AFG2A-Related Encephalopathy

Mendelian MONDO:0014698 Pathograph 21 Show in embeddings browser Developmental and epileptic encephalopathy Mendelian neurodevelopmental disorder Ribosome biogenesis disorder

AFG2A-related encephalopathy is an ultra-rare autosomal recessive neurodevelopmental disorder caused by biallelic variants in AFG2A, the gene formerly and still most widely known as SPATA5. Its cardinal triad is congenital microcephaly, sensorineural hearing loss and epilepsy, on a background of severe to profound intellectual disability with absent speech, motor impairment that combines axial hypotonia with peripheral spasticity, cortical visual impairment and gastrointestinal dysfunction. When epilepsy is present it most often begins as an infantile epileptic spasms syndrome in the first two years and is usually drug resistant, so the disorder is frequently classified as a developmental and epileptic encephalopathy. AFG2A encodes an AAA+ ATPase that, together with AFG2B (SPATA5L1), C1orf109 and CINP, forms the 55LCC complex; the complex drives the last cytoplasmic maturation step of the pre-60S ribosomal subunit and also governs replisome proteostasis. Loss of AFG2A function in neurons produces a mitochondrial fusion-fission imbalance, reduced ATP production and short axons, which is why the clinical picture is repeatedly mistaken for a primary mitochondrial disease.

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Classifications

Harrison's Chapter

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Inheritance

Autosomal recessive HP:0000007

Biallelic (homozygous or, more often, compound heterozygous) AFG2A variants are required. Heterozygous carriers, including the parents of affected children, are unaffected.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:27683084 SUPPORT Human Clinical

"We thus independently confirm that bi-allelic pathogenic variants in SPATA5 cause a syndromic form of intellectual disability, and we delineate its clinical presentation."

Independent confirmation, in a consanguineous family plus an unrelated compound heterozygous case, that the disorder is recessive.

PMID:41933351 SUPPORT Human Clinical

"AFG2A-RE is an ultra-rare, recessive disorder, sometimes presenting as a developmental and epileptic encephalopathy (DEE), characterised by the triad of epilepsy, congenital microcephaly, and deafness, and typically associated with intellectual disability, spasticity, and movement disorders."

The largest published cohort restates recessive inheritance.

Discussions and Knowledge Gaps

Can any constitutive mouse Afg2a model represent AFG2A-related encephalopathy, given that every reported human genotype retains partial ATPase function?

HUMAN MODEL MISMATCH OPEN afg2a_mouse_null_model_mismatch

Attached to

pathophysiology#Biallelic AFG2A Loss of Function

No published human genotype combines two unambiguous null alleles: more than half of the 42 reported disease variants are missense and the remainder are always found in trans with a missense or in-frame allele. The disease is therefore hypomorphic. The IMPC constitutive knockout of the mouse orthologue is reported as embryonic lethal before organogenesis, which if correct means a complete null cannot model the human disorder at all and that a faithful model would have to be a knock-in of a patient hypomorphic allele or a conditional neural hypomorph. No such model has been published. The mouse phenotype is recorded here from an IMPC database entry surfaced by the deep-research run and is deliberately NOT cited as an evidence item, because it has no PMID and this entry does not cite un-fetchable sources.

Verification status: the missense-majority claim is cited in the entry from PMID:41933351. The mouse embryonic lethality claim is unverified against any cached reference and is recorded as an open question, not as an assertion.

Is the mitochondrial dysfunction in AFG2A deficiency a direct consequence of a mitochondrial pool of the protein, or is it secondary to reduced translational capacity?

CONTROVERSY OPEN afg2a_mitochondrial_localisation_tension

Attached to

pathophysiology#Neuronal Mitochondrial Fusion-Fission Imbalance

The protein carries a putative mitochondrial matrix-targeting sequence and was originally described as a mitochondrial morphogenesis factor in spermatogenesis, and patient cells reproducibly show bioenergetic deficits. Against a direct mitochondrial role: the overexpressed protein is dominantly cytosolic in cortical neurons and does not co-localise with mitochondrial markers (PMID:29343804), no patient shows a consistent mitochondrial biomarker abnormality (PMID:41933351), respiratory chain findings are inconsistent between patients, and the established molecular function of the 55LCC complex is cytoplasmic ribosome maturation. The entry models the mitochondrial arm as downstream and provisional, but the question is genuinely open.

Show evidence (2 references)

PMID:29343804 SUPPORT In Vitro

"To our surprise the localization of overexpressed SPATA5 in cultured primary cortical neurons was dominantly cytosolic and clearly not co-localizing with the mitochondrial marker"

The observation that motivates the question.

PMID:35354024 SUPPORT In Vitro

"We provide evidence that these factors, together with CINP and SPATA5L1, control a late step of human pre-60S maturation in the cytoplasm."

The established molecular function is cytoplasmic, which is the main argument against a primary mitochondrial role.

Why do siblings carrying the identical biallelic AFG2A genotype range from isolated sensorineural hearing loss to full developmental and epileptic encephalopathy?

OPEN QUESTION OPEN afg2a_intrafamilial_variability

Attached to

phenotypes#Sensorineural hearing impairment

In the family reported in PMID:28293831 the proband had the typical encephalopathy while her younger sister's only manifestation was isolated sensorineural hearing loss, on the same two variants. Comparable variability in epilepsy status occurred within the large consanguineous family of PMID:27683084. No modifier gene has been identified. Plausible but untested candidates are variation in the other 55LCC subunits or in general ribosome biogenesis capacity. Until this is resolved, genotype cannot be used to counsel on severity.

Show evidence (1 reference)

PMID:28293831 SUPPORT Human Clinical

"The proband had a similar clinical picture to the previous descriptions of EHLMRS. In the sister, the only manifestation was an isolated sensorineural hearing loss."

Documents the two extremes of expressivity within a single sibship sharing the same two variants.

What is the natural history, life expectancy and quality-of-life burden of AFG2A-related encephalopathy?

KNOWLEDGE GAP OPEN afg2a_natural_history_gap

No prospective natural history study, survival curve, population prevalence estimate, carrier frequency or validated quality-of-life measurement exists. All fifty-one pooled individuals come from retrospective case reports and series, three of whom had died, at ages 3, 4.9 and 13.4 years, while two individuals from the attenuated consanguineous family were alive at 39 and 41 years. The 2026 systematic review states directly that prospective natural history studies across multiple reference centres are needed. This entry therefore carries no survival or quality-of-life claims.

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Pathophysiology

Biallelic AFG2A Loss of Function

Biallelic pathogenic variants in AFG2A (formerly SPATA5) reduce the amount or the activity of an 892-amino-acid AAA+ ATPase. Most reported alleles are missense or small in-frame changes rather than complete nulls, and no individual carrying two unequivocal null alleles has been reported, which is consistent with hypomorphic rather than complete loss of function being compatible with life. The protein carries two conserved ATPase modules.

AFG2A hgnc:18119

Cytosol GO:0005829

Downstream

55LCC ATPase Complex Dysfunction AFG2A is the catalytic core of the 55LCC complex, so reduced AFG2A ATPase activity is directly a deficiency of the complex.

Neuronal Mitochondrial Fusion-Fission Imbalance Knockdown of the gene in rat cortical neurons shifts the mitochondrial fusion-fission balance, but the molecular steps between the ATPase defect and the mitochondrial phenotype have not been identified.

Skeletal Muscle Mitochondrial Pathology Muscle biopsy in a genotyped patient shows a mitochondrial histochemical pattern and a dysregulated mitochondrial proteome.

Show evidence (2 references)

PMID:26299366 SUPPORT Human Clinical

"SPATA5 encodes a ubiquitously expressed member of the ATPase associated with diverse activities (AAA) protein family and is involved in mitochondrial morphogenesis during early spermatogenesis."

Establishes the gene product as a ubiquitously expressed AAA ATPase.

PMID:41933351 SUPPORT Human Clinical

"Most of the variants were missense (58.82%), with others being frameshift (14.71%), nonsense (9.8%), deletion (6.68%), splice site/splice donor (6.68%), non-frameshift (1.96%) and start loss (0.98%)."

Shows that the majority of disease alleles are missense, supporting a hypomorphic rather than a complete-null mechanism.

55LCC ATPase Complex Dysfunction

AFG2A does not act alone. It assembles with its paralogue AFG2B (SPATA5L1) and the heterodimeric partners C1orf109 and CINP into a 4:2:2:2 assembly named 55LCC, built from an N-terminal ring of C1orf109, CINP and the N-terminal domains of AFG2A and AFG2B sitting above two hexameric AAA+ ATPase rings. Reduced AFG2A activity therefore compromises a shared machine rather than a single enzyme, which is the structural reason AFG2A and AFG2B disease phenotypes overlap.

55LCC complex

Downstream

Impaired Cytoplasmic Pre-60S Ribosomal Maturation The complex performs the terminal cytoplasmic maturation step on the pre-60S particle.

Replisome Proteostasis Failure The same complex extracts and licenses degradation of replisome components at damaged replication forks.

Show evidence (2 references)

PMID:40268917 SUPPORT In Vitro

"Here we reveal that SPATA5 forms a 4:2:2:2 complex with SPATA5L1, C1orf109, and CINP."

Defines the stoichiometry and composition of the complex by cryo-EM.

PMID:38554706 SUPPORT In Vitro

"Here, we identify replisome factor interactions with a protein complex composed of AAA+ ATPases SPATA5-SPATA5L1 together with heterodimeric partners C1orf109-CINP (55LCC)."

Names the complex and its four components.

Impaired Cytoplasmic Pre-60S Ribosomal Maturation

In yeast the AFG2A orthologue Drg1 strips the assembly factor Rlp24, a placeholder for the ribosomal protein Rpl24, off pre-60S particles as soon as they reach the cytoplasm; the human equivalent step is performed by AFG2A within the 55LCC complex, with recognition of the pre-60S particle mediated by the human-specific subunit CINP. When AFG2A activity falls, large ribosomal subunits stall at this last maturation checkpoint.

Ribosomal large subunit biogenesis GO:0042273 Ribosome assembly GO:0042255

Preribosome, large subunit precursor GO:0030687

Downstream

Reduced Global Protein Synthesis Fewer mature 60S subunits reach the translating pool, so bulk translation capacity falls.

Show evidence (4 references)

PMID:40268917 SUPPORT In Vitro

"In yeast, AAA+ protein Drg1 releases an assembly factor Rlp24, a placeholder for Rpl24, from pre-60S particles just exported to cytosol."

Defines the conserved reaction that the human AFG2A complex is the orthologue of.

PMID:35354024 SUPPORT In Vitro

"We provide evidence that these factors, together with CINP and SPATA5L1, control a late step of human pre-60S maturation in the cytoplasm."

A genome-wide loss-of-function screen with differential ribosome labelling places SPATA5 at a late cytoplasmic pre-60S step in human cells.

PMID:31703473 SUPPORT In Vitro

"Rix7, Rea1, and Drg1, which are well conserved across eukaryotes, are involved in different maturation steps of pre-60S ribosomal particles."

Establishes the evolutionary conservation of the Drg1 step that AFG2A performs in human cells.

+ 1 more reference

Reduced Global Protein Synthesis

Depletion of AFG2A or of its partner C1orf109 lowers bulk protein synthesis in human cells. Neurons are among the cell types least able to tolerate a reduced translational capacity during the period of rapid dendritic and axonal growth, which is the proposed link between a housekeeping ribosome assembly defect and a brain-restricted clinical phenotype.

Cytoplasmic translation GO:0002181

Downstream

Neuroepithelial Vulnerability During Differentiation A fall in ribosome availability is only pathogenic where translational reserve is already low, which is what makes the effect brain-specific.

Show evidence (2 references)

PMID:35354024 SUPPORT In Vitro

"Loss of either C1orf109 or SPATA5 impairs global protein synthesis."

Direct demonstration of the translational consequence of SPATA5 loss.

PMID:35354024 SUPPORT In Vitro

"These results link ribosome assembly with neurodevelopmental disorders associated with recessive SPATA5 mutations."

The authors themselves connect the ribosome assembly defect to the recessive neurodevelopmental disorder.

Neuroepithelial Vulnerability During Differentiation

This node answers the central puzzle of the disorder: why a defect in a ubiquitous housekeeping machine produces an almost purely neurological phenotype. Human cerebral organoid work on the sister 55LCC subunit AIRIM/C1orf109 showed that ribosome levels fall physiologically during neuroepithelial differentiation, creating a developmental window in which any further reduction in 60S output crosses a threshold and selectively impairs translation of specific transcripts, disrupting both survival and cell fate commitment. The window is embryonic, which is why no postnatal intervention reverses the microcephaly. Enhancing mTOR activity suppressed the organoid phenotype, making mTOR the first rationally derived candidate target for this disease family.

Differentiating neuroepithelium CL:0011020

Cytoplasmic translation GO:0002181

Downstream

Impaired Cortical Neuron Growth Attrition and mis-specification of differentiating neuroepithelium is the proposed route to reduced brain growth, but the intervening steps have not been mapped in AFG2A deficiency itself.

Show evidence (2 references)

PMID:40760247 PARTIAL In Vitro

"We find that ribosome levels decrease during neuroepithelial differentiation, making differentiating cells particularly vulnerable to perturbations in ribosome biogenesis during this time."

Supplies the tissue-specificity mechanism, but in organoids carrying AIRIM/C1orf109 rather than AFG2A variants, so support is partial.

PMID:40760247 PARTIAL In Vitro

"Enhancing mTOR activity suppresses the growth and developmental defects associated with AIRIM/C1orf109 variants."

Identifies mTOR enhancement as a candidate rescue axis for 55LCC-complex ribosome biogenesis defects; untested in AFG2A.

Replisome Proteostasis Failure

The 55LCC complex has a second, ribosome-independent job: its ATPase activity is stimulated by replication fork DNA and it couples cysteine protease-dependent cleavage of replisome substrates to replication fork damage. Losing that activity produces ubiquitin-independent proteotoxicity, replication stress and chromosome instability. Whether this branch contributes to the human neurodevelopmental phenotype is proposed by the authors but not established in patient material, so the node is provisional.

DNA replication GO:0006260

Replisome GO:0030894

Show evidence (2 references)

PMID:38554706 SUPPORT In Vitro

"Deficiency in the 55LCC complex elicited ubiquitin-independent proteotoxicity, replication stress, and severe chromosome instability."

Establishes the cellular consequence of losing complex activity at the replication fork.

PMID:38554706 PARTIAL In Vitro

"These findings define 55LCC-mediated proteostasis as critical for replication fork progression and genome stability and provide a rationale for pathogenic variants seen in associated human neurodevelopmental disorders."

The link to the human disorder is offered as a rationale by the authors and was not tested in patient cells, so this is recorded as partial support.

Neuronal Mitochondrial Fusion-Fission Imbalance

Silencing the gene in rat primary cortical neurons shortens mitochondria by about 20% and halves the fusion-to-fission ratio. Patient-derived fibroblasts likewise show altered mitochondrial morphology and dynamics. This occurs even though the protein itself is dominantly cytosolic and does not co-localise with mitochondrial markers, so the effect is indirect; the intervening steps are unknown.

Cerebral cortex neuron CL:0010012

Mitochondrial fusion GO:0008053 Mitochondrial fission GO:0000266

Mitochondrion GO:0005739

Downstream

Neuronal ATP Deficit The fusion-fission imbalance is accompanied by a measured fall in the axonal ATP/ADP ratio in the same experiments.

Show evidence (3 references)

PMID:29343804 SUPPORT Model Organism

"SPATA5-deficient neurons had a significant imbalance in the mitochondrial fusion-fission rate, impaired energy production and short axons."

shRNA knockdown in rat primary cortical neurons demonstrates the mitochondrial dynamics defect.

PMID:29343804 PARTIAL In Vitro

"To our surprise the localization of overexpressed SPATA5 in cultured primary cortical neurons was dominantly cytosolic and clearly not co-localizing with the mitochondrial marker"

Shows the protein is not itself mitochondrial, which is why the mitochondrial phenotype is modelled as an indirect consequence.

PMID:40712368 SUPPORT In Vitro

"In vitro studies demonstrated that AFG2A-deficient fibroblasts exhibited altered mitochondrial morphology and dynamics, as well as reduced ATP production and ROS levels."

Replicates the mitochondrial dynamics abnormality in cells taken from genotyped patients rather than in a knockdown model.

Neuronal ATP Deficit

The axonal ATP/ADP ratio falls by roughly 12% in knockdown neurons and is restored by re-expression of the wild-type human protein, establishing specificity. The same energy failure is detectable in patient blood cells, where oxygen consumption rates in platelets and peripheral blood mononuclear cells are impaired and monocyte mitochondrial mass is reduced.

Neuron CL:0000540

ATP biosynthetic process GO:0006754

Downstream

Impaired Cortical Neuron Growth Axon extension is one of the most energy-demanding processes in a developing neuron.

Show evidence (2 references)

PMID:36849973 SUPPORT Human Clinical

"Oxygen consumption rates in platelets and PBMCs were impaired in the patient when compared to a healthy control."

Demonstrates impaired oxidative metabolism in accessible cells from a genotyped patient.

PMID:36849973 SUPPORT Human Clinical

"Also, a decrease in mitochondrial mass was observed in the patient monocytes with respect to the control."

Reduced mitochondrial mass accompanies the respiratory deficit.

Impaired Cortical Neuron Growth

Developing cortical neurons deficient in the protein grow markedly shorter axons, and the defect is rescued by re-expressing the wild-type human protein. This is the most proximate cellular correlate available for the congenital microcephaly, hypomyelination and thin corpus callosum seen in patients, although no experiment has yet connected the neuronal growth defect to the human imaging findings directly.

Cerebral cortex neuron CL:0010012

Axon extension GO:0048675

Downstream

Congenital Microcephaly Reduced growth of individual cortical neurons is the presumed cellular cause of the whole-organism reduction in brain and head growth, but no experiment has connected the two directly in AFG2A deficiency.

Show evidence (1 reference)

PMID:29343804 SUPPORT Model Organism

"In conclusion, SPATA5 protein has an important role in mitochondrial dynamics and axonal growth."

The authors' own conclusion from the rescue experiments on axonal length in rat cortical neurons.

Congenital Microcephaly

The organism-level endpoint of the pathway. Reduced brain growth is present at birth in the large majority of affected children and, with sensorineural deafness and epilepsy, forms the diagnostic triad. It is the one feature that no postnatal intervention can reverse, because the vulnerable window is the embryonic period of neuroepithelial differentiation.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"characterised by the triad of epilepsy, congenital microcephaly, and deafness"

Establishes congenital microcephaly as a cardinal organism-level manifestation.

PMID:26299366 SUPPORT Human Clinical

"Mutations in SPATA5 might affect brain development and function, resulting in microcephaly, developmental delay, and intellectual disability."

The founding paper's own causal statement linking the gene defect to impaired brain development and microcephaly.

Skeletal Muscle Mitochondrial Pathology

Muscle is affected as well as brain. A quadriceps biopsy from an 8-year-old girl with a typical presentation and two compound heterozygous variants showed a histochemical pattern suggesting mitochondrial pathology, and proteomic profiling found 82 dysregulated proteins of which 15 are mitochondrial. This provides the tissue-level counterpart of the mitochondrial dysfunction seen in neurons and fibroblasts, and it is one reason the disorder is investigated as a suspected mitochondrial myopathy.

Skeletal muscle fiber CL:0008002

Mitochondrion GO:0005739

Show evidence (2 references)

PMID:34360601 SUPPORT Human Clinical

"Proteomic profiling of a quadriceps biopsy showed the dysregulation of 82 proteins, out of which 15 were localized in the mitochondrion, while 19 were associated with diseases presenting with phenotypical overlap to EHLMRS."

Quantifies the muscle proteomic abnormality in a genotyped patient.

PMID:34360601 SUPPORT Human Clinical

"Histological staining of our patient's muscle biopsy hints towards mitochondrial pathology, while the identification of dysregulated proteins attested to the vulnerability of the cell beyond the mitochondria."

Histochemistry supports mitochondrial involvement in muscle while stopping short of a pure mitochondrial myopathy.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Digestive 1

Feeding difficulties FREQUENT Feeding difficulties HP:0011968

Gastrointestinal symptoms 78.95% in the 51-individual pooled cohort, of which dysphagia 30%, gastro-oesophageal reflux 20% and constipation 16.67%; gastrointestinal problems 73% in the earlier 30-patient summary.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"A high proportion of individuals (78.95%) experienced gastrointestinal symptoms. Dysphagia was the most common symptom (30%), followed by gastroesophageal reflux (20%), and constipation (16.67%)"

Gives the gastrointestinal symptom profile and its frequency.

PMID:27683084 SUPPORT Human Clinical

"Further symptoms were hearing loss, vision impairment, gastrointestinal disturbances, and slow and asymmetric waves in the EEG."

Independent family with gastrointestinal disturbance.

Ear 1

Sensorineural hearing impairment VERY_FREQUENT Sensorineural hearing impairment HP:0000407

93.62% in the 51-individual pooled cohort; 77% specifically sensorineural in the earlier 30-patient summary.

Show evidence (2 references)

PMID:26299366 SUPPORT Human Clinical

"Using whole-exome sequencing, we have identified in ten families 14 individuals with microcephaly, developmental delay, intellectual disability, hypotonia, spasticity, seizures, sensorineural hearing loss, cortical visual impairment, and rare autosomal-recessive predicted pathogenic variants in..."

Sensorineural hearing loss is part of the founding phenotype description in ten families.

PMID:28293831 SUPPORT Human Clinical

"In the sister, the only manifestation was an isolated sensorineural hearing loss."

Demonstrates that the hearing loss can occur in isolation, defining the mild end of the spectrum.

Head and Neck 2

Microcephaly VERY_FREQUENT Microcephaly HP:0000252

85.71% in the 51-individual pooled cohort; 90% in the earlier 30-patient summary.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"The vast majority of the individuals presented with microcephaly (85.71%)."

Pooled frequency across 51 individuals.

PMID:29343804 SUPPORT Human Clinical

"Other prominent features are microcephaly (90%), gastrointestinal problems (73%), abnormal brain MRI (67%, predominantly brain atrophy and delayed myelination), visual impairment (most frequently cortical visual impairment, 41%) and no or reduced eye contact (48%)."

Independent pooled estimate from the 30-patient literature summary.

Depressed nasal bridge Depressed nasal bridge HP:0005280

Show evidence (1 reference)

PMID:27246907 SUPPORT Human Clinical

"Common facies were a depressed nasal bridge/ridge, broad eyebrows, and retrognathia."

Describes the shared facial gestalt in three genotyped children.

Musculoskeletal 2

Hypotonia FREQUENT Hypotonia HP:0001252

71.74% in the 51-individual pooled cohort.

Show evidence (1 reference)

PMID:41933351 SUPPORT Human Clinical

"The most common motor symptoms were hypotonia (71.74%) and spasticity (60.87%)."

Gives the pooled frequency of hypotonia.

Spasticity FREQUENT Spasticity HP:0001257

60.87% in the 51-individual pooled cohort. Motor impairment overall was 97.83% of those with data, and 59.09% were GMFCS level V.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"The most common motor symptoms were hypotonia (71.74%) and spasticity (60.87%)."

Gives the pooled frequency of spasticity.

PMID:26299366 SUPPORT Human Clinical

Spasticity co-occurring with hypotonia in the founding cohort.

Nervous System 7

Intellectual disability VERY_FREQUENT Intellectual disability HP:0001249

97.92% in the 51-individual pooled cohort; severity was moderate-to-severe in 25% and severe-to-profound in 75% of the 32 cases with graded data.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"The most frequently described clinical features included intellectual disability (97.92%), hearing loss (93.62%), microcephaly (85.71%), visual impairment (79.49%), hypotonia (71.74%), spasticity (60.87%), and movement disorders (36.96%)."

Gives the pooled frequency from the largest cohort.

PMID:27683084 SUPPORT Human Clinical

"We examined an extended, consanguineous family with seven individuals with severe intellectual disability and microcephaly."

Independent family documenting severe intellectual disability.

Absent speech VERY_FREQUENT Absent speech HP:0001344

Show evidence (2 references)

PMID:29343804 SUPPORT Human Clinical

"Symptoms start in early infancy with all of the patients developing global developmental delay with severely limited speech or no words, hearing impairment (most frequently sensorineural hearing loss, 77%), and a pathological EEG with symptomatic epilepsy being present in 73% of patients."

All patients in the pooled 30-case series had severely limited speech or no words.

PMID:41933351 SUPPORT Human Clinical

"Absence of speech was reported in all individuals with ID."

Confirms absent speech in the whole intellectually disabled subgroup.

Global developmental delay VERY_FREQUENT Global developmental delay HP:0001263

Neurodevelopmental delay 84.31% in the 51-individual pooled cohort; global developmental delay in all patients in the earlier 30-patient summary.

Show evidence (1 reference)

PMID:29343804 SUPPORT Human Clinical

All pooled patients had global developmental delay from early infancy.

Seizure FREQUENT Seizure HP:0001250

38 of 51 individuals (74.5%) in the pooled cohort; 73% in the earlier 30-patient summary. Drug resistance was reported in 82.35% of the 17 individuals with anti-seizure medication data, but that denominator is small and conditioned on having epilepsy, so no separate frequency band is asserted for drug resistance.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"Epilepsy was present in 74.71% of cases, with seizures of generalized onset being the most common (70.83%), and infantile epileptic spasms syndrome (IESS) was the predominant epilepsy syndrome at onset (66.67%)."

Gives the pooled epilepsy frequency and the seizure-type breakdown.

PMID:41933351 SUPPORT Human Clinical

"Epilepsy was often drug-resistant (82.35%)."

Documents the drug-resistant character of the epilepsy.

Dystonia OCCASIONAL Dystonia HP:0001332

Dystonia 21.74% in the 51-individual pooled cohort; movement disorders of any kind 36.96%.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"movement disorders were present in 36.96% of the individuals, with dystonia being the most prevalent (21.74%), followed by dyskinesia (6.52%), ataxia (6.52%), chorea (4.35%), and athetosis (2.17%)."

Gives the movement-disorder breakdown with dystonia predominant. The quote starts mid-sentence because the preceding word, "Non-paroxysmal", is split across a line break by a hyphen in the cached PDF text.

PMID:27683084 SUPPORT Human Clinical

"in a further individual with global developmental delay, infantile spasms, profound dystonia, and sensorineural hearing loss."

Individual case with profound dystonia and a confirmed genotype.

Cerebral hypomyelination FREQUENT Cerebral hypomyelination HP:0006808

Hypomyelination 39.02% and abnormal MRI overall 68.29% in the 51-individual pooled cohort; abnormal brain MRI 67% in the earlier 30-patient summary. Brain MRI was normal in 31.71% of cases.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"Brain MRI abnormalities were frequently observed (68.29%), including hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum (29.27%)."

Gives the imaging frequencies from the largest cohort.

PMID:27246907 SUPPORT Human Clinical

"Magnetic resonance imaging revealed hypomyelination, thin corpus callosum, and progressive cerebral atrophy."

Independent imaging description in three genotyped children.

Cerebral atrophy FREQUENT Cerebral atrophy HP:0002059

Global brain atrophy 34.15% in the 51-individual pooled cohort.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"Brain MRI abnormalities were frequently observed (68.29%), including hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum (29.27%)."

Gives the pooled frequency of brain atrophy.

PMID:27246907 SUPPORT Human Clinical

"Magnetic resonance imaging revealed hypomyelination, thin corpus callosum, and progressive cerebral atrophy."

Documents that the atrophy is progressive.

Other 7

Infantile spasms Infantile spasms HP:0012469

Frequency band deliberately omitted. Infantile epileptic spasms syndrome was reported in 16 of the 24 individuals with detailed epilepsy data (66.67%), which is 16 of the whole 51-individual cohort (31%). The band would be FREQUENT on one denominator and would sit at the top of FREQUENT on the other, so the raw fractions are recorded here instead of an asserted band.

Show evidence (3 references)

PMID:40712368 SUPPORT Human Clinical

"In all but one case, the initial epilepsy presentation was infantile epileptic spasms syndrome (IESS), with a mean age at onset of 13.6 months."

Infantile epileptic spasms syndrome was the presenting epilepsy in four of five patients.

PMID:27246907 SUPPORT Human Clinical

"Epileptic spasms or tonic seizures emerged at 6-12 months of age."

Independent series giving the age window for spasm onset.

PMID:33063670 SUPPORT Human Clinical

"The epileptic clinical features were characterized by infantile spasms associated with seizures with a complex ocular movement; a predominant involvement of the posterior cerebral area and cortical visual impairment were also noticed."

Single-case electroclinical description of the spasm phenotype.

Multifocal epileptiform discharges Multifocal epileptiform discharges HP:0010841

Show evidence (2 references)

PMID:27246907 SUPPORT Human Clinical

"Interictal electroencephalography showed multifocal spikes and bursts of asynchronous diffuse spike-wave complexes."

Describes the interictal EEG pattern in three genotyped children.

PMID:27683084 PARTIAL Human Clinical

"Further symptoms were hearing loss, vision impairment, gastrointestinal disturbances, and slow and asymmetric waves in the EEG."

Reports an abnormal but non-specific EEG in a large consanguineous family, supporting EEG abnormality without confirming the multifocal pattern.

Cerebral visual impairment FREQUENT Cerebral visual impairment HP:0100704

Visual impairment 79.49% overall in the 51-individual pooled cohort, of which cortical blindness 9.68%, refractive abnormality 9.68% and strabismus 9.68%; cortical visual impairment specifically 41% in the earlier 30-patient summary.

Show evidence (2 references)

PMID:29343804 SUPPORT Human Clinical

Identifies cortical visual impairment as the dominant visual phenotype.

PMID:26299366 SUPPORT Human Clinical

Cortical visual impairment is part of the founding phenotype description.

Inability to walk VERY_FREQUENT Inability to walk HP:0002540

Denominator, stated explicitly because it is not the pooled cohort. The GMFCS percentages do not run over the 51 pooled individuals; they resolve arithmetically to n=22, since 59.09% is 13/22, 27.27% is 6/22, 9.09% is 2/22 and 4.55% is 1/22, which sum to 22 individuals and to 100%. The deep research artifact records the GMFCS subgroup as n=22 explicitly, and the same paper reports motor impairment over a different subgroup again (97.83%, i.e. 45/46), so denominators vary from section to section. The cached paper's own prose conflicts with its own arithmetic. It reads "All individuals were assessed using the Gross Motor Function Classification System (GMFCS)", which taken literally would put the denominator at 51. The arithmetic is preferred here over the prose. The band is chosen on the n=22 reading: 19 of the 22 individuals actually graded (86.36%) were at GMFCS level IV or V, both of which denote non-ambulatory status requiring physical assistance, and 86.36% is above 80% and so maps to VERY_FREQUENT. On the alternative reading, in which the same 19 individuals are taken over the full pooled cohort, 19/51 is 37% and the band would be FREQUENT. The n=22 reading is used because individuals who were not graded are unknown rather than known to be ambulatory, which is the usual convention for frequency denominators; a reader who instead treats the paper's "All individuals" wording as authoritative should read this band as FREQUENT. Note that the entry deliberately omits three other frequency bands (for example infantile epileptic spasms syndrome, 16/24 with detailed epilepsy data but 16/51 of the cohort) where the denominator is unknown, is very small, or is conditioned in a way that leaves no principled choice between readings. Here the band is retained rather than dropped because the subgroup denominator is recoverable exactly from the published percentages and both readings are recorded. The 9.09% at level III walk with a handheld mobility device and the 4.55% at level II are ambulatory with limitations.

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"All individuals were assessed using the Gross Motor Function... System (GMFCS): 59.09% were classified as level V, 27.27% as level IV, 9.09% as level III"

Gives the GMFCS distribution from which the non-ambulatory fraction is derived. The elided word is "Classification", split across a line break by a hyphen in the cached PDF text.

PMID:41933351 SUPPORT Human Clinical

"ment was present in almost all individuals with available data (97.83%)."

Records that motor impairment of some degree is near-universal. The quote starts mid-word because "Motor impairment" is split across a line break by a hyphen in the cached PDF text.

Thin corpus callosum OCCASIONAL Thin corpus callosum HP:0033725

29.27% in the 51-individual pooled cohort.

Show evidence (1 reference)

PMID:41933351 SUPPORT Human Clinical

"Brain MRI abnormalities were frequently observed (68.29%), including hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum (29.27%)."

Gives the pooled frequency of thin corpus callosum.

Retrognathia Retrognathia HP:0000278

Show evidence (1 reference)

PMID:27246907 SUPPORT Human Clinical

"Common facies were a depressed nasal bridge/ridge, broad eyebrows, and retrognathia."

Retrognathia in the described facial gestalt.

Increased circulating lactate concentration Increased circulating lactate concentration HP:0002151

Frequency band deliberately omitted. Two individuals (Patient IDs 43 and 45) had a persistent mild lactate elevation of 1.9 to 3.9 mmol/l, but the denominator is not the full 51-individual cohort: the phrase used is "two individuals in our cohort", and the discussion identifies them as cases 3 and 5 of the authors' own five-patient ketogenic-diet series, so systematic metabolic data are not available for the pooled literature cases. Against a denominator of 51 the band would be VERY_RARE and against a denominator of 5 it would be VERY_FREQUENT, so no band is asserted.

Show evidence (1 reference)

PMID:41933351 SUPPORT Human Clinical

"Two individuals in our cohort (Patient ID 43, 45)... a persistent mild elevation of lactate (1.9-3.9 mmol/l) without other abnormalities in mitochondrial... including acid-base balance, creatine kinase... organic acids, amino acids, carnitines, oxidative stress markers, circulating cytokines, or..."

Quantifies the lactate finding and, importantly, records the absence of other mitochondrial biomarker abnormalities.

🧬

Genetic Associations

AFG2A

Gene: AFG2A hgnc:18119 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal recessive

Show evidence (2 references)

PMID:26299366 SUPPORT Human Clinical

The founding gene-disease association across ten families.

PMID:41933351 SUPPORT Human Clinical

"Regarding pathogenicity, variants were classified into pathogenic (72.55%), likely pathogenic (21.57%) and variant of uncertain significance (5.88%)."

Summarises the pathogenicity distribution of the 42 reported disease alleles.

💊

Medical Actions

Ketogenic diet

Category: Therapeutic Action: Ketogenic diet Ontology label: Ketogenic Diet NCIT:C173168

The ketogenic diet is the only intervention with disease-specific evidence. In a series of five genotyped patients, four received the diet for drug-resistant epilepsy with seizure reduction rates of 0%, 30%, 70% and 100%; the patient who became seizure free is maintained on ketogenic diet monotherapy. Non-seizure benefits (social interaction, attention, motor function) were reported in three. Fibroblasts from these patients cultured in a ketogenic-diet-mimicking medium showed reversal of the mitochondrial morphology, dynamics and ATP abnormalities, giving a plausible mechanistic rationale. The evidence is a small uncontrolled series and is recorded as partial.

Mechanism Target:

RESTORES Neuronal Mitochondrial Fusion-Fission Imbalance — Fibroblasts from these same genotyped patients, cultured in a ketogenic-diet-mimicking medium, recovered the altered mitochondrial morphology and dynamics and the reduced ATP production. The diet is therefore hypothesised to act on this node rather than on a conventional anti-seizure target; the link is between a clinical response and an ex vivo readout in the same patients, not a demonstrated in vivo mechanism.

Show evidence (1 reference)

PMID:40712368 PARTIAL In Vitro

"These abnormalities were significantly reversed when the fibroblasts were cultured in KD-MM."

Direct evidence that the ketogenic-diet condition reverses the mitochondrial abnormality modelled by this node, in cells from treated patients.

Target Phenotypes: Seizure HP:0001250 Infantile spasms HP:0012469

Show evidence (4 references)

PMID:40712368 PARTIAL Human Clinical

"Four patients received KD treatment for DRE, with seizure reduction rates of 0 %, 30 %, 70 % and 100 %, respectively."

The primary clinical outcome data, from an uncontrolled series of four treated patients.

PMID:40712368 SUPPORT In Vitro

"These abnormalities were significantly reversed when the fibroblasts were cultured in KD-MM."

Patient fibroblasts in a ketogenic-diet-mimicking medium recover their mitochondrial phenotype, supplying the mechanistic rationale.

PMID:41933351 PARTIAL Human Clinical

"The KD showed... efficacy in selected cases, particularly when initiated early."

The systematic review's assessment, which stops short of recommending the diet as standard care. The elided word is "partial", split across a line break by a hyphen in the cached PDF text.

+ 1 more reference

Anti-seizure medication polytherapy

Category: Therapeutic Action: Pharmacotherapy NCIT:C15986

Most individuals with epilepsy require more than one anti-seizure medication and remain refractory. No agent has shown disease-specific superiority; the reported regimens span valproate, levetiracetam, lamotrigine, vigabatrin, ACTH, topiramate, zonisamide, clobazam, phenobarbital, rufinamide, cannabidiol and others. Only four of sixteen individuals with follow-up data achieved seizure freedom. Notably, the standard first-line treatments for infantile epileptic spasms syndrome do not work here.

Target Phenotypes: Seizure HP:0001250

Show evidence (2 references)

PMID:41933351 SUPPORT Human Clinical

"Epilepsy was often drug-resistant (82.35%)."

Establishes that most treated epilepsy is drug resistant.

PMID:41933351 SUPPORT Human Clinical

"As we recently reported, individuals with IESS do not achieve seizure control with usual first-line treatment (neither corticosteroids nor vigabatrin)."

Specifically records the failure of corticosteroids and vigabatrin, which is directly actionable for clinicians.

Early hearing habilitation

Category: Therapeutic Action: hearing habilitation Ontology label: Rehabilitation NCIT:C15315

Sensorineural deafness is congenital and detectable on newborn or neonatal brainstem audiometry, so amplification or implantation can be started in the first months. One genotyped child received a hearing device before the age of two months after postnatal brainstem audiometry showed sensorineural deafness. No systematic outcome data for cochlear implantation in this disorder exist, and profound intellectual disability with cerebral visual impairment complicates candidacy assessment, so this is curated as supportive habilitation rather than as an intervention with demonstrated efficacy in this genotype.

Target Phenotypes: Sensorineural hearing impairment HP:0000407

Show evidence (1 reference)

PMID:34360601 PARTIAL Human Clinical

"Postnatal brainstem audiometry showed sensorineural deafness, for which she received a hearing device before the age of two months."

Single genotyped patient documenting that hearing habilitation is feasible within the first two months of life; no outcome is reported, hence PARTIAL.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from AFG2A-Related Encephalopathy:

AFG2B-related neurodevelopmental disorder Not Yet Curated MONDO:0859206

Overlapping Features Caused by biallelic variants in AFG2B, the gene formerly called SPATA5L1 and therefore one character away from this disorder's own former gene symbol. The two proteins are partners in the same 55LCC ATPase complex, so the disorders overlap for a real mechanistic reason and are routinely discussed together. The discriminators are quantitative and developmental rather than absolute: in AFG2B disease sensorineural hearing loss is present in all affected individuals but only about half have any neurodevelopmental involvement at all, the neurodevelopmental phenotype is described as non-progressive and mixed with spastic-dystonic cerebral palsy prominent, and microcephaly is not a defining feature. In AFG2A disease microcephaly is present in around 86%, intellectual disability in around 98%, and the epilepsy is typically an infantile epileptic spasms syndrome.

Distinguishing Features

Caused by AFG2B (SPATA5L1, HGNC:28762), not AFG2A (SPATA5, HGNC:18119)
Sensorineural hearing loss is universal but the neurodevelopmental phenotype is present in only about half of affected individuals
Neurodevelopmental involvement is described as non-progressive and mixed, with spastic-dystonic cerebral palsy prominent
Congenital microcephaly is not a cardinal feature, whereas it is one of the AFG2A triad
Periventricular leukomalacia and reduced white matter volume are reported, rather than the hypomyelination plus progressive cerebral atrophy pattern of AFG2A disease

Show evidence (3 references)

PMID:34626583 SUPPORT Human Clinical

"We report 28 bi-allelic variants in SPATA5L1 associated with sensorineural hearing loss in 47 individuals from 28 (26 unrelated) families. In addition, 25/47 affected individuals (53%) presented with microcephaly, developmental delay/intellectual disability, cerebral palsy, and/or epilepsy."

Establishes the AFG2B cohort and the key quantitative discriminator, that only 53% have neurodevelopmental involvement.

PMID:34626583 SUPPORT Human Clinical

"Collectively, our results indicate that bi-allelic SPATA5L1 variants lead to a human disease characterized by sensorineural hearing loss (SNHL) with or without a nonprogressive mixed neurodevelopmental phenotype."

The authors' own summary, which contrasts with the progressive cerebral atrophy described in AFG2A disease.

PMID:41933351 SUPPORT Human Clinical

"Pathogenic variants in AFG2B, previously named SPATA5L1, are associated with a... disorders characterized by overlapping clinical features, including ID, neurodevelopmental delay... hearing loss, and dystonia"

The AFG2A review itself flags the AFG2B disorder as the closest phenotypic neighbour. The elided words are "neurodevelopmental" and "epilepsy", each split across a line break by a hyphen in the cached PDF text.

Primary mitochondrial disease Not Yet Curated MONDO:0044970

Overlapping Features This is the differential that actually costs patients time. Congenital microcephaly with deafness, cortical visual impairment, epilepsy, hypotonia and a mildly raised lactate is a classic mitochondrial presentation, and both the auditory and the optic nerve are selectively vulnerable to energy failure. Several published AFG2A cohorts were assembled precisely because the children were being investigated for suspected mitochondrial disease. The discriminator is that no consistent mitochondrial biomarker abnormality has been found in AFG2A disease: lactate is normal in all but a few individuals and is normal in urine and cerebrospinal fluid even in those, and acid-base balance, creatine kinase, pyruvate, organic acids, amino acids and carnitines are unremarkable. Mitochondrial DNA studies in the reported patients were normal. AFG2A dysfunction does produce secondary mitochondrial abnormalities, but the primary lesion is in cytoplasmic ribosome maturation, not in oxidative phosphorylation.

Distinguishing Features

No consistent mitochondrial biomarker abnormality; lactate elevation is mild and confined to a small minority, and urine and cerebrospinal fluid lactate are normal
Mitochondrial DNA depletion, deletion and sequencing studies were normal in the reported patients
Congenital microcephaly with sensorineural deafness as an obligate pairing is unusual in primary mitochondrial disease
The primary molecular lesion is in cytoplasmic pre-60S ribosome maturation, with mitochondrial dysfunction as a secondary consequence

Show evidence (3 references)

PMID:41933351 SUPPORT Human Clinical

"The cardinal clinical features of AFG2A-RE may mimic those of a mitochondrial disease."

The systematic review names mitochondrial disease as the principal clinical mimic.

PMID:29343804 SUPPORT Human Clinical

"Biallelic variants in the SPATA5 gene can affect mitochondria in cortical neurons and should be considered in patients with a neurodegenerative disorder and/or with clinical presentation resembling a mitochondrial disorder."

Explicitly recommends considering this gene in patients presenting as mitochondrial disease.

PMID:41933351 SUPPORT Human Clinical

Supplies the biochemical discriminator: the absence of a mitochondrial biomarker signature.

Autosomal recessive nonsyndromic sensorineural hearing loss

Overlapping Features At the mild end of the AFG2A spectrum, a confirmed biallelic genotype can produce isolated sensorineural hearing impairment with no microcephaly, intellectual disability or epilepsy, as documented in the younger sister of a typically affected proband. Such an individual is indistinguishable on phenotype from nonsyndromic recessive deafness, and the diagnosis can only be made molecularly. The practical consequence runs in both directions: AFG2A belongs on hearing loss gene panels, and an apparently nonsyndromic deaf child with an AFG2A genotype has a recurrence risk for the full encephalopathy in siblings.

Distinguishing Features

Indistinguishable clinically; separation is molecular only
Absence of microcephaly, intellectual disability, epilepsy and cortical visual impairment despite a confirmed biallelic AFG2A genotype
Within-family variability means a sibling of an isolated-deafness case may have the full encephalopathy

Show evidence (2 references)

PMID:28293831 SUPPORT Human Clinical

"In the sister, the only manifestation was an isolated sensorineural hearing loss."

Documents the isolated-deafness presentation that is clinically indistinguishable from nonsyndromic recessive hearing loss.

PMID:28293831 SUPPORT Human Clinical

"Our findings extend the phenotypic spectrum of SPATA5-associated diseases and indicate that SPATA5 defects may account for a fraction of isolated sensorineural hearing impairment cases."

States the authors' inference that the gene contributes to apparently isolated hearing impairment.

AIRIM/C1orf109-related neurodevelopmental disorder

Overlapping Features The third disease gene of the same 55LCC complex, described in 2025. Eleven unrelated families comprising eighteen individuals presented with severe global developmental delay and intellectual disability, muscular hypotonia with limb spasticity and dystonia, microcephaly, hearing and vision impairment and infantile seizures. This is close enough to AFG2A-related encephalopathy that the two are separable only by gene. It is included here partly because the 2026 AFG2A systematic review states that no neurological disorder has been linked to C1orf109 or CINP, a statement that this paper, published five months earlier, already contradicted; a curator relying on the review alone would omit this differential entirely.

Distinguishing Features

Caused by AIRIM/C1orf109 (hgnc:26039), a different subunit of the same 55LCC complex
Hearing impairment is less consistent than in AFG2A disease (9 of 17 versus around 94%)
Reported seizure semiology is dominated by generalised tonic-clonic and myoclonic seizures and Lennox-Gastaut syndrome rather than by infantile epileptic spasms syndrome
Neuroimaging emphasises severe supratentorial atrophy with ex-vacuum ventricular dilatation, rather than the hypomyelination-predominant AFG2A pattern

Show evidence (4 references)

PMID:40760247 SUPPORT Human Clinical

"Here we describe variants in the ribosome biogenesis factor AIRIM/C1orf109 that are primarily associated with neurodevelopmental disorders."

Establishes AIRIM/C1orf109 as a third 55LCC neurodevelopmental disease gene.

PMID:40760247 SUPPORT Human Clinical

"The majority of individuals from whom information was available concomitantly showed muscular hypotonia accompanied by limb spasticity and dystonia (each 11 of 17), microcephaly (14 of 17), as well as hearing (9 of 17) and vision impairment (6 of 17)"

Gives the AIRIM cohort's phenotype counts, which are the basis of the discriminators listed above.

PMID:41933351 REFUTE Human Clinical

"In contrast, no... disorders have been linked to the other... of the complex, C1orf109 and CINP, to date."

Recorded as REFUTE because this sentence, from the most recent systematic review, is superseded by PMID:40760247. It is kept in the entry so the next curator sees the contradiction rather than rediscovering it. The elided words are "neurological" and "components", each split across a line break by a hyphen in the cached PDF text.

+ 1 more reference

📊

Related Datasets

Quantitative proteomic profiling of a quadriceps muscle biopsy from a child with AFG2A-related encephalopathy proteomexchange:PXD026182

Mass-spectrometry proteome of a skeletal muscle biopsy from an 8-year-old girl with two compound heterozygous AFG2A variants. 1778 proteins were robustly quantified and 82 were dysregulated, 15 of them mitochondrial. This is the only deposited omics dataset from AFG2A patient tissue located during curation.

Homo sapiens PROTEOMICS n=1

PMID:34360601

Show evidence (1 reference)

PMID:34360601 SUPPORT Human Clinical

"An examination of the proteomic profile performed on the muscle biopsy of the patient revealed the robust quantification of 1778 proteins (ProteomeXchange project accession #: PXD026182)."

Gives the accession and the scale of the deposited proteome.

{ }

Source YAML

click to show

name: AFG2A-Related Encephalopathy
creation_date: '2026-08-01T00:00:00Z'
category: Mendelian
synonyms:
- AFG2A-RE
- SPATA5-related encephalopathy
- SPATA5 syndrome
- EHLMRS
- epilepsy, hearing loss, and mental retardation syndrome
- neurodevelopmental disorder with hearing loss, seizures, and brain abnormalities
- NEDHSB
- microcephaly-intellectual disability-sensorineural hearing loss-epilepsy-abnormal
  muscle tone syndrome
description: >-
  AFG2A-related encephalopathy is an ultra-rare autosomal recessive
  neurodevelopmental disorder caused by biallelic variants in AFG2A, the gene
  formerly and still most widely known as SPATA5. Its cardinal triad is
  congenital microcephaly, sensorineural hearing loss and epilepsy, on a
  background of severe to profound intellectual disability with absent speech,
  motor impairment that combines axial hypotonia with peripheral spasticity,
  cortical visual impairment and gastrointestinal dysfunction. When epilepsy is
  present it most often begins as an infantile epileptic spasms syndrome in the
  first two years and is usually drug resistant, so the disorder is frequently
  classified as a developmental and epileptic encephalopathy. AFG2A encodes an
  AAA+ ATPase that, together with AFG2B (SPATA5L1), C1orf109 and CINP, forms the
  55LCC complex; the complex drives the last cytoplasmic maturation step of the
  pre-60S ribosomal subunit and also governs replisome proteostasis. Loss of
  AFG2A function in neurons produces a mitochondrial fusion-fission imbalance,
  reduced ATP production and short axons, which is why the clinical picture is
  repeatedly mistaken for a primary mitochondrial disease.
disease_term:
  preferred_term: AFG2A-related encephalopathy
  term:
    id: MONDO:0014698
    label: microcephaly-intellectual disability-sensorineural hearing loss-epilepsy-abnormal
      muscle tone syndrome
parents:
- Developmental and epileptic encephalopathy
- Mendelian neurodevelopmental disorder
- Ribosome biogenesis disorder
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:26299366
      reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
        Disability, Seizures, and Hearing Loss.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Using whole-exome sequencing, we have identified in ten families 14
        individuals with microcephaly, developmental delay, intellectual disability,
        hypotonia, spasticity, seizures, sensorineural hearing loss, cortical visual
        impairment, and rare autosomal-recessive predicted pathogenic variants in
        spermatogenesis-associated protein 5 (SPATA5).
      explanation: >-
        A monogenic autosomal recessive disorder defined and diagnosed by exome
        sequencing belongs to the genetics chapter.
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:41933351
      reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
        and epileptic spectrum.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "AFG2A-RE is an ultra-rare, recessive disorder, sometimes presenting\
        \ as a developmental and epileptic encephalopathy (DEE), characterised by\
        \ the triad of epilepsy, congenital microcephaly, and deafness, and typically\
        \ associated with intellectual disability, spasticity, and movement disorders."
      explanation: >-
        The presentation is dominated by epilepsy, intellectual disability,
        microcephaly and motor signs, which places the entity in the neurology
        chapter.
  - classification_value: DISORDER_OF_EAR
    evidence:
    - reference: PMID:28293831
      reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a
        Family with Variable Phenotypic Expression.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Our findings extend the phenotypic spectrum of SPATA5-associated diseases
        and indicate that SPATA5 defects may account for a fraction of isolated sensorineural
        hearing impairment cases.
      explanation: >-
        Sensorineural hearing loss is near-universal in the disorder and can be
        its only manifestation, so the entity also belongs to the disorders of
        the ear chapter.
notes: >-
  Scope, naming and provenance notes for this entry.


  (1) GENE SYMBOL HISTORY - READ THIS FIRST. The causative gene is AFG2A
  (HGNC:18119). It was renamed from SPATA5 (spermatogenesis associated 5); older
  aliases in the literature include SPAF (spermatogenesis-associated factor) and
  AFG2. Essentially all clinical literature published between 2015 and 2024 uses
  SPATA5, and only papers from 2025 onward (PMID:41933351, PMID:40712368) use
  AFG2A. A PubMed title search on 2026-08-01 returned 12 records for SPATA5[TI]
  and 3 for AFG2A[TI], with no overlap, so searching either symbol alone misses
  most of the disease literature. The rename is also incompletely propagated
  through the ontology stack this repository uses: MONDO's
  `RO:0004003` axiom on MONDO:0014698 already reads `HGNC:18119 ! AFG2A`, but the
  HGNC adapter shipped with `sqlite:obo:hgnc` still returns `hgnc:18119 ! SPATA5`
  with `AFG2` and `SPAF` as exact synonyms. The `gene_term` bindings in this
  entry therefore carry the label `SPATA5`, because that is the label the term
  validator resolves; this is a lag in the cached HGNC build, not a curation
  error, and it must not be "fixed" to `AFG2A` until the adapter is refreshed.


  (2) NAMED-ENTITY CONFUSION WITH AFG2B / SPATA5L1. AFG2B (HGNC:28762, formerly
  SPATA5L1) is a DIFFERENT gene one suffix away from the old symbol of this one.
  Its biallelic variants cause a separate, clinically overlapping disorder
  (MONDO:0859206, neurodevelopmental disorder with hearing loss and spasticity;
  PMID:34626583). The two proteins are obligate partners inside the same 55LCC
  ATPase complex (PMID:38554706, PMID:40268917), so mechanism papers legitimately
  name both, and review articles discuss the two diseases side by side
  (PMID:41933351). Every clinical citation in this entry was checked for which
  gene the reported cohort actually carries variants in: PMID:26299366,
  PMID:27246907, PMID:27683084, PMID:28293831, PMID:29343804, PMID:30552426,
  PMID:33063670, PMID:34360601, PMID:36849973, PMID:40712368 and PMID:41933351 are
  all AFG2A/SPATA5 cohorts. PMID:34626583 is an AFG2B/SPATA5L1 cohort and is cited
  ONLY inside `differential_diagnoses`, never as support for a phenotype of this
  entry. The two structural/biochemical papers that study the complex as a whole
  (PMID:38554706, PMID:40268917) are cited for complex composition and function,
  not for any gene-specific clinical claim.


  (3) DISEASE NAME. The file is named for the clinically preferred current term.
  Three papers title the disorder "AFG2A-related encephalopathy" (PMID:41933351,
  PMID:40712368, PMID:40846618) and one titles it "SPATA5-related encephalopathy"
  (PMID:27246907); none uses "AFG2A-related neurodevelopmental disorder". The
  MONDO canonical label, the OMIM label (NEDHSB) and the older acronym EHLMRS are
  all recorded as synonyms.


  (4) NO GENEREVIEWS CHAPTER EXISTS. PubMed searches run on 2026-08-01 for
  "SPATA5[All Fields] AND GeneReviews[All Fields]", "AFG2A[All Fields] AND
  GeneReviews[All Fields]" and "AFG2A-related encephalopathy GeneReviews" each
  returned zero records; the single GeneReviews PMID surfaced by a broader
  phenotype-phrase search (PMID:20301382) is the chapter on Single Large-Scale
  Mitochondrial DNA Deletion Syndromes and is unrelated. The mandatory
  GeneReviews baseline therefore does not apply. The phenotype baseline used
  instead is the 2026 systematic review of 51 individuals (PMID:41933351), which
  is the largest published cohort, cross-checked against the earlier
  30-patient summary in PMID:29343804.


  (5) FREQUENCY DERIVATIONS. Bands come from published denominators, not from
  narrative language. PMID:41933351 pooled 51 individuals (45 from the literature
  plus 6 new) and reported per-feature percentages against feature-specific
  denominators: intellectual disability 97.92%, hearing loss 93.62%, microcephaly
  85.71% and absence of speech in all individuals with intellectual disability
  map to VERY_FREQUENT (80-100%); visual impairment 79.49%, epilepsy 38/51
  (74.5%), gastrointestinal symptoms 78.95%, hypotonia 71.74%, abnormal brain MRI
  68.29%, spasticity 60.87%, hypomyelination 39.02% and brain atrophy 34.15% map
  to FREQUENT (30-79%); thin corpus callosum 29.27% and dystonia 21.74% map to
  OCCASIONAL (5-29%). Three bands are deliberately OMITTED rather than guessed.
  Infantile epileptic spasms syndrome was reported in 16 of the 24 individuals
  with detailed epilepsy data (66.67%) but that is 16/51 (31%) of the whole
  cohort, so the band depends entirely on which denominator is chosen. Drug
  resistance was 82.35% of the 17 individuals with anti-seizure medication data,
  a denominator of seventeen that is both small and conditioned on having
  epilepsy. Mild lactate elevation was reported in two individuals described as
  being "in our cohort", which the review's discussion identifies as two of the
  authors' own five ketogenic-diet patients rather than two of the 51, so the
  denominator is genuinely unknown. All three raw numbers are recorded in the
  relevant `notes:` instead of being converted into bands. One band, inability
  to walk, is retained despite a subgroup denominator: the GMFCS percentages
  resolve exactly to n=22 rather than to the pooled 51, giving VERY_FREQUENT on
  the graded subgroup (19/22, 86.36%) and FREQUENT on the pooled cohort (19/51,
  37%). Both readings and the reason for preferring the former are recorded in
  that phenotype's `notes:`.


  (6) MITOCHONDRIAL LOCALISATION IS DISPUTED AND IS CURATED AS SUCH. The original
  1990s characterisation of SPAF/SPATA5 assigned it a mitochondrial
  matrix-targeting sequence and a role in mitochondrial morphogenesis during
  spermatogenesis, and PMID:26299366 repeats this. PMID:29343804 then showed
  directly that overexpressed SPATA5 is dominantly cytosolic in cortical neurons,
  SH-SY5Y, HeLa and COS7 cells and does not co-localise with a mitochondrial
  marker, while nevertheless demonstrating a real mitochondrial fusion-fission
  imbalance and ATP deficit on knockdown. The current mechanistic consensus
  (PMID:35354024, PMID:40268917) places AFG2A in cytoplasmic pre-60S ribosome
  maturation. The pathophysiology DAG in this entry therefore models the
  mitochondrial phenotype as a downstream consequence of AFG2A loss rather than
  as a direct mitochondrial-protein defect, and the mitochondrial node carries
  `mechanism_confidence: PROVISIONAL`. Calling this disorder a mitochondrial
  disease would be wrong; it merely mimics one.


  (7) STRUCTURED SOURCES SKIPPED, AND THE ABSENCE WAS CHECKED RATHER THAN ASSUMED.
  No Orphanet (ORPHA:457351), ClinGen gene-disease validity (CGGV) or ClinGen
  dosage (CGDS) record is cited. The cache does contain 327 ORPHA_* files, 478
  CGGV_* files and several CGDS_* files, so their absence here is specific, not
  general: `ls references_cache/ORPHA_457351.md` returns no such file, and
  `grep -l -i -e SPATA5 -e AFG2A CGGV_*.md CGDS_*.md` returns nothing. Generating
  the missing records would require bumping a structured-source
  `data/*/MANIFEST.yaml` pin; those pins are stale and un-refreshable (tracked in
  #7622) and the curation PR scope check forbids touching them, so the citation is
  skipped rather than fabricated. Note that the deep-research run reports a
  ClinGen Definitive AR classification for AFG2A evaluated 2024-07-23; that is
  almost certainly citable once the CGGV pin is refreshed.


  (7a) THE 2026 REVIEW IS ALREADY OUT OF DATE ON ONE POINT, AND THE ENTRY SAYS SO.
  PMID:41933351 states that no neurological disorders have been linked to the
  other components of the 55LCC complex, C1orf109 and CINP. PMID:40760247,
  published in Nature Cell Biology five months earlier, reports biallelic
  AIRIM/C1orf109 variants in eleven unrelated families with a closely overlapping
  neurodevelopmental phenotype and states that variants in AFG2A, AFG2B and CINP
  are associated with a range of neurodevelopmental disorders. The superseded
  sentence is retained in the entry as a REFUTE evidence item on the
  AIRIM/C1orf109 differential so that the contradiction is visible rather than
  silently resolved.


  (7b) TABLE 1 OF THE 2026 REVIEW WAS NOT TRANSCRIBED. The deep-research report
  identified three internal discrepancies between Table 1 of PMID:41933351 and the
  primary sources, the most consequential being a genotype inversion for the two
  Buchert 2016 families, which flips which allele is associated with absence of
  epilepsy. Every variant curated in the `variants:` block of this entry is
  therefore cited to the primary report (PMID:27246907, PMID:27683084,
  PMID:28293831, PMID:30552426) and not to the review table. No
  genotype-phenotype correlation is asserted anywhere in this entry; the review's
  own conclusion is that none was found.


  (8) DIFFERENTIAL DIAGNOSIS BINDINGS. Two of the four differentials carry a
  MONDO term. AFG2B-related disorder is bound to MONDO:0859206
  (`neurodevelopmental disorder with hearing loss and spasticity`), verified
  non-obsolete and confirmed by `runoak ancestors` NOT to be an ancestor of this
  entry's own anchor MONDO:0014698. The mitochondrial-disease mimic is bound to
  MONDO:0044970 (`mitochondrial disease`), also verified non-obsolete and not an
  ancestor of the anchor; note that the nearby label `mitochondrial disease`
  MONDO:0019055 IS obsolete and must not be used. The third differential,
  autosomal recessive nonsyndromic sensorineural hearing loss, is left UNBOUND:
  MONDO models that group only as numbered locus-specific entities (DFNB1A,
  DFNB2, DFNB3 ...), and picking any one of them would assert a locus that
  PMID:28293831 never implicates. No honest grouping term for it exists in the
  constrained ontology set, so the slot is left empty deliberately. The fourth,
  AIRIM/C1orf109-related neurodevelopmental disorder, is also UNBOUND because
  `runoak -i sqlite:obo:mondo search` returns no term for either "AIRIM" or
  "C1orf109"; the disorder was described in 2025 and MONDO has not yet minted an
  entity for it. Its gene resolves (hgnc:26039 ! C1orf109) but a gene identifier
  is not a disease term.


  (9) WHAT IS KNOWINGLY ABSENT. No treatment in this entry is disease-modifying;
  the ketogenic-diet evidence rests on four treated patients (PMID:40712368) and
  is curated as PARTIAL. No animal model of AFG2A deficiency is curated because
  the only in vivo work located is rat primary cortical neuron knockdown
  (PMID:29343804), which is a cell model rather than an organism model; the IMPC
  mouse-null result surfaced by the deep-research run has no PMID and is therefore
  recorded in a `discussions` entry rather than as evidence. Elevated blood copper
  was reported by PMID:27246907 in three children but has never been replicated
  and is recorded only in the diagnosis notes, not as a biochemical finding. No
  ClinGen gene-disease validity citation appears even though the deep-research run
  reports a Definitive AFG2A classification, for the structured-source reason in
  note (7). No survival, life-expectancy or quality-of-life claim is made; see the
  `afg2a_natural_history_gap` discussion. The mTOR rescue axis is curated as a
  pathophysiology observation only and NOT as a treatment, because it has been
  demonstrated in AIRIM/C1orf109 organoids and never in an AFG2A model.
inheritance:
- name: Autosomal recessive
  description: >-
    Biallelic (homozygous or, more often, compound heterozygous) AFG2A variants
    are required. Heterozygous carriers, including the parents of affected
    children, are unaffected.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:27683084
    reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
      of intellectual disability, hypotonia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We thus independently confirm that bi-allelic pathogenic variants in
      SPATA5 cause a syndromic form of intellectual disability, and we delineate
      its clinical presentation.
    explanation: >-
      Independent confirmation, in a consanguineous family plus an unrelated
      compound heterozygous case, that the disorder is recessive.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "AFG2A-RE is an ultra-rare, recessive disorder, sometimes presenting\
      \ as a developmental and epileptic encephalopathy (DEE), characterised by the\
      \ triad of epilepsy, congenital microcephaly, and deafness, and typically associated\
      \ with intellectual disability, spasticity, and movement disorders."
    explanation: The largest published cohort restates recessive inheritance.
prevalence:
- population: Global
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Fifty-one individuals had been reported in total as of the 2026 systematic
    review (45 from the published literature plus 6 newly recruited). Earlier
    tallies were 30 patients in 2018 (PMID:29343804) and 37 as of 2019
    (PMID:33063670). No population prevalence estimate has been published, so the
    qualitative ULTRA_RARE tier is used with the case count recorded here rather
    than converting a case series into a rate.
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A total of 51 individuals with AFG2A-RE were included, 29 males; mean
      age 8.35 years.
    explanation: >-
      The largest pooled cohort assembled to date numbers 51 individuals
      worldwide, which places the disorder in the ultra-rare tier.
- population: Children with early-onset epileptic encephalopathy or developmental
    and epileptic encephalopathy
  measure_type: PERIOD_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 3000.0
  notes: >-
    Derived from a stated denominator. Papuc and colleagues found causative
    biallelic SPATA5 variants in 2 of 63 research patients with early-onset
    epileptic encephalopathy, then replicated the finding in 1 of 39 diagnostic
    cases, giving 3 of 102 combined patients (2.9%, reported as 3%). READ THE
    `population:` FIELD BEFORE USING THE RATE. The 3000 per 100,000 figure is the
    diagnostic yield WITHIN a selected early-onset epileptic encephalopathy
    cohort, not a population prevalence, and it must never be compared with a
    general-population rate. The deprecated free-text `percentage:` slot is
    deliberately not used.
  evidence:
  - reference: PMID:30552426
    reference_title: "The role of recessive inheritance in early-onset epileptic encephalopathies:\
      \ a combined whole-exome sequencing and copy number study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Notably, we found the recessive gene SPATA5 causative in as much as 3%
      of our cohort, indicating that it may have been underdiagnosed in previous
      studies.
    explanation: >-
      Gives the diagnostic yield of AFG2A/SPATA5 within a deeply phenotyped
      early-onset epileptic encephalopathy cohort.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The prevalence of AFG2A-RE has been estimated at around 3% of early-onset
      developmental and epileptic encephalopathies
    explanation: The 2026 review carries the same 3% yield forward.
progression:
- age_range: Birth to 2 years
  notes: >-
    Onset is in early infancy. Microcephaly is usually congenital, hearing loss
    and global developmental delay are apparent from the first months, and
    epileptic spasms typically emerge between 6 and 27 months.
  evidence:
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The three patients manifested microcephaly, psychomotor retardation,
      hypotonus or hypertonus, and bilateral hearing loss from early infancy.
    explanation: Documents onset of the cardinal features in early infancy.
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Symptoms start in early infancy with all of the patients developing global
      developmental delay with severely limited speech or no words, hearing impairment
      (most frequently sensorineural hearing loss, 77%), and a pathological EEG with
      symptomatic epilepsy being present in 73% of patients.
    explanation: Confirms early-infantile onset across the pooled 30-patient series.
- age_range: Childhood onwards
  notes: >-
    The course is one of severe static-to-slowly-progressive encephalopathy.
    Serial imaging in some children shows progressive cerebral atrophy, and a
    minority die in childhood; three of 51 pooled individuals had died, at ages
    3, 4.9 and 13.4 years.
  evidence:
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Magnetic resonance imaging revealed hypomyelination, thin corpus callosum,
      and progressive cerebral atrophy.
    explanation: >-
      Documents that the cerebral atrophy component of the imaging phenotype is
      progressive rather than static.
pathophysiology:
- name: Biallelic AFG2A Loss of Function
  description: >-
    Biallelic pathogenic variants in AFG2A (formerly SPATA5) reduce the amount or
    the activity of an 892-amino-acid AAA+ ATPase. Most reported alleles are
    missense or small in-frame changes rather than complete nulls, and no
    individual carrying two unequivocal null alleles has been reported, which is
    consistent with hypomorphic rather than complete loss of function being
    compatible with life. The protein carries two conserved ATPase modules.
  role: root
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  gene:
    preferred_term: AFG2A
    term:
      id: hgnc:18119
      label: SPATA5
  cellular_components:
  - preferred_term: Cytosol
    term:
      id: GO:0005829
      label: cytosol
  downstream:
  - target: 55LCC ATPase Complex Dysfunction
    causal_link_type: DIRECT
    description: >-
      AFG2A is the catalytic core of the 55LCC complex, so reduced AFG2A ATPase
      activity is directly a deficiency of the complex.
  - target: Neuronal Mitochondrial Fusion-Fission Imbalance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Knockdown of the gene in rat cortical neurons shifts the mitochondrial
      fusion-fission balance, but the molecular steps between the ATPase defect
      and the mitochondrial phenotype have not been identified.
  - target: Skeletal Muscle Mitochondrial Pathology
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Muscle biopsy in a genotyped patient shows a mitochondrial histochemical
      pattern and a dysregulated mitochondrial proteome.
  evidence:
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: SPATA5 encodes a ubiquitously expressed member of the ATPase associated
      with diverse activities (AAA) protein family and is involved in mitochondrial
      morphogenesis during early spermatogenesis.
    explanation: Establishes the gene product as a ubiquitously expressed AAA ATPase.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Most of the variants were missense (58.82%), with others being frameshift
      (14.71%), nonsense (9.8%), deletion (6.68%), splice site/splice donor (6.68%),
      non-frameshift (1.96%) and start loss (0.98%).
    explanation: >-
      Shows that the majority of disease alleles are missense, supporting a
      hypomorphic rather than a complete-null mechanism.
- name: 55LCC ATPase Complex Dysfunction
  description: >-
    AFG2A does not act alone. It assembles with its paralogue AFG2B (SPATA5L1)
    and the heterodimeric partners C1orf109 and CINP into a 4:2:2:2 assembly
    named 55LCC, built from an N-terminal ring of C1orf109, CINP and the
    N-terminal domains of AFG2A and AFG2B sitting above two hexameric AAA+ ATPase
    rings. Reduced AFG2A activity therefore compromises a shared machine rather
    than a single enzyme, which is the structural reason AFG2A and AFG2B disease
    phenotypes overlap.
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  protein_complexes:
  - preferred_term: 55LCC complex
  downstream:
  - target: Impaired Cytoplasmic Pre-60S Ribosomal Maturation
    causal_link_type: DIRECT
    description: >-
      The complex performs the terminal cytoplasmic maturation step on the
      pre-60S particle.
  - target: Replisome Proteostasis Failure
    causal_link_type: DIRECT
    description: >-
      The same complex extracts and licenses degradation of replisome components
      at damaged replication forks.
  evidence:
  - reference: PMID:40268917
    reference_title: Cryo-EM structure of the AAA+ SPATA5 complex and its role in
      human cytoplasmic pre-60S maturation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Here we reveal that SPATA5 forms a 4:2:2:2 complex with SPATA5L1, C1orf109,
      and CINP.
    explanation: Defines the stoichiometry and composition of the complex by cryo-EM.
  - reference: PMID:38554706
    reference_title: The SPATA5-SPATA5L1 ATPase complex directs replisome proteostasis
      to ensure genome integrity.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we identify replisome factor interactions with a protein complex\
      \ composed of AAA+ ATPases SPATA5-SPATA5L1 together with heterodimeric partners\
      \ C1orf109-CINP (55LCC)."
    explanation: Names the complex and its four components.
- name: Impaired Cytoplasmic Pre-60S Ribosomal Maturation
  description: >-
    In yeast the AFG2A orthologue Drg1 strips the assembly factor Rlp24, a
    placeholder for the ribosomal protein Rpl24, off pre-60S particles as soon as
    they reach the cytoplasm; the human equivalent step is performed by AFG2A
    within the 55LCC complex, with recognition of the pre-60S particle mediated
    by the human-specific subunit CINP. When AFG2A activity falls, large
    ribosomal subunits stall at this last maturation checkpoint.
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  biological_processes:
  - preferred_term: Ribosomal large subunit biogenesis
    term:
      id: GO:0042273
      label: ribosomal large subunit biogenesis
  - preferred_term: Ribosome assembly
    term:
      id: GO:0042255
      label: ribosome assembly
  cellular_components:
  - preferred_term: Preribosome, large subunit precursor
    term:
      id: GO:0030687
      label: preribosome, large subunit precursor
  downstream:
  - target: Reduced Global Protein Synthesis
    causal_link_type: DIRECT
    description: >-
      Fewer mature 60S subunits reach the translating pool, so bulk translation
      capacity falls.
  evidence:
  - reference: PMID:40268917
    reference_title: Cryo-EM structure of the AAA+ SPATA5 complex and its role in
      human cytoplasmic pre-60S maturation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In yeast, AAA+ protein Drg1 releases an assembly factor Rlp24, a placeholder
      for Rpl24, from pre-60S particles just exported to cytosol.
    explanation: >-
      Defines the conserved reaction that the human AFG2A complex is the
      orthologue of.
  - reference: PMID:35354024
    reference_title: Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5
      control a late step in human ribosome assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: We provide evidence that these factors, together with CINP and SPATA5L1,
      control a late step of human pre-60S maturation in the cytoplasm.
    explanation: >-
      A genome-wide loss-of-function screen with differential ribosome labelling
      places SPATA5 at a late cytoplasmic pre-60S step in human cells.
  - reference: PMID:31703473
    reference_title: "Shaping the Nascent Ribosome: AAA-ATPases in Eukaryotic Ribosome\
      \ Biogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Rix7, Rea1, and Drg1, which are well conserved across eukaryotes, are\
      \ involved in different maturation steps of pre-60S ribosomal particles."
    explanation: >-
      Establishes the evolutionary conservation of the Drg1 step that AFG2A
      performs in human cells.
  - reference: PMID:40268917
    reference_title: Cryo-EM structure of the AAA+ SPATA5 complex and its role in
      human cytoplasmic pre-60S maturation.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "Different from yeast, the recognition of the pre-60S particle is mediated\
      \ by human-specific factor CINP, through two distinct sets of interactions:\
      \ one with GTPBP4 and the other with ES27A."
    explanation: >-
      Records the limit of the yeast analogy: substrate recognition in humans
      uses a subunit with no yeast counterpart, so Drg1 data inform the
      enzymology but not the recognition step.
- name: Reduced Global Protein Synthesis
  description: >-
    Depletion of AFG2A or of its partner C1orf109 lowers bulk protein synthesis
    in human cells. Neurons are among the cell types least able to tolerate a
    reduced translational capacity during the period of rapid dendritic and
    axonal growth, which is the proposed link between a housekeeping ribosome
    assembly defect and a brain-restricted clinical phenotype.
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  biological_processes:
  - preferred_term: Cytoplasmic translation
    term:
      id: GO:0002181
      label: cytoplasmic translation
  downstream:
  - target: Neuroepithelial Vulnerability During Differentiation
    causal_link_type: DIRECT
    description: >-
      A fall in ribosome availability is only pathogenic where translational
      reserve is already low, which is what makes the effect brain-specific.
  evidence:
  - reference: PMID:35354024
    reference_title: Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5
      control a late step in human ribosome assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Loss of either C1orf109 or SPATA5 impairs global protein synthesis.
    explanation: Direct demonstration of the translational consequence of SPATA5 loss.
  - reference: PMID:35354024
    reference_title: Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5
      control a late step in human ribosome assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: These results link ribosome assembly with neurodevelopmental disorders
      associated with recessive SPATA5 mutations.
    explanation: >-
      The authors themselves connect the ribosome assembly defect to the
      recessive neurodevelopmental disorder.
- name: Neuroepithelial Vulnerability During Differentiation
  description: >-
    This node answers the central puzzle of the disorder: why a defect in a
    ubiquitous housekeeping machine produces an almost purely neurological
    phenotype. Human cerebral organoid work on the sister 55LCC subunit
    AIRIM/C1orf109 showed that ribosome levels fall physiologically during
    neuroepithelial differentiation, creating a developmental window in which any
    further reduction in 60S output crosses a threshold and selectively impairs
    translation of specific transcripts, disrupting both survival and cell fate
    commitment. The window is embryonic, which is why no postnatal intervention
    reverses the microcephaly. Enhancing mTOR activity suppressed the organoid
    phenotype, making mTOR the first rationally derived candidate target for this
    disease family.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  notes: >-
    The organoid evidence is from AIRIM/C1orf109, a different subunit of the same
    55LCC complex, not from AFG2A itself. The node is therefore provisional and
    its evidence is recorded as PARTIAL. No AFG2A cerebral organoid model has been
    published.
  biological_processes:
  - preferred_term: Cytoplasmic translation
    term:
      id: GO:0002181
      label: cytoplasmic translation
  cell_types:
  - preferred_term: Differentiating neuroepithelium
    term:
      id: CL:0011020
      label: neural progenitor cell
  downstream:
  - target: Impaired Cortical Neuron Growth
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Attrition and mis-specification of differentiating neuroepithelium is the
      proposed route to reduced brain growth, but the intervening steps have not
      been mapped in AFG2A deficiency itself.
  evidence:
  - reference: PMID:40760247
    reference_title: A programmed decline in ribosome levels governs human early neurodevelopment.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: We find that ribosome levels decrease during neuroepithelial differentiation,
      making differentiating cells particularly vulnerable to perturbations in ribosome
      biogenesis during this time.
    explanation: >-
      Supplies the tissue-specificity mechanism, but in organoids carrying
      AIRIM/C1orf109 rather than AFG2A variants, so support is partial.
  - reference: PMID:40760247
    reference_title: A programmed decline in ribosome levels governs human early neurodevelopment.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: Enhancing mTOR activity suppresses the growth and developmental defects
      associated with AIRIM/C1orf109 variants.
    explanation: >-
      Identifies mTOR enhancement as a candidate rescue axis for 55LCC-complex
      ribosome biogenesis defects; untested in AFG2A.
- name: Replisome Proteostasis Failure
  description: >-
    The 55LCC complex has a second, ribosome-independent job: its ATPase activity
    is stimulated by replication fork DNA and it couples cysteine
    protease-dependent cleavage of replisome substrates to replication fork
    damage. Losing that activity produces ubiquitin-independent proteotoxicity,
    replication stress and chromosome instability. Whether this branch
    contributes to the human neurodevelopmental phenotype is proposed by the
    authors but not established in patient material, so the node is provisional.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  biological_processes:
  - preferred_term: DNA replication
    term:
      id: GO:0006260
      label: DNA replication
  cellular_components:
  - preferred_term: Replisome
    term:
      id: GO:0030894
      label: replisome
  evidence:
  - reference: PMID:38554706
    reference_title: The SPATA5-SPATA5L1 ATPase complex directs replisome proteostasis
      to ensure genome integrity.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Deficiency in the 55LCC complex elicited ubiquitin-independent proteotoxicity,
      replication stress, and severe chromosome instability.
    explanation: >-
      Establishes the cellular consequence of losing complex activity at the
      replication fork.
  - reference: PMID:38554706
    reference_title: The SPATA5-SPATA5L1 ATPase complex directs replisome proteostasis
      to ensure genome integrity.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: These findings define 55LCC-mediated proteostasis as critical for replication
      fork progression and genome stability and provide a rationale for pathogenic
      variants seen in associated human neurodevelopmental disorders.
    explanation: >-
      The link to the human disorder is offered as a rationale by the authors and
      was not tested in patient cells, so this is recorded as partial support.
- name: Neuronal Mitochondrial Fusion-Fission Imbalance
  description: >-
    Silencing the gene in rat primary cortical neurons shortens mitochondria by
    about 20% and halves the fusion-to-fission ratio. Patient-derived fibroblasts
    likewise show altered mitochondrial morphology and dynamics. This occurs even
    though the protein itself is dominantly cytosolic and does not co-localise
    with mitochondrial markers, so the effect is indirect; the intervening steps
    are unknown.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  cell_types:
  - preferred_term: Cerebral cortex neuron
    term:
      id: CL:0010012
      label: cerebral cortex neuron
  biological_processes:
  - preferred_term: Mitochondrial fusion
    term:
      id: GO:0008053
      label: mitochondrial fusion
  - preferred_term: Mitochondrial fission
    term:
      id: GO:0000266
      label: mitochondrial fission
  cellular_components:
  - preferred_term: Mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  downstream:
  - target: Neuronal ATP Deficit
    causal_link_type: DIRECT
    description: >-
      The fusion-fission imbalance is accompanied by a measured fall in the
      axonal ATP/ADP ratio in the same experiments.
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: SPATA5-deficient neurons had a significant imbalance in the mitochondrial
      fusion-fission rate, impaired energy production and short axons.
    explanation: >-
      shRNA knockdown in rat primary cortical neurons demonstrates the
      mitochondrial dynamics defect.
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: To our surprise the localization of overexpressed SPATA5 in cultured
      primary cortical neurons was dominantly cytosolic and clearly not co-localizing
      with the mitochondrial marker
    explanation: >-
      Shows the protein is not itself mitochondrial, which is why the
      mitochondrial phenotype is modelled as an indirect consequence.
  - reference: PMID:40712368
    reference_title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet\
      \ in epilepsy and mitochondrial dynamics modulation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In vitro studies demonstrated that AFG2A-deficient fibroblasts exhibited
      altered mitochondrial morphology and dynamics, as well as reduced ATP production
      and ROS levels.
    explanation: >-
      Replicates the mitochondrial dynamics abnormality in cells taken from
      genotyped patients rather than in a knockdown model.
- name: Neuronal ATP Deficit
  description: >-
    The axonal ATP/ADP ratio falls by roughly 12% in knockdown neurons and is
    restored by re-expression of the wild-type human protein, establishing
    specificity. The same energy failure is detectable in patient blood cells,
    where oxygen consumption rates in platelets and peripheral blood mononuclear
    cells are impaired and monocyte mitochondrial mass is reduced.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  biological_processes:
  - preferred_term: ATP biosynthetic process
    term:
      id: GO:0006754
      label: ATP biosynthetic process
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  downstream:
  - target: Impaired Cortical Neuron Growth
    causal_link_type: DIRECT
    description: >-
      Axon extension is one of the most energy-demanding processes in a
      developing neuron.
  evidence:
  - reference: PMID:36849973
    reference_title: Computational and mitochondrial functional studies of novel compound
      heterozygous variants in SPATA5 gene support a causal link with epileptogenic
      encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Oxygen consumption rates in platelets and PBMCs were impaired in the
      patient when compared to a healthy control.
    explanation: >-
      Demonstrates impaired oxidative metabolism in accessible cells from a
      genotyped patient.
  - reference: PMID:36849973
    reference_title: Computational and mitochondrial functional studies of novel compound
      heterozygous variants in SPATA5 gene support a causal link with epileptogenic
      encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Also, a decrease in mitochondrial mass was observed in the patient monocytes
      with respect to the control.
    explanation: Reduced mitochondrial mass accompanies the respiratory deficit.
- name: Impaired Cortical Neuron Growth
  description: >-
    Developing cortical neurons deficient in the protein grow markedly shorter
    axons, and the defect is rescued by re-expressing the wild-type human
    protein. This is the most proximate cellular correlate available for the
    congenital microcephaly, hypomyelination and thin corpus callosum seen in
    patients, although no experiment has yet connected the neuronal growth defect
    to the human imaging findings directly.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  cell_types:
  - preferred_term: Cerebral cortex neuron
    term:
      id: CL:0010012
      label: cerebral cortex neuron
  biological_processes:
  - preferred_term: Axon extension
    term:
      id: GO:0048675
      label: axon extension
  downstream:
  - target: Congenital Microcephaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced growth of individual cortical neurons is the presumed cellular
      cause of the whole-organism reduction in brain and head growth, but no
      experiment has connected the two directly in AFG2A deficiency.
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: In conclusion, SPATA5 protein has an important role in mitochondrial
      dynamics and axonal growth.
    explanation: >-
      The authors' own conclusion from the rescue experiments on axonal length in
      rat cortical neurons.
- name: Congenital Microcephaly
  description: >-
    The organism-level endpoint of the pathway. Reduced brain growth is present
    at birth in the large majority of affected children and, with sensorineural
    deafness and epilepsy, forms the diagnostic triad. It is the one feature that
    no postnatal intervention can reverse, because the vulnerable window is the
    embryonic period of neuroepithelial differentiation.
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: characterised by the triad of epilepsy, congenital microcephaly, and
      deafness
    explanation: >-
      Establishes congenital microcephaly as a cardinal organism-level
      manifestation.
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in SPATA5 might affect brain development and function, resulting\
      \ in microcephaly, developmental delay, and intellectual disability."
    explanation: >-
      The founding paper's own causal statement linking the gene defect to
      impaired brain development and microcephaly.
- name: Skeletal Muscle Mitochondrial Pathology
  description: >-
    Muscle is affected as well as brain. A quadriceps biopsy from an 8-year-old
    girl with a typical presentation and two compound heterozygous variants
    showed a histochemical pattern suggesting mitochondrial pathology, and
    proteomic profiling found 82 dysregulated proteins of which 15 are
    mitochondrial. This provides the tissue-level counterpart of the mitochondrial
    dysfunction seen in neurons and fibroblasts, and it is one reason the disorder
    is investigated as a suspected mitochondrial myopathy.
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  cell_types:
  - preferred_term: Skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  cellular_components:
  - preferred_term: Mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:34360601
    reference_title: Muscular and Molecular Pathology Associated with SPATA5 Deficiency
      in a Child with EHLMRS.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Proteomic profiling of a quadriceps biopsy showed the dysregulation of
      82 proteins, out of which 15 were localized in the mitochondrion, while 19 were
      associated with diseases presenting with phenotypical overlap to EHLMRS.
    explanation: Quantifies the muscle proteomic abnormality in a genotyped patient.
  - reference: PMID:34360601
    reference_title: Muscular and Molecular Pathology Associated with SPATA5 Deficiency
      in a Child with EHLMRS.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histological staining of our patient's muscle biopsy hints towards mitochondrial\
      \ pathology, while the identification of dysregulated proteins attested to the\
      \ vulnerability of the cell beyond the mitochondria."
    explanation: >-
      Histochemistry supports mitochondrial involvement in muscle while stopping
      short of a pure mitochondrial myopathy.
phenotypes:
- name: Intellectual disability
  category: Neurologic
  description: >-
    Intellectual disability is essentially universal and is severe to profound in
    three quarters of those with graded data. Absence of speech was reported in
    every individual with intellectual disability. The single individual without
    intellectual disability in the pooled cohort was a toddler too young to
    assess, who had delayed gross motor development.
  frequency: VERY_FREQUENT
  notes: >-
    97.92% in the 51-individual pooled cohort; severity was
    moderate-to-severe in 25% and severe-to-profound in 75% of the 32 cases with
    graded data.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most frequently described clinical features included intellectual
      disability (97.92%), hearing loss (93.62%), microcephaly (85.71%), visual impairment
      (79.49%), hypotonia (71.74%), spasticity (60.87%), and movement disorders (36.96%).
    explanation: Gives the pooled frequency from the largest cohort.
  - reference: PMID:27683084
    reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
      of intellectual disability, hypotonia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We examined an extended, consanguineous family with seven individuals
      with severe intellectual disability and microcephaly.
    explanation: Independent family documenting severe intellectual disability.
- name: Absent speech
  category: Neurologic
  description: >-
    No affected individual with intellectual disability has developed speech.
    Earlier series described severely limited speech or no words in all patients.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Absent speech
    term:
      id: HP:0001344
      label: Absent speech
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Symptoms start in early infancy with all of the patients developing global
      developmental delay with severely limited speech or no words, hearing impairment
      (most frequently sensorineural hearing loss, 77%), and a pathological EEG with
      symptomatic epilepsy being present in 73% of patients.
    explanation: >-
      All patients in the pooled 30-case series had severely limited speech or no
      words.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Absence of speech was reported in all individuals with ID.
    explanation: Confirms absent speech in the whole intellectually disabled subgroup.
- name: Sensorineural hearing impairment
  category: Auditory
  description: >-
    Bilateral sensorineural hearing loss, usually detectable from early infancy,
    is one of the three cardinal features. It is the single most consistent
    finding across families and, in at least one sibling, has been the ONLY
    manifestation of a confirmed biallelic genotype.
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: >-
    93.62% in the 51-individual pooled cohort; 77% specifically
    sensorineural in the earlier 30-patient summary.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Using whole-exome sequencing, we have identified in ten families 14 individuals
      with microcephaly, developmental delay, intellectual disability, hypotonia,
      spasticity, seizures, sensorineural hearing loss, cortical visual impairment,
      and rare autosomal-recessive predicted pathogenic variants in spermatogenesis-associated
      protein 5 (SPATA5).
    explanation: >-
      Sensorineural hearing loss is part of the founding phenotype description in
      ten families.
  - reference: PMID:28293831
    reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family
      with Variable Phenotypic Expression.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In the sister, the only manifestation was an isolated sensorineural hearing
      loss.
    explanation: >-
      Demonstrates that the hearing loss can occur in isolation, defining the
      mild end of the spectrum.
- name: Microcephaly
  category: Neurologic
  description: >-
    Microcephaly is present in the large majority and is usually congenital
    rather than acquired, which is one of the features that separates this
    disorder from the AFG2B disease and from most other developmental and
    epileptic encephalopathies.
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: 85.71% in the 51-individual pooled cohort; 90% in the earlier 30-patient summary.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The vast majority of the individuals presented with microcephaly (85.71%).
    explanation: Pooled frequency across 51 individuals.
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Other prominent features are microcephaly (90%), gastrointestinal problems
      (73%), abnormal brain MRI (67%, predominantly brain atrophy and delayed myelination),
      visual impairment (most frequently cortical visual impairment, 41%) and no or
      reduced eye contact (48%).
    explanation: Independent pooled estimate from the 30-patient literature summary.
- name: Global developmental delay
  category: Neurologic
  description: >-
    Neurodevelopmental delay is evident from the first months of life and affects
    all streams, with motor milestones and communication most severely involved.
  frequency: VERY_FREQUENT
  notes: >-
    Neurodevelopmental delay 84.31% in the 51-individual pooled cohort; global
    developmental delay in all patients in the earlier 30-patient summary.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Symptoms start in early infancy with all of the patients developing global
      developmental delay with severely limited speech or no words, hearing impairment
      (most frequently sensorineural hearing loss, 77%), and a pathological EEG with
      symptomatic epilepsy being present in 73% of patients.
    explanation: All pooled patients had global developmental delay from early infancy.
- name: Seizure
  category: Neurologic
  description: >-
    Epilepsy affects roughly three quarters of individuals. Generalised-onset
    seizures predominate, and the epilepsy is usually drug resistant, requiring
    polytherapy. A minority of individuals never develop seizures at all, so
    epilepsy is a frequent but not obligate feature despite the historical name
    of the syndrome.
  frequency: FREQUENT
  notes: >-
    38 of 51 individuals (74.5%) in the pooled cohort; 73% in the earlier
    30-patient summary. Drug resistance was reported in 82.35% of the 17
    individuals with anti-seizure medication data, but that denominator is small
    and conditioned on having epilepsy, so no separate frequency band is asserted
    for drug resistance.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Epilepsy was present in 74.71% of cases, with seizures of generalized
      onset being the most common (70.83%), and infantile epileptic spasms syndrome
      (IESS) was the predominant epilepsy syndrome at onset (66.67%).
    explanation: Gives the pooled epilepsy frequency and the seizure-type breakdown.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Epilepsy was often drug-resistant (82.35%).
    explanation: Documents the drug-resistant character of the epilepsy.
- name: Infantile spasms
  category: Neurologic
  description: >-
    When epilepsy occurs, it most often declares itself as an infantile epileptic
    spasms syndrome in the first two years of life, with a mean onset around 9 to
    14 months. Epileptic spasms or tonic seizures typically emerge between 6 and
    12 months in the smaller Japanese series. Neither corticosteroids nor
    vigabatrin, the standard first-line treatments for infantile spasms, achieve
    seizure control in this disorder.
  notes: >-
    Frequency band deliberately omitted. Infantile epileptic spasms syndrome was
    reported in 16 of the 24 individuals with detailed epilepsy data (66.67%),
    which is 16 of the whole 51-individual cohort (31%). The band would be
    FREQUENT on one denominator and would sit at the top of FREQUENT on the
    other, so the raw fractions are recorded here instead of an asserted band.
  phenotype_term:
    preferred_term: Infantile spasms
    term:
      id: HP:0012469
      label: Infantile spasms
  evidence:
  - reference: PMID:40712368
    reference_title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet\
      \ in epilepsy and mitochondrial dynamics modulation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In all but one case, the initial epilepsy presentation was infantile epileptic
      spasms syndrome (IESS), with a mean age at onset of 13.6 months.
    explanation: Infantile epileptic spasms syndrome was the presenting epilepsy in
      four of five patients.
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Epileptic spasms or tonic seizures emerged at 6-12 months of age.
    explanation: Independent series giving the age window for spasm onset.
  - reference: PMID:33063670
    reference_title: Description of a peculiar alternating ictal electroclinical pattern
      in a young boy with a novel SPATA5 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The epileptic clinical features were characterized by infantile spasms\
      \ associated with seizures with a complex ocular movement; a predominant involvement\
      \ of the posterior cerebral area and cortical visual impairment were also noticed."
    explanation: Single-case electroclinical description of the spasm phenotype.
- name: Multifocal epileptiform discharges
  category: Neurologic
  description: >-
    Interictal EEG typically shows a slow, disorganised background with
    multifocal spikes and bursts of asynchronous diffuse spike-wave complexes.
    The consanguineous family reported in 2016 showed slow and asymmetric waves.
    No single EEG signature has been established, because detailed tracings are
    available for only a minority of reported individuals.
  phenotype_term:
    preferred_term: Multifocal epileptiform discharges
    term:
      id: HP:0010841
      label: Multifocal epileptiform discharges
  evidence:
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Interictal electroencephalography showed multifocal spikes and bursts
      of asynchronous diffuse spike-wave complexes.
    explanation: Describes the interictal EEG pattern in three genotyped children.
  - reference: PMID:27683084
    reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
      of intellectual disability, hypotonia and hearing loss.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Further symptoms were hearing loss, vision impairment, gastrointestinal
      disturbances, and slow and asymmetric waves in the EEG.
    explanation: >-
      Reports an abnormal but non-specific EEG in a large consanguineous family,
      supporting EEG abnormality without confirming the multifocal pattern.
- name: Cerebral visual impairment
  category: Ophthalmologic
  description: >-
    Visual impairment is common and is most often cortical rather than ocular in
    origin. Reduced or absent eye contact is frequent, and strabismus and
    refractive errors also occur.
  frequency: FREQUENT
  notes: >-
    Visual impairment 79.49% overall in the 51-individual pooled cohort, of
    which cortical blindness 9.68%, refractive abnormality 9.68% and strabismus
    9.68%; cortical visual impairment specifically 41% in the earlier 30-patient
    summary.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Other prominent features are microcephaly (90%), gastrointestinal problems
      (73%), abnormal brain MRI (67%, predominantly brain atrophy and delayed myelination),
      visual impairment (most frequently cortical visual impairment, 41%) and no or
      reduced eye contact (48%).
    explanation: Identifies cortical visual impairment as the dominant visual phenotype.
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Using whole-exome sequencing, we have identified in ten families 14 individuals
      with microcephaly, developmental delay, intellectual disability, hypotonia,
      spasticity, seizures, sensorineural hearing loss, cortical visual impairment,
      and rare autosomal-recessive predicted pathogenic variants in spermatogenesis-associated
      protein 5 (SPATA5).
    explanation: Cortical visual impairment is part of the founding phenotype description.
- name: Hypotonia
  category: Neurologic
  description: >-
    Central hypotonia, characteristically axial, is the commonest motor sign and
    is often present in the neonatal period. It coexists with peripheral
    hypertonia rather than replacing it.
  frequency: FREQUENT
  notes: 71.74% in the 51-individual pooled cohort.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most common motor symptoms were hypotonia (71.74%) and spasticity
      (60.87%).
    explanation: Gives the pooled frequency of hypotonia.
- name: Spasticity
  category: Neurologic
  description: >-
    Peripheral spasticity develops in the majority and combines with axial
    hypotonia to give the mixed abnormal muscle tone that names the MONDO term.
    Gross motor function is severely limited: nearly six in ten individuals are
    GMFCS level V.
  frequency: FREQUENT
  notes: >-
    60.87% in the 51-individual pooled cohort. Motor impairment overall was
    97.83% of those with data, and 59.09% were GMFCS level V.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most common motor symptoms were hypotonia (71.74%) and spasticity
      (60.87%).
    explanation: Gives the pooled frequency of spasticity.
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Using whole-exome sequencing, we have identified in ten families 14 individuals
      with microcephaly, developmental delay, intellectual disability, hypotonia,
      spasticity, seizures, sensorineural hearing loss, cortical visual impairment,
      and rare autosomal-recessive predicted pathogenic variants in spermatogenesis-associated
      protein 5 (SPATA5).
    explanation: Spasticity co-occurring with hypotonia in the founding cohort.
- name: Inability to walk
  category: Neurologic
  description: >-
    Gross motor function is severely limited. Among the individuals graded on
    the Gross Motor Function Classification System, roughly six in ten were
    level V with a further quarter at level IV, so about 86% of those graded
    are non-ambulatory and require full physical assistance. Motor impairment
    of some degree was present in almost all individuals with available data.
  frequency: VERY_FREQUENT
  notes: >-
    Denominator, stated explicitly because it is not the pooled cohort. The
    GMFCS percentages do not run over the 51 pooled individuals; they resolve
    arithmetically to n=22, since 59.09% is 13/22, 27.27% is 6/22, 9.09% is
    2/22 and 4.55% is 1/22, which sum to 22 individuals and to 100%. The deep
    research artifact records the GMFCS subgroup as n=22 explicitly, and the
    same paper reports motor impairment over a different subgroup again
    (97.83%, i.e. 45/46), so denominators vary from section to section.
    The cached paper's own prose conflicts with its own arithmetic. It reads
    "All individuals were assessed using the Gross Motor Function
    Classification System (GMFCS)", which taken literally would put the
    denominator at 51. The arithmetic is preferred here over the prose.
    The band is chosen on the n=22 reading: 19 of the 22 individuals actually
    graded (86.36%) were at GMFCS level IV or V, both of which denote
    non-ambulatory status requiring physical assistance, and 86.36% is above
    80% and so maps to VERY_FREQUENT. On the alternative reading, in which the
    same 19 individuals are taken over the full pooled cohort, 19/51 is 37% and
    the band would be FREQUENT. The n=22 reading is used because individuals
    who were not graded are unknown rather than known to be ambulatory, which
    is the usual convention for frequency denominators; a reader who instead
    treats the paper's "All individuals" wording as authoritative should read
    this band as FREQUENT. Note that the entry deliberately omits three other
    frequency bands (for example infantile epileptic spasms syndrome, 16/24
    with detailed epilepsy data but 16/51 of the cohort) where the denominator
    is unknown, is very small, or is conditioned in a way that leaves no
    principled choice between readings. Here the band is retained rather than
    dropped because the subgroup denominator is recoverable exactly from the
    published percentages and both readings are recorded. The 9.09% at level
    III walk with a handheld mobility device and the 4.55% at level II are
    ambulatory with limitations.
  phenotype_term:
    preferred_term: Inability to walk
    term:
      id: HP:0002540
      label: Inability to walk
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All individuals were assessed using the Gross Motor Function... System\
      \ (GMFCS): 59.09% were classified as level V, 27.27% as level IV, 9.09% as level\
      \ III"
    explanation: >-
      Gives the GMFCS distribution from which the non-ambulatory fraction is
      derived. The elided word is "Classification", split across a line break by
      a hyphen in the cached PDF text.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: ment was present in almost all individuals with available data (97.83%).
    explanation: >-
      Records that motor impairment of some degree is near-universal. The quote
      starts mid-word because "Motor impairment" is split across a line break by
      a hyphen in the cached PDF text.
- name: Dystonia
  category: Neurologic
  description: >-
    Non-paroxysmal movement disorders affect over a third of individuals, with
    dystonia the commonest, followed by dyskinesia, ataxia, chorea and athetosis.
    Movement disorders are probably under-recognised, as in other developmental
    and epileptic encephalopathies.
  frequency: OCCASIONAL
  notes: >-
    Dystonia 21.74% in the 51-individual pooled cohort; movement disorders of
    any kind 36.96%.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "movement disorders were present in 36.96% of the individuals, with\
      \ dystonia being the most prevalent (21.74%), followed by dyskinesia (6.52%),\
      \ ataxia (6.52%), chorea (4.35%), and athetosis (2.17%)."
    explanation: >-
      Gives the movement-disorder breakdown with dystonia predominant. The quote
      starts mid-sentence because the preceding word, "Non-paroxysmal", is split
      across a line break by a hyphen in the cached PDF text.
  - reference: PMID:27683084
    reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
      of intellectual disability, hypotonia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: in a further individual with global developmental delay, infantile spasms,
      profound dystonia, and sensorineural hearing loss.
    explanation: Individual case with profound dystonia and a confirmed genotype.
- name: Feeding difficulties
  category: Gastrointestinal
  description: >-
    Gastrointestinal symptoms affect around four in five individuals. Dysphagia
    is the commonest, followed by gastro-oesophageal reflux and constipation;
    intestinal obstruction and recurrent gastroenteritis are occasional.
  frequency: FREQUENT
  notes: >-
    Gastrointestinal symptoms 78.95% in the 51-individual pooled cohort, of
    which dysphagia 30%, gastro-oesophageal reflux 20% and constipation 16.67%;
    gastrointestinal problems 73% in the earlier 30-patient summary.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A high proportion of individuals (78.95%) experienced gastrointestinal\
      \ symptoms. Dysphagia was the most common symptom (30%), followed by gastroesophageal\
      \ reflux (20%), and constipation (16.67%)"
    explanation: Gives the gastrointestinal symptom profile and its frequency.
  - reference: PMID:27683084
    reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
      of intellectual disability, hypotonia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Further symptoms were hearing loss, vision impairment, gastrointestinal
      disturbances, and slow and asymmetric waves in the EEG.
    explanation: Independent family with gastrointestinal disturbance.
- name: Cerebral hypomyelination
  category: Neuroimaging
  description: >-
    Hypomyelination or delayed myelination is the commonest MRI abnormality.
    Brain MRI is abnormal in about two thirds of individuals and entirely normal
    in about a third, so normal imaging does not exclude the diagnosis.
  frequency: FREQUENT
  notes: >-
    Hypomyelination 39.02% and abnormal MRI overall 68.29% in the
    51-individual pooled cohort; abnormal brain MRI 67% in the earlier
    30-patient summary. Brain MRI was normal in 31.71% of cases.
  phenotype_term:
    preferred_term: Cerebral hypomyelination
    term:
      id: HP:0006808
      label: Cerebral hypomyelination
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Brain MRI abnormalities were frequently observed (68.29%), including
      hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum
      (29.27%).
    explanation: Gives the imaging frequencies from the largest cohort.
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Magnetic resonance imaging revealed hypomyelination, thin corpus callosum,
      and progressive cerebral atrophy.
    explanation: Independent imaging description in three genotyped children.
- name: Cerebral atrophy
  category: Neuroimaging
  description: >-
    Global brain atrophy is seen in about a third of individuals and can be
    progressive on serial imaging, which contributed to the disorder being
    described in early reports as neurodegenerative.
  frequency: FREQUENT
  notes: Global brain atrophy 34.15% in the 51-individual pooled cohort.
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Brain MRI abnormalities were frequently observed (68.29%), including
      hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum
      (29.27%).
    explanation: Gives the pooled frequency of brain atrophy.
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Magnetic resonance imaging revealed hypomyelination, thin corpus callosum,
      and progressive cerebral atrophy.
    explanation: Documents that the atrophy is progressive.
- name: Thin corpus callosum
  category: Neuroimaging
  description: A thin corpus callosum is seen in roughly three in ten individuals.
  frequency: OCCASIONAL
  notes: 29.27% in the 51-individual pooled cohort.
  phenotype_term:
    preferred_term: Thin corpus callosum
    term:
      id: HP:0033725
      label: Thin corpus callosum
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Brain MRI abnormalities were frequently observed (68.29%), including
      hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum
      (29.27%).
    explanation: Gives the pooled frequency of thin corpus callosum.
- name: Depressed nasal bridge
  category: Craniofacial
  description: >-
    A recognisable but subtle facies has been described in a small Japanese
    series: a depressed nasal bridge or ridge with broad eyebrows and
    retrognathia. This has not been systematically assessed in the larger pooled
    cohorts, so it is recorded without a frequency band.
  phenotype_term:
    preferred_term: Depressed nasal bridge
    term:
      id: HP:0005280
      label: Depressed nasal bridge
  evidence:
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common facies were a depressed nasal bridge/ridge, broad eyebrows, and
      retrognathia.
    explanation: Describes the shared facial gestalt in three genotyped children.
- name: Retrognathia
  category: Craniofacial
  description: >-
    Retrognathia was part of the shared facies in the Japanese series and mild
    retrognathia was also noted in the Estonian and German patients.
  phenotype_term:
    preferred_term: Retrognathia
    term:
      id: HP:0000278
      label: Retrognathia
  evidence:
  - reference: PMID:27246907
    reference_title: Characterization of SPATA5-related encephalopathy in early childhood.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common facies were a depressed nasal bridge/ridge, broad eyebrows, and
      retrognathia.
    explanation: Retrognathia in the described facial gestalt.
- name: Increased circulating lactate concentration
  category: Metabolic
  description: >-
    Mild, persistent elevation of plasma lactate has been observed in a small
    minority of individuals, without any other abnormality of mitochondrial
    biomarkers and without elevated lactate in urine or cerebrospinal fluid. This
    is the only biochemical abnormality reported with any consistency, and it is
    important mainly because it reinforces the mistaken impression of a primary
    mitochondrial disease.
  notes: >-
    Frequency band deliberately omitted. Two individuals (Patient IDs 43 and 45)
    had a persistent mild lactate elevation of 1.9 to 3.9 mmol/l, but the
    denominator is not the full 51-individual cohort: the phrase used is "two
    individuals in our cohort", and the discussion identifies them as cases 3 and
    5 of the authors' own five-patient ketogenic-diet series, so systematic
    metabolic data are not available for the pooled literature cases. Against a
    denominator of 51 the band would be VERY_RARE and against a denominator of 5
    it would be VERY_FREQUENT, so no band is asserted.
  phenotype_term:
    preferred_term: Increased circulating lactate concentration
    term:
      id: HP:0002151
      label: Increased circulating lactate concentration
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two individuals in our cohort (Patient ID 43, 45)... a persistent mild\
      \ elevation of lactate (1.9-3.9 mmol/l) without other abnormalities in mitochondrial...\
      \ including acid-base balance, creatine kinase... organic acids, amino acids,\
      \ carnitines, oxidative stress markers, circulating cytokines, or mitochondrial\
      \ growth factors. No elevated lactate was detected in urine or cerebrospinal\
      \ fluid."
    explanation: >-
      Quantifies the lactate finding and, importantly, records the absence of
      other mitochondrial biomarker abnormalities.
genetic:
- name: AFG2A
  gene_term:
    preferred_term: AFG2A
    term:
      id: hgnc:18119
      label: SPATA5
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: Biallelic pathogenic or likely pathogenic variants
  notes: >-
    AFG2A is the current HGNC-approved symbol for the gene published throughout
    the clinical literature as SPATA5. The gene lies at 4q28.1 and encodes an
    892-amino-acid AAA+ ATPase with two conserved ATPase modules. Forty-two
    different disease-associated variants had been reported across the 51 pooled
    individuals; the majority are compound heterozygous rather than homozygous,
    and four recurrent alleles (c.2081G>A, c.989_991del, c.251G>A and
    c.1714+1G>A) account for 42% of individuals. See the entry-level notes for
    the full symbol history and the reason the term label reads SPATA5.
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:27683084
      reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
        of intellectual disability, hypotonia and hearing loss.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We thus independently confirm that bi-allelic pathogenic variants in
        SPATA5 cause a syndromic form of intellectual disability, and we delineate
        its clinical presentation.
      explanation: Confirms biallelic requirement for the gene-level association.
  evidence:
  - reference: PMID:26299366
    reference_title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual
      Disability, Seizures, and Hearing Loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Using whole-exome sequencing, we have identified in ten families 14 individuals
      with microcephaly, developmental delay, intellectual disability, hypotonia,
      spasticity, seizures, sensorineural hearing loss, cortical visual impairment,
      and rare autosomal-recessive predicted pathogenic variants in spermatogenesis-associated
      protein 5 (SPATA5).
    explanation: The founding gene-disease association across ten families.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Regarding pathogenicity, variants were classified into pathogenic (72.55%),\
      \ likely pathogenic (21.57%) and variant of uncertain significance (5.88%)."
    explanation: >-
      Summarises the pathogenicity distribution of the 42 reported disease
      alleles.
  variants:
  - name: c.989_991del (p.Thr330del)
    description: >-
      A recurrent in-frame single-amino-acid deletion reported in multiple
      unrelated families, including the Japanese siblings, the Polish family in
      which one sibling had isolated hearing loss, and several of the Estonian
      and German compound heterozygotes.
    type: in-frame deletion
    clinical_significance: PATHOGENIC
    gene:
      preferred_term: AFG2A
      term:
        id: hgnc:18119
        label: SPATA5
    evidence:
    - reference: PMID:27246907
      reference_title: Characterization of SPATA5-related encephalopathy in early
        childhood.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Two siblings carried compound heterozygous mutations, c.989_991del\
        \ (p.Thr330del) and c.2130_2133del (p.Glu711Profs*21), and the third child\
        \ had c.967T>A (p.Phe323Ile) and c.2146G>C (p.Ala716Pro) mutations."
      explanation: Documents the recurrent p.Thr330del allele in trans with a frameshift.
    - reference: PMID:28293831
      reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a
        Family with Variable Phenotypic Expression.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Herein we describe a family in which two SPATA5 mutations with established\
        \ pathogenicity (p.Thr330del and c.1714+1G>A) were found in the proband and\
        \ her younger sister."
      explanation: >-
        The same recurrent allele in a family with strikingly variable expression
        between siblings.
  - name: c.1822_1824del (p.Asp608del)
    description: >-
      Homozygous in-frame deletion segregating with severe intellectual
      disability and microcephaly in an extended consanguineous family with seven
      affected individuals; molecular modelling predicted a deleterious effect on
      protein function.
    type: in-frame deletion
    clinical_significance: LIKELY_PATHOGENIC
    gene:
      preferred_term: AFG2A
      term:
        id: hgnc:18119
        label: SPATA5
    evidence:
    - reference: PMID:27683084
      reference_title: SPATA5 mutations cause a distinct autosomal recessive phenotype
        of intellectual disability, hypotonia and hearing loss.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Linkage analysis followed by exome sequencing revealed a homozygous\
        \ variant in SPATA5 (c.1822_1824del; p.Asp608del), which segregates with the\
        \ phenotype in the family."
      explanation: Segregation evidence in a seven-affected consanguineous family.
  - name: c.251G>A (p.Arg84Gln)
    description: >-
      Recurrent missense allele; found homozygous through maternal uniparental
      isodisomy of chromosome 4 in a diagnostic case of developmental
      encephalopathy with late-onset epilepsy, and one of the four alleles
      accounting for 42% of reported individuals.
    type: missense
    clinical_significance: PATHOGENIC
    gene:
      preferred_term: AFG2A
      term:
        id: hgnc:18119
        label: SPATA5
    evidence:
    - reference: PMID:30552426
      reference_title: "The role of recessive inheritance in early-onset epileptic\
        \ encephalopathies: a combined whole-exome sequencing and copy number study."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This diagnostic case with developmental encephalopathy with late-onset\
        \ epilepsy also had an unusual mutational mechanism with homozygotization\
        \ of a... inherited variant due to maternal isodisomy of..."
      explanation: >-
        Documents an unusual route to homozygosity, maternal uniparental
        isodisomy of chromosome 4, which is relevant to recurrence-risk
        counselling. The quote is elided at two points because "maternally" and
        "chromosome" are each split across a line break by a hyphen in the
        cached PDF text.
diagnosis:
- name: Exome or genome sequencing
  description: >-
    The diagnosis is molecular. Every reported cohort was ascertained by
    whole-exome sequencing, usually after a clinical suspicion of a mitochondrial
    disorder or of an unexplained developmental and epileptic encephalopathy.
    Targeted epilepsy or hearing loss panels may not include the gene, and the
    symbol under which it is listed may still be SPATA5.
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This study describes five patients with psychomotor developmental delay,
      microcephaly, epilepsy and hearing impairment, who were thought clinically to
      have a mitochondrial disease with subsequent whole-exome sequencing analysis
      detecting compound heterozygous variants in the SPATA5 gene.
    explanation: >-
      Illustrates the usual diagnostic route: a suspected mitochondrial disorder
      resolved by exome sequencing.
  notes: >-
    Elevated or high-normal blood copper was reported in the three Japanese
    children (PMID:27246907) but has never been replicated in any later cohort,
    so it is recorded here as an unreplicated observation and not curated as a
    biochemical feature of the disease.
- name: Audiological assessment
  description: >-
    Because sensorineural hearing loss is near-universal and may be the earliest
    or, rarely, the only sign, formal audiological testing is indicated in any
    child with unexplained microcephaly and developmental delay, and biallelic
    AFG2A variants should be considered in apparently isolated sensorineural
    hearing impairment.
  evidence:
  - reference: PMID:28293831
    reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family
      with Variable Phenotypic Expression.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our findings extend the phenotypic spectrum of SPATA5-associated diseases
      and indicate that SPATA5 defects may account for a fraction of isolated sensorineural
      hearing impairment cases.
    explanation: Supports including the gene in the workup of isolated hearing loss.
treatments:
- name: Ketogenic diet
  description: >-
    The ketogenic diet is the only intervention with disease-specific evidence.
    In a series of five genotyped patients, four received the diet for
    drug-resistant epilepsy with seizure reduction rates of 0%, 30%, 70% and
    100%; the patient who became seizure free is maintained on ketogenic diet
    monotherapy. Non-seizure benefits (social interaction, attention, motor
    function) were reported in three. Fibroblasts from these patients cultured in
    a ketogenic-diet-mimicking medium showed reversal of the mitochondrial
    morphology, dynamics and ATP abnormalities, giving a plausible mechanistic
    rationale. The evidence is a small uncontrolled series and is recorded as
    partial.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Ketogenic diet
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  notes: >-
    Four treated patients is the entire published experience. The 2026 review
    adds that neither corticosteroids nor vigabatrin, the standard first-line
    treatments for infantile epileptic spasms syndrome, achieved seizure control
    in this disorder, which is why the diet is being explored.
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Infantile spasms
    term:
      id: HP:0012469
      label: Infantile spasms
  target_mechanisms:
  - target: Neuronal Mitochondrial Fusion-Fission Imbalance
    treatment_effect: RESTORES
    description: >-
      Fibroblasts from these same genotyped patients, cultured in a
      ketogenic-diet-mimicking medium, recovered the altered mitochondrial
      morphology and dynamics and the reduced ATP production. The diet is
      therefore hypothesised to act on this node rather than on a conventional
      anti-seizure target; the link is between a clinical response and an ex vivo
      readout in the same patients, not a demonstrated in vivo mechanism.
    evidence:
    - reference: PMID:40712368
      reference_title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet\
        \ in epilepsy and mitochondrial dynamics modulation."
      supports: PARTIAL
      evidence_source: IN_VITRO
      snippet: These abnormalities were significantly reversed when the fibroblasts
        were cultured in KD-MM.
      explanation: >-
        Direct evidence that the ketogenic-diet condition reverses the
        mitochondrial abnormality modelled by this node, in cells from treated
        patients.
  evidence:
  - reference: PMID:40712368
    reference_title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet\
      \ in epilepsy and mitochondrial dynamics modulation."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Four patients received KD treatment for DRE, with seizure reduction\
      \ rates of 0 %, 30 %, 70 % and 100 %, respectively."
    explanation: >-
      The primary clinical outcome data, from an uncontrolled series of four
      treated patients.
  - reference: PMID:40712368
    reference_title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet\
      \ in epilepsy and mitochondrial dynamics modulation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: These abnormalities were significantly reversed when the fibroblasts were
      cultured in KD-MM.
    explanation: >-
      Patient fibroblasts in a ketogenic-diet-mimicking medium recover their
      mitochondrial phenotype, supplying the mechanistic rationale.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: The KD showed... efficacy in selected cases, particularly when initiated
      early.
    explanation: >-
      The systematic review's assessment, which stops short of recommending the
      diet as standard care. The elided word is "partial", split across a line
      break by a hyphen in the cached PDF text.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The fourth individual (Patient ID 41), with refractory IESS, became\
      \ seizure free with the ketogenic diet (KD) and is now on KD monotherapy."
    explanation: >-
      Documents the single individual in the pooled cohort who achieved seizure
      freedom on ketogenic diet monotherapy.
- name: Anti-seizure medication polytherapy
  description: >-
    Most individuals with epilepsy require more than one anti-seizure medication
    and remain refractory. No agent has shown disease-specific superiority; the
    reported regimens span valproate, levetiracetam, lamotrigine, vigabatrin,
    ACTH, topiramate, zonisamide, clobazam, phenobarbital, rufinamide,
    cannabidiol and others. Only four of sixteen individuals with follow-up data
    achieved seizure freedom. Notably, the standard first-line treatments for
    infantile epileptic spasms syndrome do not work here.
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Epilepsy was often drug-resistant (82.35%).
    explanation: Establishes that most treated epilepsy is drug resistant.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As we recently reported, individuals with IESS do not achieve seizure\
      \ control with usual first-line treatment (neither corticosteroids nor vigabatrin)."
    explanation: >-
      Specifically records the failure of corticosteroids and vigabatrin, which
      is directly actionable for clinicians.
- name: Early hearing habilitation
  description: >-
    Sensorineural deafness is congenital and detectable on newborn or neonatal
    brainstem audiometry, so amplification or implantation can be started in the
    first months. One genotyped child received a hearing device before the age of
    two months after postnatal brainstem audiometry showed sensorineural
    deafness. No systematic outcome data for cochlear implantation in this
    disorder exist, and profound intellectual disability with cerebral visual
    impairment complicates candidacy assessment, so this is curated as supportive
    habilitation rather than as an intervention with demonstrated efficacy in
    this genotype.
  action_category: THERAPEUTIC
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: hearing habilitation
    term:
      id: NCIT:C15315
      label: Rehabilitation
  notes: >-
    The treatment term is deliberately the generic Rehabilitation action.
    NCIT:C157820 `Cochlear Implant` exists but denotes the device, not a clinical
    action, and is not reachable from NCIT:C25218, so it fails the
    TreatmentActionTerm dynamic enum. No NCIT clinical-action term for cochlear
    implantation or hearing-aid fitting was found by `runoak` search, so the
    nearest honest action term is used and the specificity is carried by
    `preferred_term`.
  target_phenotypes:
  - preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:34360601
    reference_title: Muscular and Molecular Pathology Associated with SPATA5 Deficiency
      in a Child with EHLMRS.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Postnatal brainstem audiometry showed sensorineural deafness, for which
      she received a hearing device before the age of two months.
    explanation: >-
      Single genotyped patient documenting that hearing habilitation is feasible
      within the first two months of life; no outcome is reported, hence PARTIAL.
differential_diagnoses:
- name: AFG2B-related neurodevelopmental disorder
  description: >-
    Caused by biallelic variants in AFG2B, the gene formerly called SPATA5L1 and
    therefore one character away from this disorder's own former gene symbol. The
    two proteins are partners in the same 55LCC ATPase complex, so the disorders
    overlap for a real mechanistic reason and are routinely discussed together.
    The discriminators are quantitative and developmental rather than absolute:
    in AFG2B disease sensorineural hearing loss is present in all affected
    individuals but only about half have any neurodevelopmental involvement at
    all, the neurodevelopmental phenotype is described as non-progressive and
    mixed with spastic-dystonic cerebral palsy prominent, and microcephaly is not
    a defining feature. In AFG2A disease microcephaly is present in around 86%,
    intellectual disability in around 98%, and the epilepsy is typically an
    infantile epileptic spasms syndrome.
  distinguishing_features:
  - Caused by AFG2B (SPATA5L1, HGNC:28762), not AFG2A (SPATA5, HGNC:18119)
  - Sensorineural hearing loss is universal but the neurodevelopmental phenotype is
    present in only about half of affected individuals
  - Neurodevelopmental involvement is described as non-progressive and mixed, with
    spastic-dystonic cerebral palsy prominent
  - Congenital microcephaly is not a cardinal feature, whereas it is one of the AFG2A
    triad
  - Periventricular leukomalacia and reduced white matter volume are reported, rather
    than the hypomyelination plus progressive cerebral atrophy pattern of AFG2A disease
  disease_term:
    preferred_term: AFG2B-related neurodevelopmental disorder
    term:
      id: MONDO:0859206
      label: neurodevelopmental disorder with hearing loss and spasticity
  evidence:
  - reference: PMID:34626583
    reference_title: Bi-allelic variants in SPATA5L1 lead to intellectual disability,
      spastic-dystonic cerebral palsy, epilepsy, and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report 28 bi-allelic variants in SPATA5L1 associated with sensorineural\
      \ hearing loss in 47 individuals from 28 (26 unrelated) families. In addition,\
      \ 25/47 affected individuals (53%) presented with microcephaly, developmental\
      \ delay/intellectual disability, cerebral palsy, and/or epilepsy."
    explanation: >-
      Establishes the AFG2B cohort and the key quantitative discriminator, that
      only 53% have neurodevelopmental involvement.
  - reference: PMID:34626583
    reference_title: Bi-allelic variants in SPATA5L1 lead to intellectual disability,
      spastic-dystonic cerebral palsy, epilepsy, and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Collectively, our results indicate that bi-allelic SPATA5L1 variants\
      \ lead to a human disease characterized by sensorineural hearing loss (SNHL)\
      \ with or without a nonprogressive mixed neurodevelopmental phenotype."
    explanation: >-
      The authors' own summary, which contrasts with the progressive cerebral
      atrophy described in AFG2A disease.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pathogenic variants in AFG2B, previously named SPATA5L1, are associated\
      \ with a... disorders characterized by overlapping clinical features, including\
      \ ID, neurodevelopmental delay... hearing loss, and dystonia"
    explanation: >-
      The AFG2A review itself flags the AFG2B disorder as the closest phenotypic
      neighbour. The elided words are "neurodevelopmental" and "epilepsy", each
      split across a line break by a hyphen in the cached PDF text.
- name: Primary mitochondrial disease
  description: >-
    This is the differential that actually costs patients time. Congenital
    microcephaly with deafness, cortical visual impairment, epilepsy, hypotonia
    and a mildly raised lactate is a classic mitochondrial presentation, and both
    the auditory and the optic nerve are selectively vulnerable to energy
    failure. Several published AFG2A cohorts were assembled precisely because the
    children were being investigated for suspected mitochondrial disease. The
    discriminator is that no consistent mitochondrial biomarker abnormality has
    been found in AFG2A disease: lactate is normal in all but a few individuals
    and is normal in urine and cerebrospinal fluid even in those, and acid-base
    balance, creatine kinase, pyruvate, organic acids, amino acids and carnitines
    are unremarkable. Mitochondrial DNA studies in the reported patients were
    normal. AFG2A dysfunction does produce secondary mitochondrial abnormalities,
    but the primary lesion is in cytoplasmic ribosome maturation, not in
    oxidative phosphorylation.
  distinguishing_features:
  - No consistent mitochondrial biomarker abnormality; lactate elevation is mild and
    confined to a small minority, and urine and cerebrospinal fluid lactate are normal
  - Mitochondrial DNA depletion, deletion and sequencing studies were normal in the
    reported patients
  - Congenital microcephaly with sensorineural deafness as an obligate pairing is unusual
    in primary mitochondrial disease
  - The primary molecular lesion is in cytoplasmic pre-60S ribosome maturation, with
    mitochondrial dysfunction as a secondary consequence
  disease_term:
    preferred_term: Mitochondrial disease
    term:
      id: MONDO:0044970
      label: mitochondrial disease
  evidence:
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The cardinal clinical features of AFG2A-RE may mimic those of a mitochondrial
      disease.
    explanation: >-
      The systematic review names mitochondrial disease as the principal clinical
      mimic.
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Biallelic variants in the SPATA5 gene can affect mitochondria in cortical
      neurons and should be considered in patients with a neurodegenerative disorder
      and/or with clinical presentation resembling a mitochondrial disorder.
    explanation: >-
      Explicitly recommends considering this gene in patients presenting as
      mitochondrial disease.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two individuals in our cohort (Patient ID 43, 45)... a persistent mild\
      \ elevation of lactate (1.9-3.9 mmol/l) without other abnormalities in mitochondrial...\
      \ including acid-base balance, creatine kinase... organic acids, amino acids,\
      \ carnitines, oxidative stress markers, circulating cytokines, or mitochondrial\
      \ growth factors. No elevated lactate was detected in urine or cerebrospinal\
      \ fluid."
    explanation: >-
      Supplies the biochemical discriminator: the absence of a mitochondrial
      biomarker signature.
- name: Autosomal recessive nonsyndromic sensorineural hearing loss
  description: >-
    At the mild end of the AFG2A spectrum, a confirmed biallelic genotype can
    produce isolated sensorineural hearing impairment with no microcephaly,
    intellectual disability or epilepsy, as documented in the younger sister of a
    typically affected proband. Such an individual is indistinguishable on
    phenotype from nonsyndromic recessive deafness, and the diagnosis can only be
    made molecularly. The practical consequence runs in both directions: AFG2A
    belongs on hearing loss gene panels, and an apparently nonsyndromic deaf
    child with an AFG2A genotype has a recurrence risk for the full
    encephalopathy in siblings.
  distinguishing_features:
  - Indistinguishable clinically; separation is molecular only
  - Absence of microcephaly, intellectual disability, epilepsy and cortical visual
    impairment despite a confirmed biallelic AFG2A genotype
  - Within-family variability means a sibling of an isolated-deafness case may have
    the full encephalopathy
  notes: >-
    Deliberately left UNBOUND. MONDO models autosomal recessive nonsyndromic
    hearing loss only as numbered locus-specific entities (for example
    MONDO:0009076 autosomal recessive nonsyndromic hearing loss 1A,
    MONDO:0010807 ... 2, MONDO:0010860 ... 3), and binding any one of them would
    assert a specific locus that PMID:28293831 never implicates. No honest
    grouping term for the category exists within the ontology set this repository
    constrains itself to, so the slot is left empty rather than filled with an
    approximate term.
  evidence:
  - reference: PMID:28293831
    reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family
      with Variable Phenotypic Expression.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In the sister, the only manifestation was an isolated sensorineural hearing
      loss.
    explanation: >-
      Documents the isolated-deafness presentation that is clinically
      indistinguishable from nonsyndromic recessive hearing loss.
  - reference: PMID:28293831
    reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family
      with Variable Phenotypic Expression.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our findings extend the phenotypic spectrum of SPATA5-associated diseases
      and indicate that SPATA5 defects may account for a fraction of isolated sensorineural
      hearing impairment cases.
    explanation: >-
      States the authors' inference that the gene contributes to apparently
      isolated hearing impairment.
- name: AIRIM/C1orf109-related neurodevelopmental disorder
  description: >-
    The third disease gene of the same 55LCC complex, described in 2025. Eleven
    unrelated families comprising eighteen individuals presented with severe
    global developmental delay and intellectual disability, muscular hypotonia
    with limb spasticity and dystonia, microcephaly, hearing and vision
    impairment and infantile seizures. This is close enough to AFG2A-related
    encephalopathy that the two are separable only by gene. It is included here
    partly because the 2026 AFG2A systematic review states that no neurological
    disorder has been linked to C1orf109 or CINP, a statement that this paper,
    published five months earlier, already contradicted; a curator relying on the
    review alone would omit this differential entirely.
  distinguishing_features:
  - Caused by AIRIM/C1orf109 (hgnc:26039), a different subunit of the same 55LCC
    complex
  - Hearing impairment is less consistent than in AFG2A disease (9 of 17 versus
    around 94%)
  - Reported seizure semiology is dominated by generalised tonic-clonic and myoclonic
    seizures and Lennox-Gastaut syndrome rather than by infantile epileptic spasms
    syndrome
  - Neuroimaging emphasises severe supratentorial atrophy with ex-vacuum ventricular
    dilatation, rather than the hypomyelination-predominant AFG2A pattern
  notes: >-
    Deliberately left UNBOUND. A `runoak` search of MONDO for both "AIRIM" and
    "C1orf109" returns no term, so no disease entity exists in MONDO for this
    disorder yet. The gene itself resolves (hgnc:26039 ! C1orf109) but a gene is
    not a disease term and must not be put in `disease_term`.
  evidence:
  - reference: PMID:40760247
    reference_title: A programmed decline in ribosome levels governs human early neurodevelopment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we describe variants in the ribosome biogenesis factor AIRIM/C1orf109
      that are primarily associated with neurodevelopmental disorders.
    explanation: >-
      Establishes AIRIM/C1orf109 as a third 55LCC neurodevelopmental disease
      gene.
  - reference: PMID:40760247
    reference_title: A programmed decline in ribosome levels governs human early neurodevelopment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The majority of individuals from whom information was available concomitantly\
      \ showed muscular hypotonia accompanied by limb spasticity and dystonia (each\
      \ 11 of 17), microcephaly (14 of 17), as well as hearing (9 of 17) and vision\
      \ impairment (6 of 17)"
    explanation: >-
      Gives the AIRIM cohort's phenotype counts, which are the basis of the
      discriminators listed above.
  - reference: PMID:41933351
    reference_title: AFG2A-related encephalopathy, expanding the neurodevelopmental
      and epileptic spectrum.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, no... disorders have been linked to the other... of the\
      \ complex, C1orf109 and CINP, to date."
    explanation: >-
      Recorded as REFUTE because this sentence, from the most recent systematic
      review, is superseded by PMID:40760247. It is kept in the entry so the next
      curator sees the contradiction rather than rediscovering it. The elided
      words are "neurological" and "components", each split across a line break
      by a hyphen in the cached PDF text.
  - reference: PMID:40760247
    reference_title: A programmed decline in ribosome levels governs human early neurodevelopment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "human genetic studies have identified a growing number of allelic variants\
      \ in AFG2A, AFG2B and CINP that are specifically... with a range of NDDs, including\
      \ intellectual disabilities, seizures, hearing loss and microcephaly"
    explanation: >-
      The same authors record that CINP too is now a neurodevelopmental disease
      gene, which is the direct contradiction of the review sentence above. The
      elided word is "associated", split across a line break by a hyphen.
discussions:
- discussion_id: afg2a_mouse_null_model_mismatch
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Can any constitutive mouse Afg2a model represent AFG2A-related
    encephalopathy, given that every reported human genotype retains partial
    ATPase function?
  attaches_to:
  - pathophysiology#Biallelic AFG2A Loss of Function
  rationale: >-
    No published human genotype combines two unambiguous null alleles: more than
    half of the 42 reported disease variants are missense and the remainder are
    always found in trans with a missense or in-frame allele. The disease is
    therefore hypomorphic. The IMPC constitutive knockout of the mouse orthologue
    is reported as embryonic lethal before organogenesis, which if correct means a
    complete null cannot model the human disorder at all and that a faithful model
    would have to be a knock-in of a patient hypomorphic allele or a conditional
    neural hypomorph. No such model has been published. The mouse phenotype is
    recorded here from an IMPC database entry surfaced by the deep-research run and
    is deliberately NOT cited as an evidence item, because it has no PMID and this
    entry does not cite un-fetchable sources.
  notes: >-
    Verification status: the missense-majority claim is cited in the entry from
    PMID:41933351. The mouse embryonic lethality claim is unverified against any
    cached reference and is recorded as an open question, not as an assertion.
- discussion_id: afg2a_mitochondrial_localisation_tension
  kind: CONTROVERSY
  status: OPEN
  prompt: >-
    Is the mitochondrial dysfunction in AFG2A deficiency a direct consequence of
    a mitochondrial pool of the protein, or is it secondary to reduced
    translational capacity?
  attaches_to:
  - pathophysiology#Neuronal Mitochondrial Fusion-Fission Imbalance
  rationale: >-
    The protein carries a putative mitochondrial matrix-targeting sequence and was
    originally described as a mitochondrial morphogenesis factor in
    spermatogenesis, and patient cells reproducibly show bioenergetic deficits.
    Against a direct mitochondrial role: the overexpressed protein is dominantly
    cytosolic in cortical neurons and does not co-localise with mitochondrial
    markers (PMID:29343804), no patient shows a consistent mitochondrial biomarker
    abnormality (PMID:41933351), respiratory chain findings are inconsistent
    between patients, and the established molecular function of the 55LCC complex
    is cytoplasmic ribosome maturation. The entry models the mitochondrial arm as
    downstream and provisional, but the question is genuinely open.
  evidence:
  - reference: PMID:29343804
    reference_title: Compound heterozygous SPATA5 variants in four families and functional
      studies of SPATA5 deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: To our surprise the localization of overexpressed SPATA5 in cultured
      primary cortical neurons was dominantly cytosolic and clearly not co-localizing
      with the mitochondrial marker
    explanation: The observation that motivates the question.
  - reference: PMID:35354024
    reference_title: Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5
      control a late step in human ribosome assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: We provide evidence that these factors, together with CINP and SPATA5L1,
      control a late step of human pre-60S maturation in the cytoplasm.
    explanation: >-
      The established molecular function is cytoplasmic, which is the main
      argument against a primary mitochondrial role.
- discussion_id: afg2a_intrafamilial_variability
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Why do siblings carrying the identical biallelic AFG2A genotype range from
    isolated sensorineural hearing loss to full developmental and epileptic
    encephalopathy?
  attaches_to:
  - phenotypes#Sensorineural hearing impairment
  rationale: >-
    In the family reported in PMID:28293831 the proband had the typical
    encephalopathy while her younger sister's only manifestation was isolated
    sensorineural hearing loss, on the same two variants. Comparable variability
    in epilepsy status occurred within the large consanguineous family of
    PMID:27683084. No modifier gene has been identified. Plausible but untested
    candidates are variation in the other 55LCC subunits or in general ribosome
    biogenesis capacity. Until this is resolved, genotype cannot be used to
    counsel on severity.
  evidence:
  - reference: PMID:28293831
    reference_title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family
      with Variable Phenotypic Expression.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The proband had a similar clinical picture to the previous descriptions\
      \ of EHLMRS. In the sister, the only manifestation was an isolated sensorineural\
      \ hearing loss."
    explanation: >-
      Documents the two extremes of expressivity within a single sibship sharing
      the same two variants.
- discussion_id: afg2a_natural_history_gap
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What is the natural history, life expectancy and quality-of-life burden of
    AFG2A-related encephalopathy?
  rationale: >-
    No prospective natural history study, survival curve, population prevalence
    estimate, carrier frequency or validated quality-of-life measurement exists.
    All fifty-one pooled individuals come from retrospective case reports and
    series, three of whom had died, at ages 3, 4.9 and 13.4 years, while two
    individuals from the attenuated consanguineous family were alive at 39 and 41
    years. The 2026 systematic review states directly that prospective natural
    history studies across multiple reference centres are needed. This entry
    therefore carries no survival or quality-of-life claims.
datasets:
- accession: proteomexchange:PXD026182
  title: Quantitative proteomic profiling of a quadriceps muscle biopsy from a child
    with AFG2A-related encephalopathy
  description: >-
    Mass-spectrometry proteome of a skeletal muscle biopsy from an 8-year-old girl
    with two compound heterozygous AFG2A variants. 1778 proteins were robustly
    quantified and 82 were dysregulated, 15 of them mitochondrial. This is the only
    deposited omics dataset from AFG2A patient tissue located during curation.
  data_type: PROTEOMICS
  sample_count: 1
  publication: PMID:34360601
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  evidence:
  - reference: PMID:34360601
    reference_title: Muscular and Molecular Pathology Associated with SPATA5 Deficiency
      in a Child with EHLMRS.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An examination of the proteomic profile performed on the muscle biopsy\
      \ of the patient revealed the robust quantification of 1778 proteins (ProteomeXchange\
      \ project accession #: PXD026182)."
    explanation: Gives the accession and the scale of the deposited proteome.
references:
- reference: PMID:26299366
  title: Mutations in SPATA5 Are Associated with Microcephaly, Intellectual Disability,
    Seizures, and Hearing Loss.
- reference: PMID:27246907
  title: Characterization of SPATA5-related encephalopathy in early childhood.
- reference: PMID:27683084
  title: SPATA5 mutations cause a distinct autosomal recessive phenotype of intellectual
    disability, hypotonia and hearing loss.
- reference: PMID:28293831
  title: Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family with Variable
    Phenotypic Expression.
- reference: PMID:29343804
  title: Compound heterozygous SPATA5 variants in four families and functional studies
    of SPATA5 deficiency.
- reference: PMID:30552426
  title: "The role of recessive inheritance in early-onset epileptic encephalopathies:\
    \ a combined whole-exome sequencing and copy number study."
- reference: PMID:31703473
  title: "Shaping the Nascent Ribosome: AAA-ATPases in Eukaryotic Ribosome Biogenesis."
- reference: PMID:33063670
  title: Description of a peculiar alternating ictal electroclinical pattern in a young
    boy with a novel SPATA5 mutation.
- reference: PMID:34360601
  title: Muscular and Molecular Pathology Associated with SPATA5 Deficiency in a Child
    with EHLMRS.
- reference: PMID:34626583
  title: Bi-allelic variants in SPATA5L1 lead to intellectual disability, spastic-dystonic
    cerebral palsy, epilepsy, and hearing loss.
- reference: PMID:35354024
  title: Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5 control a
    late step in human ribosome assembly.
- reference: PMID:36849973
  title: Computational and mitochondrial functional studies of novel compound heterozygous
    variants in SPATA5 gene support a causal link with epileptogenic encephalopathy.
- reference: PMID:38554706
  title: The SPATA5-SPATA5L1 ATPase complex directs replisome proteostasis to ensure
    genome integrity.
- reference: PMID:40268917
  title: Cryo-EM structure of the AAA+ SPATA5 complex and its role in human cytoplasmic
    pre-60S maturation.
- reference: PMID:40712368
  title: "AFG2A-related encephalopathy: Effectiveness of ketogenic diet in epilepsy\
    \ and mitochondrial dynamics modulation."
- reference: PMID:40760247
  title: A programmed decline in ribosome levels governs human early neurodevelopment.
- reference: PMID:40846618
  title: Deepening the understanding of mechanisms of antiepileptic effects of the
    ketogenic diet in children with AFG2A-related encephalopathy.
- reference: PMID:41933351
  title: AFG2A-related encephalopathy, expanding the neurodevelopmental and epileptic
    spectrum.

📚

References & Deep Research

References

PMID:26299366

Mutations in SPATA5 Are Associated with Microcephaly, Intellectual Disability, Seizures, and Hearing Loss.

No top-level findings curated for this source.

PMID:27246907

Characterization of SPATA5-related encephalopathy in early childhood.

No top-level findings curated for this source.

PMID:27683084

SPATA5 mutations cause a distinct autosomal recessive phenotype of intellectual disability, hypotonia and hearing loss.

No top-level findings curated for this source.

PMID:28293831

Isolated Hearing Impairment Caused by SPATA5 Mutations in a Family with Variable Phenotypic Expression.

No top-level findings curated for this source.

PMID:29343804

Compound heterozygous SPATA5 variants in four families and functional studies of SPATA5 deficiency.

No top-level findings curated for this source.

PMID:30552426

The role of recessive inheritance in early-onset epileptic encephalopathies: a combined whole-exome sequencing and copy number study.

No top-level findings curated for this source.

PMID:31703473

Shaping the Nascent Ribosome: AAA-ATPases in Eukaryotic Ribosome Biogenesis.

No top-level findings curated for this source.

PMID:33063670

Description of a peculiar alternating ictal electroclinical pattern in a young boy with a novel SPATA5 mutation.

No top-level findings curated for this source.

PMID:34360601

Muscular and Molecular Pathology Associated with SPATA5 Deficiency in a Child with EHLMRS.

No top-level findings curated for this source.

PMID:34626583

Bi-allelic variants in SPATA5L1 lead to intellectual disability, spastic-dystonic cerebral palsy, epilepsy, and hearing loss.

No top-level findings curated for this source.

PMID:35354024

Labeling of heterochronic ribosomes reveals C1ORF109 and SPATA5 control a late step in human ribosome assembly.

No top-level findings curated for this source.

PMID:36849973

Computational and mitochondrial functional studies of novel compound heterozygous variants in SPATA5 gene support a causal link with epileptogenic encephalopathy.

No top-level findings curated for this source.

PMID:38554706

The SPATA5-SPATA5L1 ATPase complex directs replisome proteostasis to ensure genome integrity.

No top-level findings curated for this source.

PMID:40268917

Cryo-EM structure of the AAA+ SPATA5 complex and its role in human cytoplasmic pre-60S maturation.

No top-level findings curated for this source.

PMID:40712368

AFG2A-related encephalopathy: Effectiveness of ketogenic diet in epilepsy and mitochondrial dynamics modulation.

No top-level findings curated for this source.

PMID:40760247

A programmed decline in ribosome levels governs human early neurodevelopment.

No top-level findings curated for this source.

PMID:40846618

Deepening the understanding of mechanisms of antiepileptic effects of the ketogenic diet in children with AFG2A-related encephalopathy.

No top-level findings curated for this source.

PMID:41933351

AFG2A-related encephalopathy, expanding the neurodevelopmental and epileptic spectrum.

No top-level findings curated for this source.

Deep Research

Claude Code ▸

AFG2A-Related Encephalopathy — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-opus-5[1m] 24 citations 2026-08-01T07:28:35.351791

AFG2A-Related Encephalopathy — Comprehensive Research Report

Prepared: 2026-08-01 · Target for KB entry: kb/disorders/AFG2A-Related_Encephalopathy.yaml · MONDO:0014698

Scope note on evidence provenance: Every PMID cited below was verified against a cached PubMed record in references_cache/ or fetched live during this session. Quotes marked with > are verbatim from the cited abstract or open-access full text and are suitable as evidence snippet: values after running just validate-references. Ontology IDs are flagged [verified] (checked this session against HPO/OLS/HGNC/MGI APIs) or [suggested — verify with OAK]. Three published-literature discrepancies that would propagate into the KB if copied uncritically are flagged in §4.6.

1. Disease Information

1.1 Overview

AFG2A-related encephalopathy (AFG2A-RE) is an ultra-rare autosomal recessive neurodevelopmental disorder caused by biallelic variants in AFG2A (formerly SPATA5), encoding a AAA+ ATPase that is the human orthologue of yeast Drg1 and a core subunit of the 55LCC complex responsible for late cytoplasmic maturation of the pre-60S ribosomal subunit and for replisome proteostasis.

The most recent and largest synthesis (Nou-Fontanet et al. 2026, n=51; PMID:41933351) defines it as follows:

"AFG2A-RE is an ultra-rare, recessive disorder, sometimes presenting as a developmental and epileptic encephalopathy (DEE), characterised by the triad of epilepsy, congenital microcephaly, and deafness, and typically associated with intellectual disability, spasticity, and movement disorders."

The disorder was first delineated by Tanaka et al. 2015 (PMID:26299366):

"Using whole-exome sequencing, we have identified in ten families 14 individuals with microcephaly, developmental delay, intellectual disability, hypotonia, spasticity, seizures, sensorineural hearing loss, cortical visual impairment, and rare autosomal-recessive predicted pathogenic variants in spermatogenesis-associated protein 5 (SPATA5)."

Independent confirmation followed within a year (Buchert et al. 2016, PMID:27683084):

"We thus independently confirm that bi-allelic pathogenic variants in SPATA5 cause a syndromic form of intellectual disability, and we delineate its clinical presentation."

1.2 Identifiers

Resource	Identifier	Status
MONDO	MONDO:0014698 — microcephaly-intellectual disability-sensorineural hearing loss-epilepsy-abnormal muscle tone syndrome	[verified] via OLS4
OMIM (phenotype)	#616577 — NEURODEVELOPMENTAL DISORDER WITH HEARING LOSS, SEIZURES, AND BRAIN ABNORMALITIES (NEDHSB)	verified via MedGen/GTR + MONDO xref
OMIM (gene)	*613940 — AFG2 AAA ATPase HOMOLOG A; AFG2A	verified via HGNC
Orphanet	ORPHA:457351	verified via MONDO xref + GTR
UMLS / MedGen	C4225276 / MedGen 895574	verified
GARD	0017804	verified via MONDO xref
HGNC	HGNC:18119 (`hgnc:18119` in repo casing)	[verified] via HGNC REST
Ensembl / NCBI Gene / UniProt	ENSG00000145375 / 166378 / Q8NB90	[verified] via HGNC REST
ClinGen gene-disease validity	AFG2A — Definitive, AR, Syndromic Disorders GCEP, evaluated 2024-07-23, against MONDO:0800439 (includes MIM:616577)	verified via ClinGen search
Cytogenetic locus	4q28.1 (GRCh38 chr4:122,923,070–123,319,433)	verified
ICD-10 / ICD-11	Not verified in this session (Orphanet blocked automated retrieval). Orphanet typically maps such syndromes to ICD-10 Q87.8 — treat as unconfirmed.
MeSH	No dedicated descriptor; indexed via Microcephaly, Intellectual Disability, Hearing Loss, Seizures, ATPases Associated with Diverse Cellular Activities

1.3 Synonyms and nomenclature

AFG2A-related encephalopathy (AFG2A-RE) — current preferred clinical term (PMID:41933351, PMID:40712368)
SPATA5-related encephalopathy — prior term (PMID:27246907)
NEDHSB — Neurodevelopmental disorder with hearing loss, seizures, and brain abnormalities (OMIM #616577; MONDO exact synonym)
EHLMRS — "Epilepsy, hearing loss, and mental retardation syndrome" (PMID:28293831, PMID:34360601). MONDO flags this and the spelled-out form as discouraged/historic synonyms — do not use as preferred_term.
Gene aliases: SPATA5, SPAF (spermatogenesis-associated factor), AFG2

Nomenclature caution for curation: the gene symbol change SPATA5 → AFG2A and the paralogue SPATA5L1 → AFG2B (HGNC:28762, [verified]) means literature searches must cover both symbol eras. This is a mild named-entity-confusion (NEC) risk class: AFG2A and AFG2B cause phenotypically overlapping but distinct disorders (see §10.4).

1.4 Data provenance

All human knowledge on this disorder derives from individual-patient case reports and small case series aggregated by systematic review, plus targeted research cohorts of early-onset epileptic encephalopathy. There is no EHR-derived, registry-derived, or population-scale dataset. The largest single aggregation is the PRISMA systematic review of Nou-Fontanet et al. 2026 (51 individuals: 45 published + 6 new). An ERN ITHACA / SPATA Foundation natural-history collaboration led by Barbara Vona (Göttingen) has collected ~30 additional unpublished AFG2A cases; the call is currently closed to new submissions. Formal natural-history data do not yet exist — the 2026 review explicitly states: "Prospective natural history studies across multiple reference centres are needed."

2. Etiology

2.1 Primary causal factor

Monogenic: biallelic (homozygous or compound heterozygous) pathogenic variants in AFG2A (4q28.1). No environmental, infectious, or multifactorial contribution has been demonstrated or proposed. Heterozygous carriers (including obligate-carrier parents in every reported family) are unaffected.

2.2 Genetic risk factors

Causal variants: >40 distinct AFG2A variants reported (PMID:41933351). Reference transcript NM_145207.3 (older papers use NM_145207.2).
Consanguinity: a recognized route to homozygosity — the largest single-family cluster (7 affected individuals) came from an extended consanguineous family (PMID:27683084). Most compound-heterozygous cases arose in non-consanguineous European families (PMID:29343804).
Uniparental disomy: an unusual mechanism producing homozygosity without consanguinity was documented — homozygotization of a maternally inherited c.251G>A variant "due to maternal isodisomy of chromosome 4" (PMID:30552426). This has direct implications for recurrence-risk counselling.
Copy-number variants as one allele: a 51 kb deletion spanning exons 12–13 (c.2080_2213del; p.(Gly694Phefs*23)) in trans with a sequence variant (PMID:30552426) — i.e., CNV analysis is required for complete allele ascertainment.
Modifier genes: none identified. Genotype–phenotype analysis in the largest cohort was negative: "No significant associations between genotype and epilepsy phenotype were observed." (PMID:41933351)

2.3 Environmental risk factors, protective factors, gene–environment interactions

None identified, and none biologically expected for a fully penetrant recessive Mendelian disorder. No protective alleles, dietary, or exposure modifiers have been described. Ketogenic diet (§12) is a treatment, not a protective/preventive factor.

The single evidence-supported "environmental" modifier of disease expression (not risk) is metabolic state: ketogenic-diet-mimicking medium reversed mitochondrial abnormalities in patient fibroblasts (PMID:40712368).

3. Phenotypes

3.1 Core frequency table (largest cohort, n=51; PMID:41933351)

All percentages below are from the Nou-Fontanet 2026 systematic review; denominators vary by feature because data availability differs. Verbatim abstract source:

"The most frequently described clinical features included intellectual disability (97.92%), hearing loss (93.62%), microcephaly (85.71%), visual impairment (79.49%), hypotonia (71.74%), spasticity (60.87%), and movement disorders (36.96%). Epilepsy was present in 74.71% of cases, with seizures of generalized onset being the most common (70.83%), and infantile epileptic spasms syndrome (IESS) was the predominant epilepsy syndrome at onset (66.67%). Epilepsy was often drug-resistant (82.35%). Brain MRI abnormalities were frequently observed (68.29%), including hypomyelination (39.02%), brain atrophy (34.15%), and a thin corpus callosum (29.27%)."

Phenotype	%	HPO frequency band	Suggested HP term	Verification
Intellectual disability	97.92	Very frequent (80–99%)	HP:0001249 Intellectual disability	[suggested]
— severe-to-profound subset	75 of those graded		HP:0002187 Intellectual disability, profound / HP:0010864 severe	[suggested]
Absent speech (all with ID)	~100 of ID cases	Very frequent	HP:0001344 Absent speech	[verified]
Hearing loss (sensorineural)	93.62	Very frequent	HP:0000407 Sensorineural hearing impairment	[verified]
Microcephaly	85.71	Very frequent	HP:0000252 Microcephaly; congenital form → HP:0011451 Primary microcephaly	[verified]
Motor impairment (any)	97.83	Very frequent	HP:0002500 / composite	[suggested]
Visual impairment	79.49	Frequent	HP:0000505 Visual impairment	[suggested]
— cortical/cerebral blindness	9.68	Occasional	HP:0100704 Cerebral visual impairment	[verified]
— strabismus	9.68	Occasional	HP:0000486 Strabismus	[suggested]
— refraction abnormality	9.68	Occasional	HP:0000539 Abnormality of refraction	[suggested]
Epilepsy	74.71 (38/51)	Frequent	HP:0001250 Seizure	[suggested]
Hypotonia	71.74	Frequent	HP:0001252 Hypotonia	[verified]
Spasticity	60.87	Frequent	HP:0001257 Spasticity	[suggested]
Movement disorder (non-paroxysmal, any)	36.96	Frequent	HP:0100022 Abnormality of movement	[suggested]
— dystonia	21.74	Occasional	HP:0001332 Dystonia	[suggested]
— dyskinesia	6.52	Occasional	HP:0100660 Dyskinesia	[suggested]
— ataxia	6.52	Occasional	HP:0001251 Ataxia	[suggested]
— chorea	4.35	Very rare	HP:0002072 Chorea	[suggested]
— athetosis	2.17	Very rare	HP:0002305 Athetosis	[suggested]
Neurodevelopmental delay	84.31	Very frequent	HP:0001263 Global developmental delay	[suggested]
GI symptoms (any)	78.95	Frequent	HP:0011024 Abnormality of the gastrointestinal tract	[suggested]
— dysphagia	30	Frequent	HP:0002015 Dysphagia	[suggested]
— gastroesophageal reflux	20	Occasional	HP:0002020 Gastroesophageal reflux	[suggested]
— constipation	16.67	Occasional	HP:0002019 Constipation	[suggested]
Short stature	13.33	Occasional	HP:0004322 Short stature	[suggested]
Failure to thrive	13.33	Occasional	HP:0001508 Failure to thrive	[suggested]
Neonatal hypotonia (perinatal)	12.5	Occasional	HP:0001319 Neonatal hypotonia	[suggested]
Neonatal respiratory distress	9.38	Occasional	HP:0002643 Neonatal respiratory distress	[suggested]
Preterm birth (mod-to-late)	6.25	Occasional	HP:0001622 Premature birth	[suggested]
IUGR	6.25	Occasional	HP:0001511 Intrauterine growth retardation	[suggested]
Normal growth	73.33	—	—
Normal perinatal course	75	—	—

Gross motor function (GMFCS, n=22): level V 59.09%, IV 27.27%, III 9.09%, II 4.55% — i.e., ~86% are GMFCS IV–V (non-ambulatory, requiring full physical assistance). Suggested term: HP:0002540 Inability to walk [verified].

3.2 Epilepsy phenotype (detailed data n=24; PMID:41933351)

Infantile epileptic spasms syndrome (IESS) is the predominant presentation: 16/24 (66.67%), mean age at onset 9.53 months (range 2.5–27 months). HP terms: HP:0011097 Epileptic spasm [verified], HP:0012469 Infantile spasms [verified].
Independent series (PMID:40712368): "In all but one case, the initial epilepsy presentation was infantile epileptic spasms syndrome (IESS), with a mean age at onset of 13.6 months."
Generalized-onset seizures 70.83%; focal 2 individuals; both types in 5.
Semiologies: tonic 33.4%, tonic-clonic 25%, myoclonic 12.5%, atonic 4.17%, atypical absence 4.17%; focal clonic 12.5%, focal myoclonic 12.5%; gelastic and focal impaired-awareness in 1 each.
Seizures with complex ocular movements in 3/24 (12.5%) — a distinctive feature first highlighted by Zanus et al. 2020 (PMID:33063670): "The epileptic clinical features were characterized by infantile spasms associated with seizures with a complex ocular movement; a predominant involvement of the posterior cerebral area and cortical visual impairment were also noticed."
EEG (n=20 detailed): interictal epileptiform activity 95%; multifocal epileptiform discharges 75% (occipital/posterior predominance recurrently noted); hypsarrhythmia 20% (HP:0002521 Hypsarrhythmia [verified]); photoparoxysmal response 5%. Kurata et al. 2016 (PMID:27246907): "Interictal electroencephalography showed multifocal spikes and bursts of asynchronous diffuse spike-wave complexes. Augmented amplitudes of visually evoked potentials were detected in two patients."
Drug resistance: the abstract states 82.35%; the results text reports 82.35% (14/17) were on polytherapy. Only 4/16 with follow-up were seizure-free. Treat the 82.35% figure as "polytherapy/drug-resistant" and cite the results text rather than over-claiming.

3.3 Neuroimaging phenotypes

MRI abnormal in 68.29%; normal in 31.71%.

Finding	%	Suggested HP term
Hypomyelination	39.02	HP:0006808 Cerebral hypomyelination or HP:0003429 CNS hypomyelination [both verified]
Global brain atrophy	34.15	HP:0002059 Cerebral atrophy [suggested]
Thin corpus callosum	29.27	HP:0033725 Thin corpus callosum [verified]
Leukoencephalopathy	7.32	HP:0002352 Leukoencephalopathy [suggested]
Cerebral white matter atrophy	7.32	HP:0012762 Cerebral white matter atrophy [suggested]
Small basal ganglia	4.88	HP:0006989 Abnormal basal ganglia morphology [suggested]

Kurata et al. (PMID:27246907): "Magnetic resonance imaging revealed hypomyelination, thin corpus callosum, and progressive cerebral atrophy." — note the explicit progressive qualifier on atrophy (clinical_course: PROGRESSIVE).

3.4 Laboratory / biochemical phenotypes

Biochemistry is characteristically near-normal, which is diagnostically important because the clinical picture mimics mitochondrial disease.

Mild persistent lactate elevation in 2/6 new cases (1.9–3.9 mmol/L), plasma only: "Two individuals in our cohort exhibited a persistent mild elevation of lactate (1.9–3.9 mmol/l) without other abnormalities in mitochondrial biomarkers, including acid-base balance, creatine kinase, pyruvate, organic acids, amino acids, carnitines, oxidative stress markers, circulating cytokines, or mitochondrial growth factors. No elevated lactate was detected in urine or cerebrospinal fluid." (PMID:41933351). HP term: HP:0002151 Increased circulating lactate concentration [verified] (note: the label is not "Increased serum lactate").
Elevated or high-normal blood copper in 3/3 Japanese patients: "Blood copper levels were also elevated or close to the upper normal levels in these children." (PMID:27246907). This finding has not been replicated in any subsequent cohort — curate as a single-study observation, not a disease-level biomarker.
Broad metabolic/mitochondrial screening "mostly unremarkable" (PMID:29343804).
Muscle respiratory chain: combined complex I + IV deficiency in 1/3 tested (PMID:29343804); "low activity within the reference range" for complexes I, II/III, IV with elevated citrate synthase in another patient (PMID:34360601). Inconsistent — do not curate as a defining biochemical feature.

3.5 Dysmorphology

A recurrent but non-universal facial gestalt was described by Kurata et al. (PMID:27246907): "Common facies were a depressed nasal bridge/ridge, broad eyebrows, and retrognathia." Braun et al. explicitly note this "does not seem to be shared with other cases in the literature" (PMID:34360601) — curate as low-frequency / single-cohort. Suggested terms: HP:0005280 Depressed nasal bridge, HP:0011229 Broad eyebrow, HP:0000278 Retrognathia [all suggested].

3.6 Other systems

Skeletal: congenital hip luxation and coxa valga antetorta requiring multiple surgeries in one patient (PMID:34360601); scoliosis listed among HPO annotations in MedGen.
Cardiac: rare — atrial septal defect (1), heart failure (1) across 51 (PMID:41933351).
Hepatosplenomegaly (mild): 3.33% (PMID:41933351).
Muscle: a bona fide myopathology exists but is subtle. Braun et al. (PMID:34360601): "Histological staining of our patient's muscle biopsy hints towards mitochondrial pathology, while the identification of dysregulated proteins attested to the vulnerability of the cell beyond the mitochondria." Enzyme histochemistry showed reduced SDH reaction with normal COX; routine H&E, Gomori, PAS, NADH and ATPase stains were normal.
Fertility/spermatogenesis: despite the gene's original "spermatogenesis-associated" naming, no human fertility phenotype has been reported — all patients are severely affected children/young adults.

3.7 Attenuated end of the spectrum — isolated sensorineural hearing loss

Critical for penetrance/expressivity modelling. Szczałuba et al. 2017 (PMID:28293831):

"Herein we describe a family in which two SPATA5 mutations with established pathogenicity (p.Thr330del and c.1714+1G>A) were found in the proband and her younger sister. The proband had a similar clinical picture to the previous descriptions of EHLMRS. In the sister, the only manifestation was an isolated sensorineural hearing loss. Our findings extend the phenotypic spectrum of SPATA5-associated diseases and indicate that SPATA5 defects may account for a fraction of isolated sensorineural hearing impairment cases."

Two additional individuals in the Buchert consanguineous family had ID + microcephaly without epilepsy or developmental delay (PMID:27683084; Table 1 rows 18–24 of PMID:41933351). Intrafamilial variability with an identical genotype demonstrates variable expressivity with additional unidentified modifying factors.

3.8 Quality-of-life impact

No disease-specific QoL instrument (EQ-5D, PROMIS, SF-36, CPCHILD) has been applied to any AFG2A-RE cohort — a genuine gap. Functional burden is nonetheless inferable and severe: ~86% GMFCS IV–V, absent speech in all with ID, near-universal deafness plus ~80% visual impairment (a dual sensory impairment that compounds communication access), drug-resistant epilepsy in the majority, and dysphagia in 30% requiring feeding support. This combination places the disorder at the highest-dependency end of the DEE spectrum. Curate QoL as a KNOWLEDGE_GAP discussion.

4. Genetic / Molecular Information

4.1 Gene

Field	Value
Approved symbol	AFG2A (previous: SPATA5; aliases SPAF, AFG2)
Approved name	AAA ATPase AFG2A
HGNC	`hgnc:18119`
Locus	4q28.1
Transcript	NM_145207.3 (canonical; earlier literature NM_145207.2)
Protein	892 aa, UniProt Q8NB90; two conserved AAA+ ATPase modules (D1, D2) plus an N-terminal domain; a putative mitochondrial matrix-targeting sequence that is not functional in neurons (see §6.2)
Mouse orthologue	Afg2a, MGI:1927170
Yeast orthologue	Drg1
Expression	Ubiquitous — testis, spleen, skin, intestine, brain, skeletal muscle (PMID:34360601, PMID:41933351)

4.2 Variant spectrum

"Over 40 variants in AFG2A have been described as causative of AFG2A-RE. The most frequent variants are c.2081G>A, c.989_991del, c.251G>A, and c.1714+1G>A, present in 42% of the individuals, and more than half of the variants are missense." (PMID:41933351)

Recurrent alleles:

Variant (NM_145207.3)	Protein	Class	Notes
c.989_991del	p.(Thr330del)	in-frame single-codon deletion	Most widely recurrent allele; rs748291365; ClinVar Pathogenic; ExAC ~0.02–0.03% (highest European MAF among EE-associated recessive variants in PMID:30552426), incl. one homozygote in population data
c.251G>A	p.(Arg84Gln)	missense	Recurrent; seen homozygous incl. via chr4 maternal isodisomy
c.2081G>A	p.(Gly694Glu)	missense	See §4.6 discrepancy flag
c.1714+1G>A	canonical +1 splice donor	splice	Recurrent, incl. homozygous
c.1822_1824del	p.(Asp608del)	in-frame deletion	Homozygous in the extended consanguineous family (PMID:27683084)
c.2130_2133del	p.(Glu711Profs*21)	frameshift	Recurrent (Japan, Spain)
c.556C>T	p.(Arg186*)	nonsense	Recurrent

Variant classes represented: missense (>50%), nonsense, frameshift, canonical splice-site, in-frame codon deletions, start-loss (c.1A>C, p.Met1?), and a multi-exon deletion CNV (51 kb, exons 12–13).

Functional consequence: loss of function / hypomorphic. No gain-of-function or dominant-negative mechanism has been proposed. Two arguments strongly support residual-activity (hypomorphic) rather than complete-null biology in humans: 1. No patient carries two unambiguous complete-null alleles — biallelic combinations always include at least one missense or in-frame allele, and true null/null combinations are absent from the published cohort. 2. Homozygous Afg2a knockout mice die before organogenesis (§15) — complete loss is not compatible with mammalian development.

This is a load-bearing mechanistic inference for the KB: model the trigger node as hypomorphic reduction of AFG2A ATPase activity, not as complete ablation.

Somatic vs germline: exclusively germline. One notable exception in transmission mechanism — a de novo variant on the paternal allele combined with a maternally inherited variant (patient 73068, PMID:30552426), demonstrating that recessive disease can arise with a de novo second hit and therefore cannot be excluded on the basis of negative parental carrier testing alone.

Population/constraint data: gnomAD constraint metrics (pLI/LOEUF) could not be programmatically retrieved in this session — do not populate these fields without direct gnomAD verification. ClinGen has performed zero dosage-sensitivity curations for AFG2A, and heterozygous exon-deletion carriers are healthy, so haploinsufficiency is not a disease mechanism. ClinVar (queried 2026-08-01 via E-utilities): 970 total records for AFG2A[gene], of which 104 carry a pathogenic clinical-significance property.

4.3 Modifier genes

None identified. The intrafamilial variability in the Szczałuba family (severe encephalopathy vs isolated SNHL with the identical biallelic genotype, PMID:28293831) and in the Buchert consanguineous family (epilepsy present in some homozygous relatives, absent in others) is unexplained and constitutes a well-defined open question. Plausible but untested candidates: variation in the other 55LCC subunits (AFG2B, AIRIM/C1orf109, CINP) or in general ribosome-biogenesis capacity.

4.4 Epigenetics

No DNA-methylation episignature, histone-modification, or chromatin study of AFG2A-RE exists. Given that episignatures have been established for many DEEs, this is a tractable gap.

4.5 Chromosomal abnormalities

No recurrent cytogenetic syndrome. The relevant structural finding is intragenic CNV as a disease allele (51 kb exon 12–13 deletion, PMID:30552426) — mandating CMA or exome/genome CNV calling alongside sequencing. Maternal uniparental isodisomy of chromosome 4 is a documented route to homozygosity.

4.6 ⚠ Three published-data discrepancies to avoid propagating

These were identified by cross-checking Table 1 of PMID:41933351 against the primary sources. Do not transcribe the review table verbatim into the KB.

Genotype inversion for the Buchert 2016 families. Table 1 of PMID:41933351 assigns homozygous c.2081G>A p.(Gly694Glu) to the extended consanguineous family (patients 18–24, no epilepsy) and homozygous c.1822_1824del p.(Asp608del) to patient B1 (with epilepsy). The Buchert abstract states the opposite: "Linkage analysis followed by exome sequencing revealed a homozygous variant in SPATA5 (c.1822_1824del; p.Asp608del), which segregates with the phenotype in the family. In an unrelated family, we identified compound heterozygous variants in SPATA5 (c.[2081G > A];[989_991delCAA]; p.[Gly694Glu];[.Thr330del]) in a further individual with global developmental delay, infantile spasms, profound dystonia, and sensorineural hearing loss." Consequence: the review's discussion claim that "the c.2081G>A variant was associated with absence of epilepsy" is, per the primary source, attributable to p.(Asp608del), not p.(Gly694Glu) — and p.(Gly694Glu) was in fact found in an individual with infantile spasms. Any genotype–phenotype statement here must cite Buchert directly.
Splice variant given a protein-deletion annotation. Table 1 repeatedly renders c.1714+1G>A; p.Thr339del. A canonical +1 donor variant should be annotated p.?; Tanaka 2015 correctly lists c.1714+1G>A; p.?. Use p.?.
Internally inconsistent row. Patient 50 is listed as c.554G>A; p.Lys648Glu — c.554G>A corresponds to p.(Gly185Glu) elsewhere in the same table; p.Lys648Glu corresponds to c.1942A>G. Treat this row's genotype as unreliable.

5. Environmental Information

Not applicable. No environmental, toxic, occupational, radiation, lifestyle, dietary, or infectious factor has been implicated in causation or triggering. No infectious agent is involved (NCBI Taxonomy: N/A). Seizure-provoking factors beyond those generic to DEE have not been characterized (notably, fever-sensitivity has not been reported — unlike some channelopathy DEEs).

6. Mechanism / Pathophysiology

The mechanistic understanding has undergone a substantial revision between 2015 and 2025: from a presumed mitochondrial disorder to a ribosome-biogenesis disorder (ribosomopathy) with secondary mitochondrial and proteostatic consequences. Curating the causal chain correctly requires respecting this revision.

6.1 Primary mechanism — defective cytoplasmic pre-60S ribosome maturation

AFG2A is the human orthologue of yeast Drg1, the AAA+ ATPase that strips the placeholder assembly factor Rlp24 from newly exported pre-60S particles (Prattes et al. 2019, PMID:31703473):

"Rix7, Rea1, and Drg1, which are well conserved across eukaryotes, are involved in different maturation steps of pre-60S ribosomal particles. These AAA-ATPases provide energy for the efficient removal of specific assembly factors from pre-60S particles after they have fulfilled their function in the maturation cascade."

The human step was defined by a genome-wide screen (Ni et al. 2022, Cell Rep, PMID:35354024):

"These efforts identify two functionally uncharacterized genes, C1orf109 and SPATA5. We provide evidence that these factors, together with CINP and SPATA5L1, control a late step of human pre-60S maturation in the cytoplasm. Loss of either C1orf109 or SPATA5 impairs global protein synthesis. These results link ribosome assembly with neurodevelopmental disorders associated with recessive SPATA5 mutations."

Structural resolution followed (Dai et al. 2025, Nat Commun, PMID:40268917):

"Here we reveal that SPATA5 forms a 4:2:2:2 complex with SPATA5L1, C1orf109, and CINP. This complex features an N-terminal ring made of C1orf109, CINP and NTDs of SPATA5/SPATA5L1, and two hexameric AAA+ ATPase rings. Intriguingly, a conserved cysteine C672 in the P-loop of SPATA5 is sulfinylated, generating an inactive conformation incompatible with ATP binding… Different from yeast, the recognition of the pre-60S particle is mediated by human-specific factor CINP, through two distinct sets of interactions: one with GTPBP4 and the other with ES27A."

Two points of curation value: (i) human-specific architecture — CINP-mediated pre-60S recognition has no yeast counterpart, limiting how far yeast Drg1 data can be extrapolated; (ii) the redox-sensitive P-loop cysteine C672 provides a candidate regulatory/therapeutic node.

6.2 The 55LCC complex also governs replisome proteostasis and genome stability

Krishnamoorthy et al. 2024, Cell (PMID:38554706):

"Here, we identify replisome factor interactions with a protein complex composed of AAA+ ATPases SPATA5-SPATA5L1 together with heterodimeric partners C1orf109-CINP (55LCC)… Deficiency in the 55LCC complex elicited ubiquitin-independent proteotoxicity, replication stress, and severe chromosome instability. 55LCC showed ATPase activity that was specifically enhanced by replication fork DNA and was coupled to cysteine protease-dependent cleavage of replisome substrates in response to replication fork damage. These findings define 55LCC-mediated proteostasis as critical for replication fork progression and genome stability and provide a rationale for pathogenic variants seen in associated human neurodevelopmental disorders."

Note the mechanism is explicitly ubiquitin-independent — distinguishing 55LCC from the VCP/p97 pathway. Replication stress in rapidly dividing neural progenitors is a plausible route to congenital microcephaly, complementary to the translation-capacity route.

6.3 Why a housekeeping defect produces a brain-and-ear-specific phenotype

The most consequential mechanistic advance of 2025 comes from Ni, Wei, Vona, Buszczak et al., Nat Cell Biol (PMID:40760247), studying the sister 55LCC subunit AIRIM/C1orf109:

"Many neurodevelopmental defects are linked to genes involved in housekeeping functions, such as those encoding ribosome biogenesis factors. How reductions in ribosome biogenesis can result in tissue- and developmental-specific defects remains unclear. Here we describe variants in the ribosome biogenesis factor AIRIM/C1orf109 that are primarily associated with neurodevelopmental disorders. Using human cerebral organoids in combination with proteomic, single-cell RNA sequencing and single-organoid translation analyses, we identify a previously unappreciated drop in protein production during early brain development. We find that ribosome levels decrease during neuroepithelial differentiation, making differentiating cells particularly vulnerable to perturbations in ribosome biogenesis during this time. Reduced ribosome availability more profoundly impacts the translation of specific transcripts, disrupting both survival and cell fate commitment of transitioning neuroepithelia. Enhancing mTOR activity suppresses the growth and developmental defects associated with AIRIM/C1orf109 variants."

This supplies the long-missing tissue-specificity explanation: a physiological trough in ribosome abundance during neuroepithelial differentiation creates a developmental window in which any further reduction in 60S output crosses a threshold. Selectively impaired transcripts included ribosomal proteins, the neurogenesis factor FABP7, and mitochondrial components bearing 5′ TOP-like motifs — which also supplies a translational explanation for the observed mitochondrial phenotype. mTOR pathway enhancement (TSC1 haploinsufficiency, PI3Kα activation) rescued organoid growth and cell-death phenotypes — the first rational therapeutic target for this disease family.

Curation flag: PMID:41933351 states "no neurological disorders have been linked to the other components of the complex, C1orf109 and CINP, to date." This was superseded ~5 months before that review's publication by PMID:40760247, which reports biallelic AIRIM/C1orf109 variants in eleven unrelated families with global developmental delay, microcephaly, seizures and hearing loss — a phenotype closely overlapping AFG2A-RE. Curate the 55LCC complex as harbouring at least three neurodevelopmental disease genes (AFG2A, AFG2B, AIRIM/C1orf109).

6.4 Mitochondrial dysfunction — real, but likely downstream

Puusepp et al. 2018 (PMID:29343804) performed the foundational cell-biology work in rat cortical neurons and made a finding that reframes the mitochondrial hypothesis:

"SPATA5 protein has a putative mitochondrial matrix-targeting sequence and has been shown to localize in mitochondria in mouse testis. However, subcellular localization data of SPATA5 in neurons and other cell types has not been reported. To our surprise the localization of overexpressed SPATA5 in cultured primary cortical neurons was dominantly cytosolic and clearly not co-localizing with the mitochondrial marker."

Yet knockdown produced clear mitochondrial consequences:

"there was a significant, 20% decrease in mitochondrial length in SPATA5 shRNA-treated neurons" "SPATA5 shRNA tends to decrease the fusion rate and increase the fission rate leading to significant decrease in fusion–fission ratio" "experiments performed at axonal endings… showed a statistically significant 12% decrease in signal in the SPATA5 shRNA group, suggesting a decrease in ATP levels… Overexpression of human shRNA-insensitive SPATA5 restored the ATP/ADP ratio in the SPATA5 shRNA-treated group demonstrating the specificity of shRNA."

Plus impaired neuronal maturation (short axons — PMID:34360601 summarizes: "an imbalance in mitochondrial fusion–fission rates, impaired energy production and short axons").

Independently corroborated in patient-derived material (Raggio et al. 2023, PMID:36849973):

"Oxygen consumption rates in platelets and PBMCs were impaired in the patient when compared to a healthy control. Also, a decrease in mitochondrial mass was observed in the patient monocytes with respect to the control. This suggests a true pathogenic effect of the mutations in mitochondrial function, especially in energy production and possibly biogenesis, leading to the observed phenotype."

And in patient fibroblasts (Nou-Fontanet et al. 2025, PMID:40712368):

"In vitro studies demonstrated that AFG2A-deficient fibroblasts exhibited altered mitochondrial morphology and dynamics, as well as reduced ATP production and ROS levels. These abnormalities were significantly reversed when the fibroblasts were cultured in KD-MM."

Recommended causal ordering for the pathograph: hypomorphic AFG2A → impaired 55LCC ATPase activity → (a) defective pre-60S cytoplasmic maturation → reduced ribosome availability → selective translational insufficiency (including 5′-TOP-motif mitochondrial transcripts) → secondary mitochondrial fusion/fission imbalance, shortened mitochondria, reduced ATP; and (b) impaired replisome proteostasis → replication stress and chromosomal instability. Both converge on neuroepithelial/neural progenitor attrition and impaired neuronal maturation → microcephaly, hypomyelination, cortical atrophy, cortical hyperexcitability (IESS), sensorineural hearing loss, cerebral visual impairment.

The mitochondrial arm should be curated as a downstream consequence with a documented HUMAN_MODEL_MISMATCH/hypothesis tension: the protein is cytosolic in neurons, mitochondrial biomarkers are normal in patients, respiratory-chain findings are inconsistent, yet multiple independent patient-cell assays show real bioenergetic deficits. This is exactly the shape of a mechanistic_hypotheses entry with status: EMERGING for the "mitochondrial dysfunction as secondary to translational insufficiency" model.

6.5 Tissue/muscle proteomics

Braun et al. 2021 (PMID:34360601): "Proteomic profiling of a quadriceps biopsy showed the dysregulation of 82 proteins, out of which 15 were localized in the mitochondrion, while 19 were associated with diseases presenting with phenotypical overlap to EHLMRS." (31 up-, 51 down-regulated; ProteomeXchange PXD026182; upregulated disease-associated proteins included PURA1 and LAMA2.)

6.6 Immune involvement, metabolic pathways, fibrosis

No autoimmune or inflammatory mechanism. MedGen lists thrombocytopenia and immunodeficiency among annotated HPO features, but neither is supported by the 51-patient review and both should be treated as unreplicated single-report annotations. Intermediary metabolism is intact (normal organic acids, amino acids, carnitines, acid-base). No fibrosis, ischemia, or necrosis mechanism.

6.7 Suggested ontology terms for mechanism nodes

GO biological process / molecular function [all suggested — verify with OAK]: - GO:0042273 ribosomal large subunit biogenesis - GO:0000027 ribosomal large subunit assembly - GO:0006412 translation - GO:0016887 ATP hydrolysis activity; GO:0005524 ATP binding - GO:0000226 / GO:0007005 mitochondrion organization - GO:0008053 mitochondrial fusion; GO:0000266 mitochondrial fission - GO:0006119 oxidative phosphorylation - GO:0006260 DNA replication; GO:0031297 replication fork processing - GO:0030163 protein catabolic process (ubiquitin-independent) - GO:0021987 cerebral cortex development; GO:0022008 neurogenesis - GO:0031175 neuron projection development (axon growth) - GO:0031929 TOR signaling (rescue axis)

GO cellular component: GO:0005829 cytosol (primary neuronal localization, PMID:29343804); GO:0030687 preribosome, large subunit precursor; GO:0022625 cytosolic large ribosomal subunit; GO:0005739 mitochondrion (secondary/context).

CL cell types [suggested]: CL:0000540 neuron; CL:0000047 neuronal stem cell / neuroepithelial cell; CL:0000128 oligodendrocyte (hypomyelination); CL:0000855 auditory hair cell (paralogue AFG2B is expressed in "neurosensory hair cells and inner ear supporting cells", PMID:34626583 — direct AFG2A inner-ear expression data are lacking); CL:0008002 skeletal muscle fiber.

UBERON [suggested]: UBERON:0000955 brain; UBERON:0000956 cerebral cortex; UBERON:0002336 corpus callosum; UBERON:0002316 white matter; UBERON:0001844 cochlea; UBERON:0000970 eye; UBERON:0002240 spinal cord (corticospinal involvement / spasticity); UBERON:0001630 muscle organ; UBERON:0000473 testis (expression only).

CHEBI [suggested]: ATP, ADP, lactate, copper cation, ketone bodies (3-hydroxybutyrate).

7. Anatomical Structures Affected

Primary organ: brain (UBERON:0000955), bilaterally and diffusely. - Cerebral cortex — global/cortico-subcortical atrophy (34%), often progressive; posterior/occipital predominance recurrently noted electrographically and clinically (cortical visual impairment, occipital-dominant spikes). - Cerebral white matter / myelin — hypomyelination (39%), leukoencephalopathy (7%), white matter atrophy (7%); periventricular posterior predominance in at least one detailed case. - Corpus callosum — thin in 29%. - Basal ganglia — small in 5%; dystonia in 22% implicates extrapyramidal circuitry functionally even when imaging is normal. - Corticospinal tracts — spasticity 61%, hyperreflexia.

Sensory organs: - Cochlea / auditory pathway (UBERON:0001844) — sensorineural hearing loss in 94%, frequently detected on neonatal brainstem audiometry (i.e., congenital). - Visual system — impairment in 79%, predominantly cerebral/cortical (post-geniculate) rather than ocular; strabismus and refractive error also present. Augmented visual evoked potential amplitudes (PMID:27246907) point to cortical hyperexcitability rather than retinal/optic-nerve failure. Note the 2026 review speculates about optic-nerve energy vulnerability by analogy with mitochondrial disease, but the primary data support a cerebral localization.

Secondary/systemic: - GI tract — dysphagia (bulbar), GER, constipation (79% any GI symptom). - Skeletal muscle (UBERON:0005090) — subtle myopathology (reduced SDH histochemistry, dysregulated proteome). - Musculoskeletal — hip dysplasia/luxation, coxa valga, scoliosis (secondary to tone abnormality and non-ambulation). - Growth — microcephaly is the cardinal growth abnormality; somatic growth is normal in 73%. - Heart — rarely involved.

Subcellular: cytosol (site of AFG2A action and of pre-60S maturation), pre-ribosome/large subunit precursor, replication fork/replisome, mitochondrion (secondary).

Lateralization: bilateral and symmetric throughout.

8. Temporal Development

Onset: congenital to early infancy. - Congenital: microcephaly (often present at birth — "congenital microcephaly" is part of the defining triad); sensorineural hearing loss detectable on newborn/neonatal brainstem audiometry. - Perinatal: 75% uncomplicated; neonatal hypotonia 12.5%, respiratory distress 9.4%. - Epilepsy onset: IESS at a mean 9.53 months (range 2.5–27 months) in the review cohort; mean 13.6 months in the KD series. Kurata: "Epileptic spasms or tonic seizures emerged at 6-12 months of age." Rarely later — one case is described as "developmental encephalopathy with late-onset epilepsy" (PMID:30552426).

Onset pattern: insidious/developmental — global developmental delay is apparent from early infancy, punctuated by an acute-subacute epilepsy onset in the first-to-second year.

Course: predominantly static-with-progressive-elements, not classically neurodegenerative. - Developmental trajectory: severe global impairment reaching a plateau at a very low functional ceiling (absent speech, GMFCS IV–V). - Progressive elements documented: "progressive cerebral atrophy" on serial MRI (PMID:27246907); the 2018 series characterizes the association as with "a neurodegenerative disease" (PMID:29343804). Formal developmental regression (HP:0002376 [verified]) is not a reported feature — distinguish "progressive atrophy on imaging" from "clinical regression." - Epilepsy course: chronic, drug-resistant in the majority, requiring polytherapy. - Duration: lifelong; oldest reported living individuals are 39 and 41 years (both from the attenuated, epilepsy-free consanguineous family) — i.e., long survival is possible at the mild end.

Remission: seizure freedom is achievable in a minority (4/16 with follow-up), always treatment-induced, never spontaneous. No spontaneous remission of any core feature.

Critical intervention windows: 1. Neuroepithelial differentiation (embryonic) — the mechanistic window of maximal vulnerability (PMID:40760247); largely inaccessible therapeutically but defines why postnatal intervention cannot reverse microcephaly. 2. Early childhood, for ketogenic diet — "Greater seizure control was achieved when the ketogenic diet was initiated during early childhood." (PMID:40712368) 3. First months of life, for hearing habilitation — congenital deafness, detectable neonatally; one patient received a hearing device before 2 months of age (PMID:34360601).

9. Inheritance and Population

9.1 Epidemiology

No formal prevalence or incidence estimate exists. Orphanet ORPHA:457351 epidemiology could not be retrieved automatically; the disorder is consistently described as "ultra-rare" (PMID:41933351).
Cumulative published cases: 51 (PMID:41933351, July 2025 literature cut-off), plus ~30 additional unpublished cases collected by the ERN ITHACA / SPATA Foundation natural-history initiative → a real-world total on the order of ~80 known individuals worldwide.
Enriched-cohort frequency: the most quotable quantitative figure is the fraction among early-onset epileptic encephalopathies (Papuc et al. 2019, PMID:30552426):

"Notably, we found the recessive gene SPATA5 causative in as much as 3% of our cohort, indicating that it may have been underdiagnosed in previous studies." Confirmed on replication: "our overall finding of 3 out of 102 combined research and diagnostic patients carrying causative biallelic variants indicates that SPATA5 is a frequent cause of developmental epileptic disorders accounting for 3% of cases."
Yield in mitochondrial-suspicion cohorts is much lower: "The diagnostic yield was 0.6% and 0.8% in those two cohorts" (Estonian n=21 of 181; German n=353) (PMID:29343804).
Underdiagnosis: "This disorder is likely underdiagnosed, despite exhibiting clinical features that constitute a hallmark of AFG2A-RE (microcephaly, deafness, and DEE)." (PMID:41933351)

For the KB prevalence block, the defensible structured records are: measure_type: UNKNOWN / prevalence_class: ULTRA_RARE for population occurrence, plus a separate qualitative note recording the 3%-of-early-onset-EE/DEE figure (which is a case-mix fraction, not a population prevalence — do not convert it to rate_per_100000).

9.2 Inheritance genetics

Pattern: autosomal recessive (HP:0000007). ClinGen: Definitive, AR.
Penetrance: complete for the biochemical/genetic defect but with markedly variable expressivity — the same biallelic genotype produced full EHLMRS in one sister and isolated SNHL in the other (PMID:28293831). Practically: penetrance for some phenotype appears complete; penetrance for epilepsy is ~75%, for microcephaly ~86%.
Expressivity: variable, including intrafamilial. Sensorineural hearing loss is the most consistently penetrant single feature (94%) and the sole feature at the mildest end.
Genetic anticipation: not applicable (no repeat expansion).
Germline mosaicism: not reported. However, a paternal de novo second allele has been documented (PMID:30552426) — recurrence counselling must account for both standard 25% AR recurrence and the possibility of de novo contribution.
Founder effects: none established. The recurrent c.989_991del is present at low frequency across European population databases (rs748291365, highest European MAF 0.03%) and recurs in Japanese, European, and Uruguayan patients — consistent with either an old shared haplotype or recurrent mutation at a repetitive CAA tract; haplotype analysis has not been published.
Consanguinity: contributes; the largest family cluster was consanguineous, but most reported cases are non-consanguineous compound heterozygotes.
Carrier frequency: no published estimate. From ExAC/gnomAD, c.989_991del alone is ~0.02–0.03% allele frequency; aggregate carrier frequency across all pathogenic alleles has not been computed.

9.3 Demographics

Sex ratio: 29 M / 22 F among 51 (56.7% male) — consistent with 1:1 and no sex effect (PMID:41933351).
Geography: cases reported from the USA, Netherlands, Japan, Germany, Estonia, Poland, Italy, Switzerland, Bulgaria, Spain, Uruguay, and Canada — global distribution, no endemic cluster, likely reflecting exome-sequencing access rather than true prevalence.
Ancestry: predominantly European in published series, almost certainly an ascertainment artefact.
Age distribution of reported individuals: mean 8.35 years, range 9 months – 41 years.

10. Diagnostics

10.1 Genetic testing — the definitive diagnostic modality

First-line: whole-exome or whole-genome sequencing (trio preferred). Every published diagnosis was made by WES or WGS. Nou-Fontanet: "Genetic diagnosis was performed via clinical whole-exome sequencing, and variants were confirmed by Sanger sequencing."
CNV detection is mandatory alongside sequencing — a 51 kb intragenic deletion formed one allele in a published patient; the combined CMA+WES design is precisely what allowed Papuc et al. to detect it. WGS or exome-based CNV calling can substitute for standalone CMA.
Gene-panel testing: AFG2A is included on epileptic-encephalopathy/DEE panels and on syndromic-hearing-loss panels; GTR lists 54 tests for this condition. Panels lacking CNV analysis will miss deletion alleles.
Sanger confirmation and parental segregation required (recall the de novo paternal allele case).
SNP-array/UPD assessment is warranted when apparent homozygosity occurs in a non-consanguineous family (maternal chr4 isodisomy precedent).
Not indicated: karyotype, FISH, mtDNA sequencing (though mtDNA testing is frequently performed before diagnosis because of the mitochondrial-disease mimicry), repeat-expansion testing.

10.2 Clinical and laboratory workup

Test	Expected finding	Role
Head circumference (serial)	≤ −2 SD in 86%	Cardinal sign
Newborn/brainstem audiometry (ABR/BAEP)	Bilateral SNHL, congenital	Near-universal; often the earliest objective abnormality
EEG	Interictal epileptiform activity 95%; multifocal discharges 75%, occipital predominance; hypsarrhythmia 20%	Essential for IESS diagnosis
Brain MRI	Abnormal in 68% — hypomyelination, atrophy, thin CC; normal in 32%	Supportive; a normal MRI does not exclude
Visual evoked potentials	Augmented amplitudes reported	Supports cortical rather than ocular visual impairment
Ophthalmology assessment	CVI, strabismus, refractive error	Habilitation planning
Plasma lactate	Normal or mildly elevated (1.9–3.9 mmol/L)	Non-specific; usually normal
Broad metabolic screen (organic/amino acids, carnitines, pyruvate, CK, acid–base, CSF and urine lactate)	Normal	Its normality alongside a mitochondrial-like phenotype is a diagnostic clue
Muscle biopsy	Usually normal light microscopy; reduced SDH histochemistry with normal COX; inconsistent respiratory-chain results	Not recommended as a diagnostic step now that the gene is known
Blood copper	Elevated/high-normal in one small series	Unreplicated; not a validated biomarker

LOINC candidates: lactate (plasma) LOINC:2524-7 / LOINC:32693-4; copper (serum/plasma) LOINC:5631-7 [all suggested — verify].

10.3 Omics-based diagnostics

No validated omics diagnostic exists. Research-grade assays with demonstrated patient-level signal, potentially deployable as functional-evidence adjuncts for VUS resolution: - Cellular bioenergetics on blood cells — oxygen consumption in platelets/PBMCs and monocyte mitochondrial mass (PMID:36849973); explicitly framed by that group as minimizing "the need for invasive procedures such as muscle biopsy." - Fibroblast mitochondrial morphology/dynamics and ATP (PMID:40712368). - Muscle proteomics (PMID:34360601). - Fibroblast transcriptomics distinguished affected from controls by principal components for the paralogous AFG2B disorder (PMID:34626583) — a plausible transferable approach. - Global protein-synthesis / ribosome-profiling assays would be the mechanistically ideal functional readout given PMID:35354024 and PMID:40760247, but have not been applied diagnostically.

10.4 Differential diagnosis

Differential	Distinguishing features
Primary mitochondrial disease (the single most important mimic)	"The cardinal clinical features of AFG2A-RE may mimic those of a mitochondrial disease" (PMID:41933351). AFG2A-RE has normal metabolic screening, no lactate elevation in CSF/urine, no stroke-like episodes, and a normal or mildly abnormal muscle biopsy. Historically most patients were first enrolled in mitochondrial-disease cohorts.
*AFG2B (SPATA5L1)-related disorders*	The closest genetic phenocopy. Two OMIM entities: DFNB119 (#619615), nonsyndromic AR deafness; and NEDHLS (#619616), neurodevelopmental disorder with hearing loss and spasticity. PMID:34626583: "We report 28 bi-allelic variants in SPATA5L1 associated with sensorineural hearing loss in 47 individuals from 28 (26 unrelated) families. In addition, 25/47 affected individuals (53%) presented with microcephaly, developmental delay/intellectual disability, cerebral palsy, and/or epilepsy." Distinguished only by gene; a shared 55LCC mechanism explains the overlap.
AIRIM/C1orf109-related NDD	Newly described (PMID:40760247) — global developmental delay, microcephaly, seizures, hearing loss in 11 families; same complex.
Other IESS/West syndrome genetic causes (CDKL5, ARX, STXBP1, SCN2A, TSC1/2, ST3GAL3)	Deafness plus congenital microcephaly is unusual in these; the AFG2A triad is discriminating.
Congenital CMV	Also causes microcephaly + SNHL + seizures + periventricular white-matter change; excluded by newborn/dried-blood-spot CMV PCR and characteristic calcifications.
Peroxisomal disorders, congenital disorders of glycosylation	Excluded by VLCFA and transferrin isoform testing.
Perinatal hypoxic-ischaemic injury / "cerebral palsy"	Frequently the initial working label given spastic-dystonic motor findings; 75% had uncomplicated perinatal courses. AFG2B disorders were explicitly presented as a genetic cause of "spastic-dystonic cerebral palsy."

Practical diagnostic heuristic: congenital microcephaly + congenital sensorineural deafness + infantile epileptic spasms + normal metabolic screen should prompt AFG2A/AFG2B testing directly.

10.5 Screening

No newborn screening. AFG2A-RE is not on the RUSP or comparable panels. However, newborn hearing screening reliably flags these infants — universal hearing screening is, incidentally, the earliest existing detection touchpoint, and AFG2A/AFG2B should be represented on genetic-deafness follow-up panels (per PMID:28293831, AFG2A "may account for a fraction of isolated sensorineural hearing impairment cases").
Carrier screening: not on ACMG-recommended expanded carrier panels; would be reasonable in families with a known proband. The Dor Yeshorim programme participated in the AFG2B study, indicating community-based carrier-screening interest in this gene family.
Cascade testing of at-risk relatives and reproductive partners of carriers is appropriate.

11. Outcome / Prognosis

11.1 Survival and mortality

48/51 alive at reporting; three deaths at ages 3, 4.9, and 13.4 years. Cause was respiratory failure in one; unstated in two (PMID:41933351). (Note: the review reports this as 4.89%; 3/51 = 5.88% — cite the counts rather than the percentage.)
Puusepp's series independently records two sibling deaths at 3 years and 4 years 11 months (PMID:29343804).
Long survival is possible: two brothers from the attenuated consanguineous family were alive at ages 39 and 41 (PMID:27683084 / Table 1 of PMID:41933351).
No survival curve, median life expectancy, or standardized mortality ratio has been published. Deaths appear driven by respiratory complications in the context of profound motor impairment and dysphagia — the standard mortality profile for severe non-ambulatory DEE.

11.2 Morbidity and function

Uniformly high burden: absent speech in essentially all with ID; ~86% GMFCS IV–V; dual sensory impairment (deafness ~94% + visual impairment ~79%); drug-resistant epilepsy in the majority; dysphagia 30%. No formal disability instrument (ICF-based, CPCHILD, PedsQL) has been applied. Recovery potential is nil for the neurodevelopmental core — no treatment reverses microcephaly, deafness, or intellectual disability; the achievable gains are seizure control and functional/behavioural improvement.

11.3 Prognostic factors

Evidence is thin, but the following emerge: - Presence of epilepsy (particularly IESS) marks the severe end; the epilepsy-free individuals in the Buchert family were the longest-lived. - Genotype: no significant genotype–epilepsy association was found (PMID:41933351). The apparent "epilepsy-free" association with one homozygous in-frame deletion is confounded by all carriers belonging to a single family — and the allele's identity is disputed (§4.6). - Age at ketogenic-diet initiation predicts seizure response: earlier is better (PMID:40712368). - No prognostic biomarker exists.

12. Treatment

There is no disease-modifying therapy. Management is symptomatic, supportive, and multidisciplinary.

12.1 Antiseizure medications

Agents actually used in reported patients: phenobarbital, valproate, levetiracetam, lacosamide, lamotrigine, zonisamide, ACTH/corticosteroids, vigabatrin. Response is poor: only 4/16 with follow-up achieved seizure freedom, all on polytherapy — lacosamide + levetiracetam; valproate + levetiracetam + ACTH; lamotrigine + valproate; and one on ketogenic-diet monotherapy.

A clinically important negative finding: "individuals with IESS do not achieve seizure control with usual first-line treatment (neither corticosteroids nor vigabatrin)." (PMID:41933351) — i.e., the standard IESS first-line algorithm underperforms in this genetic aetiology, which is itself an actionable, curatable claim.

NCIT: NCIT:C15986 Pharmacotherapy, with therapeutic_agent per drug (CHEBI/NCIT IDs not verified this session — resolve with OAK before curation).

12.2 Ketogenic diet — the most promising current intervention

Nou-Fontanet et al. 2025 (PMID:40712368):

"Four patients received KD treatment for DRE, with seizure reduction rates of 0 %, 30 %, 70 % and 100 %, respectively. Improvement in social interaction improvement was observed in one patient, while improvements in attentional and motor function were noted in two. In vitro studies demonstrated that AFG2A-deficient fibroblasts exhibited altered mitochondrial morphology and dynamics, as well as reduced ATP production and ROS levels. These abnormalities were significantly reversed when the fibroblasts were cultured in KD-MM. In conclusion, this small series of patients with AFG2A-RE showed beneficial effects from KD treatment. Greater seizure control was achieved when the ketogenic diet was initiated during early childhood. These findings are preliminary and validation in multicenter prospective study is required."

The pairing of a clinical response with a matched ex vivo mechanistic readout (mitochondrial dynamics rescue in patient fibroblasts in KD-mimicking medium) is unusual for an ultra-rare disorder and makes KD the strongest mechanism-linked treatment claim available. An accompanying editorial (Catsman-Berrevoets, PMID:40846618, "Deepening the understanding of mechanisms of antiepileptic effects of the ketogenic diet in children with AFG2A-related encephalopathy") marks its reception in the field. Evidence grade: n=4–5, uncontrolled, retrospective — curate as PARTIAL/emerging, not established.

NCIT: NCIT:C173168 Ketogenic Diet [verified], or NCIT:C15447 Dietary Intervention; therapeutic_modality: BEHAVIORAL.

12.3 Sensory habilitation

Hearing amplification / cochlear implantation — congenital profound SNHL; early fitting documented (hearing device before 2 months of age, PMID:34360601). Systematic outcome data for cochlear implantation in AFG2A-RE are absent, and profound cognitive impairment plus cerebral visual impairment complicate candidacy assessment. NCIT: NCIT:C157820 Cochlear Implant [verified]; therapeutic_modality: DEVICE.
Vision — CVI-adapted intervention, refractive correction, strabismus management.

12.4 Supportive, rehabilitative, and surgical

Physiotherapy, occupational therapy, tone management for spasticity/dystonia, postural and seating management (GMFCS IV–V). NCIT: NCIT:C15302 Physical Therapy, NCIT:C121351 Occupational Therapy, NCIT:C159273 speech/communication therapy (AAC given absent speech).
Nutrition and feeding: dysphagia management, gastrostomy where indicated, GER treatment.
Orthopaedic surgery for hip dysplasia/luxation and scoliosis (documented: multiple hip surgeries, PMID:34360601). NCIT: NCIT:C16186 Orthopedic Surgical Procedure.
Respiratory surveillance — the documented cause of death in one patient.
Genetic counselling (NCIT:C15240).
Palliative/supportive care (NCIT:C15747).

12.5 Experimental and future directions

ClinicalTrials.gov: no interventional trial registered for AFG2A/SPATA5 as of this search. A multicentre prospective KD study is called for by PMID:40712368 but not yet registered.
mTOR pathway enhancement is the first rationally derived target: in AIRIM/C1orf109-variant cerebral organoids, "Enhancing mTOR activity suppresses the growth and developmental defects" (PMID:40760247). Whether this transfers to AFG2A hypomorphs is untested, and the therapeutic window would be prenatal/neonatal for the structural phenotype — but it may be relevant to postnatal translation capacity. Curate as a hypothesis with evidence_source: IN_VITRO, not as a treatment.
The sulfinylated P-loop cysteine C672 (PMID:40268917) identifies a redox-regulated switch that the authors note "might be harnessed for therapeutic purposes."
Natural-history study (ERN ITHACA / SPATA Foundation, Vona, Göttingen) — prerequisite infrastructure for any future trial.
No gene therapy, ASO, enzyme-replacement, or cell-therapy programme exists. Note that ASO and gene-replacement strategies are conceptually poorly matched here: the phenotype is largely established prenatally, and the deficiency is of a ubiquitously required housekeeping ATPase.

12.6 Pharmacogenomics

None specific. Standard ASM pharmacogenomic considerations apply (e.g., HLA-B*15:02 with aromatic ASMs, POLG-status before valproate — the latter especially relevant given the frequent initial mitochondrial-disease working diagnosis).

13. Prevention

Primary prevention: not possible for an autosomal recessive Mendelian disorder. The only routes to occurrence-prevention are reproductive: genetic counselling with a 25% recurrence risk per pregnancy for carrier couples; prenatal diagnosis (CVS/amniocentesis) and preimplantation genetic testing for monogenic disease (PGT-M) once the familial variants are known; carrier/cascade screening of relatives and reproductive partners. Community-based carrier-screening programmes (e.g., Dor Yeshorim, which participated in the AFG2B study) provide a precedent model.
Secondary prevention (early detection): universal newborn hearing screening is the existing system that reliably catches these infants earliest; inclusion of AFG2A/AFG2B on genetic-deafness follow-up panels would shorten the diagnostic odyssey. No newborn biochemical screen is applicable (metabolic screening is normal by design).
Tertiary prevention (complication prevention) — this is where the actionable content lies:
Early hearing habilitation to preserve whatever auditory/communication access is achievable.
Early ketogenic diet initiation in drug-resistant epilepsy (the one evidence-linked timing recommendation).
Aspiration prevention through dysphagia assessment and feeding management; respiratory surveillance (documented mortality route).
Hip surveillance and scoliosis monitoring in the non-ambulatory (GMFCS IV–V) majority.
Avoidance of an unnecessary invasive diagnostic cascade (muscle biopsy) once the genetic diagnosis is available.
Immunization: no disease-specific vaccine strategy; routine immunization plus respiratory-pathogen vaccination (influenza, RSV, pneumococcus) is standard of care for children with severe neurodisability and dysphagia.
Public/environmental health interventions: not applicable.

14. Other Species / Natural Disease

Taxonomy: Homo sapiens NCBITaxon:9606 is the only species with naturally occurring disease. Laboratory species used: Mus musculus (NCBITaxon:10090), Rattus norvegicus (NCBITaxon:10116), Saccharomyces cerevisiae (NCBITaxon:4932).
Orthologues: mouse Afg2a MGI:1927170 (NCBI Gene ortholog of human 166378); yeast Drg1 — the functional orthologue whose pre-60S role framed the human mechanism (PMID:31703473, PMID:40268917).
Breed (VBO): not applicable.
Natural disease in other species: none identified. No OMIA entry for SPATA5/AFG2A in dog, cattle, horse, or other domestic species was found. No veterinary relevance.
Comparative biology / evolutionary conservation: the AAA+ ATPase and its pre-60S maturation role are conserved from yeast to human — "Rix7, Rea1, and Drg1, which are well conserved across eukaryotes, are involved in different maturation steps of pre-60S ribosomal particles" (PMID:31703473). But the conservation is partial and the difference matters: the human complex is a 4:2:2:2 hetero-assembly (AFG2A:AFG2B:AIRIM/C1orf109:CINP) and "Different from yeast, the recognition of the pre-60S particle is mediated by human-specific factor CINP" (PMID:40268917). Yeast Drg1 data therefore inform the enzymology but not the substrate-recognition step or the disease-relevant complex composition. Curate this as an explicit conservation caveat.
Zoonotic potential / cross-species transmission: not applicable.

15. Model Organisms

15.1 Mouse — Afg2a (MGI:1927170)

Alleles available: MGI records 27 mutations across classes — 3 targeted, 21 gene-trapped, 2 radiation-induced, 1 endonuclease-mediated; 38 strains/lines available through IMSR.
IMPC knockout phenotype (allele Afg2a^tm1b(KOMP)Wtsi, homozygous, BCM phenotyping centre):
"Embryonic lethality prior to organogenesis" (p = 0.0)
"Preweaning lethality, complete penetrance" (p = 0.0)
Interpretation — a first-class HUMAN_MODEL_MISMATCH: the mouse constitutive null is embryonic lethal before organogenesis and therefore cannot model the human disease at all. Human AFG2A-RE necessarily results from hypomorphic biallelic combinations retaining partial ATPase function. Any faithful mouse model would need to be a knock-in of a patient hypomorphic allele (e.g., p.Thr330del, p.Arg84Gln) or a conditional/neural-specific hypomorph. No such model has been published. This is the single largest resource gap in the field and should be curated as a HUMAN_MODEL_MISMATCH discussion with proposed experiments.

15.2 Rat primary neuron model (the workhorse to date)

Puusepp et al. 2018 (PMID:29343804) — shRNA knockdown in primary neonatal Wistar rat cortical neurons, with rescue by shRNA-insensitive human SPATA5. - Recapitulates: 20% reduction in mitochondrial length; significantly decreased fusion:fission ratio; 12% reduction in axonal ATP/ADP ratio (rescued by wild-type human SPATA5 — establishing specificity); impaired neuronal maturation with short axons. - Does not capture: microcephaly, hearing loss, epilepsy, or any organismal phenotype. Acute knockdown also models complete loss rather than hypomorphic function. - Evidence source: MODEL_ORGANISM (rat primary culture; arguably IN_VITRO for the cultured-neuron assays — split evidence items so each carries a single source type).

15.3 Human cell and organoid models

Patient fibroblasts (n=3) — altered mitochondrial morphology and dynamics, reduced ATP production and ROS, all reversed in ketogenic-diet-mimicking medium (PMID:40712368). IN_VITRO. The best available pharmacodynamic model.
Patient PBMCs, platelets, monocytes — impaired oxygen consumption, reduced mitochondrial mass (PMID:36849973). IN_VITRO / HUMAN_CLINICAL hybrid; split accordingly.
Patient muscle biopsy proteomics — 82 dysregulated proteins, ProteomeXchange PXD026182 (PMID:34360601). HUMAN_CLINICAL.
Genome-wide CRISPR loss-of-function screen with heterochronic ribosome labelling in human cells — the discovery platform that assigned SPATA5 to pre-60S maturation (PMID:35354024). IN_VITRO.
Human cerebral organoids — the most disease-relevant system available, established for the paralogous 55LCC subunit AIRIM/C1orf109 with proteomics, scRNA-seq, single-organoid translation analysis, ribosome profiling, and a genetic mTOR rescue (PMID:40760247). Directly transferable to AFG2A and the obvious next model to build. IN_VITRO.
Cryo-EM / integrative structural biology of the purified 55LCC and pre-60S-bound complex (PMID:40268917, PMID:38554706). IN_VITRO / structural.
In silico: molecular modelling of variant effects on protein stability was used as supporting evidence in PMID:27683084, PMID:30552426, PMID:34626583, PMID:36849973 → COMPUTATIONAL.

15.4 Yeast

S. cerevisiae Drg1 is the established genetic and biochemical model for the ATPase step, with well-characterized specific AAA inhibitors available (diazaborine; PMID:31703473). Useful for enzymology and inhibitor/chaperone-modulator screens; not a disease model, and limited by the human-specific CINP-mediated substrate recognition (§14).

15.5 Model databases

MGI (MGI:1927170), IMPC (Afg2a), IMSR (38 lines), KOMP/EuMMCR (tm1b allele), Alliance of Genome Resources, SGD (Drg1), ProteomeXchange (PXD026182), Cellosaurus (no dedicated AFG2A patient line deposited).

Curation summary — recommended KB structure

Pathophysiology chain (proposed nodes, upstream → downstream):

AFG2A Hypomorphic Loss of Function — MOLECULAR — biallelic hypomorphic variants reduce AAA+ ATPase activity (evidence: PMID:26299366, PMID:27683084, PMID:29343804; hypomorphic inference supported by mouse null lethality, IMPC).
55LCC Complex Dysfunction — MOLECULAR — the 4:2:2:2 AFG2A/AFG2B/AIRIM/CINP assembly loses ATPase output (PMID:40268917, PMID:38554706).
Impaired Cytoplasmic Pre-60S Ribosome Maturation — MOLECULAR — late-step block in 60S subunit maturation (PMID:35354024, PMID:40268917, PMID:31703473).
Reduced Global Protein Synthesis Capacity — CELLULAR — with selective impact on 5′-TOP-like and neurogenesis transcripts (PMID:35354024, PMID:40760247).
Neuroepithelial Vulnerability During Differentiation — CELLULAR — physiological ribosome trough creates a developmental window of susceptibility (PMID:40760247).
(Parallel branch) Replisome Proteostasis Failure → Replication Stress and Chromosomal Instability — CELLULAR — ubiquitin-independent (PMID:38554706).
(Downstream/secondary) Mitochondrial Fusion–Fission Imbalance and Bioenergetic Deficit — CELLULAR — shortened mitochondria, reduced fusion:fission ratio, reduced axonal ATP (PMID:29343804, PMID:36849973, PMID:40712368). Attach a mechanistic_hypotheses entry (status: EMERGING) recording that AFG2A is cytosolic in neurons and that this arm is probably secondary to translational insufficiency rather than a primary mitochondrial-targeting defect.
Impaired Neuronal Maturation and Cortical Development — TISSUE — short axons, hypomyelination, reduced brain growth.
Congenital Microcephaly / Cortical Hyperexcitability / Cochlear and Cortical Sensory Failure — ORGANISM.

Suggested module conformance to evaluate: epilepsy_excitation_inhibition_imbalance#Excitation-Inhibition Imbalance (for the IESS/DEE arm) and sensorineural_hair_cell_loss#Hair Cell Mechanotransduction Failure and Death (for the SNHL arm — noting that direct AFG2A cochlear cell-type data are absent and the supporting expression evidence is from the AFG2B paralogue, so conformance should be declared cautiously or deferred).

Treatment target_mechanisms pattern: ketogenic diet → INHIBITS/modulates the Mitochondrial Fusion–Fission Imbalance and Bioenergetic Deficit node (PMID:40712368 provides the matched clinical + fibroblast-rescue evidence).

Discussions to open: (i) HUMAN_MODEL_MISMATCH — mouse null is embryonic lethal, no hypomorphic knock-in exists; (ii) HUMAN_MODEL_MISMATCH — neuronal cytosolic localization vs the annotated mitochondrial targeting sequence; (iii) KNOWLEDGE_GAP — no QoL instrument, no natural history, no prevalence, no episignature, no gnomAD-derived carrier frequency; (iv) KNOWLEDGE_GAP — unexplained intrafamilial variability (isolated SNHL vs full encephalopathy on identical genotypes).

Before committing: run just fetch-reference for the four PMIDs not yet in references_cache/ (40760247, and confirm 41933351, 40712368, 40846618 are complete), then just validate, just validate-references, and just validate-terms — every HP/GO/CL/UBERON/NCIT/CHEBI ID marked [suggested] above must clear term validation before it enters the YAML.

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AFG2A-Related Encephalopathy — Comprehensive Research Report

1. Disease Information

1.1 Overview

1.2 Identifiers

1.3 Synonyms and nomenclature

1.4 Data provenance

2. Etiology

2.1 Primary causal factor

2.2 Genetic risk factors

2.3 Environmental risk factors, protective factors, gene–environment interactions

3. Phenotypes

3.1 Core frequency table (largest cohort, n=51; PMID:41933351)

3.2 Epilepsy phenotype (detailed data n=24; PMID:41933351)

3.3 Neuroimaging phenotypes

3.4 Laboratory / biochemical phenotypes

3.5 Dysmorphology

3.6 Other systems

3.7 Attenuated end of the spectrum — isolated sensorineural hearing loss

3.8 Quality-of-life impact

4. Genetic / Molecular Information

4.1 Gene

4.2 Variant spectrum

4.3 Modifier genes

4.4 Epigenetics

4.5 Chromosomal abnormalities

4.6 ⚠ Three published-data discrepancies to avoid propagating

5. Environmental Information

6. Mechanism / Pathophysiology

6.1 Primary mechanism — defective cytoplasmic pre-60S ribosome maturation

6.2 The 55LCC complex also governs replisome proteostasis and genome stability

6.3 Why a housekeeping defect produces a brain-and-ear-specific phenotype

6.4 Mitochondrial dysfunction — real, but likely downstream

6.5 Tissue/muscle proteomics

6.6 Immune involvement, metabolic pathways, fibrosis

6.7 Suggested ontology terms for mechanism nodes

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

9.1 Epidemiology

9.2 Inheritance genetics

9.3 Demographics

10. Diagnostics

10.1 Genetic testing — the definitive diagnostic modality

10.2 Clinical and laboratory workup

10.3 Omics-based diagnostics

10.4 Differential diagnosis

10.5 Screening

11. Outcome / Prognosis

11.1 Survival and mortality

11.2 Morbidity and function

11.3 Prognostic factors

12. Treatment

12.1 Antiseizure medications

12.2 Ketogenic diet — the most promising current intervention

12.3 Sensory habilitation

12.4 Supportive, rehabilitative, and surgical

12.5 Experimental and future directions

12.6 Pharmacogenomics

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

15.1 Mouse — Afg2a (MGI:1927170)

15.2 Rat primary neuron model (the workhorse to date)

15.3 Human cell and organoid models