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
3
MT-TL1 m.3243A>G (classic MELAS)
The most common form, caused by the m.3243A>G transition in MT-TL1 (mitochondrial tRNA-Leu(UUR)), accounting for roughly 80% of MELAS cases.
Show evidence (1 reference)
"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.
Other MT-TL1 (tRNA-Leu(UUR)) variants
A minority of MELAS cases caused by non-3243 pathogenic variants in MT-TL1, most notably m.3271T>C, which also impair tRNA-Leu(UUR) function through the same loss of the wobble taurine modification.
Show evidence (1 reference)
"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-ND5 and other mitochondrial-gene MELAS
MELAS-spectrum disease caused by variants outside MT-TL1, particularly in the complex I subunit genes MT-ND1, MT-ND5, and MT-ND6, and occasionally other mitochondrial tRNA or protein-coding genes. These genotypes attack complex I directly rather than through a translation defect and are enriched in MELAS/Leigh overlap presentations.
Show evidence (1 reference)
"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 complex I subunit genes that define this non-MT-TL1 subtype.
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.
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
7Is 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. The likeliest resolution is that these are not rival explanations of one event but two required components - capillary angiopathy supplying the leaky substrate on which epileptic activity produces cortical vasogenic edema - which is how the pathograph is wired here.
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, and its FSGS biopsy pattern is indistinguishable from the idiopathic form, so patients are treated with immunosuppression before the mitochondrial cause is found. 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. Frequencies for these features cannot be curated from the present literature because the denominators come from neurology cohorts, and a systematic multi-organ screening study of unselected carriers has not been done.
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.
Pathophysiology
11Taurine 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.
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.
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, whose subunits are the most dependent on mtDNA-encoded synthesis, is disproportionately affected, 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, so active mitophagy - not only failed assembly - contributes to the neuronal deficit. This is the mechanistic reason why one heteroplasmic variant produces 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.
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 cerebral small 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.
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 preferentially involves cerebral cortex with variable subcortical edema, spreads into surrounding cortex over weeks, and leaves 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.
Show evidence (3 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.
Stroke-like episodes
Acute neurological deficits with neuroimaging lesions that do not conform to classic vascular territories, the defining clinical manifestation of MELAS, arising from mitochondrial angiopathy, NO deficiency, and neuronal energy failure.
Downstream
Repeated stroke-like episodes accumulate cortical tissue loss; brain atrophy and cognitive decline are the residue left in survivors.
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.
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.
Histopathology
3
Ragged-red fibers on modified Gomori trichrome
VERY_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 in a cohort where every patient underwent muscle biopsy.
Strongly SDH-reactive blood vessels with preserved cytochrome c oxidase activity
VERY_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 (2 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-versus-MERRF distinction in the enzyme histochemistry of strongly SDH-reactive vessels.
"SDH strongly reactive blood vessels (SSV) were observed in 28 patients (71.8%)"
Quantifies SSV yield on muscle biopsy in a MELAS cohort.
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
30Blood 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 (2 references)
"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."
Identifies anemia as an independent mortality predictor in a long-followed 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.
Cardiovascular 3
Cardiomyopathy
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 (1 reference)
"Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
GeneReviews documents cardiomyopathy and cardiac conduction defects as manifestations of MELAS requiring standard management.
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 (2 references)
"Myocardial abnormalities include myocardial thickening, hypertrophic cardiomyopathy, dilated cardiomyopathy, noncompaction, myocardial fibrosis, systolic dysfunction, heart failure, or arterial hypertension."
Enumerates the myocardial phenotypes reported in m.3243A>G carriers.
"Myocardial abnormalities are much more frequent than arrhythmias or conduction defects."
Establishes the relative frequency of myocardial versus electrical cardiac involvement.
Wolff-Parkinson-White syndrome and conduction defects
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 (2 references)
"Conduction defects in this group of patients include Wolff-Parkinson-White syndrome and left/right bundle branch block."
Names the specific conduction abnormalities reported with m.3243A>G.
"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."
Documents the arrhythmia spectrum including sudden cardiac death.
Digestive 2
Recurrent vomiting
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 (1 reference)
"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.
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 (2 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.
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)
"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 hearing impairment among the broad manifestations of MELAS.
Endocrine 1
Diabetes mellitus
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 (1 reference)
"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.
Eye 2
Mitochondrial retinal dystrophy
VERY_FREQUENT
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 (2 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.
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 (1 reference)
"Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
GeneReviews lists ptosis among the MELAS manifestations requiring standard management.
Genitourinary 1
Nephropathy with 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 (2 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.
"Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
GeneReviews lists nephropathy among the MELAS manifestations requiring standard management.
Metabolism 1
Lactic acidosis
VERY_FREQUENT
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)
"Lactic acidemia is very common and muscle biopsies typically show ragged red fibers."
GeneReviews documents lactic acidemia as a very common feature of MELAS.
Musculoskeletal 1
Mitochondrial myopathy
HP:0003198
Human Phenotype Ontology (HP)
Relation: this clinical feature is this phenotype
This clinical feature is Myopathy (HP:0003198). HP:0003198 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 muscle weakness and exercise intolerance, the clinical expression of mitochondrial myopathy, among common manifestations.
Nervous System 8
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)
"Common clinical manifestations include stroke-like episodes, encephalopathy with seizures and/or dementia, muscle weakness and exercise intolerance"
GeneReviews lists encephalopathy with seizures among the common manifestations of MELAS.
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 (1 reference)
"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 headaches among the common manifestations; these are typically migraine-like and often herald stroke-like episodes.
Peripheral neuropathy
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 (1 reference)
"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.
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 (2 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.
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 (2 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.
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 (1 reference)
"(8) brain dysfunction and atrophy are slowly progressive"
Documents progressive brain atrophy as a listed feature of the MELAS course.
Hemiparesis and aphasia
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)
"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"
Establishes that focal deficits follow lesion site rather than vascular territory.
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
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 (1 reference)
"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.
Other 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.
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.
Learning disability
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 (1 reference)
"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.
Cortical visual impairment
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 sudden, transient, and recurrent development of stroke-resembling symptoms (headache, nausea/vomiting, visual disturbance/visual field abnormalities, seizures, and impaired consciousness: ictus)"
Visual field abnormalities (e.g., hemianopia) commonly accompany occipital stroke-like episodes in MELAS.
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 (2 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.
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.
Progressive external ophthalmoplegia
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 (1 reference)
"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.
Genetic Associations
2
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 (3 references)
"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.
"Mitochondrial DNA (mtDNA) mutations were prevalent (87.4%), with m.3243A>G being the most common locus (48.7%)."
Independent multicentre confirmation that m.3243A>G is the single commonest mitochondrial-disease locus, in a cohort where MELAS was the predominant phenotype.
MT-ND5 and other mitochondrial-gene variants
(A minority of MELAS cases are caused by variants outside MT-TL1, including the complex I subunit genes MT-ND1, MT-ND5, and MT-ND6. These behave differently from the tRNA genotype: because they hit complex I structural subunits directly rather than through a translation defect, they are enriched in MELAS/Leigh overlap presentations, where m.13513G>A in MT-ND5 is the commonest single variant. Genotype should therefore be read as a partial predictor of which end of the MELAS-Leigh spectrum a patient sits on, not merely as a footnote to the m.3243A>G majority.)
Show evidence (3 references)
"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.
"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 full set of complex I subunit genes reported as non-MT-TL1 causes of MELAS.
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).
Show evidence (2 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).
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 (2 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.
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 head-to-head meta-analysis GDF-15 outperforms FGF-21 on every diagnostic metric, which makes it the better first-line serum screen when a mitochondrial disorder is suspected.
Show evidence (1 reference)
"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.
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 (2 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.
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. Earlier seizure onset also predicts drug-resistant epilepsy.
Show evidence (1 reference)
"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.
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 (3 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.
"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.
"Progressive brain atrophy and dementia are the sequalae of recurrent stroke-like episode, and the underlying genotype in part predicts prognosis."
Identifies the long-term neurological endpoint of recurrent stroke-like episodes.
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, mostly from acute stroke-like episodes or status epilepticus, and about 40% of survivors needed help with daily life. Epilepsy is typically drug-resistant, and recurrent stroke-like episodes leave progressive brain atrophy and dementia. No disease-modifying therapy is established.
Show evidence (2 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.
"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."
Establishes drug-resistant epilepsy as a major contributor to burden, while noting partial treatability.
Differential Diagnoses
3Conditions with similar clinical presentations that must be differentiated from MELAS Syndrome:
Acute ischemic stroke
Overlapping Features
The default misdiagnosis, and the one with therapeutic consequences. Separating them rests on lesion distribution that crosses arterial territories, posterior predilection, contiguous spread over weeks, accompanying seizures, elevated rather than restricted diffusion, focal hyperperfusion rather than hypoperfusion, and a lactate peak on spectroscopy.
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 (1 reference)
"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.
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 (1 reference)
"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 COX-activity criterion that distinguishes MERRF from MELAS vascular pathology.
Overlapping Features
Bilateral symmetrical basal ganglia, thalamic, and brainstem lesions define Leigh syndrome, whereas MELAS lesions are cortical and asymmetric. 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 asymmetric cortical lesions
- Ataxia, spastic paraplegia, and bulbar palsy as leading features
- Enriched for MT-ND (complex I subunit) variants in overlap cases
Show evidence (2 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-syndrome features that separate it clinically from core MELAS.
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. 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
has_subtypes:
- name: MT-TL1 m.3243A>G
display_name: MT-TL1 m.3243A>G (classic MELAS)
description: >-
The most common form, caused by the m.3243A>G transition in MT-TL1
(mitochondrial tRNA-Leu(UUR)), accounting for roughly 80% of MELAS cases.
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.
- name: Other MT-TL1 variants
display_name: Other MT-TL1 (tRNA-Leu(UUR)) variants
description: >-
A minority of MELAS cases caused by non-3243 pathogenic variants in MT-TL1,
most notably m.3271T>C, which also impair tRNA-Leu(UUR) function through
the same loss of the wobble taurine modification.
evidence:
- 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-ND5 and other genes
display_name: MT-ND5 and other mitochondrial-gene MELAS
description: >-
MELAS-spectrum disease caused by variants outside MT-TL1, particularly in
the complex I subunit genes MT-ND1, MT-ND5, and MT-ND6, and occasionally
other mitochondrial tRNA or protein-coding genes. These genotypes attack
complex I directly rather than through a translation defect and are
enriched in MELAS/Leigh overlap presentations.
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: "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 complex I subunit genes that define this non-MT-TL1 subtype.
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: Onset before ~18 years
notes: >-
Short stature is significantly more frequent in the juvenile form, and
juvenile onset carries a substantially higher risk of death than adult
onset. Earlier seizure onset also predicts 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.
- 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: "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, mostly from acute
stroke-like episodes or status epilepticus, and about 40% of survivors
needed help with daily life. Epilepsy is typically drug-resistant, and
recurrent stroke-like episodes leave progressive brain atrophy and dementia.
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: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 major contributor to burden, while noting partial treatability.
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: 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.
- 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, whose subunits are the most
dependent on mtDNA-encoded synthesis, is disproportionately affected, 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, so active mitophagy - not only
failed assembly - contributes to the neuronal deficit. This is the
mechanistic reason why one heteroplasmic variant produces 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
- name: Mitochondrial angiopathy and NO deficiency
biological_scale: TISSUE
description: >-
Mitochondrial proliferation in the smooth muscle and endothelial cells of
cerebral small 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 the endothelial-dysfunction link to stroke-like episodes; PARTIAL because the ischemic causal step itself remains contested.
- 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.
- 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 preferentially involves cerebral cortex
with variable subcortical edema, spreads into surrounding cortex over
weeks, and leaves 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.
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.
- name: Stroke-like episodes
biological_scale: ORGANISM
description: >-
Acute neurological deficits with neuroimaging lesions that do not conform to
classic vascular territories, the defining clinical manifestation of MELAS,
arising from mitochondrial angiopathy, NO deficiency, and neuronal energy
failure.
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.
- 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.
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: Lactic acidosis
frequency: VERY_FREQUENT
description: >-
Elevated lactate in blood and cerebrospinal fluid from the shift toward
anaerobic glycolysis.
phenotype_term:
preferred_term: Lactic acidosis
term:
id: HP:0003128
label: Lactic acidosis
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.
- 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: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 among the common
manifestations of MELAS.
- 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: Proximal muscle weakness, exercise intolerance, and ragged-red fibers on muscle biopsy.
phenotype_term:
preferred_term: Myopathy
term:
id: HP:0003198
label: 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.
- 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.
- 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: Progressive sensorineural hearing impairment, common in m.3243A>G carriers.
phenotype_term:
preferred_term: Sensorineural hearing impairment
term:
id: HP:0000407
label: Sensorineural hearing impairment
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 hearing impairment among the broad
manifestations of MELAS.
- category: Endocrine
name: Diabetes mellitus
description: Diabetes mellitus, part of the maternally inherited diabetes and deafness (MIDD) overlap of the m.3243A>G mutation.
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.
- category: Neurologic
name: Migraine-like headaches
description: Recurrent migraine-like headaches, often heralding stroke-like episodes.
phenotype_term:
preferred_term: Migraine
term:
id: HP:0002076
label: Migraine
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 headaches among the common manifestations;
these are typically migraine-like and often herald stroke-like episodes.
- 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.
- 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.
- 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.
- 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.
- category: Cardiac
name: Cardiomyopathy
description: >-
Cardiomyopathy and cardiac conduction defects occur in MELAS, reflecting
energy failure in cardiac tissue.
phenotype_term:
preferred_term: Cardiomyopathy
term:
id: HP:0001638
label: Cardiomyopathy
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and
migraine headache are treated in the standard manner.
explanation: >-
GeneReviews documents cardiomyopathy and cardiac conduction defects as
manifestations of MELAS requiring standard management.
- category: Ophthalmologic
name: Cortical visual impairment
description: Visual impairment, including hemianopia or cortical blindness following occipital stroke-like episodes.
phenotype_term:
preferred_term: Hemianopia
term:
id: HP:0012377
label: Hemianopia
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: >-
the sudden, transient, and recurrent development of stroke-resembling
symptoms (headache, nausea/vomiting, visual disturbance/visual field
abnormalities, seizures, and impaired consciousness: ictus)
explanation: >-
Visual field abnormalities (e.g., hemianopia) commonly accompany
occipital stroke-like episodes in MELAS.
- category: Neurologic
name: Focal-onset seizures
description: >-
Focal seizures are near-universal in MELAS with epilepsy and are the
dominant semiology, though generalized seizures also occur in about a
third. There is no MELAS-specific seizure semiology or EEG signature, so
epilepsy alone never makes the diagnosis; what it does do is mark the
cortical hyperexcitability that the current mechanistic model puts at the
start of a stroke-like episode. Earlier seizure onset predicts
drug-resistant epilepsy and more severe organ involvement.
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.
- category: Neurologic
name: Status epilepticus
description: >-
Status epilepticus is not merely a complication of MELAS epilepsy but one
of its two leading proximate causes of death, alongside the acute
stroke-like episode itself. This is the clinical reason aggressive seizure
control is treated as the priority 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.
- category: Neurologic
name: Dementia and progressive cognitive decline
description: >-
Cognitive decline in MELAS has two components that should not be
conflated: stepwise loss following each stroke-like episode, and a slowly
progressive interictal deterioration in brain function. Together they
produce dementia in survivors of recurrent episodes.
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.
- category: Neurologic
name: Cerebral atrophy
description: >-
Brain atrophy accumulates between as well as during episodes, tracking the
slowly progressive component of the encephalopathy rather than any single
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.
- 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: >-
A pigmentary macular dystrophy distinct from the cortical visual loss above
and easily mistaken for an unrelated retinal disease. It is graded 1-4 from
fine pigment change visible only on autofluorescence, through macular
pigment deposits encircling the disc, to chorioretinal atrophy and finally
foveal involvement with visual-acuity loss. Grade correlates with age and
visual acuity but not with heteroplasmy level or overall systemic disease
severity - one of several places where heteroplasmy fails to predict
organ-level outcome.
frequency: VERY_FREQUENT
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.
- 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: m.3243A>G carriers; overlap phenotype rather than a core MELAS feature
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.
- category: Ophthalmologic
name: Ptosis
description: Eyelid ptosis, part of the ocular myopathy of MELAS, managed by standard means.
phenotype_term:
preferred_term: Ptosis
term:
id: HP:0000508
label: Ptosis
evidence:
- reference: PMID:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
explanation: GeneReviews lists ptosis among the MELAS manifestations requiring standard management.
- category: Renal
name: Nephropathy with proteinuria
description: >-
Renal involvement is under-recognized in MELAS and typically presents as
subnephrotic proteinuria with progressive loss of kidney function. Focal
segmental glomerulosclerosis is the biopsy pattern usually described in
m.3243A>G kidney disease; because it is indistinguishable on histology from
idiopathic FSGS, patients risk being given ineffective immunosuppression
before the mitochondrial cause is recognized.
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:20301411
reference_title: MELAS.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Ptosis, cardiomyopathy, cardiac conduction defects, nephropathy, and migraine headache are treated in the standard manner."
explanation: GeneReviews lists nephropathy among the MELAS manifestations requiring standard management.
- category: Gastrointestinal
name: Intestinal pseudo-obstruction
description: >-
Chronic intestinal pseudo-obstruction presents with abdominal distension,
nausea, vomiting, and pain from failed propulsive activity, mimicking
mechanical obstruction. It is better known in MNGIE but occurs in MELAS,
particularly with m.3243A>G, and can be the presenting problem years before
a neurological diagnosis is made. It is not an incidental comorbidity:
reviews recommend treating it as part of stroke-like-episode management,
since the resulting catabolic and nutritional stress can precipitate
neurological decompensation.
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.
- category: Cardiac
name: Hypertrophic cardiomyopathy
description: >-
Myocardial disease is the commonest form of cardiac involvement in
m.3243A>G carriers - considerably more common than arrhythmia or conduction
disease - and ranges from myocardial thickening and hypertrophic
cardiomyopathy through fibrosis and noncompaction to systolic dysfunction
and heart failure. Asymptomatic carriers usually do not develop it.
phenotype_term:
preferred_term: Hypertrophic cardiomyopathy
term:
id: HP:0001639
label: Hypertrophic cardiomyopathy
evidence:
- 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: Enumerates the myocardial phenotypes reported in 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: Establishes the relative frequency of myocardial versus electrical cardiac involvement.
- category: Cardiac
name: Wolff-Parkinson-White syndrome and conduction defects
description: >-
Pre-excitation and bundle branch block are the conduction abnormalities
described in m.3243A>G carriers, alongside supraventricular and ventricular
arrhythmias and reports of sudden cardiac death. Systematic cardiac
screening of all carriers, symptomatic or not, is recommended.
phenotype_term:
preferred_term: Wolff-Parkinson-White syndrome
term:
id: HP:0001716
label: Wolff-Parkinson-White syndrome
evidence:
- 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: Names the specific conduction abnormalities reported with m.3243A>G.
- 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: Documents the arrhythmia spectrum including sudden cardiac death.
- category: Hematologic
name: Anemia
description: >-
Anemia is common enough in MELAS to act as an independent predictor of
mortality and correlates inversely with disability scores. It is more
plausibly a marker of systemic disease severity than an independent cause
of death, but it is cheap to measure and, unlike heteroplasmy, actually
tracks outcome.
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: "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: Identifies anemia as an independent mortality predictor in a long-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: "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.
- category: Neurologic
name: Hemiparesis and aphasia
description: >-
The acute focal deficits of a stroke-like episode. Because the lesion
respects cortical rather than arterial boundaries and tends to be partly
reversible, the deficit pattern often does not fit a single vascular
syndrome - which is precisely what should prompt the diagnosis rather than
an ischemic-stroke pathway.
phenotype_term:
preferred_term: Hemiparesis
term:
id: HP:0001269
label: Hemiparesis
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; (2) epileptic seizures are often present; (3) lesion distribution is inconsistent with vascular territory"
explanation: Establishes that focal deficits follow lesion site rather than vascular territory.
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: VERY_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 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: VERY_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-versus-MERRF distinction in the enzyme histochemistry of strongly SDH-reactive vessels.
- 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.
- 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.
- 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 head-to-head meta-analysis GDF-15 outperforms FGF-21 on
every diagnostic metric, which makes it the better first-line serum screen
when a mitochondrial disorder is suspected.
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.
- 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.
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.
subtype: MT-TL1 m.3243A>G
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: >-
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.
- name: MT-ND5 and other mitochondrial-gene variants
gene_term:
preferred_term: MT-ND5
term:
id: hgnc:7461
label: MT-ND5
association: >-
A minority of MELAS cases are caused by variants outside MT-TL1, including
the complex I subunit genes MT-ND1, MT-ND5, and MT-ND6. These behave
differently from the tRNA genotype: because they hit complex I structural
subunits directly rather than through a translation defect, they are
enriched in MELAS/Leigh overlap presentations, where m.13513G>A in MT-ND5
is the commonest single variant. Genotype should therefore be read as a
partial predictor of which end of the MELAS-Leigh spectrum a patient sits
on, not merely as a footnote to the m.3243A>G majority.
subtype: MT-ND5 and other genes
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 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.
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).
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).
- 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: >-
The default misdiagnosis, and the one with therapeutic consequences.
Separating them rests on lesion distribution that crosses arterial
territories, posterior predilection, contiguous spread over weeks,
accompanying seizures, elevated rather than restricted diffusion, focal
hyperperfusion rather than hypoperfusion, and a lactate peak on
spectroscopy.
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.
- 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 COX-activity criterion that distinguishes MERRF from MELAS vascular pathology.
- name: Leigh syndrome
description: >-
Bilateral symmetrical basal ganglia, thalamic, and brainstem lesions define
Leigh syndrome, whereas MELAS lesions are cortical and asymmetric.
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 asymmetric 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-syndrome features that separate it clinically from core MELAS.
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. 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. The
likeliest resolution is that these are not rival explanations of one event
but two required components - capillary angiopathy supplying the leaky
substrate on which epileptic activity produces cortical vasogenic edema -
which is how the pathograph is wired here.
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#Nephropathy with 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, and its FSGS biopsy pattern is indistinguishable from the
idiopathic form, so patients are treated with immunosuppression before the
mitochondrial cause is found. 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. Frequencies
for these features cannot be curated from the present literature because
the denominators come from neurology cohorts, and a systematic
multi-organ screening study of unselected carriers has not been done.
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.
References & Deep Research
References
1MELAS.
No top-level findings curated for this source.
Deep Research
1
Falcon
▸
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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(NCT01339494 chunk 1): Fernando Scaglia. Nitric Oxide Production in MELAS Syndrome. Baylor College of Medicine. 2009. ClinicalTrials.gov Identifier: NCT01339494
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(NCT03952234 chunk 1): Fernando Scaglia. L-Citrulline Dose Finding Safety Study in MELAS. Baylor College of Medicine. 2021. ClinicalTrials.gov Identifier: NCT03952234
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(NCT06644534 chunk 1): A Study to Assess TTI-0102 vs Placebo in MELAS Patients. Thiogenesis Therapeutics, Inc.. 2025. ClinicalTrials.gov Identifier: NCT06644534
