provisional.
- target: Arrhythmia
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Myocardial remodeling can contribute to cardiac rhythm disorders in MELAS;
the electrical intermediates and contributions of primary conduction-pathway
dysfunction remain unresolved.
evidence:
- reference: PMID:39930534
reference_title: Cardiac manifestations in adult MELAS syndrome (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome)- a cross-sectional study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In MELAS syndrome, hypertrophic remodeling represents an early pattern of
cardiomyopathy, which can lead to dilated cardiomyopathy and results in
significant heart rhythm disorders in many MELAS patients.
explanation: >-
The clinical study explicitly describes rhythm disorders as a consequence of
the remodeling sequence. This qualified edge represents the
cardiomyopathy-associated route, without assigning every arrhythmia or bundle
branch block to that route.
- name: Glomerular mitochondrial dysfunction
biological_scale: TISSUE
description: >-
Glomerular mitochondrial dysfunction can impair renal protein retention and produce proteinuria. The cell-specific injury sequence is unresolved in the reviewed clinical synthesis.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44].
explanation: The MELAS renal section assigns proteinuria to glomerular mitochondrial defects; podocyte-specific intermediates are not established by this passage.
downstream:
- target: Proteinuria
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44].
explanation: The MELAS renal section assigns proteinuria to glomerular mitochondrial defects; podocyte-specific intermediates are not established by this passage.
- name: Peripheral nerve mitochondrial dysfunction
biological_scale: TISSUE
description: >-
Mitochondrial dysfunction compromises energy-dependent peripheral nerve function and contributes to chronic sensory and motor neuropathy.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Furthermore, patients with MELAS often experience peripheral neuropathy, which presents as chronic sensory and motor deficits in the extremities. Peripheral nerves, which are energy-intensive tissues, are especially vulnerable to mitochondrial dysfunction, leading to symptoms such as muscle weakness, numbness, and tingling [38].
explanation: The review identifies mitochondrial dysfunction in peripheral nerves as the basis of the described sensory and motor neuropathy.
downstream:
- target: Peripheral neuropathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Clinical expression of the proposed tissue-specific mitochondrial dysfunction.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Furthermore, patients with MELAS often experience peripheral neuropathy, which presents as chronic sensory and motor deficits in the extremities. Peripheral nerves, which are energy-intensive tissues, are especially vulnerable to mitochondrial dysfunction, leading to symptoms such as muscle weakness, numbness, and tingling [38].
explanation: The review identifies mitochondrial dysfunction in peripheral nerves as the basis of the described sensory and motor neuropathy.
- name: Retinal pigment epithelium metabolic dysfunction
biological_scale: TISSUE
description: >-
Oxidative phosphorylation failure in retinal pigment epithelium may disrupt metabolic cooperation with photoreceptors and contribute to retinal dystrophy. Human donor-eye observations support this proposed sequence but do not prove causal order.
mechanism_confidence: PROVISIONAL
evidence:
- reference: PMID:37289546
reference_title: Multimodal single-cell analysis of nonrandom heteroplasmy distribution in human retinal mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: However, a high proportion of m.3243G in the RPE, as seen in the current study, likely causes decreased electron transport chain function and leads to derangement of the RPE-photoreceptor cells cooperative metabolic ecosystem, eventually causing photoreceptor cell dysfunction and vision loss.
explanation: Human MELAS donor-eye analyses support a proposed RPE metabolic mechanism; the causal sequence is inferred rather than established by an intervention.
downstream:
- target: Mitochondrial retinal dystrophy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
RPE dysfunction is a proposed early step leading to outer retinal degeneration.
evidence:
- reference: PMID:37289546
reference_title: Multimodal single-cell analysis of nonrandom heteroplasmy distribution in human retinal mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Finally, by combining previous ophthalmologic clinical observations (24, 56) and multimodal sequencing of the RPE, we show that the RPE dysfunction that is associated with high proportions of m.3243G was likely an early step in the pathogenic sequence that results in retinal dystrophy of MELAS and related mitochondrial conditions (i.e., MIDD and Leigh Syndrome).
explanation: The authors explicitly propose RPE dysfunction as an early pathogenic step toward retinal dystrophy; this is retained as provisional.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_wobble_translation_failure
hypothesis_label: Canonical wobble-modification and mitochondrial translation-failure model
status: CANONICAL
description: >-
The molecular half of MELAS pathogenesis is not in dispute. Pathogenic
MT-TL1 variants strip the taurine-containing modification from the wobble
uridine of tRNA-Leu(UUR), degrading codon-anticodon pairing (UUG more than
UUA) and impairing synthesis of the mtDNA-encoded respiratory-chain
subunits. Complex I is the most affected, and clinical expression requires
mutant heteroplasmy above a tissue threshold. Everything downstream of the
resulting energy failure - specifically, how it produces a discrete
stroke-like episode - is where the competing accounts below begin.
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Crucial molecular mechanism includes the lack of taurine modification at the wobble uridine of mutant transfer RNAsLeu(UUR) resulting in defective translation of cognate codons due to a defect in codon-anticodon interaction."
explanation: States the molecular mechanism that both competing stroke-like-episode hypotheses take as their shared starting point.
- reference: PMID:37988592
reference_title: Penetrance and expressivity of mitochondrial variants in a large clinically unselected population.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Multi-system disease risk and penetrance of diabetes, deafness and heart failure greatly increased with m.3243A>G level ≥ 10%."
explanation: Population-scale support for the heteroplasmy-threshold component of the canonical model.
- hypothesis_group_id: ischemic_vascular_angiopathy
hypothesis_label: Ischemic vascular ("mitochondrial angiopathy") model of stroke-like episodes
status: ALTERNATIVE
description: >-
The older account holds that stroke-like episodes are ischemic events
caused by mitochondrial angiopathy: proliferation of mitochondria in the
smooth muscle and endothelium of cerebral small vessels, compounded by
reduced nitric oxide availability, impairs microvascular perfusion. The
model is what motivates L-arginine and L-citrulline therapy and the newer
soluble guanylate cyclase stimulators, and the muscle-biopsy finding of
strongly SDH-reactive vessels is real. Its difficulty is that acute lesions
show focal hyperperfusion and elevated apparent diffusion coefficient
rather than the hypoperfusion and restricted diffusion of ischemia, and
they cross vascular territories.
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The pathogenesis of stroke-like episodes in mitochondrial encephalopathy, myopathy, lactic acidosis and stroke-like episodes (MELAS) is not fully understood although two main theories have been proposed; ischemic vascular hypothesis caused by \"mitochondrial angiopathy\" and generalized cytopathic hypothesis caused by \"mitochondrial cytopathy\"."
explanation: Names the ischemic vascular hypothesis as one of the two standing accounts and records that neither is settled.
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Energy deficiency can also stimulate mitochondrial proliferation in the smooth muscle and endothelial cells of small blood vessels leading to angiopathy and impaired blood perfusion in the microvasculature of several organs."
explanation: States the angiopathy mechanism on which the vascular model rests.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: REFUTE
evidence_source: HUMAN_CLINICAL
snippet: "In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
explanation: Focal hyperperfusion over the acute lesion is the opposite of what a primarily ischemic mechanism predicts.
- hypothesis_group_id: neuronal_hyperexcitability
hypothesis_label: Non-ischemic neuronal-hyperexcitability model of stroke-like episodes
status: EMERGING
description: >-
The competing account treats the stroke-like episode as a non-ischemic
neurovascular event. Focal neuronal hyperexcitability develops where energy
supply cannot meet demand; the resulting epileptic activity depolarizes
adjacent neurons and propagates the lesion into contiguous cortex, while
increased capillary permeability - on a background of mitochondrial
angiopathy - produces the characteristic cortical vasogenic edema and,
ultimately, laminar necrosis. It accounts for the EEG discharges,
hyperperfusion, elevated ADC, contiguous spread, and posterior predilection
that the vascular model does not, and it implies that aggressive seizure
control, rather than vasodilation, is the therapeutic priority. Note that
the two models are not mutually exclusive: this one still requires the
capillary angiopathy of the vascular model as its substrate.
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Based on the clinical observations, we speculate that stroke-like episodes appear to be non-ischemic neurovascular events; once neuronal hyperexcitability developed in a localized brain region as a result from either mitochondrial dysfunction in the capillary endothelial cells, or in neurons or astrocytes, epileptic activities may depolarize the adjacent neurons leading to propagation of epileptic activities in the surrounding cortex."
explanation: The primary statement of the non-ischemic neurovascular model, including its initiating step and propagation mechanism.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
explanation: Shows the therapeutic consequence that follows from adopting the hyperexcitability model over the vascular one.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Although the precise pathophysiology is still unclear, one possible hypothesis for these episodes is a neuronal hyperexcitability theory, including neuron-astrocyte uncoupling."
explanation: A recent review presenting hyperexcitability as a leading but still unproven hypothesis, and adding neuron-astrocyte uncoupling as a proposed variant.
phenotypes:
- category: Neurologic
name: Stroke-like episodes
frequency: VERY_FREQUENT
description: >-
Acute neurological deficits with neuroimaging lesions that do not conform to
classic vascular territories, a defining feature of MELAS.
phenotype_term:
preferred_term: Stroke-like episode
term:
id: HP:0002401
label: Stroke-like episode
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
During the stroke-like episodes neuroimaging shows increased T2-weighted
signal areas that do not correspond to the classic vascular distribution
(hence the term "stroke-like").
explanation: >-
GeneReviews documents stroke-like episodes with non-vascular-territory
neuroimaging lesions as the defining MELAS feature.
- category: Metabolic
name: Elevated blood lactate
frequency: VERY_FREQUENT
description: >-
Elevated blood lactate reflects increased reliance on anaerobic glycolysis. Hyperlactatemia alone does not establish acidemia.
phenotype_term:
preferred_term: Increased circulating lactate concentration
term:
id: HP:0002151
label: Increased circulating lactate concentration
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Lactic acidemia is very common and muscle biopsies typically show ragged
red fibers.
explanation: >-
GeneReviews documents lactic acidemia as a very common feature of MELAS.
reports_on:
- target: Cellular energy failure and lactic acidosis
relationship: READOUT_OF
interpretation: Blood lactate is a biochemical readout of the glycolytic response to respiratory-chain dysfunction.
evidence:
- reference: PMID:39697439
reference_title: 'Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Mitochondrial dysfunction led to increased anaerobic glycolysis in muscle tissues, resulting in elevated blood lactate levels due to insufficient oxidative phosphorylation (14).
explanation: Links elevated blood lactate to compensatory glycolysis during oxidative phosphorylation failure.
- category: Neurologic
name: Seizures
frequency: VERY_FREQUENT
description: Epileptic seizures, often focal or generalized, frequently accompanying stroke-like episodes.
phenotype_term:
preferred_term: Seizure
term:
id: HP:0001250
label: Seizure
evidence:
- reference: PMID:38156086
reference_title: 'The clinical spectrum of MELAS and associated disorders across ages: a retrospective cohort study.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: MELAS had higher prevalence of seizures (88.1% vs. 16.7%, p < 0.05) and shorter survival from onset to death (50% mortality at 25 years vs. 10%, p < 0.05).
explanation: The 88.1% estimate is from 42 clinically defined MELAS patients; the comparator is symptomatic non-MELAS mitochondrial disease.
context: Clinically defined MELAS; 42-patient subgroup in the Mayo cohort.
sequelae:
- target: Status epilepticus
causal_link_type: DIRECT
description: >-
Seizures can persist or recur without recovery and evolve into status epilepticus.
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Seizures can be focal and generalized or evolve into status epilepticus, significantly contributing to the overall neurological burden.
explanation: The MELAS neurological section describes seizure progression to status epilepticus.
- category: Neurologic
name: Encephalopathy
description: Encephalopathy with cognitive decline, sometimes progressing to dementia.
phenotype_term:
preferred_term: Encephalopathy
term:
id: HP:0001298
label: Encephalopathy
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Common clinical manifestations include stroke-like episodes,
encephalopathy with seizures and/or dementia, muscle weakness and
exercise intolerance
explanation: >-
GeneReviews lists encephalopathy with seizures and/or dementia among the
common manifestations of MELAS.
- category: Musculoskeletal
name: Mitochondrial myopathy
description: >-
Mitochondrial muscle disease manifests as muscle weakness and exercise intolerance; muscle biopsy may show ragged-red fibers.
phenotype_term:
preferred_term: Mitochondrial myopathy
term:
id: HP:0003737
label: Mitochondrial myopathy
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Common clinical manifestations include stroke-like episodes,
encephalopathy with seizures and/or dementia, muscle weakness and
exercise intolerance
explanation: >-
GeneReviews lists muscle weakness and exercise intolerance, the clinical
expression of mitochondrial myopathy, among common manifestations.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: To confirm this hypothesis, the patient underwent MR spectroscopy (MRS) and demonstrated elevation of the lactate peak within the abnormal lesion (Figure 2D), a muscle biopsy that was consistent with mitochondrial myopathy (Figures 2E–H) and genetic testing, which revealed the presence of a mitochondrial DNA mutation (m.3243A>G) (heteroplasmy 13.1%) in the MT-TL1 gene encoding the leucine transfer RNA.
explanation: Muscle biopsy documented mitochondrial myopathy in genetically confirmed MELAS.
sequelae:
- target: Muscle weakness
causal_link_type: DIRECT
description: Clinical expression of mitochondrial muscle disease.
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: presents clinically as muscle weakness and exercise intolerance.
explanation: Identifies weakness and exercise intolerance as clinical expressions of MELAS myopathy.
- target: Exercise intolerance
causal_link_type: DIRECT
description: Clinical expression of mitochondrial muscle disease.
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: presents clinically as muscle weakness and exercise intolerance.
explanation: Identifies weakness and exercise intolerance as clinical expressions of MELAS myopathy.
- category: Musculoskeletal
name: Ragged-red fibers
description: Ragged-red fibers on modified Gomori trichrome staining of muscle biopsy, reflecting mitochondrial proliferation.
phenotype_term:
preferred_term: Ragged-red muscle fibers
term:
id: HP:0003200
label: Ragged-red muscle fibers
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Lactic acidemia is very common and muscle biopsies typically show ragged
red fibers.
explanation: >-
GeneReviews documents ragged-red fibers as a typical muscle biopsy
finding in MELAS.
reports_on:
- target: Skeletal muscle mitochondrial proliferation
relationship: READOUT_OF
interpretation: Modified Gomori trichrome staining reveals mitochondrial accumulation within muscle fibers.
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Modified Gomori Trichrome stain (40X) showing a typical Ragged Red muscle fiber (RRF) containing mitochondrial hyperproliferation.
explanation: The ragged-red fiber reflects mitochondrial proliferation in muscle.
- category: Musculoskeletal
name: Exercise intolerance
description: Reduced exercise capacity due to impaired mitochondrial energy production.
phenotype_term:
preferred_term: Exercise intolerance
term:
id: HP:0003546
label: Exercise intolerance
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Common clinical manifestations include stroke-like episodes,
encephalopathy with seizures and/or dementia, muscle weakness and
exercise intolerance
explanation: >-
GeneReviews lists exercise intolerance among the common manifestations of
MELAS.
- category: Otologic
name: Sensorineural hearing loss
description: >-
Sensorineural hearing impairment is often an early manifestation and may progress over time.
phenotype_term:
preferred_term: Sensorineural hearing impairment
term:
id: HP:0000407
label: Sensorineural hearing impairment
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: In addition to SLEs and seizures, sensorineural hearing loss is a frequent and progressive manifestation in MELAS.
explanation: Specifies the sensorineural and progressive nature of hearing impairment in MELAS.
- category: Endocrine
name: Diabetes mellitus
description: >-
Diabetes mellitus occurs in clinically defined MELAS as well as in the MIDD phenotype associated with m.3243A>G.
phenotype_term:
preferred_term: Diabetes mellitus
term:
id: HP:0000819
label: Diabetes mellitus
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS syndrome is a multi-organ disease with broad manifestations
including stroke-like episodes, dementia, epilepsy, lactic acidemia,
myopathy, recurrent headaches, hearing impairment, diabetes, and short
stature.
explanation: >-
The El-Hattab review lists diabetes among the broad manifestations of
MELAS, reflecting the endocrine involvement of the m.3243A>G mutation.
- reference: PMID:38156086
reference_title: 'The clinical spectrum of MELAS and associated disorders across ages: a retrospective cohort study.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: There was a trend toward higher rates of diabetes in symptomatic non-MELAS patients compared to MELAS (56.7% vs. 33.3, p = 0.058).
explanation: Separates diabetes in clinically defined MELAS from the broader variant-associated disease spectrum.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)
explanation: >-
The complete 25%-49% row of GeneReviews Table 3 includes diabetes mellitus. The exact source interval is retained because it crosses HPO frequency bands.
frequency: 25%-49%
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Neurologic
name: Migraine-like headaches
description: >-
Recurrent severe pulsatile migraine-like headaches, often with vomiting, can
precipitate stroke-like episodes and may become more severe during them. This
trigger relation does not establish that cortical injury causes the migraine
phenotype.
phenotype_term:
preferred_term: Migraine
term:
id: HP:0002076
label: Migraine
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
directness: INDIRECT
snippet: >-
Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and
migraine headache are treated in the standard manner.
explanation: >-
GeneReviews names migraine headache among the manifestations of MELAS that
require management. The claim follows from the management recommendation
rather than from a counted frequency, hence INDIRECT.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
in the form of recurrent attacks of severe pulsatile headaches with frequent vomiting are typical in individuals with MELAS and can precipitate stroke-like episodes.
explanation: >-
GeneReviews describes the migraine phenotype and identifies it as a possible
precipitant of stroke-like episodes.
sequelae:
- target: Stroke-like episodes
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Migrainous headache attacks can precipitate stroke-like episodes; the
intervening mechanism and circumstances determining progression are
unresolved.
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
in the form of recurrent attacks of severe pulsatile headaches with frequent vomiting are typical in individuals with MELAS and can precipitate stroke-like episodes.
explanation: >-
The source explicitly supports migraine-to-episode triggering. This qualified
relation does not assert that every migraine causes an episode or supply a
reverse causal link.
- category: Growth
name: Short stature
description: Short stature is common in individuals with MELAS.
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
muscle weakness and exercise intolerance, normal early psychomotor
development, recurrent headaches, recurrent vomiting, hearing impairment,
peripheral neuropathy, learning disability, and short stature
explanation: >-
GeneReviews lists short stature among the common manifestations of MELAS.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature
explanation: >-
The complete 50%-74% row of GeneReviews Table 3 includes short stature. The entire interval lies within FREQUENT (30-79%).
frequency: FREQUENT
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Gastrointestinal
name: Recurrent vomiting
description: Recurrent vomiting is a common manifestation of MELAS, often accompanying stroke-like episodes.
phenotype_term:
preferred_term: Recurrent vomiting
term:
id: HP:0002013
label: Vomiting
temporality: RECURRENT
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
muscle weakness and exercise intolerance, normal early psychomotor
development, recurrent headaches, recurrent vomiting, hearing impairment,
peripheral neuropathy, learning disability, and short stature
explanation: >-
GeneReviews lists recurrent vomiting among the common manifestations of
MELAS.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature
explanation: >-
The complete 50%-74% row of GeneReviews Table 3 includes recurrent vomiting. The entire interval lies within FREQUENT (30-79%).
frequency: FREQUENT
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Neurologic
name: Peripheral neuropathy
description: Peripheral neuropathy is a common manifestation of MELAS.
phenotype_term:
preferred_term: Peripheral neuropathy
term:
id: HP:0009830
label: Peripheral neuropathy
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
muscle weakness and exercise intolerance, normal early psychomotor
development, recurrent headaches, recurrent vomiting, hearing impairment,
peripheral neuropathy, learning disability, and short stature
explanation: >-
GeneReviews lists peripheral neuropathy among the common manifestations of
MELAS.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature
explanation: >-
The complete 50%-74% row of GeneReviews Table 3 includes peripheral neuropathy. The entire interval lies within FREQUENT (30-79%).
frequency: FREQUENT
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Neurodevelopmental
name: Learning disability
description: Learning disability is a common manifestation of MELAS.
phenotype_term:
preferred_term: Learning disability
term:
id: HP:0001328
label: Specific learning disability
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
muscle weakness and exercise intolerance, normal early psychomotor
development, recurrent headaches, recurrent vomiting, hearing impairment,
peripheral neuropathy, learning disability, and short stature
explanation: >-
GeneReviews lists learning disability among the common manifestations of
MELAS.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
50%-74%
• Peripheral neuropathy
• Learning disability
• Memory impairment
• Recurrent vomiting
• Short stature
explanation: >-
The complete 50%-74% row of GeneReviews Table 3 includes learning disability. The entire interval lies within FREQUENT (30-79%).
frequency: FREQUENT
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Cardiac
name: Cardiomyopathy
description: >-
Cardiomyopathy may be hypertrophic or dilated.
phenotype_term:
preferred_term: Cardiomyopathy
term:
id: HP:0001638
label: Cardiomyopathy
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Both dilated and hypertrophic cardiomyopathy have been observed, however, the more typical is a non-obstructive concentric hypertrophy
explanation: Documents myocardial phenotypes observed in MELAS.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo
explanation: >-
The complete <25% row of GeneReviews Table 3 includes cardiomyopathy. The exact source interval is retained because it crosses HPO frequency bands.
frequency: <25%
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Ophthalmologic
name: Hemianopia
description: >-
Hemianopia can accompany a posterior cortical stroke-like lesion.
phenotype_term:
preferred_term: Hemianopia
term:
id: HP:0012377
label: Hemianopia
evidence:
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The neurological evaluation revealed left hemianopia, temporal, and spatial disorientation and moderate psychic and motion slowness.
explanation: Documents hemianopia during a genetically confirmed MELAS stroke-like presentation.
- category: Neurologic
name: Focal-onset seizures
description: >-
Focal seizures predominated in a cohort of 22 children and adolescents with
MELAS and epilepsy: 21 had focal seizures and seven had generalized seizures.
Earlier seizure onset was associated with more drug-resistant epilepsy.
Seizure semiology and EEG abnormalities were not syndrome-specific, so these
findings alone do not identify MELAS.
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Focal-onset seizure
term:
id: HP:0007359
label: Focal-onset seizure
evidence:
- reference: PMID:27671241
reference_title: "Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Focal seizures occurred in 21 of 22 subjects (95.5%), whereas generalized seizures developed in seven of 22 subjects (31.8%)."
explanation: Quantifies focal versus generalized seizure frequency in a pediatric m.3243A>G MELAS cohort with epilepsy.
- reference: PMID:27671241
reference_title: "Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The subgroup with earlier seizure onset presented significantly earlier and showed significantly higher rates of drug-resistant epilepsy compared with the late onset group"
explanation: Establishes earlier seizure onset as a predictor of drug resistance.
- reference: PMID:27671241
reference_title: Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS).
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Seizure semiology and electroencephalography abnormalities showed no
syndrome-specific findings.
explanation: >-
The pediatric MELAS epilepsy cohort found no diagnostic seizure or EEG
signature; its focal-seizure frequency remains conditional on epilepsy.
context: Children and adolescents with MELAS and epilepsy; the frequency is conditional on epilepsy in the 22-patient cohort.
- category: Neurologic
name: Status epilepticus
description: >-
Status epilepticus can complicate MELAS and was a leading proximate cause of
death together with acute stroke-like episodes in followed clinical cohorts.
This mortality burden supports the priority given to active seizure
management during an episode.
phenotype_term:
preferred_term: Status epilepticus
term:
id: HP:0002133
label: Status epilepticus
evidence:
- reference: PMID:29406897
reference_title: Survival analysis of a cohort of Chinese patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) based on clinical features.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "An acute stroke-like episode and/or status epilepticus were the predominant causes of death (42.9%)."
explanation: Identifies status epilepticus as a leading cause of death in a followed MELAS cohort.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Six patients died from stroke-like episodes, with status epilepticus being the clinical manifestation prior to death."
explanation: Independent cohort confirming status epilepticus as the terminal manifestation in most MELAS deaths.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The management of stroke-like episodes should focus on aggressive seizure
management and treatment for concomitant complications such as intestinal
pseudo-obstruction.
explanation: >-
The clinical review identifies aggressive seizure management as a priority;
the cohort evidence above identifies status epilepticus among predominant
proximate causes of death.
- category: Neurologic
name: Dementia and progressive cognitive decline
description: >-
Cognitive decline combines accumulated deficits after stroke-like episodes
with a diffuse, slowly progressive neurological component. Dementia can
affect language, perception, attention, executive function, and memory; it is
not explained solely by a single cortical lesion.
phenotype_term:
preferred_term: Dementia
term:
id: HP:0000726
label: Dementia
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
explanation: Establishes dementia as the long-term neurological outcome of recurrent stroke-like episodes.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "It is a multi-system disorder with a wide range of manifestations, characterized by recurrent stroke-like episodes, progressive intellectual decline, and dementia"
explanation: Lists progressive intellectual decline and dementia among the defining manifestations.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Both the underlying neurologic dysfunction and the accumulating cortical
injuries due to stroke-like episodes contribute to dementia.
explanation: >-
GeneReviews separates the underlying neurological dysfunction from the
cumulative effects of stroke-like cortical injury.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Executive function deficits have been observed despite the relative sparing
of the frontal lobe on neuroimaging, indicating an additional diffuse
neurodegenerative process in addition to the damage caused by the stroke-like
episodes
explanation: >-
Supports an additional diffuse process rather than attributing every
cognitive deficit to a focal episode.
- category: Neurologic
name: Cerebral atrophy
description: >-
Cerebral volume loss progresses over the disease course and can accumulate
after recurrent stroke-like lesions. Slowly progressive brain dysfunction and
atrophy extend beyond the acute evolution of an individual lesion.
phenotype_term:
preferred_term: Cerebral atrophy
term:
id: HP:0002059
label: Cerebral atrophy
clinical_course: PROGRESSIVE
evidence:
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(8) brain dysfunction and atrophy are slowly progressive"
explanation: Documents progressive brain atrophy as a listed feature of the MELAS course.
- reference: PMID:36685235
reference_title: 'Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with an MT-TL1 m.3243A>G point mutation: Neuroradiological features and their implications for underlying pathogenesis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: For all 59 imaging studies, cerebral atrophy occurred in 38 (64%), and cerebellar atrophy occurred in 40 (68%).
explanation: Documents cerebral atrophy; these denominators count imaging studies, not distinct patients.
- category: Ophthalmologic
name: Cortical (cerebral) visual impairment
description: >-
Occipital cortex is the predilection site for stroke-like lesions, so
visual field loss and cortical blindness are among the most characteristic
deficits. Cortical blindness is significantly more frequent in the
adult-onset form than in the juvenile form.
phenotype_term:
preferred_term: Cerebral visual impairment
term:
id: HP:0100704
label: Cerebral visual impairment
evidence:
- reference: PMID:21443929
reference_title: "MELAS: a nationwide prospective cohort study of 96 patients in Japan."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hearing loss, cortical blindness and diabetes mellitus were significantly more frequent in the adult form"
explanation: Nationwide cohort data placing cortical blindness in the adult-onset MELAS phenotype.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Focal-onset seizures, encephalopathy, and visual disturbances are prominent findings associated with stroke-like episodes, with a predilection for the posterior cerebral cortex."
explanation: Links the visual deficits to the posterior-cortex predilection of stroke-like lesions.
- category: Ophthalmologic
name: Mitochondrial retinal dystrophy
description: >-
Retinal dystrophy is an ocular source of visual loss distinct from cortical
visual impairment. In a 29-person m.3243A>G carrier cohort, four grades
ranged from fine pigment changes visible on autofluorescence, through macular
pigment deposits, to extrafoveal chorioretinal atrophy and finally foveal
atrophy with marked visual-acuity loss. Retinal abnormalities affected 25
carriers; this is not a MELAS-specific prevalence estimate. Grade correlated
with age and visual acuity, without an observed correlation with heteroplasmy
or overall disease involvement. Variable or absent systemic features can
obscure recognition of the mitochondrial retinal disorder.
phenotype_term:
preferred_term: Mitochondrial retinal dystrophy (pigmentary macular pattern dystrophy)
term:
id: HP:0000556
label: Retinal dystrophy
context: m.3243A>G carriers, including those without a full MELAS phenotype
evidence:
- reference: PMID:23806424
reference_title: Mitochondrial retinal dystrophy associated with the m.3243A>G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Twenty-five of the 29 mutation carriers (86%) had retinal abnormalities that could be classified into 4 grades."
explanation: Quantifies retinal involvement in a systematically examined m.3243A>G carrier cohort.
- reference: PMID:23806424
reference_title: Mitochondrial retinal dystrophy associated with the m.3243A>G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The grade of mitochondrial retinal dystrophy correlated significantly with both age (r = -0.483, P = 0.008) and visual acuity (r = -0.614, P < 0.001), whereas no correlation was observed with heteroplasmy level or overall disease involvement."
explanation: Shows retinal severity is uncoupled from heteroplasmy and from systemic disease burden.
- reference: PMID:23806424
reference_title: Mitochondrial retinal dystrophy associated with the m.3243A>G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Six patients (21%) had grade 1 retinal dystrophy with fine pigment
abnormalities that were clearly visible with FAF and fluorescein angiography.
Eleven patients (38%) had grade 2 abnormalities that were characterized by
yellowish or mildly pigmented deposits in the early stage; in advanced grade
2, these pigment changes encompassed the entire macula and often encircled
the optic disc. Six patients (21%) had grade 3 disease in which profound
chorioretinal atrophy was present outside the fovea. Two patients (7%) with
retinal abnormalities had grade 4 disease, in which the fovea was affected by
atrophy, with marked loss of visual acuity.
explanation: >-
Defines the four anatomical grades in the carrier cohort, without
transferring its frequency to clinically defined MELAS.
- reference: PMID:23806424
reference_title: Mitochondrial retinal dystrophy associated with the m.3243A>G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
However, because the maternal inheritance pattern can be masked and the
systemic disease associations can be variable or even absent, the disease may
be misdiagnosed.
explanation: >-
Restores the recognition caveat for this mitochondrial retinal disorder.
- category: Ophthalmologic
name: Progressive external ophthalmoplegia
description: >-
Ocular myopathy is part of the m.3243A>G spectrum and overlaps MELAS in a
minority of patients; in the UK cohort PEO appeared both as a MELAS/CPEO
overlap and as an isolated presentation of the same variant.
phenotype_term:
preferred_term: Progressive external ophthalmoplegia
term:
id: HP:0000590
label: Progressive external ophthalmoplegia
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
evidence:
- reference: PMID:23355809
reference_title: "The UK MRC Mitochondrial Disease Patient Cohort Study: clinical phenotypes associated with the m.3243A>G mutation--implications for diagnosis and management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "10% of patients exhibited a classical MELAS phenotype, 30% had MIDD, 6% MELAS/MIDD, 2% MELAS/chronic PEO (CPEO) and 5% MIDD/CPEO overlap syndromes."
explanation: Quantifies the MELAS/CPEO overlap within the m.3243A>G phenotypic spectrum.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo
explanation: >-
The complete <25% row of GeneReviews Table 3 includes progressive external ophthalmoplegia. The exact source interval is retained because it crosses HPO frequency bands.
frequency: <25%
- category: Ophthalmologic
name: Ptosis
description: >-
Eyelid ptosis is reported in MELAS, usually alongside other extraocular
muscle involvement such as ophthalmoplegia.
phenotype_term:
preferred_term: Ptosis
term:
id: HP:0000508
label: Ptosis
evidence:
- reference: PMID:26937404
reference_title: Arrhythmia as a cardiac manifestation in MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Her clinical status included multiple medical problems related to her MELAS
diagnosis: sensorineural hearing loss, myopathy, bilateral ophthalmoplegia,
ptosis, seizures and stroke-like episodes with concern for dementia.
explanation: >-
Reports ptosis together with ophthalmoplegia as part of one patient's MELAS
phenotype. A single case supports occurrence, not a frequency or an
eyelid-muscle mechanism.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
directness: INDIRECT
snippet: >-
Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and
migraine headache are treated in the standard manner.
explanation: >-
GeneReviews names ptosis among the manifestations of MELAS that require
management, which is why the phenotype is recorded at disease level rather
than as a single-case observation.
- category: Renal
name: Proteinuria
description: >-
Proteinuria is a renal manifestation of MELAS. In the broader m.3243A>G
renal-disease literature, subnephrotic proteinuria may accompany progressive
loss of kidney function. The wider renal spectrum includes proximal
tubulopathy and focal segmental glomerulosclerosis; these distinct renal
findings are not synonyms for proteinuria.
phenotype_term:
preferred_term: Proteinuria
term:
id: HP:0000093
label: Proteinuria
evidence:
- reference: PMID:38355238
reference_title: Renal manifestations in adults with mitochondrial disease from the mtDNA m.3243A>G pathogenic variant.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Not frequently reported, renal involvement in these diseases is probably underestimated, yet it increases morbidity. It generally manifests as subnephrotic proteinuria and progressive deterioration of kidney function."
explanation: Characterizes the renal phenotype of m.3243A>G disease and notes it is probably under-ascertained.
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Additionally, mitochondrial defects in the glomeruli lead to proteinuria and nephrotic syndrome, further complicating the disease course [39,44].
explanation: The review specifically identifies proteinuria in its MELAS renal-involvement section.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
that may include Fanconi proximal tubulopathy, proteinuria, and focal segmental glomerulosclerosis
explanation: >-
Places proteinuria within the renal spectrum of MELAS. Focal segmental
glomerulosclerosis is a possible renal lesion; this passage does not
establish a treatment response or an immunosuppression error rate.
- category: Gastrointestinal
name: Intestinal pseudo-obstruction
description: >-
Intestinal pseudo-obstruction produces abdominal distension, nausea,
vomiting, and pain through impaired intestinal propulsion, mimicking
mechanical obstruction. It is under-recognized in MELAS and can prompt the
diagnosis. Bowel dysfunction and stroke-like episodes may aggravate each
other, but the cited case review explicitly leaves the direction of causation
unresolved. Concomitant pseudo-obstruction requires treatment during
stroke-like-episode management.
phenotype_term:
preferred_term: Intestinal pseudo-obstruction
term:
id: HP:0004389
label: Intestinal pseudo-obstruction
evidence:
- reference: PMID:30766507
reference_title: "Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intestinal pseudo-obstruction (IPO) is most commonly observed in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), although this symptom can also affect patients with MELAS syndrome (5), particularly those with the m.3243A>G mutation; however, IPO remains an underrecognized condition."
explanation: Documents intestinal pseudo-obstruction as an under-recognized m.3243A>G MELAS manifestation.
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
explanation: Places pseudo-obstruction inside stroke-like-episode management rather than treating it as a separate problem.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
IPO is a rare and severe condition that is characterized by abdominal
distension, nausea, vomiting, and pain due to impaired propulsive activity in
the gastrointestinal tract and resembles mechanical intestinal obstruction
(6).
explanation: >-
Defines the clinical obstruction syndrome and the failure of propulsion.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
To the best of our knowledge, gastrointestinal symptoms, especially IPO, led
to the diagnosis of MELAS in six patients (11, 13, 21).
explanation: >-
Restores the diagnostic importance of gastrointestinal presentations without
assigning carrier-cohort timing to every MELAS patient.
- reference: PMID:30766507
reference_title: Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Precisely determining that one of the two symptoms was the precipitating
cause of the other is difficult.
explanation: >-
The preceding sentence identifies IPO and the first stroke-like episode. The
authors propose interaction but cannot establish which initiated
deterioration.
- category: Cardiac
name: Hypertrophic cardiomyopathy
description: >-
Hypertrophic cardiomyopathy, often concentric and non-obstructive, is one form of myocardial involvement in MELAS.
phenotype_term:
preferred_term: Hypertrophic cardiomyopathy
term:
id: HP:0001639
label: Hypertrophic cardiomyopathy
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Both dilated and hypertrophic cardiomyopathy have been observed, however, the more typical is a non-obstructive concentric hypertrophy
explanation: Documents myocardial phenotypes observed in MELAS.
- category: Cardiac
name: Wolff-Parkinson-White syndrome
description: >-
Wolff-Parkinson-White syndrome is an occasional cardiac conduction manifestation of MELAS.
phenotype_term:
preferred_term: Wolff-Parkinson-White syndrome
term:
id: HP:0001716
label: Wolff-Parkinson-White syndrome
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Cardiac conduction abnormalities including Wolff-Parkinson-White syndrome has been reported occasionally
explanation: Documents this specific conduction phenotype in MELAS; other arrhythmias and bundle branch block are distinct findings.
- category: Hematologic
name: Anemia
description: >-
Anemia was found in 30.8% of a 39-patient MELAS cohort. Lower hemoglobin correlated with greater disability, and absence of anemia was associated with lower mortality. The observational study did not establish why anemia developed or exclude dietary and other contributors.
phenotype_term:
preferred_term: Anemia
term:
id: HP:0001903
label: Anemia
evidence:
- reference: PMID:39697439
reference_title: 'Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Blood hemoglobin tests indicated anemia, defined as hemoglobin levels below the normal range, in 30.8% of patients.
explanation: Directly documents anemia in the 39-patient clinical MELAS cohort.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In contrast, hemoglobin levels were negatively correlated with MRS scores (r = -0.375, p = 0.015)."
explanation: Links lower hemoglobin to greater disability on the modified Rankin Scale.
- reference: PMID:39697439
reference_title: 'Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients without anemia had a lower risk of death compared to those with anemia (OR = 0.175, 95% CI 0.033–0.921, p = 0.040).
explanation: The body of the article identifies absence of anemia as the lower-risk comparator; the association does not establish causation.
- category: Neurologic
name: Hemiparesis
description: >-
Hemiparesis may occur as a transient or persistent focal deficit during stroke-like episodes.
phenotype_term:
preferred_term: Hemiparesis
term:
id: HP:0001269
label: Hemiparesis
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6].
explanation: Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
- category: Musculoskeletal
name: Muscle weakness
description: >-
Muscle weakness is a clinical manifestation of mitochondrial myopathy.
phenotype_term:
preferred_term: Muscle weakness
term:
id: HP:0001324
label: Muscle weakness
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: presents clinically as muscle weakness and exercise intolerance.
explanation: Identifies weakness and exercise intolerance as clinical expressions of MELAS myopathy.
- category: Neurologic
name: Aphasia
description: >-
Aphasia can accompany a stroke-like episode involving language cortex.
phenotype_term:
preferred_term: Aphasia
term:
id: HP:0002381
label: Aphasia
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: These episodes present with transient or permanent deficits such as hemiparesis, aphasia, and cortical blindness, often evolving into progressive and irreversible neurological impairment [1,5,6].
explanation: Describes focal clinical deficits resulting from stroke-like episodes in the MELAS neurological section.
- category: Neurologic
name: Cerebellar atrophy
description: >-
Cerebellar volume loss is documented in pediatric MELAS. Repeated imaging studies in the same patient are not independent prevalence observations.
phenotype_term:
preferred_term: Cerebellar atrophy
term:
id: HP:0001272
label: Cerebellar atrophy
evidence:
- reference: PMID:36685235
reference_title: 'Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with an MT-TL1 m.3243A>G point mutation: Neuroradiological features and their implications for underlying pathogenesis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: For all 59 imaging studies, cerebral atrophy occurred in 38 (64%), and cerebellar atrophy occurred in 40 (68%).
explanation: The 24-patient pediatric series documents cerebellar atrophy in 40 imaging studies; it does not provide a 40-patient numerator.
- category: Neurologic
name: Basal ganglia calcification
description: >-
Bilateral basal ganglia calcification was observed in six of nine children who underwent CT in a 24-patient MELAS imaging series.
phenotype_term:
preferred_term: Basal ganglia calcification
term:
id: HP:0002135
label: Basal ganglia calcification
evidence:
- reference: PMID:36685235
reference_title: 'Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with an MT-TL1 m.3243A>G point mutation: Neuroradiological features and their implications for underlying pathogenesis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Bilateral basal ganglia calcifications were found in 6 of 9 (67%) patients who underwent CT.
explanation: Documents calcification in the selected CT subgroup, not an unselected MELAS population.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)
explanation: >-
The complete 25%-49% row of GeneReviews Table 3 includes basal ganglia calcification. The exact source interval is retained because it crosses HPO frequency bands.
frequency: 25%-49%
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Neurologic
name: Focal epileptiform EEG discharges
description: >-
Focal epileptiform discharges can be recorded over an acute stroke-like lesion.
phenotype_term:
preferred_term: EEG with focal epileptiform discharges
term:
id: HP:0011185
label: EEG with focal epileptiform discharges
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the acute brain lesion.
explanation: Episode-level EEG findings in six MELAS patients support focal epileptic activity during acute lesions.
reports_on:
- target: Neuronal hyperexcitability and propagating epileptic activity
relationship: READOUT_OF
interpretation: EEG records focal epileptic activity; this observation alone does not prove which process initiated the stroke-like episode.
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: In 9 of 11 episodes focal epileptiform discharges on EEG were noted in the acute brain lesion.
explanation: Episode-level EEG findings in six MELAS patients support focal epileptic activity during acute lesions.
- category: Metabolic
name: Lactic acidosis
description: >-
Lactic acidosis can accompany respiratory-chain failure; an elevated lactate concentration alone does not establish an acid-base disturbance.
phenotype_term:
preferred_term: Lactic acidosis
term:
id: HP:0003128
label: Lactic acidosis
evidence:
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The m.3243A>G mutation compromises the function of the electron transport chain (ETC), which forces cells to rely on anaerobic glycolysis, thereby leading to the accumulation of lactate and lactic acidosis, a hallmark of MELAS [16,17].
explanation: Describes lactic acidosis as a consequence of respiratory-chain dysfunction.
sequelae:
- target: Recurrent vomiting
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Lactic acidosis can contribute to recurrent vomiting; this is one metabolic route rather than an attribution of every vomiting episode.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
directness: INDIRECT
snippet: >-
Common clinical manifestations include stroke-like episodes,
encephalopathy with seizures and/or dementia, muscle weakness and
exercise intolerance, normal early psychomotor development, recurrent
headaches, recurrent vomiting
explanation: >-
GeneReviews lists recurrent vomiting among the common manifestations of
MELAS. Attributing an episode to lactic acidosis is the metabolic route
this edge proposes rather than something the source measures, hence
INDIRECT.
- category: Cardiac
name: Cardiac conduction abnormality
description: >-
Cardiac conduction abnormalities occur occasionally in MELAS;
Wolff-Parkinson-White syndrome is one specifically reported example. The
broader category does not establish bundle branch block or every arrhythmia
reported across m.3243A>G syndromes.
phenotype_term:
preferred_term: Cardiac conduction abnormality
term:
id: HP:0031546
label: Cardiac conduction abnormality
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Cardiac conduction abnormalities including Wolff-Parkinson-White syndrome has
been reported occasionally
explanation: >-
Supports the broad conduction phenotype in MELAS and the separately
represented WPW subtype.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
<25%
• Optic atrophy
• Pigmentary retinopathy
• Progressive external ophthalmoplegia
• Motor developmental delay
• Cardiomyopathy
• Cardiac conduction abnormalities
• Nephropathy
• Vitiligo
explanation: >-
The complete <25% row of GeneReviews Table 3 includes cardiac conduction abnormality. The exact source interval is retained because it crosses HPO frequency bands.
frequency: <25%
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Neurologic
name: Ataxia
description: >-
Ataxia is included among the clinical manifestations of MELAS in GeneReviews.
This clinical finding is distinct from imaging-detected cerebellar atrophy;
the table does not establish which lesion or mechanism causes it.
phenotype_term:
preferred_term: Ataxia
term:
id: HP:0001251
label: Ataxia
evidence:
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
reference_title: https://www.ncbi.nlm.nih.gov/books/NBK1233/pdf/Bookshelf_NBK1233.pdf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: |-
25%-49%
• Basal ganglia calcification
• Myoclonus
• Ataxia
• Episodic altered consciousness
• Gait disturbance
• Depression
• Anxiety
• Psychotic disorders
• Diabetes mellitus (type 1 or 2)
explanation: >-
The complete 25%-49% row of GeneReviews Table 3 includes ataxia. The exact source interval is retained because it crosses HPO frequency bands.
frequency: 25%-49%
context: >-
Frequency from GeneReviews Table 3, MELAS: Additional Clinical
Manifestations, summarizing clinically defined MELAS rather than all
m.3243A>G carriers. Other quoted cohorts retain their own denominators.
- category: Cardiac
name: Arrhythmia
description: >-
Cardiac arrhythmias occur in MELAS. A clinically and genetically confirmed
case had non-sustained atrial tachycardia with left ventricular hypertrophy;
a clinical review also describes atrial fibrillation and ventricular
tachycardia. This broad rhythm category accommodates different reported
arrhythmias and has no syndrome-wide frequency assignment. It does not
establish sudden cardiac death in the reported patients.
phenotype_term:
preferred_term: Arrhythmia
term:
id: HP:0011675
label: Arrhythmia
evidence:
- reference: PMID:26937404
reference_title: Arrhythmia as a cardiac manifestation in MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A Holter monitor demonstrated episodes of non-sustained atrial tachycardia, a
finding not been previously described in this population.
explanation: >-
The report documents arrhythmia in a 44-year-old woman with clinically
defined MELAS, stroke-like episodes, and m.3243A>G; it is occurrence evidence
rather than a prevalence estimate.
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Patients with MELAS are also at an increased risk for arrhythmias, including
atrial fibrillation and ventricular tachycardia, because of the involvement
of mitochondrial dysfunction in the conduction pathways of the heart [40].
explanation: >-
The MELAS review describes additional rhythm phenotypes and proposes
mitochondrial dysfunction in cardiac conduction pathways as a contributor.
The review does not quantify subtype-specific risks.
- category: Cardiac
name: Right bundle branch block
description: >-
Right bundle branch block was documented in one of 11 adults in a cardiac
study of clinically defined MELAS. Completeness of the block was not
specified, so the ontology binding uses the broader bundle branch block term.
The frequency applies to the participating cohort, not all MELAS patients.
phenotype_term:
preferred_term: Right bundle branch block, completeness unspecified
term:
id: HP:0011710
label: Bundle branch block
frequency: OCCASIONAL
context: >-
One of 11 participating adults with clinical MELAS and m.3243A>G, recruited
from 30 contacted patients; severe disease, nonparticipation, and deaths
limited recruitment.
evidence:
- reference: PMID:39930534
reference_title: Cardiac manifestations in adult MELAS syndrome (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome)- a cross-sectional study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
ECG was performed in all patients. Surprisingly, right branch bundle block
was only found in one (1/11, 9.1%).
explanation: >-
Directly documents right bundle branch block; 1/11 falls in OCCASIONAL
(5-29%) within this selected clinical cohort. The reported right-sided
finding does not establish complete block.
- reference: PMID:39930534
reference_title: Cardiac manifestations in adult MELAS syndrome (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome)- a cross-sectional study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Clinically, all patients reported stroke-like episodes and lactic acidosis.
explanation: >-
Establishes the clinical MELAS manifestations in this cohort, distinguishing
it from a genotype-only carrier series.
histopathology:
- name: Ragged-red fibers on modified Gomori trichrome
description: >-
Subsarcolemmal aggregates of proliferating abnormal mitochondria in
skeletal muscle, the classic morphological signature of a mitochondrial
myopathy. Present in about three quarters of biopsied MELAS patients, so a
negative biopsy does not exclude the diagnosis.
frequency: FREQUENT
diagnostic: true
evidence:
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Ragged-red fibers (RRF) were observed in 29 patients (74.4%), and SDH strongly reactive blood vessels (SSV) were observed in 28 patients (71.8%)."
explanation: Quantifies ragged-red fiber yield (74.4%, within the FREQUENT 30-79% band) in a cohort where every patient underwent muscle biopsy.
- name: Strongly SDH-reactive blood vessels with preserved cytochrome c oxidase activity
description: >-
Intramuscular arterioles stain darkly for succinate dehydrogenase,
reflecting the mitochondrial proliferation in vascular smooth muscle that
gives the "mitochondrial angiopathy" hypothesis its histological footing.
The discriminating detail is the COX result: SSV in MELAS retain normal
cytochrome c oxidase activity, whereas the morphologically identical
vessels in MERRF are COX-negative. The same lesion therefore carries a
different enzymatic meaning in the two diseases, and SSV alone should not
be read as a MELAS-specific finding.
frequency: FREQUENT
evidence:
- reference: PMID:8384773
reference_title: Cytochrome c oxidase activity is deficient in blood vessels of patients with myoclonus epilepsy with ragged-red fibers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "On the other hand, SSV in muscle biopsies from patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) had normal CCO activity as shown by light and electron microscopy."
explanation: Establishes the MELAS half of the distinction, COX-normal SSV.
- reference: PMID:8384773
reference_title: Cytochrome c oxidase activity is deficient in blood vessels of patients with myoclonus epilepsy with ragged-red fibers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "More than half of the intramuscular blood vessels in muscle biopsies from five patients with myoclonus epilepsy with ragged-fibers (MERRF) who had a point mutation in mitochondrial DNA at the tRNALys region were darkly stained with succinate dehydrogenase (SDH) stain, showing the morphologic characteristics of strongly SDH-reactive blood vessels (SSV), but they had no cytochrome c oxidase (CCO) activity."
explanation: Establishes the MERRF half of the distinction, morphologically similar SSV lacking COX activity.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "SDH strongly reactive blood vessels (SSV) were observed in 28 patients (71.8%)"
explanation: Quantifies SSV yield on muscle biopsy in a MELAS cohort; 71.8% falls in the FREQUENT (30-79%) band.
- name: Cortical laminar necrosis with intracortical gyral microhemorrhage
description: >-
The neuropathological correlate of the stroke-like lesion: neuronal loss in
a laminar or pseudo-laminar cortical distribution, with petechial gyral
microhemorrhages confirmed at autopsy and matched in life by subacute
T1-hyperintense cortical signal.
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fat-suppression MRI confirmed intracortical gyral hemorrhage in one episode. Petechial gyral microhemorrhages were also pathologically confirmed in the autopsy of another patient."
explanation: Pathological confirmation of intracortical microhemorrhage within a stroke-like lesion.
imaging_findings:
- name: Cortical T2/FLAIR hyperintensity crossing vascular territories
modality: MRI
description: >-
The defining imaging finding. Lesions favour posterior (occipital,
parietal, temporal) cortex, do not conform to an arterial territory, extend
into contiguous cortex over weeks to months, and are often at least partly
reversible - a combination no arterial infarct produces.
diagnostic: true
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "During the stroke-like episodes neuroimaging shows increased T2-weighted signal areas that do not correspond to the classic vascular distribution (hence the term \"stroke-like\")."
explanation: The reference statement of the non-vascular-territory imaging pattern.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months; (6) neurological symptoms and stroke-like lesions tend to be reversible, as presented on magnetic resonance imaging"
explanation: Adds the posterior predilection, contiguous extension, and reversibility that complete the imaging signature.
- name: Elevated apparent diffusion coefficient within the acute lesion
modality: MRI
description: >-
Acute stroke-like lesions typically show normal-to-elevated ADC, consistent
with vasogenic rather than cytotoxic edema, and this has been used to
separate them from ischemic infarcts. The rule is not absolute: diffusion
restriction is reported within the same lesions, so restricted diffusion
does not exclude MELAS.
diagnostic: false
evidence:
- reference: PMID:18289816
reference_title: Serial brain imaging analysis of stroke-like episodes in MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In the temporal lobe lesion, the apparent diffusion coefficient (ADC) at 44 days after onset was higher (average: 1.219x10(-3)mm2/s) than that in a normal region (average: 0.796x10(-3)mm2/s)."
explanation: Quantitative demonstration of elevated ADC within a stroke-like lesion.
- reference: PMID:23177587
reference_title: "[Conventional and diffusion-weighted magnetic resonance imaging and proton spectroscopy in MELAS]."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Both MRI that were performed during those episodes of stroke-like lesion revealed areas of diffusion restriction, coexisting areas of high ADC."
explanation: Qualifies the elevated-ADC rule by documenting coexisting restricted diffusion in the same lesions.
- name: Lactate peak on proton MR spectroscopy
modality: MRI
description: >-
A lactate doublet with reduced N-acetylaspartate within the lesion, and
frequently a lactate peak in normal-appearing brain as well - which makes
MRS informative even where conventional sequences are unremarkable. The
lesional peak falls as the lesion resolves.
diagnostic: true
evidence:
- reference: PMID:18289816
reference_title: Serial brain imaging analysis of stroke-like episodes in MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(1)H-MRS of the left parietal lobe lesion at the same day showed a decrease in N-acetylaspartate/(creatine+phosphocreatine) (NAA/Cr) (0.43) and a peak in lactate. 1H-MRS of the contralateral side at the same day showed NAA/Cr (1.57) and no peak in lactate."
explanation: Shows the lesional lactate peak with reduced NAA against an unaffected contralateral control.
- reference: PMID:23177587
reference_title: "[Conventional and diffusion-weighted magnetic resonance imaging and proton spectroscopy in MELAS]."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Proton spectroscopy showed the presence of lactate and reduction of N-acetyl aspartate peak in stroke-like lesion and the presence of lactate in apparently spared brain."
explanation: Documents lactate in normal-appearing brain as well as within the lesion.
- name: Focal cortical hyperperfusion during the acute episode
modality: SPECT
description: >-
Perfusion imaging over an acute stroke-like lesion shows focal
hyperperfusion, not the hypoperfusion an ischemic mechanism predicts. This
is one of the strongest single arguments against the purely vascular model
of the stroke-like episode.
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
explanation: Direct perfusion evidence contradicting an ischemic mechanism for the acute lesion.
- reference: PMID:18289816
reference_title: Serial brain imaging analysis of stroke-like episodes in MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Perfusion imaging at onset showed high intensity in bilateral occipital lobes, which indicated hyperperfusion in stroke-like lesions."
explanation: Independent MR perfusion confirmation of lesional hyperperfusion.
- name: Cerebral atrophy
modality: MRI
imaging_finding_term:
preferred_term: Cerebral atrophy
term:
id: HP:0002059
label: Cerebral atrophy
description: >-
Progressive brain atrophy accumulating across the disease course, the
imaging correlate of the interictal cognitive decline.
evidence:
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "(8) brain dysfunction and atrophy are slowly progressive"
explanation: Documents progressive atrophy as part of the MELAS imaging course.
biochemical:
- name: Blood lactate
presence: Elevated
context: >-
The "LA" of the acronym. Beyond diagnosis, the degree of elevation carries
prognostic weight: severe hyperlactatemia is an independent predictor of
mortality and correlates with disability scores.
biomarker_term:
preferred_term: Lactic Acid Measurement
term:
id: NCIT:C79450
label: Lactic Acid Measurement
reference_ranges:
- unit: mmol/L
upper_bound: 2.0
population: MELAS cohort thresholds for mild versus severe hyperlactatemia
notes: >-
Thresholds as operationalized in the cited prognostic cohort; the upper
limit of normal is assay- and laboratory-dependent.
evidence:
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Mild hyperlactatemia was defined as a blood lactate level greater than the upper limit of the normal range (>2 mmol/L), while severe hyperlactatemia was defined as a blood lactate level greater than twice the upper limit of the normal range (>4 mmol/L)."
explanation: Defines the mild and severe blood-lactate bands used in the prognostic analysis.
interpretation_bands:
- name: Normal
upper_bound: 2.0
unit: mmol/L
abnormal_flag: NORMAL
- name: Mild hyperlactatemia
lower_bound: 2.0
upper_bound: 4.0
unit: mmol/L
abnormal_flag: HIGH
severity: MILD
- name: Severe hyperlactatemia
lower_bound: 4.0
unit: mmol/L
abnormal_flag: CRITICAL_HIGH
severity: SEVERE
interpretation: >-
Independently associated with mortality in MELAS and correlated with
modified Rankin Scale disability.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Lactic acidemia is very common and muscle biopsies typically show ragged red fibers."
explanation: Establishes lactic acidemia as a very common finding in MELAS.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "There was a positive correlation between lactic acid levels and MRS scores (r = 0.460, p = 0.003)."
explanation: Links the magnitude of lactate elevation to disability, supporting its prognostic use.
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In multivariate analysis, severe lactate elevation (OR = 7.279, 95% CI 1.102-48.086, p = 0.039) and anemia (OR = 0.137, 95% CI 0.021-0.908, p = 0.039) were identified as independent predictors of mortality."
explanation: Supports severe hyperlactatemia as an independent predictor of mortality, as stated in the context.
- name: Cerebrospinal fluid lactate
presence: Elevated
context: >-
CSF lactate can be raised when blood lactate is normal, so a normal serum
value does not exclude MELAS. Proton MR spectroscopy detects the same
signal non-invasively, including in normal-appearing brain.
biomarker_term:
preferred_term: Lactic Acid Measurement
term:
id: NCIT:C79450
label: Lactic Acid Measurement
reference_ranges:
- unit: mmol/L
upper_bound: 2.2
population: MELAS cohort thresholds for mild versus severe CSF lactate elevation
notes: Thresholds as operationalized in the cited prognostic cohort.
evidence:
- reference: PMID:39697439
reference_title: "Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Similarly, mild elevation in cerebrospinal fluid (CSF) lactate was defined as a level exceeding the upper normal limit (>2.2 mmol/L), and severe elevation was defined as a level exceeding two times the upper normal limit (>4.4 mmol/L)."
explanation: Defines the CSF lactate bands used in the prognostic analysis.
interpretation_bands:
- name: Normal
upper_bound: 2.2
unit: mmol/L
abnormal_flag: NORMAL
- name: Mild elevation
lower_bound: 2.2
upper_bound: 4.4
unit: mmol/L
abnormal_flag: HIGH
severity: MILD
- name: Severe elevation
lower_bound: 4.4
unit: mmol/L
abnormal_flag: CRITICAL_HIGH
severity: SEVERE
evidence:
- reference: PMID:23177587
reference_title: "[Conventional and diffusion-weighted magnetic resonance imaging and proton spectroscopy in MELAS]."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Proton spectroscopy showed the presence of lactate and reduction of N-acetyl aspartate peak in stroke-like lesion and the presence of lactate in apparently spared brain."
explanation: Demonstrates elevated brain lactate detectable by spectroscopy even outside the visible lesion.
- name: Growth differentiation factor 15 (GDF-15)
presence: Elevated
context: >-
A circulating marker of mitochondrial disease rather than of MELAS
specifically. In a meta-analysis of diagnostic accuracy for mitochondrial
disease, GDF-15 had higher pooled sensitivity, specificity, diagnostic odds
ratio, and SROC than FGF-21, and the authors conclude that GDF-15 had the
highest diagnostic accuracy of the two. The meta-analysis did not report
MELAS-specific accuracy.
specificity: Mitochondrial disease as a class; not specific to MELAS
biomarker_term:
preferred_term: Growth Differentiation Factor 15 Measurement
term:
id: NCIT:C181406
label: Growth Differentiation Factor 15 Measurement
evidence:
- reference: PMID:32585080
reference_title: "Accuracy of FGF-21 and GDF-15 for the diagnosis of mitochondrial disorders: A meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Pooled sensitivity, specificity, DOR and SROC of FGF-21 were 0.71 (95% CI 0.53, 0.84), 0.88(95% CI 0.82, 0.93), 18 (95% CI 6, 54), 0.90 (95% CI 0.87, 0.92), respectively, which were lower than GDF-15 values; 0.83 (95% CI 0.65, 0.92), 0.92 (95% CI 0.84, 0.96), 52 (95% CI 13, 205), 0.94 (95% CI 0.92, 0.96)."
explanation: Meta-analytic diagnostic performance of GDF-15 against FGF-21 for mitochondrial disease as a class, not MELAS specifically.
- reference: PMID:32585080
reference_title: "Accuracy of FGF-21 and GDF-15 for the diagnosis of mitochondrial disorders: A meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "FGF-21 and GDF-15 showed acceptable sensitivity and high specificity. Of the biomarkers, GDF-15 had the highest diagnostic accuracy."
explanation: The authors' own conclusion on the comparison.
- name: Fibroblast growth factor 21 (FGF-21)
presence: Elevated
context: >-
Useful for diagnosis but poor for monitoring. In adult m.3243A>G carriers
FGF-21 correlates only moderately with cross-sectional disease severity and
showed no correlation with disease progression over two years, so it does
not substitute for clinical scoring as a longitudinal endpoint.
specificity: Mitochondrial disease as a class; not specific to MELAS
biomarker_term:
preferred_term: Fibroblast Growth Factor 21 Measurement
term:
id: NCIT:C112280
label: Fibroblast Growth Factor 21 Measurement
evidence:
- reference: PMID:24907231
reference_title: "Serum FGF21 levels in adult m.3243A>G carriers: clinical implications."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Our analysis revealed a moderate, significant correlation between FGF21 concentration and disease severity (r = 0.49; p = <0.001)."
explanation: Establishes only a moderate cross-sectional relationship with severity in m.3243A>G carriers.
- reference: PMID:24907231
reference_title: "Serum FGF21 levels in adult m.3243A>G carriers: clinical implications."
supports: REFUTE
evidence_source: HUMAN_CLINICAL
snippet: "Repeated measurements following 25 subjects for 2 years revealed no significant correlation between FGF21 concentration and disease progression."
explanation: Refutes the use of FGF-21 as a longitudinal progression marker in this population.
- reference: PMID:32585080
reference_title: "Accuracy of FGF-21 and GDF-15 for the diagnosis of mitochondrial disorders: A meta-analysis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "FGF-21 and GDF-15 showed acceptable sensitivity and high specificity."
explanation: Supports the diagnostic usefulness of FGF-21 for mitochondrial disease as a class.
genetic:
- name: MT-TL1 m.3243A>G
gene_term:
preferred_term: MT-TL1
term:
id: hgnc:7490
label: MT-TL1
association: >-
The m.3243A>G point mutation in MT-TL1 (mitochondrial tRNA-Leu(UUR)) is the
most common cause of MELAS, found in roughly 80% of patients. Disease
expression depends on the heteroplasmy level of mutant mtDNA.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TL1
case_fractions:
- population: Individuals meeting clinical MELAS diagnostic criteria
case_fraction_percent: 80.0
notes: >-
Share of clinically diagnosed MELAS attributable to m.3243A>G, as stated by
GeneReviews. The cohort is ascertained for the MELAS phenotype, so this is
not the share of m.3243A>G carriers who develop MELAS, which is far lower.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The m.3243A>G pathogenic variant in the mitochondrial gene MT-TL1 is
present in approximately 80% of individuals with MELAS.
explanation: Quantifies the m.3243A>G share of clinically diagnosed MELAS.
inheritance:
- name: Mitochondrial inheritance
inheritance_term:
preferred_term: Mitochondrial inheritance
term:
id: HP:0001427
label: Mitochondrial inheritance
evidence:
- reference: PMID:24846800
reference_title: "Detection rates and phenotypic spectrum of m.3243A>G in the MT-TL1 gene: a molecular diagnostic laboratory perspective."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
factors including random mitochondrial segregation and consequent
variable tissue heteroplasmy are recognised to contribute to a much
broader phenotypic spectrum associated with the MT-TL1 m.3243A>G
mutation
explanation: >-
Supports maternal mitochondrial inheritance with heteroplasmy-dependent,
variable phenotypic expression of the m.3243A>G mutation.
- reference: PMID:37988592
reference_title: Penetrance and expressivity of mitochondrial variants in a large clinically unselected population.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Multi-system disease risk and penetrance of diabetes, deafness and
heart failure greatly increased with m.3243A>G level ≥ 10%.
explanation: >-
UK Biobank data quantifying the heteroplasmy threshold effect: penetrance
of multisystem disease rises sharply once m.3243A>G heteroplasmy reaches
≥10%.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The m.3243A>G pathogenic variant in the mitochondrial gene MT-TL1 is
present in approximately 80% of individuals with MELAS.
explanation: >-
GeneReviews establishes m.3243A>G in MT-TL1 as the most common cause of
MELAS (~80% of cases).
- reference: PMID:2102678
reference_title: A mutation in the tRNA(Leu)(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The mutation was present in 26 out of 31 independent MELAS patients and 1
out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested.
explanation: >-
Original genotyping data establishing the m.3243A>G variant as
MELAS-specific.
- reference: PMID:39118480
reference_title: "The clinical and genetic spectrum of mitochondrial diseases in China: A multicenter retrospective cross-sectional study."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Mitochondrial DNA (mtDNA) mutations were prevalent (87.4%), with m.3243A>G being the most common locus (48.7%)."
explanation: Independent multicentre confirmation that m.3243A>G is the single commonest mitochondrial-disease locus, in a cohort where MELAS was the predominant phenotype.
notes: >-
GERMLINE here means a constitutional mtDNA variant transmitted through the
maternal line. GeneReviews states that the mother of a proband usually, but
not invariably, carries the variant.
- name: MT-ND5
gene_term:
preferred_term: MT-ND5
term:
id: hgnc:7461
label: MT-ND5
association: >-
MT-ND5 is the leading non-MT-TL1 cause of MELAS named by GeneReviews.
Unlike the tRNA genotypes, it encodes a complex I structural subunit rather
than a component of the translation apparatus. In a MELAS/Leigh overlap
cohort, MT-ND gene variants predominated and m.13513G>A in MT-ND5 was the
commonest single variant, so genotype may partly indicate where a patient
sits on the MELAS-Leigh spectrum; the cited cohort does not test this
prediction directly.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-ND5
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Pathogenic variants in MT-TL1 or other mtDNA genes, particularly MT-ND5,
can also cause this disorder.
explanation: >-
GeneReviews documents MT-ND5 and other mtDNA genes as additional causes of
MELAS beyond the common MT-TL1 m.3243A>G variant.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
explanation: Identifies MT-ND5 m.13513G>A as the leading variant in MELAS/Leigh overlap, the presentation most enriched for complex I subunit genotypes.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Names the full set of complex I subunit genes reported as non-MT-TL1 causes of MELAS.
notes: >-
GERMLINE here means a constitutional mtDNA variant transmitted through the
maternal line. GeneReviews states that the mother of a proband usually, but
not invariably, carries the variant.
- name: MT-ND1
gene_term:
preferred_term: MT-ND1
term:
id: hgnc:7455
label: MT-ND1
association: >-
Variants in the complex I subunit gene MT-ND1 are reported in MELAS. Unlike
the mitochondrial tRNA genotypes, MT-ND1 variants lower complex I activity by
altering a structural subunit rather than by impairing mitochondrial
translation.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-ND1
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sequencing of the mitochondrial DNA revealed two novel MT-ND1 gene
missense mutations, m.3959G>A and m.3995A>G, which are highly conserved
among species.
explanation: Reports MT-ND1 missense variants in probands presenting with MELAS features.
- reference: PMID:23834081
reference_title: "Novel mutations m.3959G>A and m.3995A>G in mitochondrial gene MT-ND1 associated with MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A respiratory chain function study showed decreased activity of
mitochondrial respiratory chain complex I in both probands.
explanation: Establishes reduced complex I activity as the biochemical consequence in these MT-ND1 patients.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Independent cohort listing MT-ND1 among the complex I subunit genes reported in MELAS.
notes: >-
GERMLINE here means a constitutional mtDNA variant transmitted through the
maternal line. GeneReviews states that the mother of a proband usually, but
not invariably, carries the variant.
- name: MT-ND6
gene_term:
preferred_term: MT-ND6
term:
id: hgnc:7462
label: MT-ND6
association: >-
Variants in the complex I subunit gene MT-ND6 are reported in MELAS,
including m.14453G>A. As with MT-ND1 and MT-ND5, the lesion is in a complex I
structural subunit rather than in the translation apparatus.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-ND6
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:32552696
reference_title: "Late-onset MELAS syndrome with mtDNA 14453G→A mutation masquerading as an acute encephalitis: a case report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "broadens the phenotypic spectrum of MELAS syndrome associated with ND6 gene mutation"
explanation: The authors attribute a MELAS presentation to an MT-ND6 variant and treat it as extending that gene's MELAS spectrum.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "whereas mutations in polypeptide-coding genes, including subunits 1, 5, and 6 of complex I (MT-ND1, MT-ND5, and MT-ND6), have also been identified in MELAS"
explanation: Independent cohort listing MT-ND6 among the complex I subunit genes reported in MELAS.
notes: >-
GERMLINE here means a constitutional mtDNA variant transmitted through the
maternal line. GeneReviews states that the mother of a proband usually, but
not invariably, carries the variant.
- name: MT-TQ
gene_term:
preferred_term: MT-TQ
term:
id: hgnc:7495
label: MT-TQ
association: >-
A heteroplasmic m.4332G>A variant in MT-TQ (mitochondrial tRNA-Gln) was
reported in a patient given a MELAS-spectrum diagnosis, with pathogenicity
argued from the correlation between mutation load and a respiratory-chain
defect in single muscle fibres.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TQ
notes: >-
The evidence base for this gene is one reported patient whose onset and
neuroimaging the authors themselves called atypical for MELAS. The record is
kept because MONDO:0800033 asserts the gene-disease relationship, but it
should not be read as carrying the weight of the MT-TL1 or MT-ND5 evidence.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:11171912
reference_title: Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A heteroplasmic G to A transition at nucleotide 4332 in the tRNA glutamine
gene was identified in the patient's muscle mitochondrial DNA.
explanation: Identifies the MT-TQ variant in the reported MELAS-spectrum patient.
- reference: PMID:11171912
reference_title: Atypical MELAS syndrome associated with a new mitochondrial tRNA glutamine point mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The pathogenicity of the mutation was shown in single muscle fibers by the
correlation between high mutation load and cytochrome c oxidase defect.
explanation: The mutation-load-to-defect correlation is the pathogenicity argument offered for this variant.
- name: MT-TH
gene_term:
preferred_term: MT-TH
term:
id: hgnc:7487
label: MT-TH
association: >-
Variants in MT-TH (mitochondrial tRNA-His) are reported with lactic acidosis
and stroke-like episodes. For m.12146A>G, transmitochondrial cybrids showed
that the tRNA-His variant itself, not the nuclear background, produced the
respiratory-chain enzyme deficiency.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TH
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:21704194
reference_title: New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We report a new mutation in m.12146 A>G in the mt-tRNA(His) in a family
with a remarkable clinical history having different degrees of lactic
acidosis and stroke-like episodes.
explanation: Ties an MT-TH variant to the MELAS-defining combination of lactic acidosis and stroke-like episodes in one family.
- reference: PMID:21704194
reference_title: New mitochondrial tRNA HIS mutation in a family with lactic acidosis and stroke-like episodes (MELAS).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Transmitochondrial cybrid analysis proved that this tRNA(His) mutation
causes the enzymatic deficiency.
explanation: Cybrid transfer isolates the mtDNA variant as the cause of the enzyme deficiency.
- name: MT-TK
gene_term:
preferred_term: MT-TK
term:
id: hgnc:7489
label: MT-TK
association: >-
m.8296A>G in MT-TK (mitochondrial tRNA-Lys) was reported in a patient with
optic atrophy, cardiomyopathy and bilateral striatal necrosis who later
developed stroke-like episodes. The same variant had been reported earlier
in patients with diabetes mellitus or with myoclonus epilepsy with ragged-red
fibres, so the genotype does not predict a MELAS phenotype.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TK
notes: >-
The evidence base is one reported patient, and the authors note the same
variant in unrelated phenotypes. Treat the MELAS attribution as reported
rather than established.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Skeletal muscle total mitochondrial DNA analysis identified a
heteroplasmic A to G point mutation in the tRNA(Lys) gene at position
8296.
explanation: Identifies the MT-TK variant in the reported MELAS patient.
- reference: PMID:12504210
reference_title: Atypical MELAS associated with mitochondrial tRNA(Lys) gene A8296G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We conclude that the 8296 mutation is likely to be pathogenic"
explanation: The authors' pathogenicity assessment for this MT-TK variant.
- name: MT-TC
gene_term:
preferred_term: MT-TC
term:
id: hgnc:7477
label: MT-TC
association: >-
m.5783G>A in MT-TC (mitochondrial tRNA-Cys) was reported in a late-onset
MELAS patient in whom blood lymphocyte DNA testing was negative and the
variant was found only by sequencing mtDNA from urinary sediment.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TC
notes: >-
The evidence base is one reported patient. The case is retained partly for
its diagnostic point: a negative blood result does not exclude a
heteroplasmic mtDNA variant, because heteroplasmy is distributed unevenly
across tissues.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:38881794
reference_title: "Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the patient was eventually diagnosed with MELAS with the mtDNA 5783G>A
mutation in the MT-TC gene with a urinary sediment genetic test
explanation: Names MT-TC as the gene carrying the variant in a patient diagnosed with MELAS.
- reference: PMID:38881794
reference_title: "Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This case report expands the genetic repertoire associated with MELAS syndrome"
explanation: The authors present the genotype as an addition to the MELAS gene spectrum rather than an established cause.
- name: MT-TS1
gene_term:
preferred_term: MT-TS1
term:
id: hgnc:7497
label: MT-TS1
association: >-
A heteroplasmic m.7512T>C variant in MT-TS1 (mitochondrial tRNA-Ser(UCN)),
disrupting a conserved acceptor-stem base pair, was reported in a family
presenting as MERRF/MELAS overlap syndrome rather than as classical MELAS.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TS1
notes: >-
The reported phenotype is an overlap syndrome, so this gene sits at the
MERRF boundary of the MELAS spectrum rather than inside classical MELAS.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:7669057
reference_title: A novel point mutation in the mitochondrial tRNA(Ser(UCN)) gene detected in a family with MERRF/MELAS overlap syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We found a new point mutation in the mitochondrial tRNA(Ser(UCN)) gene in
a family with MERRF/MELAS overlap syndrome by screening for heteroplasmy
explanation: Links MT-TS1 to a MELAS-overlap phenotype in one family.
- reference: PMID:7669057
reference_title: A novel point mutation in the mitochondrial tRNA(Ser(UCN)) gene detected in a family with MERRF/MELAS overlap syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "revealed a heteroplasmic mutation at nt 7512 in the tRNA(Ser(UCN)) gene"
explanation: Gives the specific heteroplasmic MT-TS1 variant.
- name: MT-TS2
gene_term:
preferred_term: MT-TS2
term:
id: hgnc:7498
label: MT-TS2
association: >-
Variants in MT-TS2 (mitochondrial tRNA-Ser(AGY)) are reported in MELAS. For
m.12244G>A the presentation was a classical MELAS phenotype, with functional
work showing impaired mitochondrial translation and oxidative
phosphorylation. Across reported MT-TS2 variants the phenotype is variable.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
subtype: MT-TS2
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We identified a rare m.12244G > A variant in the tRNASer(AGY) gene
associated with classical MELAS phenotype.
explanation: Ties an MT-TS2 variant to a classical MELAS presentation.
- reference: PMID:41692888
reference_title: "A novel tRNASer(AGY) 12244G > a variant impairs mitochondrial function and presents with classical MELAS phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Literature review showed that MT-TS2 variants are associated with variable
phenotypes including encephalopathy, myopathy, deafness, diabetes, and
retinopathy.
explanation: Records that MT-TS2 genotypes are not MELAS-specific.
- name: MT-TV
gene_term:
preferred_term: MT-TV
term:
id: hgnc:7500
label: MT-TV
association: >-
A heteroplasmic m.1616A>G variant in MT-TV (mitochondrial tRNA-Val) was
reported in a man with MELAS whose course was dominated by rapidly
progressive cardiomyopathy and severe heart failure. The authors present the
respiratory-chain consequence as a possibility rather than a measurement.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
notes: >-
MONDO has no MELAS child term for this gene, so this record carries no
subtype anchor; the children of MONDO:0010789 were enumerated in OLS on
2026-09-24 and cover ten genes, none of them MT-TV. The evidence base is one
reported patient.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:28893805
reference_title: "MELAS syndrome associated with a new mitochondrial tRNA-Val gene mutation (m.1616A>G)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
He had a mitochondrial transfer RNA (tRNA) mutation (m.1616A>G) of the
(tRNA-Val) gene, and it was not found in MELAS syndrome ever before.
explanation: Identifies the MT-TV variant in a patient diagnosed with MELAS.
- reference: PMID:28893805
reference_title: "MELAS syndrome associated with a new mitochondrial tRNA-Val gene mutation (m.1616A>G)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
directness: INDIRECT
snippet: >-
The presence of this newly observed tRNA-Val mutation (m.1616A>G) may
induce multiple respiratory chain enzyme deficiencies and contribute to
MELAS syndrome symptoms that are associated with mitochondrial DNA (mtDNA)
mutations.
explanation: >-
The respiratory-chain link is stated by the authors as a possibility, which
is why this gene is recorded without a claim of established pathogenicity.
- name: MT-TW
gene_term:
preferred_term: MT-TW
term:
id: hgnc:7501
label: MT-TW
association: >-
A heteroplasmic m.5541C>T variant in MT-TW (mitochondrial tRNA-Trp) was
reported in a patient with MELAS and multiple organ involvement. Functional
work put the translation defect first and the respiratory dysfunction after
it, which places this genotype in the same mechanism class as the other
mitochondrial tRNA variants. Patient-derived induced pluripotent stem cells
carrying near-homoplasmic mutant mtDNA were used separately to show
cell-type-specific phenotypes.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
notes: >-
MONDO has no MELAS child term for this gene, so this record carries no
subtype anchor. The evidence base is one reported patient, but unlike the
other single-patient mt-tRNA genotypes here it is supported by functional and
patient-derived cellular work.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:26297375
reference_title: Molecular pathomechanisms and cell-type-specific disease phenotypes of MELAS caused by mutant mitochondrial tRNA(Trp).
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We found a disease-causative mutation, m.5541C>T heteroplasmy in MT-TW
gene, in a patient exhibiting mitochondrial myopathy, encephalopathy,
lactic acidosis, and stroke-like episodes (MELAS) with multiple organ
involvement.
explanation: Names MT-TW as the gene carrying the variant in a patient diagnosed with MELAS.
- reference: PMID:26297375
reference_title: Molecular pathomechanisms and cell-type-specific disease phenotypes of MELAS caused by mutant mitochondrial tRNA(Trp).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
This mutation firstly disturbed the translation machinery of mitochondrial
tRNA(Trp) and induced mitochondrial respiratory dysfunction, followed by
severely injured mitochondrial homeostasis.
explanation: >-
Places the primary lesion in mitochondrial translation rather than in the
respiratory chain, which is the mechanism this entry models for mt-tRNA
genotypes.
- name: MT-TM
gene_term:
preferred_term: MT-TM
term:
id: hgnc:7492
label: MT-TM
association: >-
A heteroplasmic m.4450G>A variant in MT-TM (mitochondrial tRNA-Met) was
reported in a girl who met the clinical criteria for MELAS. Heteroplasmy was
measured in six tissues and ranged from 20% in blood to 59% in urinary
sediment, and patient fibroblasts showed reduced oxygen consumption with
decreased complex I and IV activities.
relationship_type: CAUSATIVE
variant_origin: GERMLINE
notes: >-
MONDO has no MELAS child term for this gene, so this record carries no
subtype anchor. The evidence base is one reported patient, and the earlier
MT-TM literature the authors summarise describes myopathy rather than MELAS.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS is caused by pathogenic variants in mtDNA and is transmitted by
maternal inheritance.
explanation: >-
GeneReviews states that the mtDNA variants causing MELAS are maternally
transmitted, i.e. constitutional (germline) rather than somatically acquired,
which supports variant_origin GERMLINE for this genetic record.
- reference: PMID:30739820
reference_title: "MELAS syndrome with m.4450 G > A mutation in mitochondrial tRNA(Met) gene."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mitochondrial gene analysis revealed a heteroplasmic m.4450G > A mutation
in the mitochondrial tRNAMet.
explanation: Identifies the MT-TM variant and records that it is heteroplasmic.
- reference: PMID:30739820
reference_title: "MELAS syndrome with m.4450 G > A mutation in mitochondrial tRNA(Met) gene."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Stroke-like episodes, lactic acidosis, encephalopathy with brain magnetic
resonance imaging findings, and declined mitochondrial function were
consistent with mitochondrial myopathy, encephalopathy, lactic acidosis,
and stroke-like episodes (MELAS) syndrome.
explanation: The authors' basis for calling this presentation MELAS rather than an isolated myopathy.
- reference: PMID:30739820
reference_title: "MELAS syndrome with m.4450 G > A mutation in mitochondrial tRNA(Met) gene."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The heteroplasmic rate of the m.4450G > A mutation in blood, skin, urinary
sediment, hair, saliva, and nail samples were 20, 38, 59, 41, 27, and 35%,
respectively.
explanation: >-
Gives the measured tissue distribution of heteroplasmy quoted in this
record, and shows why a blood measurement understates the load in other
tissues.
treatments:
- name: L-arginine therapy
description: >-
Intravenous L-arginine in the acute phase and oral supplementation for
prophylaxis aims to restore nitric oxide availability and improve
endothelial function, reducing the frequency and severity of stroke-like
episodes.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: L-arginine
term:
id: CHEBI:16467
label: L-arginine
target_mechanisms:
- target: Mitochondrial angiopathy and NO deficiency
treatment_effect: RESTORES
description: >-
L-arginine, a nitric oxide precursor, aims to restore nitric oxide
availability and improve endothelial function at the angiopathy node,
reducing the frequency and severity of stroke-like episodes.
evidence:
- reference: PMID:31693521
reference_title: Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "MELAS is associated with endothelial dysfunction by decreased plasma L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate."
explanation: Names the NO-deficient endothelial node that arginine supplementation is intended to correct.
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Unblinded studies showed that l-arginine therapy improves stroke-like
episode symptoms and decreases the frequency and severity of these
episodes.
explanation: >-
Supports L-arginine as a therapy that reduces stroke-like episode
frequency and severity in MELAS.
- reference: PMID:31693521
reference_title: Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
the systematic administration of L-arginine to patients with MELAS
significantly improved the survival curve of patients compared with
natural history.
explanation: >-
Clinical trial follow-up data supporting survival benefit of systematic
L-arginine therapy in MELAS.
- name: Taurine supplementation
description: >-
Oral taurine supplementation aims to restore taurine modification of the
wobble uridine of mutant mitochondrial tRNA-Leu(UUR), improving codon
decoding and reducing stroke-like episode recurrence. Unusually for MELAS,
this is a therapy aimed at the proximal molecular lesion rather than at a
downstream consequence.
therapeutic_modality: SMALL_MOLECULE
target_mechanisms:
- target: Taurine wobble-modification deficiency of tRNA-Leu(UUR)
treatment_effect: RESTORES
description: >-
Supplying taurine is intended to restore the 5-taurinomethyluridine
modification at the anticodon wobble position, correcting the
codon-specific decoding defect at its source.
evidence:
- reference: PMID:29666206
reference_title: "Taurine supplementation for prevention of stroke-like episodes in MELAS: a multicentre, open-label, 52-week phase III trial."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a taurine modification defect at the first anticodon nucleotide of mitochondrial tRNALeu(UUR), resulting in failure to decode codons accurately"
explanation: States the molecular target that taurine supplementation is designed to correct.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: taurine
term:
id: CHEBI:15891
label: taurine
evidence:
- reference: PMID:29666206
reference_title: "Taurine supplementation for prevention of stroke-like episodes in MELAS: a multicentre, open-label, 52-week phase III trial."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Taurine reduced the annual relapse rate of stroke-like episodes from 2.22
to 0.72 (P=0.001).
explanation: >-
A multicentre phase III trial showing high-dose taurine significantly
reduced stroke-like episode recurrence in MELAS.
- reference: PMID:29666206
reference_title: "Taurine supplementation for prevention of stroke-like episodes in MELAS: a multicentre, open-label, 52-week phase III trial."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
a taurine modification defect at the first anticodon nucleotide of
mitochondrial tRNALeu(UUR), resulting in failure to decode codons
accurately
explanation: >-
Provides the molecular rationale: taurine restores wobble-uridine
modification of mutant tRNA-Leu(UUR), improving codon decoding.
- name: Citrulline supplementation
description: >-
Oral citrulline, a nitric oxide precursor, increases arginine availability
and nitric oxide production. Stable-isotope studies suggest citrulline may be
a more effective NO precursor than arginine in MELAS.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: L-citrulline
term:
id: CHEBI:16349
label: L-citrulline
target_mechanisms:
- target: Mitochondrial angiopathy and NO deficiency
treatment_effect: RESTORES
description: >-
Citrulline increases intracellular arginine availability and nitric oxide
synthesis, targeting the NO-deficient endothelial dysfunction at the
angiopathy node.
evidence:
- reference: PMID:26851065
reference_title: Impaired nitric oxide production in children with MELAS syndrome and the effect of arginine and citrulline supplementation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The greater effect of citrulline in increasing NO production is due to its greater ability to increase arginine availability particularly in the intracellular compartment in which NO synthesis takes place."
explanation: Stable-isotope evidence that citrulline raises NO production at the intracellular site where NO synthase acts.
evidence:
- reference: PMID:26851065
reference_title: Impaired nitric oxide production in children with MELAS syndrome and the effect of arginine and citrulline supplementation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The greater effect of citrulline in increasing NO production is due to its
greater ability to increase arginine availability particularly in the
intracellular compartment in which NO synthesis takes place.
explanation: >-
Stable-isotope study showing citrulline increases NO production more
effectively than arginine in children with MELAS, supporting it as a NO
precursor therapy.
- name: Supportive mitochondrial disease management
description: >-
Supportive care including antiseizure medications, management of diabetes and
hearing loss, avoidance of mitochondrial toxins, and mitochondrial cofactor
supplementation (e.g., coenzyme Q10, L-carnitine). GeneReviews recommends
annual ophthalmologic, audiologic, and cardiac assessment, including ECG and
echocardiography, plus annual urinalysis and fasting glucose to detect
multisystem involvement.
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Management is largely symptomatic and should involve a multidisciplinary
team.
explanation: >-
Supports symptomatic, multidisciplinary supportive management as the
mainstay of MELAS care.
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Additionally, carnitine and coenzyme Q10 are commonly used in MELAS
syndrome without proven efficacy.
explanation: >-
Supports common use of carnitine and coenzyme Q10 cofactors, while noting
their efficacy is unproven (hence PARTIAL).
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Annual ophthalmologic, audiology, and cardiologic (electrocardiogram and
echocardiogram) evaluations are recommended. Annual urinalysis and fasting
blood glucose level are also recommended.
explanation: >-
The 2018 GeneReviews surveillance recommendations cover cardiac conduction
and myocardial disease as well as hearing, vision, renal, and endocrine
involvement.
- name: Aggressive antiseizure therapy
description: >-
Under the neuronal-hyperexcitability model, seizure control is not merely
symptomatic management but treatment aimed at the mechanism that initiates
and propagates the stroke-like lesion. Epilepsy in MELAS is typically drug
resistant, yet most patients achieve substantial seizure reduction with
combinations of two or more antiseizure medications. Valproic acid is
specifically avoided as a mitochondrial toxin.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Anticonvulsant Therapy
term:
id: NCIT:C64172
label: Anticonvulsant Therapy
target_mechanisms:
- target: Neuronal hyperexcitability and propagating epileptic activity
treatment_effect: INHIBITS
description: >-
Suppressing epileptiform activity is intended to interrupt the
depolarization cascade that spreads the cortical lesion into adjacent
cortex.
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The management of stroke-like episodes should focus on aggressive seizure management and treatment for concomitant complications such as intestinal pseudo-obstruction."
explanation: Places seizure suppression at the centre of stroke-like-episode management, which follows from the hyperexcitability model.
evidence:
- reference: PMID:27671241
reference_title: "Epilepsy Characteristics and Clinical Outcome in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Twenty of 22 subjects (90.9%) achieved partial to complete reduction of clinical seizures for more than one year with a combination of more than two antiepileptic drugs."
explanation: Quantifies achievable seizure control with multi-drug antiseizure therapy in MELAS.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Mitochondrial toxins, including aminoglycoside antibiotics, linezolid, cigarettes, and alcohol; valproic acid for seizure treatment; metformin because of its propensity to cause lactic acidosis; dichloroacetate (DCA) because of increased risk for peripheral neuropathy."
explanation: Records the constraint that valproic acid must be avoided when choosing antiseizure medication in MELAS.
- name: Soluble guanylate cyclase stimulation (investigational)
description: >-
Zagociguat and the earlier IW-6463 are CNS-penetrant stimulators of soluble
guanylate cyclase, the receptor for nitric oxide. They act one step
downstream of the arginine and citrulline strategy: rather than supplying
more NO precursor, they amplify signalling through the NO-cGMP axis whose
failure defines the endothelial-dysfunction node. Both have been taken into
MELAS-specific trials; neither is approved, and the IW-6463 study was
terminated.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: zagociguat
term:
id: NCIT:C188581
label: Zagociguat
- preferred_term: soluble guanylate cyclase stimulator
term:
id: NCIT:C210759
label: Soluble Guanylate Cyclase Stimulator
target_mechanisms:
- target: Mitochondrial angiopathy and NO deficiency
treatment_effect: RESTORES
description: >-
Direct stimulation of soluble guanylate cyclase is intended to restore
cGMP signalling in cerebral microvasculature where nitric oxide
availability is reduced.
evidence:
- reference: PMID:31693521
reference_title: Arginine therapy in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "MELAS is associated with endothelial dysfunction by decreased plasma L-arginine, nitric oxide (NO), and cyclic guanosine monophosphate."
explanation: Documents the reduced cGMP that soluble guanylate cyclase stimulation is designed to raise.
evidence:
- reference: clinicaltrials:NCT06402123
reference_title: "Phase 2b Randomized, Double-blind, Placebo-controlled Crossover Study Evaluating the Efficacy and Safety of Zagociguat in Participants With MELAS (PRIZM)"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "PRIZM is a Phase 2b randomized, double-blind, placebo-controlled, 3-treatment, 2-period, crossover study evaluating the efficacy and safety of oral zagociguat 15 and 30 mg vs. placebo when administered daily for 12 weeks in participants with genetically and phenotypically defined MELAS."
explanation: A completed randomized placebo-controlled MELAS-specific trial of a soluble guanylate cyclase stimulator.
- reference: clinicaltrials:NCT04475549
reference_title: "A Phase 2a Safety, Tolerability, Pharmacokinetic, and Pharmacodynamic Study in Individuals With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS)"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This is a single-arm study to evaluate safety and tolerability of oral IW-6463 in adults diagnosed with MELAS."
explanation: The earlier single-arm MELAS study of the same mechanism, which was terminated.
inheritance:
- name: Mitochondrial inheritance
inheritance_term:
preferred_term: Mitochondrial inheritance
term:
id: HP:0001427
label: Mitochondrial inheritance
description: >-
MELAS is maternally inherited through the mitochondrial genome. Clinical
expression depends on the heteroplasmy level of mutant mtDNA, with a
threshold effect.
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like
episodes (MELAS) syndrome is one of the most frequent maternally inherited
mitochondrial disorders.
explanation: >-
Establishes MELAS as a maternally inherited mitochondrial disorder.
- reference: PMID:2102678
reference_title: A mutation in the tRNA(Leu)(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Southern blot analysis confirmed that the mutant DNA always coexists with
the wild-type DNA
explanation: >-
Documents heteroplasmy (coexistence of mutant and wild-type mtDNA), the
basis for the threshold effect in MELAS.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A man with a mtDNA pathogenic variant cannot transmit the variant to any
of his offspring.
explanation: >-
GeneReviews genetic counseling: paternal mtDNA is not transmitted, so an
affected father carries no recurrence risk for his children. This is the
asymmetry that distinguishes mitochondrial from autosomal inheritance.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A woman with a mtDNA pathogenic variant (whether symptomatic or
asymptomatic) transmits the variant to all of her offspring.
explanation: >-
GeneReviews genetic counseling: maternal transmission is obligate for
every child regardless of the mother's own symptom status, because
transmission and clinical expression are decoupled by heteroplasmy.
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
because the mutational load in tissues sampled prenatally may shift in
utero or after birth as a result of random mitotic segregation,
prediction of the phenotype from prenatal studies cannot be made with
certainty.
explanation: >-
GeneReviews genetic counseling: prenatal and preimplantation testing can
establish the variant but not the phenotype, because random mitotic
segregation keeps the heteroplasmy level measured prenatally from
predicting the level in later tissues. This is the counseling-level
consequence of the same threshold effect modeled in the pathograph.
clinical_trials:
- name: NCT06402123
phase: PHASE_II
status: COMPLETED
description: >-
PRIZM: randomized, double-blind, placebo-controlled crossover trial of oral
zagociguat, a soluble guanylate cyclase stimulator, in genetically and
phenotypically defined MELAS. Tests the NO-cGMP arm of the vascular
hypothesis one step downstream of arginine and citrulline.
evidence:
- reference: clinicaltrials:NCT06402123
reference_title: "Phase 2b Randomized, Double-blind, Placebo-controlled Crossover Study Evaluating the Efficacy and Safety of Zagociguat in Participants With MELAS (PRIZM)"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "PRIZM is a Phase 2b randomized, double-blind, placebo-controlled, 3-treatment, 2-period, crossover study evaluating the efficacy and safety of oral zagociguat 15 and 30 mg vs. placebo when administered daily for 12 weeks in participants with genetically and phenotypically defined MELAS."
explanation: Registration record establishing design, comparator, and MELAS-specific population.
- name: NCT04475549
phase: PHASE_II
status: TERMINATED
description: >-
Single-arm safety, tolerability, pharmacokinetic and pharmacodynamic study
of the CNS-penetrant soluble guanylate cyclase stimulator IW-6463 in adults
with MELAS. Terminated.
evidence:
- reference: clinicaltrials:NCT04475549
reference_title: "A Phase 2a Safety, Tolerability, Pharmacokinetic, and Pharmacodynamic Study in Individuals With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS)"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This is a single-arm study to evaluate safety and tolerability of oral IW-6463 in adults diagnosed with MELAS."
explanation: Registration record for the earlier, uncontrolled trial of the same mechanism.
- name: NCT03952234
phase: PHASE_I
status: COMPLETED
description: >-
Dose-finding and safety study of L-citrulline in adults with MELAS,
intended to establish a dose for a later efficacy trial of nitric oxide
repletion.
evidence:
- reference: clinicaltrials:NCT03952234
reference_title: "Phase-1, Dose Finding and Safety Study on L- Citrulline Treatment of Nitric Oxide Deficiency in MELAS"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The main purpose of this study is to determine the safest maximum dose of an amino acid, citrulline, which will be used as potential treatment for adult patients with a disorder of energy metabolism called Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS)."
explanation: Establishes that citrulline dosing in MELAS was still at the dose-finding stage, before any efficacy trial.
- name: NCT01339494
status: COMPLETED
description: >-
Stable-isotope study of arginine flux and nitric oxide production in MELAS,
with arginine and citrulline supplementation. The mechanistic study behind
the finding that citrulline raises NO production more effectively than
arginine.
target_phenotypes:
- preferred_term: Stroke-like episode
term:
id: HP:0002401
label: Stroke-like episode
evidence:
- reference: clinicaltrials:NCT01339494
reference_title: "Arginine Flux and Nitric Oxide Production in Patients With MELAS Syndrome and the Effect of Arginine and Citrulline Supplementation"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The purpose of this study is to measure nitric oxide in individuals with MELAS and see if giving arginine or citrulline will increase the formation of nitric oxide."
explanation: Registration record for the NO-flux study underpinning arginine and citrulline therapy in MELAS.
- name: NCT04165239
phase: PHASE_II
status: COMPLETED
description: >-
KHENERGYZE: double-blind, randomized, placebo-controlled three-way
crossover study of two doses of sonlicromanol (KH176) in m.3243A>G
carriers, with attention-domain cognitive function as the primary endpoint.
Notable as one of the few MELAS-relevant trials to use a cognitive rather
than an episode-count endpoint.
evidence:
- reference: clinicaltrials:NCT04165239
reference_title: "A Phase IIb Double-blind, Randomised, Placebo-controlled, Multi-centre, Confirmative Three-way Cross-over Study on Cognitive Function With Two Doses of KH176 in Subjects With a Genetically Confirmed Mitochondrial DNA tRNALeu(UUR) m.3243A>G Mutation."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The primary objective is an evaluation of KH176 in the attention domain of cognitive functioning, as assessed by the visual identification test score of the Cogstate computerised cognitive testing battery."
explanation: Registration record establishing the cognitive primary endpoint of the randomized sonlicromanol crossover trial in m.3243A>G carriers.
- name: NCT06451757
phase: PHASE_III
status: RECRUITING
description: >-
KHENERFIN: randomized, double-blind, placebo-controlled pivotal trial of
sonlicromanol over 52 weeks in adults with a genetically confirmed
m.3243A>G variant, with fatigue and physical function as primary outcomes.
Enrolls by genotype rather than by MELAS syndrome label.
evidence:
- reference: clinicaltrials:NCT06451757
reference_title: "A Phase III, Randomised, Double-blind, Placebo-controlled, Parallel-group, Pivotal Trial to Assess the Efficacy and Safety of Sonlicromanol in Adult Subjects With a Genetically Confirmed Mitochondrial DNA tRNALeu(UUR) m.3243A>G Variant"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The KHENERFIN study aims to determine whether the study medicine, sonlicromanol, is able to reduce symptoms of fatigue and the impact of fatigue on daily life, and whether sonlicromanol is able to improve physical abilities of people like balance control and lower limb skeletal muscle strength in people with mitochondrial disease."
explanation: Registration record for the pivotal sonlicromanol trial in m.3243A>G carriers.
- name: NCT06013397
phase: NOT_APPLICABLE
status: NOT_RECRUITING
description: >-
Trial of a ketogenic diet in MELAS, testing an alternative-fuel strategy
rather than a vascular or translational one.
evidence:
- reference: clinicaltrials:NCT06013397
reference_title: "Clinical Trial of Ketogenic Diet in the Treatment of Mitochondrial Encephalomyopathy With Lactic Acidosis and Stroke-like Episodes(MELAS)"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The goal of this clinical trial is to evaluate the effectiveness of ketogenic diet in patients with MELAS syndrome."
explanation: Registration record establishing that ketogenic-diet efficacy in MELAS remains an open, untested question.
- name: NCT01532791
status: RECRUITING
description: >-
Natural-history study of known m.3243A>G carriers together with their
maternal relatives, enrolled regardless of carrier status, with paternal
relatives as controls. The design is what makes it relevant here: it
ascertains through the family rather than through a neurology clinic, so it
can in principle measure organ involvement in carriers who would never
present to a mitochondrial-disease service.
evidence:
- reference: clinicaltrials:NCT01532791
reference_title: "Mitochondrial Encephalomyopathies and Mental Retardation: Investigations of Clinical Syndromes Associated With MtDNA Point Mutations"
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "and their maternal relatives (carrier status not a requirement for participation). Paternal relatives will serve as controls."
explanation: Family-based rather than clinic-based ascertainment, the sampling frame needed to estimate organ involvement without neurology-referral bias.
- name: NCT05554835
status: RECRUITING
description: >-
Global mitochondrial disease registry harmonizing prior national
registries, intended to support natural-history description, outcome-measure
definition, and trial readiness.
evidence:
- reference: clinicaltrials:NCT05554835
reference_title: Global Mitochondrial Registry to Define Natural History and Outcome Measures to Achieve Definite Trial Readiness for Mitochondrial Disorders
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "provision of a global registry for mitochondrial disorders to harmonize previous national registries, enable world-wide participation and facilitate natural history studies, definition of outcome measures and conduction of clinical trials"
explanation: The registry infrastructure that both the ascertainment gap and the absent trial-ready outcome measure depend on.
differential_diagnoses:
- name: Acute ischemic stroke
description: >-
Stroke-like episodes share their onset pattern and focal neurological
symptoms with ischemic stroke. Features that favour MELAS are lesion
distribution inconsistent with an arterial territory, posterior
predilection, contiguous spread into adjacent sites over weeks to months,
accompanying seizures, focal hyperperfusion rather than hypoperfusion, and
a lactate peak on spectroscopy. Diffusion is a weaker discriminator:
lesional ADC is often elevated, but restricted diffusion can coexist in the
same lesions.
distinguishing_features:
- Lesion distribution inconsistent with a vascular territory
- Progressive spread into adjacent cortex over weeks to months
- Focal cortical hyperperfusion rather than hypoperfusion
- Lactate peak on proton MR spectroscopy, including in normal-appearing brain
- Frequent accompanying focal-onset seizures
evidence:
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a disease that should be considered as a differential diagnosis to acute ischemic stroke taking into account its onset pattern and neurological symptoms, which are similar to those of an ischemic stroke."
explanation: States the differential explicitly and the reason the two are confused.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: "Stroke-like episodes in MELAS have the following features: (1) symptoms are neurolocalized according to lesion site; (2) epileptic seizures are often present; (3) lesion distribution is inconsistent with vascular territory; (4) lesions are common in the posterior brain regions; (5) lesions continuously develop in adjacent sites over several weeks or months"
explanation: Supplies the lesion-distribution, posterior-predilection, contiguous-spread, and seizure features listed as distinguishing.
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In seven of nine episodes focal cortical hyperperfusion was seen in SPECT studies."
explanation: Supports focal hyperperfusion, rather than the hypoperfusion of ischemia, during stroke-like episodes.
- reference: PMID:23177587
reference_title: "[Conventional and diffusion-weighted magnetic resonance imaging and proton spectroscopy in MELAS]."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Proton spectroscopy showed the presence of lactate and reduction of N-acetyl aspartate peak in stroke-like lesion and the presence of lactate in apparently spared brain."
explanation: Supports the lactate peak on spectroscopy, including in normal-appearing brain.
- reference: PMID:23177587
reference_title: "[Conventional and diffusion-weighted magnetic resonance imaging and proton spectroscopy in MELAS]."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Both MRI that were performed during those episodes of stroke-like lesion revealed areas of diffusion restriction, coexisting areas of high ADC."
explanation: Supports treating diffusion as a weak discriminator, since restricted diffusion and high ADC coexist within stroke-like lesions.
- name: MERRF (myoclonic epilepsy with ragged-red fibers)
description: >-
Shares ragged-red fibers and strongly SDH-reactive vessels on muscle
biopsy, so morphology alone does not separate them. The enzyme
histochemistry does: SSV are cytochrome c oxidase deficient in MERRF and
COX-normal in MELAS. Overlap syndromes carrying both phenotypes are
described.
distinguishing_features:
- Cytochrome c oxidase activity absent from SSV in MERRF, preserved in MELAS
- Myoclonus rather than stroke-like episodes as the cardinal feature
- m.8344A>G in MT-TK rather than m.3243A>G in MT-TL1
evidence:
- reference: PMID:8384773
reference_title: Cytochrome c oxidase activity is deficient in blood vessels of patients with myoclonus epilepsy with ragged-red fibers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "More than half of the intramuscular blood vessels in muscle biopsies from five patients with myoclonus epilepsy with ragged-fibers (MERRF) who had a point mutation in mitochondrial DNA at the tRNALys region were darkly stained with succinate dehydrogenase (SDH) stain, showing the morphologic characteristics of strongly SDH-reactive blood vessels (SSV), but they had no cytochrome c oxidase (CCO) activity."
explanation: Establishes the MERRF half of the COX-activity criterion, in patients with a tRNALys point mutation.
- reference: PMID:8384773
reference_title: Cytochrome c oxidase activity is deficient in blood vessels of patients with myoclonus epilepsy with ragged-red fibers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "On the other hand, SSV in muscle biopsies from patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) had normal CCO activity as shown by light and electron microscopy."
explanation: Establishes the MELAS half of the criterion, COX-normal SSV.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: "Furthermore, a growing number of patients may exhibit overlap syndrome, such as MELAS/LS, MERRF/MELAS, and LHON/MELAS (3)."
explanation: Supports the statement that MERRF/MELAS overlap syndromes are described.
- name: Leigh syndrome
description: >-
Bilateral symmetrical basal ganglia, thalamic, and brainstem lesions define
Leigh syndrome, whereas MELAS lesions are predominantly cortical.
MELAS/Leigh overlap is a recognized entity and is enriched for complex I
subunit variants, particularly MT-ND5 m.13513G>A rather than MT-TL1
m.3243A>G.
distinguishing_features:
- Bilateral symmetrical basal ganglia and brainstem lesions rather than predominantly cortical lesions
- Ataxia, spastic paraplegia, and bulbar palsy as leading features
- Enriched for MT-ND (complex I subunit) variants in overlap cases
evidence:
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Thirteen patients were identified with MTND mutations, among which m.13513G>A mutation in the MT-ND5 gene was the most common."
explanation: Shows the genotype shift toward complex I subunit genes in MELAS/Leigh overlap.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "As for the clinical hallmarks of LS, the top three most common symptoms were ataxia, spastic paraplegia, and bulbar palsy."
explanation: Names the Leigh-type features most common in the MELAS/LS overlap cohort; it does not address lesion distribution or genotype, which the other items cover.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: "LS is defined as an early-onset progressive neurodegenerative MD typically characterized by subacute onset of psychomotor regression and encephalopathy associated with the development of bilateral symmetrical lesions in the basal ganglia, thalami, subthalamic regions, mesencephalon, and brainstem, which are the hallmarks of the disease (4)."
explanation: Supports bilateral symmetrical deep grey matter and brainstem lesions as the defining Leigh lesion pattern.
- reference: PMID:34025555
reference_title: "MELAS/LS Overlap Syndrome Associated With Mitochondrial DNA Mutations: Clinical, Genetic, and Radiological Studies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "For the lesions consistent with MELAS, multiple cerebral lobes were affected with dominant cortical lesions."
explanation: Supports the contrasting, predominantly cortical MELAS lesion pattern, observed in the overlap cohort.
synonyms:
- MELAS
- Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes
- Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes
experimental_models:
- name: m.3243A>G patient iPSC-derived neurons
experimental_model_type: IPSC_DERIVED_MODEL
description: >-
Induced pluripotent stem cells reprogrammed from m.3243A>G patients, then
differentiated to neurons and to teratoma-derived tissues. The model exists
because the mitochondrial genome cannot be edited by transgenic methods, so
patient cells are the only route to a human m.3243A>G system. Its
distinctive result is that respiratory-chain deficiency is cell-type
specific from one shared genotype, with complex I predominating as it does
in patient tissue, and that neurons additionally clear complex I by
mitophagy.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
publication: PMID:24003133
modeled_mechanisms:
- target: Complex I-predominant deficiency and neuronal mitophagy
relationship: RECAPITULATES
fidelity: MODERATE
description: >-
Reproduces the complex I-predominant respiratory-chain defect seen in
MELAS patient tissue and adds the neuron-specific mitophagic clearance
step.
limitations: >-
Heteroplasmy segregates bimodally toward homoplasmy during
reprogramming, so the clone's mutant load is not the patient's tissue
load; the model is a cultured neuron rather than cortex, and it cannot
reproduce a stroke-like episode, which requires vasculature, seizure
activity, and an intact cortical network.
readouts:
- name: Respiratory chain complex I deficiency
target: Complex I-predominant deficiency and neuronal mitophagy
direction: DECREASED
interpretation: Matches the complex I predominance observed in MELAS patient tissues.
evidence:
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Induced pluripotent stem cell-derived neurons and various tissues derived from teratomas manifested cell-type specific respiratory chain (RC) deficiency patterns. Similar to MELAS patient tissues, complex I defect predominated."
explanation: The measurement establishing complex I predominance in the model and its correspondence to patient tissue.
- name: Perinuclear PINK1/Parkin-positive autophagosomal sequestration of complex I
target: Complex I-predominant deficiency and neuronal mitophagy
direction: INCREASED
interpretation: Indicates active mitophagic degradation of complex I on neuronal differentiation.
evidence:
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Upon neuronal differentiation, complex I specifically was sequestered in perinuclear PTEN-induced putative kinase 1 (PINK1) and Parkin-positive autophagosomes, suggesting active degradation through mitophagy."
explanation: The imaging readout supporting selective mitophagy of complex I in neurons.
evidence:
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Our data show that cellular context actively modifies RC deficiency manifestation in MELAS and that autophagy is a significant component of neuronal MELAS pathogenesis."
explanation: The authors' own statement that the model is informative for neuronal MELAS pathogenesis.
notes: >-
A second use of MELAS iPSC-derived neurons is as a recipient in
mitochondrial-transfer experiments, where donated mitochondria from
purified mesenchymal stem cells restored membrane potential, ATP and ROS
production, calcium storage, and oxygen consumption rate.
evidence:
- reference: PMID:38139018
reference_title: MELAS-Derived Neurons Functionally Improve by Mitochondrial Transfer from Highly Purified Mesenchymal Stem Cells (REC).
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Here, utilizing induced pluripotent stem cells (iPSC), we differentiated neurons with impaired mitochondrial function from patients with MELAS."
explanation: Independent derivation of MELAS iPSC neurons with an impaired-mitochondrial-function phenotype, used as a therapeutic testbed.
datasets:
- accession: geo:GSE202747
title: Non-random distribution of mitochondrial m.3243A>G heteroplasmy in human retina and its impact on cellular phenotype
description: >-
Single-cell RNA-seq, mitochondrial single-cell ATAC-seq, and multimodal
single-cell sequencing of retina and choroid from a MELAS donor eye and
healthy controls, measuring per-cell m.3243A>G heteroplasmy alongside
transcriptome and chromatin state. SuperSeries; the scRNA, scATAC, and
multiome SubSeries are GSE202735, GSE202746, and GSE202886 and should not
be curated separately.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MULTI_OMICS
sample_count: 36
publication: PMID:37289546
notes: >-
The most directly informative public dataset for the genotype-phenotype
gap, because it measures heteroplasmy inside a tissue at single-cell
resolution rather than in an accessible surrogate. Also bears on the
stroke-like-episode mechanism controversy: in this tissue the
neuroectoderm-derived neural cells carried a high mutant fraction while the
mesoderm-derived choroidal vasculature was near-homoplasmic wild-type,
which is the opposite of what a primarily vascular pathogenesis would
predict. One donor eye, and retina is not cortex, so it is a lead rather
than a settled answer.
evidence:
- reference: PMID:37289546
reference_title: Multimodal single-cell analysis of nonrandom heteroplasmy distribution in human retinal mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "All neuroectoderm-derived neural cells exhibited a high percentage of the mutant variant. However, a subset of mesoderm-derived lineage, namely the vasculature of the choroid, was near homoplasmic for the WT allele."
explanation: Shows heteroplasmy partitions non-randomly by cell lineage within one tissue, which is a candidate explanation for organ-level phenotype variation that bulk heteroplasmy cannot capture.
- accession: geo:GSE56158
title: Transcriptomic analysis of human cybrid cell lines harboring increasing levels of the mitochondrial DNA (mtDNA) 3243A>G mutation
description: >-
RNA-seq of isogenic somatic-cell cybrids spanning the complete range of
m.3243A>G heteroplasmy, with paired cellular phenotyping, designed to test
how continuous variation in mutant load maps onto discrete clinical
syndromes.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 8
publication: PMID:25192935
notes: >-
Addresses the genotype-phenotype gap from the opposite direction to the
retina data: one nuclear background, heteroplasmy varied experimentally.
Its result - that the nucleus has only a few discrete states available - is
a mechanistic proposal for why a continuous variable produces named
syndromes. Cybrids are an immortalized non-neural cell line, so the
thresholds are not directly transferable to patient tissue.
evidence:
- reference: PMID:25192935
reference_title: Progressive increase in mtDNA 3243A>G heteroplasmy causes abrupt transcriptional reprogramming.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Small increases in mutant mtDNAs caused relatively modest defects in oxidative capacity but resulted in sharp transitions in cellular phenotype and gene expression."
explanation: Demonstrates threshold-like transcriptional switching rather than a graded response, which is the shape a mechanism must have to turn continuous heteroplasmy into discrete syndromes.
- reference: PMID:25192935
reference_title: Progressive increase in mtDNA 3243A>G heteroplasmy causes abrupt transcriptional reprogramming.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "a major factor in the phenotypic variation in heteroplasmic mtDNA mutations is the limited number of states that the nucleus can acquire in response to progressive changes in mitochondrial retrograde signaling"
explanation: States the proposed explanation for genotype-phenotype discordance that this dataset was generated to test.
- accession: geo:GSE129091
title: Quantitative variation in m.3243A>G mutation produce discrete changes in energy metabolism
description: >-
Expression profiling of cells carrying low versus high m.3243A>G mutation
load against wild type, paired with bioenergetic, biogenesis, and
fuel-catabolism assays, framed explicitly around the MELAS-versus-MIDD
divergence.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MICROARRAY
sample_count: 12
publication: PMID:30962477
notes: >-
Directly targets the question the entry records as open - why the same
variant yields MELAS at high load and MIDD at low load - and reports that
the transcriptional signatures are similar while the functional states
diverge, which argues against expression profiling alone resolving the gap.
evidence:
- reference: PMID:30962477
reference_title: Quantitative Variation in m.3243A > G Mutation Produce Discrete Changes in Energy Metabolism.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "despite striking similarities in the energy metabolic gene expression signature, the mitochondrial bioenergetics, biogenesis and fuel catabolic functions are distinct in cells harboring low or high levels of the m.3243 A > G mutation compared to wild type cells"
explanation: Shows the low-load and high-load states differ functionally while looking alike transcriptionally, a caution for biomarker work that relies on expression signatures.
- accession: geo:GSE14882
title: Expression data from human blood from MELAS patients and controls
description: >-
Affymetrix whole-blood transcriptomes from ten MELAS patients and controls,
analysed with regulatory- and protein-interaction-network methods to look
for master regulators and disease-modifying genes.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MICROARRAY
sample_count: 16
publication: PMID:21708074
notes: >-
One of the few MELAS datasets from an accessible tissue, so it is the
natural starting point for the prognostic-biomarker gap. It also reports
correlations between expression change, mutant load, and clinical
characteristics, which is the genotype-phenotype question in a blood
sample. Ten patients and a 2011 array platform limit what can be asked of
it; treat it as a hypothesis source, not a validation set.
evidence:
- reference: PMID:21708074
reference_title: Whole blood genome-wide expression profiling and network analysis suggest MELAS master regulators.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Correlation analyses of gene alterations and clinico-genetic data detected significant correlations between A3243G-induced nuclear gene expression changes and mutant mtDNA load as well as disease characteristics."
explanation: Establishes that an accessible-tissue transcriptome tracks both mutant load and clinical features, the property a prognostic biomarker would need.
- accession: geo:GSE324301
title: Mitochondrial DNA heteroplasmy drives cortical neuronal disturbances in human organoids harbouring the common m.3243A>G mutation
description: >-
Single-cell RNA-seq of human iPSC-derived cerebral organoid slices carrying
m.3243A>G at varying heteroplasmy, generated as a cortical model because no
animal carries the mutation. Reports heteroplasmy-dependent transcriptional
shifts and preferential impairment of deep-layer neurons with axonal
degeneration and apoptosis, compared against MELAS brain autopsy.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: SINGLE_CELL_RNA_SEQ
sample_count: 7
notes: >-
The most direct public response to the human-model-mismatch gap recorded in
this entry: a model with cortical architecture, which iPSC-derived neuron
monocultures lack, validated against patient brain tissue. It still cannot
produce a stroke-like episode - organoid slices have no vasculature and no
seizure activity - so it addresses neuronal vulnerability rather than the
episode itself. Deposited 2026 with no linked publication at the time of
curation, so nothing here is attributed to a peer-reviewed report.
- accession: pride:PXD058785
title: Metabolic remodelling in hiPSC-derived myofibres carrying the m.3243A>G mutation
description: >-
Proteomic, phosphoproteomic, and metabolomic profiling of hiPSC-derived
muscle fibres carrying variable m.3243A>G heteroplasmy, with membrane
potential and oxygen consumption measured against mutant load.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: PROTEOMICS
notes: >-
Extends the model set beyond neurons to the tissue that produces the
myopathy, and is heteroplasmy-graded, so it speaks to both the
human-model-mismatch and genotype-phenotype gaps. No linked publication in
the repository record at the time of curation.
- accession: geo:GSE61390
title: Genetic Correction and Metabolic Rescue of Pluripotent Cells from Patients with mtDNA
description: >-
Transcriptomes from iPSC lines derived from a MELAS patient with
heteroplasmic m.3243A>G and from a Leigh syndrome patient, used to evaluate
generating genetically corrected pluripotent cells as a therapeutic
strategy.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 43
publication: PMID:26176921
notes: >-
Relevant to the human-model-mismatch gap for a specific reason: it exploits
the bimodal segregation of heteroplasmy during reprogramming that is
otherwise the main limitation of iPSC models, turning it into a source of
isogenic mutant and corrected lines.
- accession: geo:GSE127478
title: Mitochondrial 3243A > G mutation confers pro-atherogenic and pro-inflammatory properties in MELAS iPS derived endothelial cells
description: >-
RNA-seq of endothelial cells differentiated from MELAS patient iPSCs and an
isogenic control, characterising reactive oxygen species, oxidised LDL,
VCAM-1 expression, and monocyte adhesion.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 6
publication: PMID:31641105
notes: >-
The vascular arm of the stroke-like-episode controversy in an isogenic
human system. Note what it does and does not show: it establishes that
m.3243A>G endothelium is intrinsically dysfunctional and inflammatory,
which the vascular hypothesis requires, but endothelial dysfunction in a
dish is not an ischemic stroke-like episode in cortex.
evidence:
- reference: PMID:31641105
reference_title: Mitochondrial 3243A > G mutation confers pro-atherogenic and pro-inflammatory properties in MELAS iPS derived endothelial cells.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "in addition to endothelial dysfunction, diseased endothelial cells (ECs) were found to be pro-atherogenic and pro-inflammation due to high levels of ROS and Ox-LDLs, and high basal expressions of VCAM-1"
explanation: Provides a cell-autonomous mechanism for the vascular arm of the controversy in isogenic human endothelium.
- accession: geo:GSE154825
title: Sonlicromanol improves neuronal network dysfunction and transcriptome changes linked to m.3243A>G heteroplasmy in iPSC-derived neurons
description: >-
Combined micro-electrode array recording and RNA-seq (MEA-seq) of excitatory
neurons differentiated from MELAS patient iPSCs at low and high m.3243A>G
heteroplasmy, co-cultured with astrocytes, with and without sonlicromanol.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 16
publication: PMID:34329596
notes: >-
The neuronal arm of the same controversy, and the only public MELAS dataset
that measures network-level electrical activity rather than inferring it.
It reports reduced presynaptic gene expression and non-cell-autonomous
changes in co-cultured astrocytes, which is directly relevant to the
neuron-astrocyte uncoupling variant of the hyperexcitability model. It also
provides the transcriptomic readout for a drug now in a phase III trial in
this entry.
evidence:
- reference: PMID:34329596
reference_title: Sonlicromanol improves neuronal network dysfunction and transcriptome changes linked to m.3243A>G heteroplasmy in iPSC-derived neurons.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "We combined micro-electrode array (MEA) measurements with RNA sequencing (MEA-seq) and found reduced expression of genes involved in mitochondrial respiration and presynaptic function, as well as non-cell autonomous processes in co-cultured astrocytes."
explanation: Couples network electrophysiology to transcriptome in m.3243A>G neurons and implicates astrocytes, the two elements the neuron-astrocyte uncoupling hypothesis requires.
- accession: geo:GSE165953
title: Glutamate pathway dysfunction in MELAS syndrome is alleviated by ketogenic diet
description: >-
Multi-omic profiling of neuronal cybrids carrying graded m.3243A>G loads,
reporting glutamate accumulation proportional to heteroplasmy, altered
glutamate, GABA, and TCA-cycle gene clusters, confirmation in MELAS
post-mortem brain, and reversal by ketone-body exposure.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MICROARRAY
sample_count: 8
publication: PMID:35884972
notes: >-
Sits across three of the gaps at once. Glutamate accumulation scaled to
heteroplasmy is a candidate mechanism for the cortical hyperexcitability
the non-ischemic model requires; the authors propose glutamate as a disease
biomarker; and the ketone-body rescue is the preclinical rationale for the
ketogenic-diet trial recorded in this entry. The post-mortem brain
confirmation is what lifts it above a cell-line result.
evidence:
- reference: PMID:35884972
reference_title: "Glutamate-Induced Deregulation of Krebs Cycle in Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-Like Episodes (MELAS) Syndrome Is Alleviated by Ketone Body Exposure."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "These results were supported by post-mortem brain tissue analysis from a MELAS patient, confirming the glutamate dysregulation."
explanation: Anchors the cell-model glutamate finding in human MELAS brain, which is what makes it usable for the cortical hyperexcitability question.
- reference: PMID:35884972
reference_title: "Glutamate-Induced Deregulation of Krebs Cycle in Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-Like Episodes (MELAS) Syndrome Is Alleviated by Ketone Body Exposure."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "a multi-omic integrated approach to MELAS cells revealed glutamate as a promising disease biomarker, while also indicating that a ketogenic diet should be tested in MELAS patients"
explanation: States both the biomarker candidacy and the therapeutic hypothesis that this dataset generated.
- accession: geo:GSE113300
title: Differential expression of miRNAs in a cellular model of MELAS.
description: >-
Small-RNA sequencing of a transmitochondrial cybrid model homoplasmic for
m.3243A>G, identifying 246 differentially expressed miRNAs whose predicted
targets fall in muscle, nervous-system, and cardiac developmental pathways.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 6
notes: >-
A candidate source for circulating-biomarker work, since miRNAs survive in
plasma where transcriptomes do not. Two limits are worth stating: the model
is 100% mutant cybrid rather than patient tissue, and the target pathways
are computationally predicted. No linked publication in the repository
record.
- accession: geo:GSE85549
title: Defects in mitochondrial RNA processing in disease
description: >-
Parallel analysis of RNA ends (PARE) comparing m.3243A>G against m.3302A>G
in mt-tRNA-Leu(UUR), mapping the 5' ends of mitochondrial RNAs to localise
where each mutation disrupts tRNA processing.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 2
publication: PMID:28189843
notes: >-
Bears on a narrower but real question: two mutations in the same gene give
different diseases (MELAS versus mitochondrial myopathy), and this dataset
asks whether their RNA-processing defects differ. Relevant to the
genotype-phenotype gap at the level of allele rather than heteroplasmy.
evidence:
- reference: PMID:28189843
reference_title: Defects in RNA metabolism in mitochondrial disease.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "identified common internal cleavage sites and new sites unique to the m.3243A>G mutants that do not correspond to transcript ends"
explanation: Identifies processing defects specific to the MELAS allele rather than shared with the myopathy allele, a candidate basis for allele-level phenotype divergence.
- accession: geo:GSE27545
title: A Systems Approach for Decoding Mitochondrial Retrograde Signaling Pathways
description: >-
Expression profiling of cells engineered to carry varying amounts of
m.3243A>G, used to infer the transcription factors mediating mitochondrial
retrograde signalling; identifies an RXRA-ROS-JNK-PGC1alpha loop that
further suppresses nuclear-encoded OXPHOS genes.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MICROARRAY
sample_count: 17
publication: PMID:23443683
notes: >-
Supplies a candidate feed-forward mechanism by which a fixed mtDNA lesion
progressively worsens nuclear OXPHOS gene expression, which is one of the
few published proposals for why MELAS is progressive rather than static.
evidence:
- reference: PMID:23443683
reference_title: A systems approach for decoding mitochondrial retrograde signaling pathways.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "This RXR pathway contributed to the decrease in mRNA abundances of oxidative phosphorylation enzymes encoded in the nuclear genome, thereby aggravating the dysfunction in oxidative phosphorylation caused by the reduced abundance of mitochondria-encoded enzymes of oxidative phosphorylation."
explanation: Describes a self-aggravating retrograde loop, a candidate mechanism for progression from a non-progressive genetic lesion.
- accession: geo:GSE89066
title: Identification of miRNA, lncRNA and mRNA-associated ceRNA networks and potential biomarker for MELAS with mitochondrial DNA A3243G mutation
description: >-
Non-coding RNA profiling of muscle from 20 MELAS patients with m.3243A>G
and 20 controls, with selected transcripts validated by qRT-PCR in muscle
and serum in independent cohorts and assessed by ROC analysis against
lactate. The GEO deposit itself holds four samples, so the 20-versus-20
cohort describes the study rather than the deposited profiles.
SuperSeries; SubSeries GSE89065 and GSE89059 should not be curated
separately.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 4
publication: PMID:28139706
notes: >-
The only public MELAS dataset built as a biomarker study proper - patient
cohort, discovery and training phases, independent validation, and a
circulating readout benchmarked against the incumbent marker. Read the
claim precisely: serum miR-27b-3p outperformed lactate on *diagnostic*
discrimination, which is not the same as predicting an individual's course,
and the gap recorded in this entry is about prognosis. It is nonetheless
the closest existing template for the longitudinal study that gap needs.
evidence:
- reference: PMID:28139706
reference_title: "Identification of miRNA, lncRNA and mRNA-associated ceRNA networks and potential biomarker for MELAS with mitochondrial DNA A3243G mutation."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "ROC curve analysis indicated reduced serum miR-27b-3p had the better diagnosis value than lactate and might serve as a novel, noninvasive biomarker for MELAS."
explanation: A circulating candidate benchmarked against lactate in patients, the design the prognostic-biomarker gap calls for even though the endpoint here is diagnosis.
- reference: PMID:28139706
reference_title: "Identification of miRNA, lncRNA and mRNA-associated ceRNA networks and potential biomarker for MELAS with mitochondrial DNA A3243G mutation."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we found that the dysregulated muscle miRNAs and lncRNAs between 20 MELAS patients with mtDNA A3243G mutation and 20 controls formed complex regulation networks"
explanation: Establishes the patient-cohort basis and sample size of the discovery phase.
- accession: massive:MSV000088237
title: Integrated proteomic and metabolomic analyses of the mitochondrial neurodegenerative disease MELAS
description: >-
Paired global proteomics (data-dependent acquisition verified by
data-independent acquisition) and polar plus nonpolar metabolomics of
patient-derived dermal fibroblasts carrying the ultra-rare MELAS variant
m.14453G>A in MT-ND6, a complex I structural subunit, against control.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MULTI_OMICS
publication: PMID:34982085
notes: >-
Two things make this worth more than its single-patient design. It is the
only public patient-tissue multi-omics deposit found for a non-m.3243A>G
MELAS genotype, so it speaks to the allele arm of the genotype-phenotype
gap and to the complex I subunit subtype curated in this entry. And it
reports downregulated arginine biosynthesis through blocked
argininosuccinate synthase - a cell-intrinsic route to arginine deficiency,
which is a different claim from the reduced plasma arginine that the
existing therapeutic rationale rests on. One patient and one ultra-rare
variant; the authors call it proof-of-principle and say validation in a
larger cohort is still needed.
evidence:
- reference: PMID:34982085
reference_title: Integrated proteomic and metabolomic analyses of the mitochondrial neurodegenerative disease MELAS.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The most clinically relevant discovery is the downregulation of the arginine biosynthesis pathway, likely due to blocked argininosuccinate synthase, which is congruent with the MELAS cardinal symptom of stroke-like episodes and its current treatment by arginine infusion."
explanation: Supplies a cell-intrinsic biosynthetic mechanism for arginine deficiency, distinct from the plasma-level observations the arginine rationale currently rests on.
- reference: PMID:34982085
reference_title: Integrated proteomic and metabolomic analyses of the mitochondrial neurodegenerative disease MELAS.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The pathogenic mechanism of MELAS remains enigmatic due to the exceptional clinical heterogeneity and the obscure genotype-phenotype correlation among MELAS patients."
explanation: The authors frame the study against the same genotype-phenotype gap this entry records.
- accession: geo:GSE1462
title: Mitochondrial disorders
description: >-
Affymetrix expression profiling of skeletal-muscle biopsies from twelve
patients with mitochondrial encephalomyopathy - four with the common
4977 bp mtDNA deletion and eight carrying m.3243A>G, the latter split
evenly between progressive external ophthalmoplegia and MELAS phenotypes -
against age-matched controls.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: MICROARRAY
sample_count: 15
publication: PMID:15728662
notes: >-
The only dataset in this entry that holds genotype constant and varies
clinical phenotype in patient tissue: four PEO and four MELAS patients, all
m.3243A>G, all muscle. That design isolates the modifier question the
genotype-phenotype gap turns on, and the authors read their result as
support for nuclear background as the modifier. Four patients per arm on a
2005 array platform, so it is a hypothesis, not a demonstration - but it is
the right experiment. Note this record is easy to mis-triage: its GEO title
is the uninformative "Mitochondrial disorders" and summary-level screening
reads it as a mixed-genotype cohort rather than a matched-genotype
phenotype contrast.
evidence:
- reference: PMID:15728662
reference_title: Skeletal muscle gene expression profiling in mitochondrial disorders.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the differential expression profile of MELAS(A3243G) vs. PEO(A3243G) may support a role of nuclear background in contributing to these different clinical phenotypes"
explanation: A patient-tissue contrast with the mtDNA genotype held fixed, nominating nuclear background as the modifier behind divergent m.3243A>G phenotypes.
- reference: PMID:15728662
reference_title: Skeletal muscle gene expression profiling in mitochondrial disorders.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the clinical phenotype is not simply a direct consequence of the relative abundance of mutated mtDNA. Other factors, such as nuclear background, can contribute to the disease process, resulting in a wide range of phenotypes caused by the same mutation"
explanation: States the premise of the genotype-phenotype gap and the modifier hypothesis this dataset was built to test.
environmental:
- name: Mitochondrial toxins and agents to avoid
notes: >-
Certain drugs and exposures can precipitate or worsen MELAS by impairing
mitochondrial function or triggering lactic acidosis, and should be avoided.
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Mitochondrial toxins, including aminoglycoside antibiotics, linezolid,
cigarettes, and alcohol; valproic acid for seizure treatment; metformin
because of its propensity to cause lactic acidosis; dichloroacetate (DCA)
because of increased risk for peripheral neuropathy.
explanation: >-
GeneReviews lists agents and circumstances to avoid in MELAS, including
aminoglycosides, linezolid, valproic acid, metformin, dichloroacetate,
cigarettes, and alcohol.
classifications:
harrisons_chapter:
- classification_value: NEUROLOGIC
notes: >-
Primary clinical home. The defining manifestation is a paroxysmal
neurological event, and epilepsy, encephalopathy, and progressive
cognitive decline dominate the course and the causes of death.
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Stroke-like episode is a paroxysmal neurological manifestation which affects a specific group of patients with mitochondrial disease."
explanation: Characterizes the cardinal feature of MELAS as a neurological manifestation, supporting the neurologic Part as its primary home.
- classification_value: GENETICS_ENVIRONMENT_DISEASE
notes: >-
Second Part for the inheritance axis. Maternal mitochondrial
transmission with heteroplasmy-dependent expression is a recurring
theme Harrison's covers separately from any organ system.
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like
episodes (MELAS) syndrome is one of the most frequent maternally
inherited mitochondrial disorders.
explanation: Establishes MELAS as a maternally inherited mitochondrial disorder, the axis this Part covers.
- classification_value: ENDOCRINOLOGY_METABOLISM
notes: >-
Third Part for the metabolic and endocrine axis: lactic acidosis is a
metabolic emergency in its own right, and diabetes is a curated
phenotype here and the dominant presentation of the same variant in
its MIDD form.
evidence:
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
MELAS syndrome is a multi-organ disease with broad manifestations
including stroke-like episodes, dementia, epilepsy, lactic acidemia,
myopathy, recurrent headaches, hearing impairment, diabetes, and short
stature.
explanation: Lists lactic acidemia and diabetes among the core manifestations, supporting the metabolic/endocrine Part alongside the neurologic one.
mechanistic_category:
- classification_value: mitochondrial disease
notes: >-
Primary mitochondrial disease: the causal lesion is in the
mitochondrial genome and the proximate defect is in mitochondrial
translation and oxidative phosphorylation.
icimd_category:
- classification_value: mtdna_encoded_trna_rrna
notes: >-
ICIMD (Ferreira et al. 2021, PMID:33340416): group "Disorders of
mtDNA-encoded tRNA and rRNA genes" under category 6, "Mitochondrial
DNA-related disorders". Covers the MT-TL1 genotypes - m.3243A>G and
m.3271T>C - that account for the large majority of MELAS.
- classification_value: mtdna_encoded_respiratory_chain_proteins
notes: >-
Second ICIMD group for the minority of MELAS caused by variants in the
mtDNA protein-coding complex I subunits MT-ND1, MT-ND5, and MT-ND6,
curated here as the "MT-ND5 and other genes" subtype. The entry
genuinely spans both groups because the two genotype classes reach the
same syndrome by different molecular routes - a translation defect
versus a structural subunit defect.
mappings:
icd10cm_mappings:
- term:
id: ICD10CM:E88.41
label: MELAS syndrome
mapping_predicate: skos:exactMatch
mapping_source: ICD-10-CM
mapping_justification: >-
ICD-10-CM carries a dedicated code for MELAS syndrome under E88.4
(mitochondrial metabolism disorders), with the same name and scope as
this entry.
icd11f_mappings:
- term:
id: icd11f:1369657886
label: Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes
mapping_predicate: skos:exactMatch
mapping_source: ICD-11 Foundation
mapping_justification: >-
The ICD-11 Foundation entity spells out the acronym this entry is named
for and denotes the same syndrome. Note that ICD-11 additionally carries
two separate cardiomyopathy-due-to-MELAS entities, which are
manifestation codes rather than alternative names for the syndrome and
are therefore not mapped here.
ncit_mappings:
- term:
id: NCIT:C84885
label: MELAS Syndrome
mapping_predicate: skos:exactMatch
mapping_source: NCIT
mapping_justification: >-
NCI Thesaurus carries MELAS Syndrome as a disease concept with the same
scope as this entry.
mondo_mappings:
- term:
id: MONDO:0010785
label: maternally-inherited diabetes and deafness
mapping_predicate: skos:relatedMatch
mapping_source: MONDO
mapping_justification: >-
MIDD is the other major clinical syndrome produced by m.3243A>G, and the
two are repeatedly contrasted in this entry - MIDD accounts for roughly
30% of carriers in a systematically phenotyped cohort against 10% for
classical MELAS, and the MELAS-versus-MIDD divergence is what the
genotype-phenotype gap turns on. The predicate is deliberately
relatedMatch, not narrowMatch: MONDO does not place MIDD under MELAS,
subsuming it instead under diabetes mellitus and mitochondrial oxidative
phosphorylation disorder, so the two are distinct classes sharing a
causal variant rather than a parent and a subtype. relatedMatch also
correctly leaves MIDD in the curation queue as a disease still owed its
own entry.
discussions:
- discussion_id: melas_sle_ischemic_versus_hyperexcitable
prompt: >-
Is the stroke-like episode an ischemic event caused by mitochondrial
angiopathy, or a non-ischemic neurovascular event initiated by neuronal
hyperexcitability?
kind: CONTROVERSY
status: OPEN
attaches_to:
- pathophysiology#Mitochondrial angiopathy and NO deficiency
- pathophysiology#Neuronal hyperexcitability and propagating epileptic activity
- mechanistic_hypotheses#ischemic_vascular_angiopathy
- mechanistic_hypotheses#neuronal_hyperexcitability
- datasets#geo:GSE127478
- datasets#geo:GSE154825
- datasets#geo:GSE165953
- datasets#geo:GSE202747
rationale: >-
This is the central unresolved question in MELAS and it is not academic: the two models point at different treatments. The vascular model motivates nitric-oxide repletion (arginine, citrulline, soluble guanylate cyclase stimulators); the hyperexcitability model makes aggressive seizure control the priority. The imaging and electrophysiology favour the non-ischemic account - lesions cross vascular territories, ADC is typically elevated, perfusion is focally increased rather than decreased, and epileptiform discharges are recorded over the acute lesion. But the vascular findings are not artefacts either: strongly SDH-reactive vessels are present on muscle biopsy in about 70% of patients, plasma arginine, NO and cGMP are reduced, and diffusion restriction does occur inside some lesions. One proposed synthesis is that capillary angiopathy supplies a leaky substrate on which epileptic activity produces cortical vasogenic edema. This remains a hypothesis; neither the necessity of both components
nor their causal order is established.
Public data now let both arms be interrogated in isogenic human cells, which is new. On the vascular side GSE127478 shows m.3243A>G endothelium is cell-autonomously dysfunctional, pro-inflammatory, and pro-atherogenic. On the neuronal side GSE154825 records network-level electrical activity alongside transcriptome and finds reduced presynaptic gene expression plus non-cell-autonomous changes in co-cultured astrocytes, which is the neuron-astrocyte uncoupling variant made measurable; GSE165953 supplies a heteroplasmy-scaled glutamate mechanism confirmed in MELAS post-mortem brain. One dataset cuts against the vascular arm: in GSE202747 the choroidal vasculature of a MELAS eye was near-homoplasmic wild-type while the neural lineages carried a high mutant fraction. That is one donor and one tissue, and retina is not cortex, so it is a lead rather than a refutation - but a vascular hypothesis does need the vessels to carry the mutation.
evidence:
- reference: PMID:16181098
reference_title: "Pathogenesis of stroke-like episodes in MELAS: analysis of neurovascular cellular mechanisms."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The pathogenesis of stroke-like episodes in mitochondrial encephalopathy, myopathy, lactic acidosis and stroke-like episodes (MELAS) is not fully understood although two main theories have been proposed; ischemic vascular hypothesis caused by \"mitochondrial angiopathy\" and generalized cytopathic hypothesis caused by \"mitochondrial cytopathy\"."
explanation: States the controversy in the terms in which the field frames it.
- reference: PMID:34118021
reference_title: "Clinical features, pathogenesis, and management of stroke-like episodes due to MELAS."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Although the precise pathophysiology is still unclear, one possible hypothesis for these episodes is a neuronal hyperexcitability theory, including neuron-astrocyte uncoupling."
explanation: Confirms that as of recent review the mechanism remains unsettled.
- discussion_id: melas_episode_trigger_gap
prompt: >-
What converts the chronic, constant energy deficit of MELAS into a discrete
stroke-like episode at a particular time and a particular cortical site?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- pathophysiology#Neuronal hyperexcitability and propagating epileptic activity
- pathophysiology#Stroke-like episodes
- datasets#geo:GSE27545
rationale: >-
The heteroplasmy load and the respiratory-chain defect are present
continuously, yet stroke-like episodes are paroxysmal, recur at
unpredictable intervals, and favour posterior cortex. Nothing in the
current models explains the timing or the site selection. The 2002 study
that established the hyperexcitability mechanism said so explicitly and the
gap has not closed since. Until it does, prophylaxis cannot be targeted at
the trigger, only at the substrate, and trials are forced to use episode
counts over long windows as their endpoint.
A survey of public repositories found no dataset that addresses the timing
question, and that absence is structural rather than an oversight: every
public MELAS dataset is a cross-sectional snapshot of cells or post-mortem
tissue, and an episode is a transition in a living cortex. The closest
available is GSE27545, which proposes a self-aggravating
RXRA-ROS-JNK-PGC1alpha retrograde loop - a candidate account of why a fixed
mtDNA lesion produces progressive rather than static dysfunction, though
not of why deterioration is punctuated by discrete episodes. Closing this
gap needs prospective human monitoring, not another omics deposit.
proposed_experiments:
- experiment_id: melas_prospective_prodrome_monitoring
name: Prospective multimodal monitoring across the transition into a stroke-like episode
description: >-
Follow a cohort of m.3243A>G carriers with recurrent episodes using
longitudinal EEG, MR spectroscopy and perfusion imaging at fixed
intervals and at symptom onset, to determine whether measurable
hyperexcitability, lactate accumulation, or perfusion change precedes the
clinical episode and by how long.
would_support:
- pathophysiology#Neuronal hyperexcitability and propagating epileptic activity
supporting_outcome:
- >-
Epileptiform activity or a rising regional lactate signal appears in the
subsequently affected cortex before the clinical deficit, identifying a
prodromal window and a treatable initiating step.
refuting_outcome:
- >-
No electrophysiological or metabolic change precedes the deficit, placing
the initiating event outside cortical excitability and outside current
monitoring reach.
evidence:
- reference: PMID:12297560
reference_title: Neuronal hyperexcitability in stroke-like episodes of MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The episodic nature of stroke-like episodes is unexplained."
explanation: The authors of the founding hyperexcitability study state this gap directly.
- discussion_id: melas_genotype_phenotype_gap
prompt: >-
Why does one variant, m.3243A>G, produce MELAS in some carriers, MIDD or
isolated deafness in others, and nothing at all in a further group?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- genetic#MT-TL1 m.3243A>G
- inheritance#Mitochondrial inheritance
- datasets#geo:GSE202747
- datasets#geo:GSE56158
- datasets#geo:GSE129091
- datasets#geo:GSE85549
- datasets#massive:MSV000088237
- datasets#geo:GSE1462
rationale: >-
Only about 10% of m.3243A>G carriers in a systematically phenotyped cohort
had classical MELAS, while 30% had MIDD, 28% had a combination fitting no
recognized syndrome, and 9% were asymptomatic. Heteroplasmy level is the
conventional explanation, but measured heteroplasmy explains far less than
it is credited with: it did not correlate with disease severity in
leukocytes or urinary epithelial cells, and it did not correlate with the
grade of retinal dystrophy either. Tissue-specific segregation, nuclear
genetic background, mtDNA copy number, and age are all candidate modifiers,
and none has been shown to account for the variance. This is what makes
genetic counselling and prognosis in m.3243A>G families so weak.
Four public datasets attached here attack the gap from different angles and
are worth reading against each other. GSE202747 measures heteroplasmy per
cell in a human MELAS tissue and finds it partitions by developmental
lineage rather than randomly, which would make any single bulk measurement
a poor proxy. GSE56158 varies heteroplasmy experimentally in one nuclear
background and finds sharp transcriptional transitions rather than a
gradient, offering a mechanism by which a continuous variable yields named
syndromes. GSE129091 compares low against high load directly on the
MELAS-versus-MIDD axis and reports that the two look alike
transcriptionally while differing functionally. GSE85549 moves the question
from heteroplasmy to allele, comparing the MELAS m.3243A>G lesion against
the myopathy-causing m.3302A>G in the same gene. MSV000088237 extends the
allele question outside MT-TL1 entirely, profiling fibroblasts from a
patient with the complex I subunit variant m.14453G>A. GSE1462 is the only
one that holds genotype constant and varies phenotype in patients - four
PEO against four MELAS, all m.3243A>G, all muscle - and its authors read
the difference as support for nuclear background as the modifier. That is
the right experimental design for this gap, at a sample size and on a 2005
platform that cannot settle it.
evidence:
- reference: PMID:23355809
reference_title: "The UK MRC Mitochondrial Disease Patient Cohort Study: clinical phenotypes associated with the m.3243A>G mutation--implications for diagnosis and management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "28% of patients demonstrated a panoply of clinical features, which were not consistent with any of the classical syndromes associated with the m.3243A>G mutation. 9% of individuals harbouring the mutation were clinically asymptomatic."
explanation: Quantifies how poorly the classical syndrome labels partition the m.3243A>G carrier population.
- reference: PMID:24907231
reference_title: "Serum FGF21 levels in adult m.3243A>G carriers: clinical implications."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "No significant correlations were found between disease severity and the heteroplasmy percentage determined in urinary epithelial cells or the heteroplasmy percentage determined in leukocytes."
explanation: Shows that accessible-tissue heteroplasmy does not explain severity, leaving the modifier question open.
- discussion_id: melas_prognostic_biomarker_gap
prompt: >-
Is there any accessible biomarker that predicts the course of m.3243A>G
disease in an individual patient?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- biochemical#Fibroblast growth factor 21 (FGF-21)
- biochemical#Blood lactate
- genetic#MT-TL1 m.3243A>G
- datasets#geo:GSE89066
- datasets#geo:GSE14882
- datasets#geo:GSE165953
- datasets#geo:GSE113300
rationale: >-
The two obvious candidates both fail. Urinary epithelial cell heteroplasmy,
widely used in cohort studies to index genotype against severity, varies by
more than 20 percentage points between samples taken from the same patient
within a fortnight, so it should not be used prognostically at all. FGF-21
correlates only moderately with cross-sectional severity and not at all
with progression over two years. What is left is crude and non-specific:
severe lactate elevation and anemia predict mortality. A trial-ready
surrogate endpoint for MELAS therefore does not currently exist, which is
part of why efficacy trials must run for a year on clinical outcomes.
The attached datasets are the accessible-tissue starting points, and their
limits are as informative as their content. GSE14882 is whole blood from
ten MELAS patients with expression changes correlated to mutant load and
clinical features - the right design, at a sample size and on an array
platform that cannot support validation. GSE165953 nominates glutamate as a
biomarker and, unusually, confirms the dysregulation in MELAS post-mortem
brain. GSE113300 profiles miRNAs, the class most likely to survive in
plasma, but does so in a homoplasmic cybrid rather than in patients.
GSE89066 is the closest to a proper biomarker study - 20 patients against
20 controls, independent validation, and a serum miRNA benchmarked against
lactate - but its endpoint is diagnosis, not prognosis. No public MELAS
dataset currently pairs a candidate marker with longitudinal clinical
outcome, which is precisely the study FGF-21 failed.
evidence:
- reference: PMID:30516030
reference_title: Intra-patient variability of heteroplasmy levels in urinary epithelial cells in carriers of the m.3243A>G mutation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Heteroplasmy levels of UEC in carriers of the m.3243A>G mutation have a significant day-to-day variation. The interpretation of a correlation between heteroplasmy levels in urine and disease severity is therefore not reliable."
explanation: Disqualifies urinary heteroplasmy as a prognostic measure on reproducibility grounds.
- reference: PMID:24907231
reference_title: "Serum FGF21 levels in adult m.3243A>G carriers: clinical implications."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Measuring FGF21 concentration had little added value in monitoring and predicting the disease course in this specific patient group."
explanation: Disqualifies FGF-21 as a monitoring biomarker in m.3243A>G carriers.
- discussion_id: melas_arginine_evidence_gap
prompt: >-
Does L-arginine actually prevent or shorten stroke-like episodes, or is its
widespread use resting on uncontrolled data?
kind: CONTROVERSY
status: OPEN
attaches_to:
- treatments#L-arginine therapy
- mechanistic_hypotheses#ischemic_vascular_angiopathy
- datasets#massive:MSV000088237
rationale: >-
L-arginine is standard practice in many centres for both acute and
prophylactic use, and the supporting data are real but uncontrolled: the
efficacy studies were unblinded, and the survival comparison was against
natural history rather than a randomized control arm. A 2023 review states
flatly that there is no robust evidence of efficacy in either setting. This
matters more than a generic call for better trials, because the newer
soluble guanylate cyclase stimulators target the same NO-cGMP axis: if the
axis is not the operative mechanism of the stroke-like episode, a whole
therapeutic programme is aimed at the wrong node. Contrast taurine, whose
prevention claim rests on a prospective multicentre phase III trial.
One public dataset speaks to the rationale rather than the efficacy
question, and is worth separating from it. MSV000088237 reports
downregulated arginine biosynthesis via blocked argininosuccinate synthase
in MELAS patient fibroblasts - a cell-intrinsic route to arginine
deficiency, not merely the reduced plasma arginine the therapy was built
on. That strengthens the mechanistic case for supplying arginine while
leaving the clinical question exactly where it was: no dataset can
substitute for the randomized trial that has never been run.
evidence:
- reference: PMID:36813321
reference_title: Stroke-like episodes in adult mitochondrial disease.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "There is no robust evidence to prove the efficacy of l-arginine for both acute and prophylactic settings."
explanation: Explicit statement that the evidence base for the most widely used MELAS therapy is inadequate.
- reference: PMID:26095523
reference_title: "MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Unblinded studies showed that l-arginine therapy improves stroke-like episode symptoms and decreases the frequency and severity of these episodes."
explanation: The supporting evidence, with its uncontrolled design stated in the source itself.
- discussion_id: melas_human_model_mismatch
prompt: >-
Can any available model system reproduce a stroke-like episode, or is the
defining feature of MELAS accessible only in patients?
kind: HUMAN_MODEL_MISMATCH
status: OPEN
attaches_to:
- experimental_models#m.3243A>G patient iPSC-derived neurons
- pathophysiology#Neuronal hyperexcitability and propagating epileptic activity
- pathophysiology#Cortical laminar necrosis and progressive lesion spread
- datasets#geo:GSE324301
- datasets#pride:PXD058785
- datasets#geo:GSE61390
rationale: >-
MELAS has no faithful animal model, and the reason is structural rather
than incidental: the mitochondrial genome cannot be edited with transgenic
technology, so a targeted m.3243A>G animal cannot be made the way a nuclear
knock-in can. The nearest attempt reached mouse ES cells carrying an
orthologous tRNA-Leu(UUR) mutation with respiration defects, explicitly
framed as a step toward a future model rather than a model itself. Patient
iPSC-derived neurons are the best available human system and do reproduce
the complex I-predominant deficiency, but they cannot produce a stroke-like
episode, which needs cortex, vasculature, and seizure activity together;
and heteroplasmy segregates toward homoplasmy during reprogramming, so
clonal mutant load is not patient tissue load. Cultured patient cells often
fail to manifest a phenotype at all. Consequently every mechanistic claim
about the stroke-like episode itself rests on human imaging,
electrophysiology, and autopsy - which is precisely why the controversy
above has stayed open for two decades.
The public model datasets attached here show the workaround maturing rather
than the gap closing. GSE324301 is a cerebral organoid slice model with
cortical architecture, generated explicitly because no animal carries the
mutation, and its deep-layer neuron degeneration was checked against MELAS
brain autopsy - a real advance on neuron monoculture. PXD058785 extends the
approach to skeletal muscle with graded heteroplasmy. GSE61390 turns the
reprogramming bottleneck into an asset by deriving isogenic corrected
lines. What none has is vasculature plus network seizure activity plus
cortex in one system, so the stroke-like episode itself remains unmodelled.
evidence:
- reference: PMID:25416367
reference_title: Induced pluripotent stem cell-derived models for mtDNA diseases.
supports: SUPPORT
evidence_source: OTHER
snippet: "Targeted modification of the mitochondrial genome has not succeeded with the current transgenic technologies. Furthermore, readily available cultured patient cells often do not manifest the disease phenotype."
explanation: >-
States both halves of the modelling problem for mtDNA disease - no
transgenic route, and weak phenotypes in patient cells.
- reference: PMID:26381171
reference_title: Mouse somatic mutation orthologous to MELAS A3302G mutation in the mitochondrial tRNA(Leu(UUR)) gene confers respiration defects.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "the ES cells harboring A2748G mtDNA may be useful for generation of transmitochondrial mice harboring A2748G mtDNA as potential disease models of MELAS"
explanation: The nearest available rodent work is framed as a precursor to a future model, confirming that no such mouse yet exists.
- reference: PMID:24003133
reference_title: Tissue- and cell-type-specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "During reprogramming, heteroplasmic mtDNA showed bimodal segregation toward homoplasmy, with concomitant changes in mtDNA organization, mimicking mtDNA bottleneck during epiblast specification."
explanation: Documents the heteroplasmy shift during reprogramming that limits how directly iPSC clones represent patient tissue.
- discussion_id: melas_renal_gi_ascertainment_gap
prompt: >-
How much of the MELAS phenotype outside the nervous system is genuinely
absent versus simply not looked for?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- phenotypes#Proteinuria
- phenotypes#Intestinal pseudo-obstruction
- phenotypes#Hypertrophic cardiomyopathy
- clinical_trials#NCT01532791
- clinical_trials#NCT05554835
rationale: >-
Three organ systems are described in their own literatures as
under-recognized in m.3243A>G disease. Renal involvement is called probably
underestimated; oligosymptomatic and kidney-limited m.3243A>G presentations
can be difficult to recognize. Intestinal pseudo-obstruction is
under-recognized and can be the presenting problem. Cardiac involvement has
rarely been studied prospectively, which the reviewers themselves offer as
the reason its reported incidence looks lower than expected. GeneReviews
provides syndrome-level frequency intervals for cardiomyopathy, conduction
abnormalities, and nephropathy. The 2025 cardiac study supplies a
right-bundle-branch-block denominator among 11 clinical MELAS participants,
but participation from 30 contacted patients was limited by severity and
deaths. Neither those results nor the GeneReviews intervals close the
separate ascertainment gap in unselected m.3243A>G carriers. This is the one
gap in the entry that omics deposits cannot close, because it is a sampling
problem rather than a mechanistic one - and a survey of public repositories
bore that out, returning no dataset that changes the denominator. The
relevant public resources are instead the two natural-history efforts
attached here: NCT01532791, which recruits through maternal relatives of
known carriers regardless of their own carrier status and uses paternal
relatives as controls, and NCT05554835, which harmonizes national registries
into a global cohort. A related class-level resource, Metabolomics Workbench
study ST003924, profiles urinary metabolites in genetically confirmed
paediatric primary mitochondrial disorders with an explicitly renal framing,
but its sample factors record only the disease-class label, so MELAS cases
cannot be identified within it and it is deliberately not curated as a MELAS
dataset here.
evidence:
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Cardiac involvement in m.3243A>G carriers has been only rarely systematically studied, which is perhaps why the incidence of cardiac diseases in MELAS is lower than would be expected."
explanation: The reviewers attribute the low reported cardiac incidence to ascertainment rather than to biology.
- reference: PMID:38355238
reference_title: Renal manifestations in adults with mitochondrial disease from the mtDNA m.3243A>G pathogenic variant.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Not frequently reported, renal involvement in these diseases is probably underestimated, yet it increases morbidity."
explanation: States the same ascertainment problem for the kidney.
- discussion_id: melas_phenotype_mechanistic_resolution
prompt: Which tissue-specific mechanisms explain the remaining clinical manifestations in clinically defined MELAS?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- phenotypes#Migraine-like headaches
- phenotypes#Short stature
- phenotypes#Learning disability
- phenotypes#Progressive external ophthalmoplegia
- phenotypes#Ptosis
- phenotypes#Wolff-Parkinson-White syndrome
- phenotypes#Anemia
- phenotypes#Cerebellar atrophy
- phenotypes#Basal ganglia calcification
- phenotypes#Cardiac conduction abnormality
- phenotypes#Ataxia
- phenotypes#Right bundle branch block
rationale: >-
The remaining clinical gaps have distinct evidence limitations. GeneReviews
supports migraine as a possible trigger of stroke-like episodes, now
represented in that direction; it does not establish the cause of migraine or
a reverse cortical-injury-to-migraine relation. Short stature and learning
disability are documented clinically, but the reviewed sources do not
identify a phenotype-specific causal relation from the curated mechanisms;
learning disability is not interchangeable with acquired dementia. The
m.3243A>G cohort documents MELAS/PEO overlap without establishing the causal
sequence from generalized myopathy to extraocular dysfunction. The ptosis
case provides occurrence evidence, including a prior myasthenia diagnosis,
without establishing eyelid-muscle pathogenesis. Broad conduction
abnormalities, right bundle branch block, and Wolff-Parkinson-White syndrome
are documented, but the reviewed sources do not establish their causal route
from the curated myocardial remodeling mechanism or explain how mitochondrial
dysfunction produces an accessory conduction pathway. The anemia cohort
explicitly leaves dietary and other contributors unresolved. The imaging
study documents cerebellar atrophy and basal ganglia calcification but does
not establish their causal route from the cortical stroke-like lesion
mechanism. Its suggestion of dystrophic calcification does not identify the
initiating injury. Lactate, ragged-red fibers, and focal epileptiform EEG
discharges are linked separately as observational readouts. GeneReviews
documents ataxia without assigning it to the cortical injury mechanism or
establishing that the imaged cerebellar atrophy causes it. The cardiac review
supports a qualified remodeling-to-arrhythmia relation, now represented, but
the right bundle branch block case is not causally assigned to that
remodeling route by the observational cohort. These gaps concern causal
attribution, not a requirement to identify every intermediate step.
evidence:
- reference: PMID:39697439
reference_title: 'Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Our study found that 30.8% of patients exhibited anemia, a slightly higher proportion than expected, potentially influenced by patient selection criteria, though dietary or other factors affecting hemoglobin levels could not be ruled out.
explanation: The authors explicitly leave the causes of anemia unresolved.
- reference: PMID:23355809
reference_title: "The UK MRC Mitochondrial Disease Patient Cohort Study: clinical phenotypes associated with the m.3243A>G mutation--implications for diagnosis and management."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "10% of patients exhibited a classical MELAS phenotype, 30% had MIDD, 6% MELAS/MIDD, 2% MELAS/chronic PEO (CPEO) and 5% MIDD/CPEO overlap syndromes."
explanation: Quantifies the MELAS/CPEO overlap within the m.3243A>G phenotypic spectrum.
- reference: PMID:26937404
reference_title: Arrhythmia as a cardiac manifestation in MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Her clinical status included multiple medical problems related to her MELAS
diagnosis: sensorineural hearing loss, myopathy, bilateral ophthalmoplegia,
ptosis, seizures and stroke-like episodes with concern for dementia.
explanation: >-
Extraocular involvement is one of the manifestations this entry records
clinically without modelling a tissue-specific mechanism for it, which is
the gap this discussion names.
- reference: PMID:36685235
reference_title: 'Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with an MT-TL1 m.3243A>G point mutation: Neuroradiological features and their implications for underlying pathogenesis.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Bilateral basal ganglia calcifications were found in 6 of 9 (67%) patients who underwent CT.
explanation: Documents calcification in the selected CT subgroup, not an unselected MELAS population.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK1233/
reference_title: MELAS - GeneReviews® - NCBI Bookshelf
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
in the form of recurrent attacks of severe pulsatile headaches with frequent vomiting are typical in individuals with MELAS and can precipitate stroke-like episodes.
explanation: >-
Supports the outgoing trigger relation; it does not identify the cause of
migraine.
- discussion_id: melas_cardiac_carrier_scope
prompt: Which cardiac findings reported across m.3243A>G carriers can be assigned specifically to clinically defined MELAS?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- phenotypes#Cardiac conduction abnormality
- phenotypes#Wolff-Parkinson-White syndrome
- phenotypes#Cardiomyopathy
- phenotypes#Hypertrophic cardiomyopathy
- phenotypes#Arrhythmia
- phenotypes#Right bundle branch block
rationale: >-
The systematic cardiac review pools m.3243A>G carriers with MELAS, MIDD,
MERRF, Leigh syndrome, and MELAS/KSS overlap. It reports left and right
bundle branch block, supraventricular and ventricular arrhythmias, sinus
tachycardia, atrial fibrillation, nonsustained ventricular tachycardia, and
sudden cardiac death. Its myocardial spectrum includes thickening,
hypertrophic and dilated cardiomyopathy, noncompaction, fibrosis, systolic
dysfunction, heart failure, and arterial hypertension; myocardial
abnormalities are reported more often than arrhythmias or conduction defects.
These observations remain relevant to cardiac assessment, but the review
abstract does not assign each manifestation or its frequency to a MELAS
subgroup. GeneReviews independently supports MELAS cardiomyopathy, broad
conduction abnormalities, and WPW, and recommends ECG and echocardiographic
surveillance. Independent clinical MELAS evidence does establish right bundle
branch block in a selected 11-patient cohort and non-sustained atrial
tachycardia in a case report; these are now represented using those sources.
The clinical review also describes atrial fibrillation and ventricular
tachycardia and proposes conduction-pathway mitochondrial dysfunction, while
the cardiac cohort review describes a remodeling-to-rhythm-disorder route.
Sudden cardiac death and left bundle branch block remain carrier-spectrum
observations here because the reviewed primary reports do not establish those
outcomes in their MELAS patients. Prophylactic device recommendations are not
evidence that a sudden-death event occurred.
evidence:
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The m.3243A>G variant may manifest phenotypically as mitochondrial
encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), maternally
inherited diabetes and deafness (MIDD), myoclonic epilepsy with ragged red
fiber (MERRF), Leigh syndrome, or MELAS/KSS (Kearns-Sayre syndrome) overlap.
explanation: >-
Defines the pooled syndromic scope of the carrier review.
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Myocardial abnormalities include myocardial thickening, hypertrophic
cardiomyopathy, dilated cardiomyopathy, noncompaction, myocardial fibrosis,
systolic dysfunction, heart failure, or arterial hypertension.
explanation: >-
Preserves the reported myocardial spectrum at carrier-population scope.
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Arrhythmias reported in m.3243A>G carriers include paroxysmal
supraventricular or ventricular arrhythmias, including sinus tachycardia,
atrial fibrillation and nonsustained ventricular tachycardia, and sudden
cardiac death.
explanation: >-
Preserves clinically relevant arrhythmia and sudden-death reports without
transferring them to a MELAS subgroup that the abstract does not identify.
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Conduction defects in this group of patients include Wolff-Parkinson-White
syndrome and left/right bundle branch block.
explanation: >-
Preserves bundle branch block as a carrier-spectrum observation; the
antecedent population is all reviewed m.3243A>G carriers.
- reference: PMID:30128910
reference_title: The heart in m.3243A>G carriers.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Myocardial abnormalities are much more frequent than arrhythmias or
conduction defects.
explanation: >-
This comparison applies to the review population; it is not a MELAS-specific
frequency estimate.
- reference: PMID:26937404
reference_title: Arrhythmia as a cardiac manifestation in MELAS syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In summary, this is the unique case of a 44-year old female with a genetic
diagnosis of MELAS syndrome with the associated cardiac manifestations of
left ventricular hypertrophy and atrial tachycardia.
explanation: >-
Provides independent clinical MELAS arrhythmia evidence.
- reference: PMID:39930534
reference_title: Cardiac manifestations in adult MELAS syndrome (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome)- a cross-sectional study.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
ECG was performed in all patients. Surprisingly, right branch bundle block
was only found in one (1/11, 9.1%).
explanation: >-
Provides independent MELAS-specific right bundle branch block evidence.
- reference: PMID:39766231
reference_title: Diagnosis and Management of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like Episodes Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Patients with MELAS are also at an increased risk for arrhythmias, including
atrial fibrillation and ventricular tachycardia, because of the involvement
of mitochondrial dysfunction in the conduction pathways of the heart [40].
explanation: >-
Records the clinical review's arrhythmia mechanism while distinguishing it
from the carrier-wide sudden-death observations.
References & Deep Research
References
1MELAS.
No top-level findings curated for this source.
Deep Research
1Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.
Evaluations and curation notes (2)
Add MassIVE and GSE1462 datasets from the OpenScientist pass · 2026-08-26T03:37:32Z · View source
Folds in the OpenScientist deep-research report (research/datasets/MELAS_Syndrome-datasets-openscientist.md, run against templates/disease_datasets_research.md) and curates the two datasets it surfaced that the deterministic and manual passes had both missed. massive:MSV000088237 - paired proteomics and metabolomics of patient-derived dermal fibroblasts carrying m.14453G>A in MT-ND6. Two things earn it a place. It is the only public patient-tissue multi-omics deposit found for a non-m.3243A>G MELAS genotype, so it speaks to the allele arm of the genotype-phenotype gap and to the complex I subunit subtype in this entry. And it reports downregulated arginine biosynthesis through blocked argininosuccinate synthase, which is a cell-intrinsic route to arginine deficiency and therefore a different claim from the reduced plasma arginine the existing therapeutic rationale rests on. Attached to both the genotype-phenotype and the arginine-evidence gaps, with the arginine rationale updated to separate the mechanistic case (strengthened) from the clinical efficacy question (unchanged - no dataset substitutes for the trial that has never been run). geo:GSE1462 - skeletal muscle from four PEO and four MELAS patients, all carrying m.3243A>G, against controls. This is the only dataset in the entry that holds genotype constant and varies clinical phenotype in patient tissue, which is precisely the design the genotype-phenotype gap calls for; the authors read the difference as support for nuclear background as the modifier. Four patients per arm on a 2005 array platform, so a hypothesis rather than a demonstration. A triage note is recorded on GSE1462 because it is easy to get wrong: its GEO title is the uninformative "Mitochondrial disorders", and summary-level screening reads it as a mixed-genotype cohort. It was dismissed on first pass for exactly that reason and recovered only by reading the full record. The OpenScientist report itself filed it under "broader mitochondrial-disease datasets containing a MELAS stratum", which understates it. Also not curated, from the same report: GSE42986 (primary respiratory-chain disease cohort, genuinely class-level), GSE106601 and GSE142741 (MERRF), GSE208690/GSE208691 (share mitochondrial-encephalomyopathy wording, different conditions), GSE33831 (mesenchymal mitochondrial transfer). Accessions appearing at lines 71-73 of the report (GSE67472, E-MTAB-2770, PXD000001, phs000424, MTBLS123, SRP123456, EGAS00001000123, OSD-737, MSV000078618, MGYS00005566) are the template's own worked examples of accession syntax, not proposals, and were checked as such rather than triaged as candidates. The report and its citations sidecar and HTML/PDF artifacts are committed under research/datasets/ per the research-artifact policy. The 29 new references_cache/GEO_*.md records were generated by the deep-research client's reference validation and follow the existing GEO_ cache convention (146 already tracked). Validation: 190/190 evidence snippets verified; all 16 dataset accessions resolve; schema, term, entity-ref, and just validate-disorders pass.
Add gap-linked public datasets from GEO, PRIDE and registries · 2026-08-26T03:28:20Z · View source
Searched public repositories for datasets bearing on the seven knowledge gaps recorded in the previous MELAS session, and curated the results with each dataset attached to the gap it speaks to. Method: deterministic search first (just discover-datasets, which found 8 GEO candidates), then targeted E-utilities queries against GEO on "3243A>G", "MELAS", and the expanded syndrome name, which surfaced substantially more; then non-NCBI repositories that GEO search cannot reach - PRIDE, MetaboLights, Metabolomics Workbench, EGA, dbGaP - and an OpenScientist deep-research pass as an independent cross-check. Every curated accession passes just verify-datasets. Curated 14 datasets (13 GEO, 1 PRIDE), each attached to a gap via Discussion.attaches_to using the datasets# entity-reference grammar: - Genotype-phenotype discordance: GSE202747 (per-cell heteroplasmy in human MELAS retina; partitions by developmental lineage, not randomly), GSE56158 (cybrids across the full heteroplasmy range; sharp transcriptional transitions rather than a gradient), GSE129091 (low vs high load on the MELAS-versus-MIDD axis), GSE85549 (allele-level: m.3243A>G vs m.3302A>G RNA processing). - Ischemic-versus-hyperexcitable controversy: GSE127478 (vascular arm - m.3243A>G iPSC endothelium is cell-autonomously dysfunctional and pro-inflammatory), GSE154825 (neuronal arm - MEA-seq network electrophysiology plus non-cell-autonomous astrocyte changes), GSE165953 (heteroplasmy-scaled glutamate dysregulation confirmed in MELAS post-mortem brain), GSE202747 (cuts against the vascular arm: choroidal vasculature near-homoplasmic wild-type while neural lineages carried high mutant load). - Human-model mismatch: GSE324301 (cerebral organoid slice model with cortical architecture, generated because no animal carries the mutation, validated against MELAS autopsy), PXD058785 (hiPSC myofibres, heteroplasmy-graded proteomics/phosphoproteomics/metabolomics), GSE61390 (isogenic corrected lines from reprogramming segregation). - Prognostic biomarker: GSE89066 (20 patients vs 20 controls, serum miR-27b-3p outperforming lactate - but on diagnosis, not prognosis), GSE14882 (MELAS whole blood correlated to mutant load and clinical features), GSE165953, GSE113300. - Episodic trigger: recorded as a negative result. No public dataset addresses the timing question, and the absence is structural - every public MELAS dataset is a cross-sectional snapshot while an episode is a transition in living cortex. GSE27545 attached as the nearest relevant work (a self-aggravating RXRA-ROS-JNK-PGC1alpha retrograde loop, which accounts for progression but not for punctuation). - Multi-organ ascertainment: also a negative result for omics. Added two natural-history registry records instead - NCT01532791, which ascertains through maternal relatives of known carriers regardless of their own carrier status with paternal relatives as controls, and NCT05554835, the global harmonized registry. Deliberately not curated, with reasons: GSE222921 (TYMP/MNGIE - a different mitochondrial disease; both the deterministic tool and OpenScientist independently flagged or rejected it); GSE105454 and GSE122198 (TARGET-seq method papers on JAK2-V617F myelofibrosis HSPCs, which OpenScientist listed as confirmed MELAS datasets - they are not); PXD063824 (disease-class-level "mitochondrial disorders", not MELAS); Metabolomics Workbench ST003924 (genetically confirmed paediatric primary mitochondrial disorders with a renal framing - relevant to the ascertainment gap, but its sample factors carry only the disease-class label so MELAS cases cannot be identified within it; referenced in the gap rationale rather than curated). SubSeries were not curated alongside their SuperSeries (GSE202735/202746/202886 under GSE202747; GSE89065/89059 under GSE89066). EGA and dbGaP returned nothing for MELAS. OpenScientist contributed one dataset the deterministic path missed (GSE89066, the strongest biomarker candidate in the set) and independently reproduced the rest of the GEO list and the GSE222921 rejection; it also returned two false positives. It searched only NCBI, so it missed the PRIDE proteomics dataset. Validation: 186/186 evidence snippets verified against the reference cache; all 14 dataset accessions resolve via just verify-datasets; schema, term, entity-ref (38 hash refs, none dangling), duplicate-key, folded-hyphen, snippet-length, title-snippet and source-defect gates pass, as does just validate-disorders. Root-level compliance is now 100%.
Falcon
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MELAS Syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes): Disease Characteristics Research Report
Executive summary
MELAS syndrome is a maternally inherited mitochondrial disorder, classically defined by mitochondrial encephalopathy, lactic acidosis, and recurrent stroke-like episodes (SLEs). It is most commonly caused by heteroplasmic mtDNA variants affecting mitochondrial tRNA genes, especially MT-TL1 m.3243A>G (~80% of cases in multiple contemporary reviews/cohorts). Clinical presentation is multisystemic, but neurologic manifestations (SLEs, seizures, cognitive decline) dominate morbidity and mortality. Recent population-based epidemiology (2024) and large “clinically unselected” genomics (2024) have refined prevalence/incidence and penetrance estimates, supporting genotype/heteroplasmy-stratified risk assessment. Therapeutics remain largely supportive; the strongest interventional evidence in MELAS-specific SLE prevention includes high-dose taurine (open-label phase III trial) and systematic L-arginine regimens (prospective multicenter), with ongoing clinical trials targeting redox/bioenergetics.
1. Disease information
1.1 What is the disease? (overview and definition)
MELAS is a rare mitochondrial syndrome characterized by encephalopathy, lactic acidosis, and stroke-like episodes (SLEs) with non-vascular-distribution brain lesions that may shift over time. Reviews emphasize its broad systemic manifestations (neurologic, muscular, endocrine, cardiac, renal), but recurrent SLEs and seizures are key clinical drivers of disability. (na2024diagnosisandmanagement pages 1-2, na2024diagnosisandmanagement pages 8-9)
Abstract-quotable definition (recent cohort/review): - Xu et al. (Orphanet J Rare Dis, 2024-12, DOI: 10.1186/s13023-024-03511-4) describes MELAS as “Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes,” a maternally inherited mitochondrial disorder affecting primarily the CNS and skeletal muscle. (xu2024multisystemclinicopathologicand pages 1-2)
1.2 Key identifiers
Available in retrieved evidence - OMIM: #540000 (explicitly stated in Xu et al. 2024). (xu2024multisystemclinicopathologicand pages 1-2)
Not found in retrieved evidence (should be confirmed from external disease ontologies/databases): - Orphanet (ORPHA), ICD-10/ICD-11, MeSH, MONDO.
1.3 Synonyms and alternative names
- “Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes” (expansion of MELAS) (na2024diagnosisandmanagement pages 1-2)
- “Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes” (common spelling variant) (ohsawa2019taurinesupplementationfor pages 1-2)
1.4 Evidence provenance (individual patients vs disease resources)
Evidence used here is derived from: - Aggregated disease-level resources: narrative reviews (e.g., Na & Lee 2024). (na2024diagnosisandmanagement pages 1-2) - Human clinical cohorts/registries: imaging cohorts (Zheng 2023), multisystem retrospective cohorts (Xu 2024; Cox 2023), and population-based epidemiology (Martikainen 2024). (zheng2023mitochondrialencephalomyopathywith pages 1-2, xu2024multisystemclinicopathologicand pages 1-2, cox2023theclinicalspectrum pages 1-2, martikainen2024incidenceandprevalence pages 1-2) - Interventional clinical trials: taurine phase III open-label trial; idebenone randomized trial; ClinicalTrials.gov interventional studies. (ohsawa2019taurinesupplementationfor pages 1-2, NCT00887562 chunk 1)
2. Etiology
2.1 Disease causal factors
Genetic (primary): MELAS is most commonly due to pathogenic mtDNA variants affecting mitochondrial translation, especially heteroplasmic MT-TL1 m.3243A>G, repeatedly cited as accounting for ~80% of MELAS cases. (na2024diagnosisandmanagement pages 7-8, xu2024multisystemclinicopathologicand pages 1-2)
Other mtDNA variants associated with MELAS include MT-ND5 (e.g., m.13513G>A, ~10–15% in one 2024 review) and other tRNA gene variants (e.g., MT-TH, MT-TK), plus rarer MT-TL1 variants (e.g., m.3271T>C). (na2024diagnosisandmanagement pages 7-8)
Mechanistic causal chain (current understanding): - Pathogenic mtDNA variants impair mitochondrial protein synthesis → defective oxidative phosphorylation (OXPHOS) → cellular energy failure and lactate accumulation. (na2024diagnosisandmanagement pages 7-8) - Stroke-like episodes are non-vascular and are hypothesized to involve multiple interacting mechanisms including mitochondrial angiopathy/vasculopathy, mitochondrial cytopathy, and neuronal excitotoxicity. (zheng2023mitochondrialencephalomyopathywith pages 1-2, xu2024multisystemclinicopathologicand pages 1-2)
2.2 Risk factors
Genetic risk factors - Presence of heteroplasmic pathogenic mtDNA variants, especially m.3243A>G, with higher heteroplasmy generally associated with greater multisystem risk. - In UK Biobank WGS, multi-system disease risk and penetrance for diabetes/deafness/heart failure increased substantially when m.3243A>G heteroplasmy reached ≥10% (see Section 9). (cannon2024penetranceandexpressivity pages 1-2)
Environmental/physiologic risk factors (evidence-limited in retrieved texts): - Episodes may be precipitated by physiologic stressors (infections, metabolic decompensation), but specific quantified environmental triggers were not systematically captured in the retrieved evidence.
2.3 Protective factors
No validated genetic “protective variants” were identified in the retrieved evidence. Nonetheless, Cannon et al. suggests that penetrance of most pathogenic mtDNA variants is low in unselected populations (exception m.3243A>G at higher heteroplasmy), implying that host genetic background (including polygenic risk) can modify expression. (cannon2024penetranceandexpressivity pages 1-2)
2.4 Gene–environment / gene–gene interactions
Cannon et al. (Human Mol Genet, 2024-11, DOI: 10.1093/hmg/ddad194) reports that diabetes risk with m.3243A>G was further influenced by type 2 diabetes genetic risk, supporting gene–gene interaction between mtDNA heteroplasmy and nuclear polygenic susceptibility. (cannon2024penetranceandexpressivity pages 1-2)
3. Phenotypes
3.1 Core phenotype spectrum (with frequencies where available)
A concise frequency summary (from a phenotype-focused review letter) reports: - SLEs: >90% - Seizures: 76% - Headache: 50% - Vomiting: 55% - Visual loss: 52% - Muscle weakness: 48% - Short stature: >25% - Diabetes: 10–24% These estimates should be interpreted cautiously because they are compiled narrative frequencies rather than from a single prospective cohort. (finsterer2020rarephenotypicmanifestations pages 1-2)
A 2023 large retrospective cohort spanning MELAS to asymptomatic carriers reported: - Seizures in MELAS: 88.1% (vs 16.7% in symptomatic non-MELAS). (cox2023theclinicalspectrum pages 1-2) - Late-onset MELAS had high diabetes (69.2%) and nephropathy (53.8%), suggesting phenotype shifts with age at first SLE. (cox2023theclinicalspectrum pages 1-2)
3.2 Phenotype characteristics (onset, severity, progression)
- SLEs are typically before age 40 in classic MELAS definitions; location of lesions can shift over time and does not respect vascular territories. (na2024diagnosisandmanagement pages 7-8, na2024diagnosisandmanagement pages 8-9)
- Disease course is progressive with recurrent neurological events contributing to reduced life expectancy. (na2024diagnosisandmanagement pages 1-2)
3.3 Quality-of-life impact
Quantitative QoL instruments (e.g., SF-36, EQ-5D, PROMIS) were not reported in the retrieved evidence. Functional outcomes, however, were captured via modified Rankin Scale (mRS) distributions in a 2024 cohort (Section 11). (gao2024longtermprognosticfactors pages 1-2)
3.4 Suggested HPO terms
A phenotype-to-HPO mapping table is provided below.
| MELAS clinical feature | Suggested HPO term | HP ID | Frequency / onset notes | Evidence source |
|---|---|---|---|---|
| Stroke-like episodes | Stroke-like episode | HP:0002401 | >90% of patients in Finsterer 2020; typically a core feature of MELAS, often before age 40 in classic diagnostic criteria; all 39 patients in Gao 2024 initially presented with stroke-like episodes | (finsterer2020rarephenotypicmanifestations pages 1-2, gao2024longtermprognosticfactors pages 1-2) |
| Seizures | Seizure | HP:0001250 | 76% in Finsterer 2020; 88.1% in MELAS group in Cox 2023 | (finsterer2020rarephenotypicmanifestations pages 1-2, cox2023theclinicalspectrum pages 1-2) |
| Lactic acidosis | Lactic acidosis | HP:0003128 | Hallmark biochemical abnormality; elevated plasma/CSF lactate and lactate peak on MRS; not quantified in retrieved evidence for symptom frequency | (na2024diagnosisandmanagement pages 7-8, na2024diagnosisandmanagement pages 8-9) |
| Migraine / headache | Headache | HP:0002315 | Headache 50% in Finsterer 2020; recurrent headache is also part of classic diagnostic criteria; migraine-like headache reported in MELAS cohorts | (finsterer2020rarephenotypicmanifestations pages 1-2, elhattab2017arginineandcitrulline pages 1-2) |
| Vomiting | Vomiting | HP:0002013 | 55% in Finsterer 2020; recurrent vomiting is part of classic diagnostic criteria | (finsterer2020rarephenotypicmanifestations pages 1-2, elhattab2017arginineandcitrulline pages 1-2) |
| Muscle weakness / myopathy / exercise intolerance | Proximal muscle weakness / Mitochondrial myopathy / Exercise intolerance | HP:0003701 / HP:0003200 / HP:0003546 | Muscle weakness 48% in Finsterer 2020; proximal muscle weakness and exercise intolerance were predominant in Xu 2024 cohort; onset variable, often childhood to young adulthood | (finsterer2020rarephenotypicmanifestations pages 1-2, xu2024multisystemclinicopathologicand pages 1-2) |
| Sensorineural hearing loss | Sensorineural hearing impairment | HP:0000407 | Diabetes and deafness associated with intermediate heteroplasmy (about 50–70%) in Na 2024; hearing loss was the first symptom in 51.6% of symptomatic non-MELAS vs 24.4% of MELAS in Cox 2023; exact overall MELAS frequency not quantified in retrieved evidence | (na2024diagnosisandmanagement pages 7-8, cox2023theclinicalspectrum pages 1-2) |
| Diabetes mellitus | Diabetes mellitus | HP:0000819 | Reported in 10–24% in Finsterer 2020; late-onset MELAS had diabetes in 69.2% vs 13.8% standard-onset in Cox 2023 | (finsterer2020rarephenotypicmanifestations pages 1-2, cox2023theclinicalspectrum pages 1-2) |
| Short stature | Short stature | HP:0004322 | >25% of cases in Finsterer 2020 | (finsterer2020rarephenotypicmanifestations pages 1-2) |
| Cortical blindness / vision loss | Cortical visual impairment / Cortical blindness | HP:0100704 / HP:0007956 | Visual loss 52% in Finsterer 2020; cortical vision loss listed as a typical phenotype in Na 2024; vision loss in first stroke-like episode helped define atypical MELAS in Alves 2023 summary | (finsterer2020rarephenotypicmanifestations pages 1-2, na2024diagnosisandmanagement pages 8-9) |
| Cerebellar atrophy | Cerebellar atrophy | HP:0001272 | 68% (40/59 imaging studies) in Zheng 2023; also highly discriminatory for stroke-like episodes vs acute ischemic stroke in Khasminsky 2023 | (zheng2023mitochondrialencephalomyopathywith pages 1-2, khasminsky2023clinicoradiologiccriteriafor pages 1-2) |
| Basal ganglia calcification | Basal ganglia calcification | HP:0002135 | 67% (6/9 patients with CT) in Zheng 2023 | (zheng2023mitochondrialencephalomyopathywith pages 1-2) |
Table: This table maps core MELAS manifestations to suggested Human Phenotype Ontology terms and summarizes frequency or onset information from the retrieved evidence. It is useful for structured phenotype curation in a disease knowledge base.
4. Genetic / molecular information
4.1 Causal genes
Primary causal locus (mtDNA): - MT-TL1 (mitochondrially encoded tRNA leucine 1) with canonical m.3243A>G heteroplasmic variant. (na2024diagnosisandmanagement pages 7-8, xu2024multisystemclinicopathologicand pages 1-2)
Other mtDNA genes/regions implicated (not exhaustive; examples from retrieved evidence): - MT-ND5 (including m.13513G>A), MT-TH, MT-TK, and other tRNA genes; additional variants reported in one 2024 cohort include m.5628T>C, m.6352-13952del, and 9-bp deletions combined with m.3243A>G. (na2024diagnosisandmanagement pages 7-8, xu2024multisystemclinicopathologicand pages 1-2)
4.2 Pathogenic variants and heteroplasmy
- m.3243A>G is typically heteroplasmic, and clinical severity varies with tissue mutation load (threshold effect) and tissue distribution; one 2024 review summarizes that higher mutant load is often found in muscle/urine than blood. (na2024diagnosisandmanagement pages 7-8)
- In a large clinically unselected cohort, higher m.3243A>G heteroplasmy (≥10%) was associated with markedly increased odds of diabetes, deafness, and heart failure. (cannon2024penetranceandexpressivity pages 1-2)
4.3 Modifier genes / nuclear factors
Direct nuclear “modifier genes” were not extracted from the retrieved texts. However, polygenic type 2 diabetes genetic risk modified diabetes risk in m.3243A>G carriers. (cannon2024penetranceandexpressivity pages 1-2)
4.4 Epigenetic and chromosomal abnormalities
No MELAS-specific epigenetic or chromosomal abnormality evidence was found in the retrieved texts.
5. Environmental information
Specific toxins, lifestyle exposures, or infectious triggers were not systematically quantified in the retrieved evidence. Physiological stressors are commonly discussed in case reports and reviews but are outside the evidence captured here.
6. Mechanism / pathophysiology
6.1 Molecular pathways and cellular processes
Upstream driver: impaired mitochondrial translation and OXPHOS defect → ATP deficit and lactate accumulation (systemic and cerebral). (na2024diagnosisandmanagement pages 7-8)
Stroke-like episode mechanisms (multiple interacting hypotheses): - Mitochondrial vasculopathy/angiopathy: microvascular dysfunction and impaired perfusion; NO deficiency is a prominent mechanistic hypothesis supporting arginine/citrulline therapy. (xu2024multisystemclinicopathologicand pages 1-2, elhattab2017arginineandcitrulline pages 1-2) - Mitochondrial cytopathy: direct neuronal/glial energy failure. (zheng2023mitochondrialencephalomyopathywith pages 1-2) - Neuronal excitotoxicity / hyperexcitability: implicated by seizure association and some imaging/clinical patterns. (zheng2023mitochondrialencephalomyopathywith pages 1-2)
6.2 Metabolic changes and biochemical abnormalities
Lactic acidosis and MRS lactate: - Proton MRS commonly shows elevated lactate peaks; e.g., in an m.3243A>G imaging cohort, lactate peaks were present in 9/10 (90%) measured cases. (zheng2023mitochondrialencephalomyopathywith pages 1-2)
31P-MRS (energetics signature): - A 2024 multisystem cohort reports abnormal Pi/PCr ratios on 31P-MRS, consistent with disturbed high-energy phosphate metabolism. (xu2024multisystemclinicopathologicand pages 1-2)
6.3 “Omics” and molecular profiling
No transcriptomic/proteomic/metabolomic multi-omics datasets specific to MELAS were retrieved here. Metabolic profiling proxies available include 1H-MRS and 31P-MRS energetics measures. (xu2024multisystemclinicopathologicand pages 1-2, zheng2023mitochondrialencephalomyopathywith pages 1-2)
6.4 Suggested ontology terms for mechanisms
GO Biological Process (suggestions; ontology IDs should be confirmed against GO): - Mitochondrial translation; oxidative phosphorylation; ATP metabolic process; response to oxidative stress; regulation of cerebral blood flow; excitatory synaptic transmission.
Cell Ontology (CL) cell types implicated (suggestions): - Cerebral vascular endothelial cell; neuron; astrocyte; skeletal muscle fiber.
7. Anatomical structures affected
7.1 Organ/system level
Commonly involved systems include: - Central nervous system (stroke-like lesions, seizures, progressive decline). (na2024diagnosisandmanagement pages 1-2) - Skeletal muscle (myopathy, weakness, exercise intolerance). (na2024diagnosisandmanagement pages 1-2, xu2024multisystemclinicopathologicand pages 1-2) - Endocrine/metabolic (diabetes). (na2024diagnosisandmanagement pages 1-2, cox2023theclinicalspectrum pages 1-2) - Cardiac (hypertrophic cardiomyopathy/arrhythmias noted in reviews; heart failure association in population genomics). (na2024diagnosisandmanagement pages 8-9, cannon2024penetranceandexpressivity pages 1-2) - Renal (nephropathy in late-onset phenotype). (cox2023theclinicalspectrum pages 1-2)
7.2 Tissue/cell and subcellular level
- Mitochondria (subcellular compartment) are central; muscle biopsy may show ragged red fibers and COX-defective fibers indicating mitochondrial proliferation and respiratory chain dysfunction. (xu2024multisystemclinicopathologicand pages 1-2, na2024diagnosisandmanagement pages 8-9)
7.3 Neuroanatomical localization patterns (quantitative imaging)
A 2023 imaging analysis of m.3243A>G MELAS reported predominant posterior cortical involvement: - Occipital: 63% (37/59) - Parietal: 54% (32/59) - Temporal: 51% (30/59) with frequent atrophy and lesion polymorphism; see quantitative table below. (zheng2023mitochondrialencephalomyopathywith pages 1-2)
8. Temporal development
8.1 Onset
- Classic MELAS definitions emphasize early-onset stroke-like episodes (often before age 40). (elhattab2017arginineandcitrulline pages 1-2, na2024diagnosisandmanagement pages 7-8)
- A 2023 cohort distinguished “standard-onset” (first SLE <40) versus late-onset; late-onset cases had longer prodromal periods and died later (mean age at death 62 vs 30). (cox2023theclinicalspectrum pages 1-2)
8.2 Progression and course
- Disease course is typically progressive with episodic neurologic decompensation (SLEs, status epilepticus) and accumulating deficits. (na2024diagnosisandmanagement pages 1-2, gao2024longtermprognosticfactors pages 1-2)
9. Inheritance and population
9.1 Inheritance
- Mitochondrial (maternal) inheritance is a defining property; heteroplasmy and tissue distribution create variable expressivity and incomplete penetrance. (na2024diagnosisandmanagement pages 7-8, xu2024multisystemclinicopathologicand pages 1-2)
9.2 Epidemiology (recent data prioritized)
A 2024 observational population-based study in Southwest Finland reported adult mtDNA disease epidemiology that can serve as a modern benchmark (not MELAS-specific only, but includes m.3243A>G-related disease): - Adult mtDNA disease prevalence (2022): 9.2/100,000 (95% CI 6.5–12.7). (martikainen2024incidenceandprevalence pages 1-2) - Adult m.3243A>G-related disease prevalence: 4.2/100,000 (95% CI 2.5–6.7). (martikainen2024incidenceandprevalence pages 1-2) - Annual incidence (2010–2022): adult mtDNA disease 0.6/100,000; adult m.3243A>G-related disease 0.3/100,000. (martikainen2024incidenceandprevalence pages 1-2) The authors explicitly note that improved diagnostics and dedicated ascertainment increase detection, and that under-recognition of oligosymptomatic cases is likely. (martikainen2024incidenceandprevalence pages 2-3, martikainen2024incidenceandprevalence pages 3-4)
9.3 Penetrance and expressivity (2024 large unselected cohort)
In UK Biobank WGS, Cannon et al. showed: - Most pathogenic mtDNA variants had low penetrance in unselected populations, except m.3243A>G. (cannon2024penetranceandexpressivity pages 1-2) - When m.3243A>G heteroplasmy ≥10%, odds ratios increased markedly: - Diabetes OR: 5.61 → 25.1 - Deafness OR: 12.3 → 55.0 - Heart failure OR: 10.1 → 39.5 This supports quantitative heteroplasmy thresholds for clinical risk stratification and incidental reporting discussions. (cannon2024penetranceandexpressivity pages 1-2)
10. Diagnostics
10.1 Clinical and biochemical tests
Common diagnostic elements include: - Lactic acidosis (plasma and/or CSF lactate/pyruvate) and lactate peaks on MRS. (na2024diagnosisandmanagement pages 8-9) - Neuroimaging: cortical/subcortical lesions not respecting vascular territories; lesions may shift over time. (na2024diagnosisandmanagement pages 8-9) - Muscle biopsy (when genetic testing inconclusive): ragged red fibers (RRF) and COX-defective fibers may support diagnosis. (xu2024multisystemclinicopathologicand pages 1-2)
10.2 Genetic testing
- Genetic diagnosis commonly relies on mtDNA testing to identify causative variants and measure heteroplasmy. A 2024 review notes tissue heteroplasmy differences (muscle/urine often higher than blood), implying that multi-tissue testing improves sensitivity. (na2024diagnosisandmanagement pages 7-8)
10.3 Clinicoradiologic criteria for stroke-like episodes (SLE) (real-world implementation)
Stroke-like episodes are frequently misdiagnosed as acute ischemic stroke. A 2023 Neurology Genetics study derived and validated pragmatic criteria and an algorithm using clinical history and CT/CTA patterns: - “Possible SLE” criteria: sensitivity 100%, specificity 81% (AUC 0.905). - “Probable SLE” criteria: sensitivity 88%, specificity 95% (AUC 0.917). (khasminsky2023clinicoradiologiccriteriafor pages 1-2)
Visual evidence (Table and diagnostic algorithm): (khasminsky2023clinicoradiologiccriteriafor media eef69170, khasminsky2023clinicoradiologiccriteriafor media 6adc2877)
11. Outcome / prognosis
11.1 Survival and mortality (cohort evidence)
- In one 2023 retrospective spectrum cohort, MELAS showed 50% mortality at 25 years from onset (comparison group 10%). (cox2023theclinicalspectrum pages 1-2)
11.2 Functional outcomes and prognostic markers (2024 cohort)
A 2024 retrospective cohort (n=39; mean follow-up 7.3±4.7 years) reported: - Deaths: 8/39, primarily due to acute SLEs and status epilepticus. (gao2024longtermprognosticfactors pages 1-2) - mRS distribution: 41% (0–2), 38.5% (3–5), 20.5% (6 or died). (gao2024longtermprognosticfactors pages 1-2) - Independent mortality predictors: - Severe lactate elevation OR 7.279 (95% CI 1.102–48.086) - Anemia associated with poor prognosis (reported OR 0.137 with CI 0.021–0.908; directionality in the paper indicates anemia as an adverse prognostic factor). (gao2024longtermprognosticfactors pages 1-2)
12. Treatment
12.1 Current standard of care (supportive)
A 2024 management review describes MELAS care as largely supportive, including anti-seizure medications, metabolic supplementation (arginine/citrulline, high-dose taurine), and dietary therapies. (na2024diagnosisandmanagement pages 1-2)
A practical dosing example from the same review for commonly used mitochondrial cofactors includes: - CoQ10: “typically” 30 mg/kg/day - Riboflavin: 50–400 mg daily - L-carnitine: 50–100 mg/kg/day These are supportive and not disease-modifying for the mtDNA defect. (na2024diagnosisandmanagement pages 8-9)
MAXO (treatment action) suggestions (confirm in MAXO): - Intravenous amino acid supplementation (L-arginine) - Oral amino acid supplementation (L-arginine; L-citrulline) - Taurine supplementation - Antiseizure therapy - Nutritional therapy / dietary intervention
12.2 Targeted symptomatic/preventive therapies for SLEs
Taurine (high-dose oral)
A multicenter open-label phase III trial in 10 patients with recurrent SLEs administered 9 g/day or 12 g/day taurine for 52 weeks: - Primary endpoint (complete prevention): 60% (95% CI 26.2–87.8) - ≥50% reduction responder rate: 80% (95% CI 44.4–97.5) - Annual relapse rate reduced 2.22 → 0.72 (P=0.001) - No severe adverse events attributed to taurine. (ohsawa2019taurinesupplementationfor pages 1-2) Mechanistically, the trial frames MELAS as a “tRNA modification disorder” in which taurine corrects defective taurine modification of mitochondrial tRNALeu(UUR), improving decoding fidelity. (ohsawa2019taurinesupplementationfor pages 1-2)
L-arginine (acute and prophylactic regimens)
A 9-year prospective multicenter Japanese clinical research program tested systematic oral and IV L-arginine: - Oral: 0.3–0.5 g/kg/day for 2 years - IV: 0.5 g/kg per dose (acute ictus regimen) - Observed benefits included decreased incidence/severity of ictuses and improvement in acute symptoms (headache, nausea/vomiting, impaired consciousness, visual disturbance) with favorable tolerability. (koga2018therapeuticregimenof pages 1-2) A 2022 systematic review synthesizing small trials reported decreases in stroke-like episode frequency and severity scores with oral prophylaxis, and symptomatic improvements with IV arginine. (argudo2022arginineforthe pages 4-5)
Citrulline
Citrulline is discussed as a nitric oxide precursor potentially increasing NO production more robustly than arginine; however, clinical efficacy studies were noted as limited in older reviews. (elhattab2017arginineandcitrulline pages 1-2)
12.3 Experimental / emerging therapies (pipeline)
A 2024 review describes experimental directions such as gene therapy and mitochondrial replacement techniques, along with redox/mitochondrial-targeted candidates. (na2024diagnosisandmanagement pages 1-2, na2024diagnosisandmanagement pages 12-14)
13. Prevention
Primary prevention of MELAS itself is genetic (maternal transmission risk reduction). The retrieved evidence mentions mitochondrial replacement therapy conceptually as a preventive reproductive strategy (without clinical outcome data in the retrieved excerpts). (na2024diagnosisandmanagement pages 12-14)
Secondary/tertiary prevention focuses on preventing or mitigating SLEs and seizures: - Taurine prophylaxis and arginine/citrulline strategies are used to reduce SLE frequency/severity. (ohsawa2019taurinesupplementationfor pages 1-2, koga2018therapeuticregimenof pages 1-2)
14. Other species / natural disease
No naturally occurring MELAS analogs in non-human species were identified in the retrieved evidence.
15. Model organisms
No animal or cellular model organism resources were identified in the retrieved evidence.
Quantitative evidence summary table
| Domain | Finding (with numbers) | Study/source | Publication date | URL/DOI | Evidence type | Notes |
|---|---|---|---|---|---|---|
| Common causal variant | MT-TL1 m.3243A>G accounts for ~80% of MELAS cases | Na & Lee, Biomolecules; Xu et al., Orphanet J Rare Dis (na2024diagnosisandmanagement pages 7-8, xu2024multisystemclinicopathologicand pages 1-2) | 2024-11; 2024-12 | https://doi.org/10.3390/biom14121524; https://doi.org/10.1186/s13023-024-03511-4 | Review; retrospective cohort | Xu reports OMIM #540000; Xu cohort n=29 |
| Neuroimaging lesion distribution | Posterior brain predominance: occipital 37/59 (63%), parietal 32/59 (54%), temporal 30/59 (51%); lesion polymorphism 37/59 (63%); cerebral atrophy 38/59 (64%); cerebellar atrophy 40/59 (68%); basal ganglia calcification 6/9 (67%); MRS lactate peak 9/10 (90%); arterial dilation 4/6 (67%) | Zheng et al., Front Neurosci (zheng2023mitochondrialencephalomyopathywith pages 1-2) | 2023-01 | https://doi.org/10.3389/fnins.2022.1028762 | Retrospective imaging cohort | 59 imaging studies in 24 genetically confirmed m.3243A>G patients |
| Prognostic markers | Mean follow-up 7.3 ± 4.7 years; deaths 8/39; severe lactate elevation predicted mortality: OR 7.279 (95% CI 1.102–48.086, p=0.039); anemia associated with poor prognosis: OR 0.137 (95% CI 0.021–0.908, p=0.039); lactate vs mRS r=0.460 (p=0.003); hemoglobin vs mRS r=-0.375 (p=0.015) | Gao et al., Front Neurol (gao2024longtermprognosticfactors pages 1-2) | 2024-12 | https://doi.org/10.3389/fneur.2024.1491283 | Retrospective cohort | Single-center MELAS cohort n=39; all initially presented with stroke-like episodes |
| Phenotype frequencies and survival | Seizures in MELAS 88.1% vs 16.7% in symptomatic non-MELAS; sensorineural hearing loss as first symptom 51.6% in symptomatic non-MELAS vs 24.4% in MELAS; mean serum heteroplasmy 39.3% (MELAS) vs 29.3% (symptomatic non-MELAS) vs 21.8% (asymptomatic); 50% mortality at 25 years in MELAS vs 10% comparison group; late-onset MELAS: diabetes 69.2%, nephropathy 53.8% | Cox et al., Front Neurol (cox2023theclinicalspectrum pages 1-2) | 2023-12 | https://doi.org/10.3389/fneur.2023.1298569 | Retrospective cohort | Overall n=81: 42 MELAS, 30 symptomatic non-MELAS, 9 asymptomatic; 13 late-onset MELAS |
| Taurine trial outcomes | High-dose taurine 9 g/day or 12 g/day for 52 weeks; 100% responder rate 60% (95% CI 26.2–87.8); ≥50% responder rate 80% (95% CI 44.4–97.5); annual relapse rate reduced 2.22 to 0.72 (P=0.001); no severe adverse events | Ohsawa et al., J Neurol Neurosurg Psychiatry (khasminsky2023clinicoradiologiccriteriafor media eef69170, khasminsky2023clinicoradiologiccriteriafor media 6adc2877) | 2019-04 | https://doi.org/10.1136/jnnp-2018-317964 | Multicentre open-label phase III trial | n=10 with recurrent stroke-like episodes; trial registration UMIN000011908 |
| Population-based prevalence/incidence | Adult mtDNA-related mitochondrial disease prevalence 9.2/100,000 (95% CI 6.5–12.7) in 2022; adult m.3243A>G-related disease prevalence 4.2/100,000 (95% CI 2.5–6.7); annual incidence of adult mtDNA disease 0.6/100,000; annual incidence of adult m.3243A>G-related disease 0.3/100,000 | Martikainen & Majamaa, BMJ Neurol Open (cox2023theclinicalspectrum pages 1-2) | 2024-02 | https://doi.org/10.1136/bmjno-2023-000546 | Population-based observational study | Southwest Finland, 2009–2022; 42 new adult patients diagnosed; mean 3.2 new diagnoses/year |
Table: This table compiles key quantitative findings on MELAS syndrome from recent and landmark studies, including genetics, imaging, prognosis, phenotype burden, treatment outcomes, and population epidemiology. It is useful as a compact evidence summary for knowledge base curation and report drafting.
Real-world implementations and clinical trials (selected)
Recent and active clinical research is visible in ClinicalTrials.gov records: - NCT01339494 (completed; Early Phase 1; n=30): oral L-arginine and L-citrulline (10 g/m²/day divided q4h for 48 h each) with primary outcome change in nitric oxide production; includes patients with m.3243A>G. (NCT01339494 chunk 1) - NCT03952234 (completed; Phase 1; n=10): L-citrulline dose-finding in adults with MELAS and m.3243A>G; primary outcome maximum tolerable dose / DLTs over 8 weeks. (NCT03952234 chunk 1) - NCT00887562 (completed; Phase IIa; randomized, placebo-controlled; n=27): idebenone 900 or 2250 mg/day for 1 month; primary outcome change in cerebral lactate by MRS. (NCT00887562 chunk 1) - NCT06644534 (recruiting; Phase 2; planned n=12): TTI-0102 (cysteamine-pantetheine disulfide) vs placebo; primary outcomes include 12-minute walk test change and safety; inclusion requires MELAS-associated mtDNA variants with heteroplasmy thresholds and clinical features including stroke-like episodes. (NCT06644534 chunk 1)
Limitations of this evidence package (important for knowledge base curation)
- PMIDs were not present in the retrieved excerpts for many sources; therefore, PMID-level citation could not be systematically provided despite the user preference. DOIs/URLs and publication dates are provided whenever available in the retrieved evidence.
- Orphanet/ICD/MeSH/MONDO codes were not explicitly captured in the retrieved texts, except OMIM #540000 from Xu 2024; these should be supplemented by direct lookup in OMIM/Orphanet/MONDO/MeSH.
- Multi-omics (transcriptomics/proteomics/metabolomics) MELAS datasets were not retrieved in this run; only MRS-based metabolic profiling proxies were available.
References
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(na2024diagnosisandmanagement pages 1-2): Ji-Hoon Na and Young-Mock Lee. Diagnosis and management of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome. Biomolecules, 14:1524, Nov 2024. URL: https://doi.org/10.3390/biom14121524, doi:10.3390/biom14121524. This article has 29 citations.
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(na2024diagnosisandmanagement pages 8-9): Ji-Hoon Na and Young-Mock Lee. Diagnosis and management of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome. Biomolecules, 14:1524, Nov 2024. URL: https://doi.org/10.3390/biom14121524, doi:10.3390/biom14121524. This article has 29 citations.
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(xu2024multisystemclinicopathologicand pages 1-2): Shuai Xu, Jialiu Jiang, Leilei Chang, Biao Zhang, Xiaolei Zhu, and Fengnan Niu. Multisystem clinicopathologic and genetic analysis of melas. Orphanet Journal of Rare Diseases, Dec 2024. URL: https://doi.org/10.1186/s13023-024-03511-4, doi:10.1186/s13023-024-03511-4. This article has 8 citations and is from a peer-reviewed journal.
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(ohsawa2019taurinesupplementationfor pages 1-2): Yutaka Ohsawa, Hiroki Hagiwara, Shin-ichiro Nishimatsu, Akihiro Hirakawa, Naomi Kamimura, Hideaki Ohtsubo, Yuta Fukai, Tatsufumi Murakami, Yasutoshi Koga, Yu-ichi Goto, Shigeo Ohta, and Yoshihide Sunada. Taurine supplementation for prevention of stroke-like episodes in melas: a multicentre, open-label, 52-week phase iii trial. Journal of Neurology, Neurosurgery, and Psychiatry, 90:529-536, Apr 2019. URL: https://doi.org/10.1136/jnnp-2018-317964, doi:10.1136/jnnp-2018-317964. This article has 171 citations.
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(zheng2023mitochondrialencephalomyopathywith pages 1-2): Helin Zheng, Xuemei Zhang, Lu Tian, Bo Liu, Xiaoya He, Longlun Wang, Shuang Ding, Yi Guo, and Jinhua Cai. Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with an mt-tl1 m.3243a>g point mutation: neuroradiological features and their implications for underlying pathogenesis. Frontiers in Neuroscience, Jan 2023. URL: https://doi.org/10.3389/fnins.2022.1028762, doi:10.3389/fnins.2022.1028762. This article has 14 citations and is from a peer-reviewed journal.
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(cox2023theclinicalspectrum pages 1-2): Benjamin C. Cox, Jennifer Y. Pearson, Jay Mandrekar, and Ralitza H. Gavrilova. The clinical spectrum of melas and associated disorders across ages: a retrospective cohort study. Frontiers in Neurology, Dec 2023. URL: https://doi.org/10.3389/fneur.2023.1298569, doi:10.3389/fneur.2023.1298569. This article has 17 citations and is from a peer-reviewed journal.
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(martikainen2024incidenceandprevalence pages 1-2): Mika H Martikainen and Kari Majamaa. Incidence and prevalence of mtdna-related adult mitochondrial disease in southwest finland, 2009–2022: an observational, population-based study. BMJ Neurology Open, 6:e000546, Feb 2024. URL: https://doi.org/10.1136/bmjno-2023-000546, doi:10.1136/bmjno-2023-000546. This article has 9 citations and is from a peer-reviewed journal.
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(NCT00887562 chunk 1): Michio Hirano. Study of Idebenone in the Treatment of Mitochondrial Encephalopathy Lactic Acidosis & Stroke-like Episodes. Michio Hirano. 2009. ClinicalTrials.gov Identifier: NCT00887562
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(na2024diagnosisandmanagement pages 7-8): Ji-Hoon Na and Young-Mock Lee. Diagnosis and management of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome. Biomolecules, 14:1524, Nov 2024. URL: https://doi.org/10.3390/biom14121524, doi:10.3390/biom14121524. This article has 29 citations.
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(cannon2024penetranceandexpressivity pages 1-2): Stuart J Cannon, Timothy Hall, Gareth Hawkes, Kevin Colclough, Roisin M Boggan, Caroline F Wright, Sarah J Pickett, Andrew T Hattersley, Michael N Weedon, and Kashyap A Patel. Penetrance and expressivity of mitochondrial variants in a large clinically unselected population. Human Molecular Genetics, 33:465-474, Nov 2024. URL: https://doi.org/10.1093/hmg/ddad194, doi:10.1093/hmg/ddad194. This article has 15 citations and is from a domain leading peer-reviewed journal.
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(finsterer2020rarephenotypicmanifestations pages 1-2): Josef Finsterer. Rare phenotypic manifestations of melas. Yonsei Medical Journal, 61:904-906, Sep 2020. URL: https://doi.org/10.3349/ymj.2020.61.10.904, doi:10.3349/ymj.2020.61.10.904. This article has 5 citations and is from a peer-reviewed journal.
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(gao2024longtermprognosticfactors pages 1-2): Rui Gao, Lihua Gu, Wenchao Zuo, and Pan Wang. Long-term prognostic factors and outcomes in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes: a clinical and biochemical marker analysis. Frontiers in Neurology, Dec 2024. URL: https://doi.org/10.3389/fneur.2024.1491283, doi:10.3389/fneur.2024.1491283. This article has 7 citations and is from a peer-reviewed journal.
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(elhattab2017arginineandcitrulline pages 1-2): Ayman W. El-Hattab, Mohammed Almannai, and Fernando Scaglia. Arginine and citrulline for the treatment of melas syndrome. Journal of inborn errors of metabolism and screening, 5:232640981769739, Mar 2017. URL: https://doi.org/10.1177/2326409817697399, doi:10.1177/2326409817697399. This article has 79 citations.
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(khasminsky2023clinicoradiologiccriteriafor pages 1-2): Vadim Khasminsky, Eitan Auriel, Judith Luckman, Ruth Eliahou, Edna Inbar, Keshet Pardo, Yuval Landau, Rani Barnea, Maor Mermelstein, Shahar Shelly, Jonathan Naftali, and Shlomi Peretz. Clinicoradiologic criteria for the diagnosis of stroke-like episodes in melas. Aug 2023. URL: https://doi.org/10.1212/nxg.0000000000200082, doi:10.1212/nxg.0000000000200082. This article has 10 citations.
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(martikainen2024incidenceandprevalence pages 2-3): Mika H Martikainen and Kari Majamaa. Incidence and prevalence of mtdna-related adult mitochondrial disease in southwest finland, 2009–2022: an observational, population-based study. BMJ Neurology Open, 6:e000546, Feb 2024. URL: https://doi.org/10.1136/bmjno-2023-000546, doi:10.1136/bmjno-2023-000546. This article has 9 citations and is from a peer-reviewed journal.
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(martikainen2024incidenceandprevalence pages 3-4): Mika H Martikainen and Kari Majamaa. Incidence and prevalence of mtdna-related adult mitochondrial disease in southwest finland, 2009–2022: an observational, population-based study. BMJ Neurology Open, 6:e000546, Feb 2024. URL: https://doi.org/10.1136/bmjno-2023-000546, doi:10.1136/bmjno-2023-000546. This article has 9 citations and is from a peer-reviewed journal.
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(khasminsky2023clinicoradiologiccriteriafor media eef69170): Vadim Khasminsky, Eitan Auriel, Judith Luckman, Ruth Eliahou, Edna Inbar, Keshet Pardo, Yuval Landau, Rani Barnea, Maor Mermelstein, Shahar Shelly, Jonathan Naftali, and Shlomi Peretz. Clinicoradiologic criteria for the diagnosis of stroke-like episodes in melas. Aug 2023. URL: https://doi.org/10.1212/nxg.0000000000200082, doi:10.1212/nxg.0000000000200082. This article has 10 citations.
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