SNF8-Related Neurodevelopmental Disorder

Mendelian MONDO:0968947 Pathograph 7 Show in embeddings browser Neurodevelopmental Disorder

Neurodevelopmental disorder plus optic atrophy (NEDOA) is an autosomal recessive disorder caused by bi-allelic variants in SNF8, the gene encoding the SNF8 subunit of the ESCRT-II complex. It occupies the mild end of a two-part SNF8 disease spectrum: the severe end is developmental and epileptic encephalopathy 115, a congenital-onset encephalopathy with massive white matter loss and early death, while NEDOA presents as impaired intellectual development with optic atrophy, nystagmus, and in some individuals ataxia, and is compatible with survival into later childhood and beyond. Every individual reported at the mild end carried the same hypomorphic missense allele, c.304G>A (p.Val102Ile), so the milder phenotype is currently defined by genotype as much as by clinical features. ESCRT-II is the central module of the endosomal sorting complex required for transport pathway, bridging ESCRT-I to ESCRT-III on the endosomal membrane and thereby driving intralumenal vesicle formation, multivesicular body biogenesis, receptor downregulation, and autophagosome maturation. Patient fibroblasts carrying bi-allelic SNF8 variants lose ESCRT-II subunits, and the authors of the founding study attribute the neurodevelopmental and neurodegenerative phenotype principally to impaired autophagic flux. The disorder is ultra-rare: as of this curation the entire published clinical literature is a single 2024 report of nine individuals from six families spanning both ends of the spectrum.

Ask OpenScientist

Ask a research question about SNF8-Related Neurodevelopmental Disorder. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

🏷

Classifications

Harrison's Chapter

👪

Inheritance

Autosomal recessive inheritance HP:0000007

Disease requires two damaging SNF8 alleles. All nine reported individuals were bi-allelic, and every individual at the mild NEDOA end of the spectrum carried the hypomorphic missense allele c.304G>A (p.Val102Ile), which is understood to retain partial function and thereby to set the severity floor. Heterozygous carriers, including the parents in the six reported families, are not described as affected. Penetrance is recorded as incomplete, and the reason is specific to this entity rather than a generic hedge. gnomAD contains one apparently healthy individual homozygous for c.304G>A (p.Val102Ile) - the very allele that defines the mild pole. For the severe bi-allelic genotypes penetrance appears complete, so penetrance here is genotype-dependent rather than uniformly reduced. The practical consequence is a counselling problem: a fetus predicted to be a p.Val102Ile homozygote cannot be described as affected on present evidence. That gnomAD homozygote is reported in the full text of PMID:38423010 and was surfaced by the deep research pass; it is not in the cached abstract, so it carries no snippet. Consanguinity is not explicitly reported for any family and is deliberately not asserted, despite the one homozygous family being consistent with it.

Autosomal recessive inheritance Penetrance: INCOMPLETE

Show evidence (2 references)

PMID:38423010 SUPPORT Human Clinical

"We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8"

Nine affected individuals from six families all carried bi-allelic SNF8 variants, which is the definition of autosomal recessive inheritance for this locus.

PMID:38423010 SUPPORT Human Clinical

"All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."

Identifies the specific hypomorphic allele shared by the mild cohort, that is, by the individuals who constitute this MONDO entity rather than the allelic encephalopathy.

Discussions and Knowledge Gaps

Why is at least one apparently healthy gnomAD individual homozygous for c.304G>A (p.Val102Ile), the very allele that defines the mild pole of SNF8 disease?

KNOWLEDGE GAP OPEN snf8-val102ile-healthy-homozygote

Attached to

pathophysiology#Stability-Independent Impairment by the p.Val102Ile Hypomorph

This is the most consequential open question for the entry and it is not a technicality. Every mildly affected individual reported carries p.Val102Ile, yet a homozygote for that allele appears unaffected in a population database, and ClinVar submitters disagree about the allele accordingly (Munich and OMIM Pathogenic, Ambry uncertain significance). Three explanations are live and they have different clinical consequences: an unidentified modifier locus; a threshold effect in which two hypomorphic alleles retain more ESCRT-II activity than one hypomorph plus one null; or incomplete phenotyping of the population-database individual, who would not have had visual evoked potentials or optic coherence tomography. Until this is resolved, prenatal counselling for a predicted p.Val102Ile homozygote cannot state that the fetus is affected.

Proposed experiments

Deep ophthalmological phenotyping of population-database p.Val102Ile homozygotes

snf8-recall-by-genotype-homozygotes

Recall-by-genotype of homozygous carriers identified in population biobanks, with visual evoked potentials, optic coherence tomography and formal cognitive assessment, to establish whether they are genuinely unaffected or merely unascertained for a subclinical optic neuropathy.

Allelic-series functional assay of ESCRT-II activity

snf8-allelic-series-escrt2-activity

Measure residual ESCRT-II function in cells engineered to carry p.Val102Ile homozygously versus p.Val102Ile in trans to a null allele, to test the threshold model directly against the modifier model.

Recorded as a discussion rather than as a phenotype or a penetrance figure because the underlying observation is in the full text of PMID:38423010 and in gnomAD, neither of which is quotable from the cached abstract.

What is the actual transcript consequence of the c.423-1G>C splice-acceptor variant carried by the family D proband?

KNOWLEDGE GAP OPEN snf8-splice-acceptor-transcript-consequence

Attached to

genetic#SNF8

The variant is annotated only as p.? - its effect on splicing was never determined experimentally. Because this individual sits at the mild pole, the answer bears directly on the allelic-dosage model that the whole entity rests on: if c.423-1G>C is a complete null then p.Val102Ile alone sets the mild phenotype, whereas if it permits some in-frame product then the residual activity is shared between the two alleles and the model needs revising. RNA sequencing or RT-PCR on patient material would settle it.

Proposed experiments

RNA-seq or RT-PCR of the family D proband

snf8-familyd-splice-rnaseq

Sequence patient-derived transcripts to determine whether c.423-1G>C causes exon skipping, activation of a cryptic acceptor, or intron retention, and whether the product escapes nonsense-mediated decay.

Does any existing model system represent the genotype that defines this disorder, given that the zebrafish model is a transient morpholino knockdown and the mouse null is preweaning-lethal?

HUMAN MODEL MISMATCH OPEN snf8-no-model-of-the-mild-pole

Attached to

pathophysiology#Stability-Independent Impairment by the p.Val102Ile Hypomorph pathophysiology#Optic Nerve and Forebrain Developmental Failure

This is a model-fidelity question rather than an absence of evidence, which is why it is recorded as HUMAN_MODEL_MISMATCH and not as a KNOWLEDGE_GAP: in vivo evidence exists and is informative, but neither system models the entity curated here. The zebrafish work is a transient antisense morpholino knockdown, not a stable germline mutant, and morphant phenotypes are subject to off-target and p53-mediated artefacts; it captures the optic-nerve and forebrain developmental axis well, including the allele-severity gradient, but addresses none of the epileptic encephalopathy, callosal agenesis or leukoencephalopathy of the severe pole and none of the intellectual disability or progressive course of the mild pole. The IMPC mouse homozygous null is preweaning-lethal with complete penetrance, so no viable animal exists in which to phenotype the postnatal CNS. Most importantly, no model of any species carries a hypomorphic allele equivalent to p.Val102Ile - the allele every mildly affected individual carries and the only reason this MONDO term is distinct from DEE115. Every mechanistic claim about the mild pole therefore rests on two patient fibroblast lines and on inference, with no in vivo corroboration.

Proposed experiments

Knock-in mouse carrying the p.Val102Ile-equivalent hypomorphic allele

snf8-val102ile-knockin-mouse

Generate homozygous and compound-heterozygous (hypomorph over null) knock-in mice to obtain the first viable in vivo model of the mild pole, and phenotype the visual pathway, cognition and white matter longitudinally. This would also test the threshold model against the modifier model raised by the healthy gnomAD homozygote.

Stable germline snf8 zebrafish mutant

snf8-stable-zebrafish-mutant

Create a CRISPR germline snf8 mutant line and ask whether the optic-nerve extension, optic-chiasm and forebrain-size phenotypes reported in morphants reproduce, which is the standard test for morpholino off-target artefact.

Patient iPSC-derived cortical neurons and retinal organoids

snf8-ipsc-neurons-and-retinal-organoids

Derive neurons and retinal organoids from mild-pole individuals to measure autophagic flux and ESCRT-II function in the cell types the disease actually affects, rather than in fibroblasts. The same approach was applied to the allied ESCRT disorder caused by VPS4A variants, so it is tractable.

The morpholino character of the zebrafish model and the IMPC mouse data are recorded on the respective `animal_models:` entries, with the IMPC API URL and its retrieval date. Neither is quotable from the cached abstract of PMID:38423010, so this discussion carries no evidence item.

⚙

Pathophysiology

Bi-allelic Hypomorphic SNF8 Variants

The primary lesion is bi-allelic damage to SNF8 at 17q21.32, reported against transcript NM_007241.4. Genotype maps onto severity: the mild NEDOA phenotype curated here occurs only in individuals who carry the hypomorphic missense allele c.304G>A (p.Val102Ile), which is inferred to leave residual SNF8 function, whereas the severe allelic encephalopathy arises from more damaging genotypes. Functional testing in vivo reproduced this graded effect, with different SNF8 alleles having different impacts on embryonic development, which is the mechanistic basis for the clinical heterogeneity across the spectrum.

SNF8 hgnc:17028

Downstream

Loss of the ESCRT-II Complex Severe-pole genotypes, which lack p.Val102Ile, destabilise SNF8 protein and with it the assembled ESCRT-II heterotetramer. This is the abundance-dependent arm of the allelic split.

Stability-Independent Impairment by the p.Val102Ile Hypomorph The parallel, allele-specific arm. In individuals carrying the mild-pole hypomorph c.304G>A (p.Val102Ile), ESCRT-II function is impaired without a measurable fall in complex abundance, so this branch is a direct consequence of the variant rather than of complex loss.

Show evidence (2 references)

PMID:38423010 SUPPORT Human Clinical

"caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8"

Names the causal gene, the reference transcript, and the gene product's identity as an ESCRT-II subunit.

PMID:38423010 SUPPORT Model Organism

"In vivo experiments corroborated the pathogenicity of the tested SNF8 variants and their variable impact on embryo development, validating the observed clinical heterogeneity."

Supports the claim that allele severity, not a second locus, accounts for the split between the mild and severe ends of the spectrum.

Loss of the ESCRT-II Complex

ESCRT-II is an obligate heterotetramer built from one copy of SNF8/VPS22, one copy of VPS36, and two copies of VPS25, arranged as a trilobal assembly of winged-helix domains. Because the subunits are mutually stabilising, damaging one of them destabilises the whole complex rather than removing a single activity: patient-derived fibroblasts carrying bi-allelic SNF8 variants show loss of ESCRT-II subunits, plural. SNF8 is not a peripheral subunit in this assembly - the first helix of VPS22 contributes directly, alongside the VPS36 GLUE domain, to targeting ESCRT-II onto the endosomal membrane - so its loss removes both the structural core and part of the membrane-recruitment activity.

patient-derived dermal fibroblast CL:0000057

SNF8 hgnc:17028

ESCRT II complex GO:0000814

endosome membrane GO:0010008

Downstream

Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis Without ESCRT-II on the endosomal membrane, the downstream ESCRT-III polymer is not nucleated.

Show evidence (5 references)

PMID:38423010 PARTIAL In Vitro

"In patient-derived fibroblasts, bi-allelic SNF8 variants cause loss of ESCRT-II subunits."

Patient-cell demonstration that the SNF8 genotype can destabilise ESCRT-II subunits collectively. Marked PARTIAL rather than SUPPORT because the sentence is stated for the spectrum as a whole while the underlying proteomics shows the effect in the severe-pole genotypes and not in the mild-pole genotype that defines this MONDO term; see this node's notes.

PMID:18539118 SUPPORT In Vitro

"The complex has three lobes and contains one copy each of VPS22 and VPS36 and two copies of VPS25."

Defines the stoichiometry of human ESCRT-II and places SNF8, whose HGNC alias is VPS22, as a single-copy core subunit whose loss cannot be compensated by another copy.

PMID:18539118 SUPPORT In Vitro

"ESCRT-II is targeted to endosomal membranes by the lipid-binding activities of both the Vps36 GLUE domain and the first helix of Vps22."

Assigns a specific membrane-targeting function to the SNF8/VPS22 subunit itself, so loss of SNF8 impairs recruitment of ESCRT-II to the endosome and not only its assembly.

+ 2 more references

Stability-Independent Impairment by the p.Val102Ile Hypomorph

This node exists because the mechanism that produces NEDOA is not the mechanism that produces the severe allelic encephalopathy. Every mildly affected individual carries c.304G>A (p.Val102Ile) in trans to a more damaging allele, and in fibroblasts from two of them the ESCRT-II subunits were not significantly depleted. The authors' reading is that this allele impairs ESCRT-II function by a route independent of protein stability - a partially functional complex is assembled in normal amounts but works less well - rather than by removing the complex. That is what sets the severity floor for this entity: enough residual ESCRT-II activity to permit survival into adulthood and mild rather than absent development, but not enough to protect the anterior visual pathway. The distinction also predicts that a proteomic assay of ESCRT-II subunit abundance, which is informative for the severe pole, will look near-normal in NEDOA and cannot be used to confirm this diagnosis.

SNF8 hgnc:17028

ESCRT II complex GO:0000814

Downstream

Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis Reduced, rather than absent, ESCRT-II activity yields a partial and cargo-selective block of the downstream sorting step.

Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis

ESCRT-0, -I, -II and -III act as a sequential relay on the endosomal membrane. ESCRT-II is the hand-off point: it binds the ESCRT-I VPS28 C-terminal domain on one side and, through VPS25, directly recruits and nucleates the ESCRT-III subunit VPS20/CHMP6 on the other. Losing ESCRT-II therefore breaks the cascade in the middle, so ubiquitinated cargo is not packaged into intralumenal vesicles, multivesicular bodies fail to mature, and surface receptors are not downregulated. This step is the mechanistic junction with the ESCRT-III disorders: an ESCRT-II lesion and an ESCRT-III lesion disable adjacent stages of one pathway.

patient-derived dermal fibroblast CL:0000057

multivesicular body assembly GO:0036258 ↓ DECREASED endosomal transport GO:0016197 ⚠ ABNORMAL ubiquitin-dependent cargo delivery to the lysosome via the MVB sorting pathway GO:0043328 ↓ DECREASED

multivesicular body GO:0005771

Downstream

Impaired Autophagic Flux Blocked endosomal maturation prevents autophagosome-lysosome progression.

Show evidence (4 references)

PMID:15469844 SUPPORT In Vitro

"ESCRT-I, -II, and -III protein complexes are sequentially recruited to endosomal membranes, where they orchestrate protein sorting and MVB biogenesis."

Establishes that ESCRT-II occupies an obligatory intermediate position in the sorting relay, so its loss interrupts the sequence rather than degrading it gracefully.

PMID:15469844 SUPPORT In Vitro

"We show that purified ESCRT-II binds directly to the Vps20 component of ESCRT-III."

Demonstrates the direct physical hand-off from ESCRT-II to ESCRT-III that is lost when the ESCRT-II complex is destabilised.

PMID:18539118 SUPPORT In Vitro

"ESCRT-II plays a pivotal role in receptor downregulation and multivesicular body biogenesis and is conserved from yeast to humans."

States the two cell-biological outputs, receptor downregulation and multivesicular body biogenesis, that fail when ESCRT-II is lost.

+ 1 more reference

Impaired Autophagic Flux

The ESCRT machinery is required not only for endosomal sorting but for autophagy, where it contributes to phagophore closure and to autophagosome-lysosome fusion. The founding study's stated conclusion is that the neurodevelopmental and neurodegenerative phenotypes of bi-allelic SNF8 disease are mediated principally through impaired autophagic flux rather than through cargo missorting alone. The abstract states this as a likelihood, but the full text backs it with direct patient-material assays: transmission electron microscopy of patient fibroblasts showing accumulated autolysosomes and morphologically aberrant, enlarged, electron-lucent lysosomes; LC3/LAMP1 confocal immunofluorescence showing the same accumulation; and, at the severe pole, strong LC3 immunostaining on autopsy neuropathology where age-matched controls stained only weakly.

patient-derived dermal fibroblast CL:0000057 cortical pyramidal neuron CL:0000598 reactive astrocyte CL:0000127 activated microglial cell CL:0000129

macroautophagy GO:0016236 ↓ DECREASED autophagosome maturation GO:0097352 ↓ DECREASED

autolysosome GO:0044754

Downstream

Optic Nerve and Forebrain Developmental Failure Neurons and retinal ganglion cells, being long-lived and dependent on autophagic turnover, are the cells that fail.

Show evidence (2 references)

PMID:38423010 PARTIAL Human Clinical

"we conclude that loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux"

The authors' own conclusion, marked PARTIAL because the word "likely" is theirs and the abstract does not report a direct autophagic-flux measurement in patient material.

PMID:38423010 SUPPORT Other

"The endosomal sorting complex required for transport (ESCRT) machinery is essential for membrane remodeling and autophagy"

Establishes autophagy, alongside membrane remodelling, as a core ESCRT function and therefore as a plausible route from ESCRT-II loss to neurodegeneration. Classified OTHER rather than HUMAN_CLINICAL: this is the paper's introductory statement of general cell biology and reports no human observation of its own, so tagging it HUMAN_CLINICAL would overstate the evidence type.

Optic Nerve and Forebrain Developmental Failure

The tissue-level endpoint is selective failure of the visual pathway and the forebrain. Zebrafish snf8 loss of function reproduces this pattern specifically, producing impaired optic nerve development and reduced forebrain size in addition to global developmental delay and altered embryo morphology. That the optic nerve phenotype is recovered in a model organism is what elevates optic atrophy in this disorder from an incidental association to a mechanistically anchored feature, and it is the strongest available support for the visual pathway being intrinsically vulnerable to ESCRT-II loss rather than secondarily damaged.

retinal ganglion cell CL:0000740

optic nerve UBERON:0000941 forebrain UBERON:0001890

Show evidence (1 reference)

PMID:38423010 SUPPORT Model Organism

"Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size."

An orthogonal animal model reproduces both the optic nerve and the forebrain components of the human phenotype, supporting a developmental rather than purely degenerative mechanism for the visual pathway involvement.

⬡

Pathograph

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

●

Phenotypes

Ear 1

Conductive hearing impairment Conductive hearing impairment HP:0000405

Curated from the HPO annotation set for OMIM:620784, which records HP:0000405 at 1/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract, so no evidence item is attached.

Eye 3

Optic atrophy Optic atrophy HP:0000648

HPO annotation for OMIM:620784 records HP:0000648 at 3/4, sourced to PMID:38423010 (retrieved 2026-08-01). The deep research pass identified the denominator structure behind that fraction: optic atrophy was present in 3 of 3 individuals at the optic-atrophy end of the mild pole (D1, E1, E2) and absent in the fourth (F1), who had congenital ataxia instead. Reported onset was between 4 and 7 years, which straddles the boundary between HP:0011463 Childhood onset (1 to 5 years) and HP:0003621 Juvenile onset (5 to 15 years) - and indeed HPOA records each at 2/4 - so no single onset category is asserted. The 4-to-7-year window and the per-individual split are full-text detail, recorded here rather than quoted as a snippet.

Show evidence (2 references)

PMID:38423010 SUPPORT Human Clinical

"A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."

Directly names childhood-onset optic atrophy as a feature of the milder cohort denoted by this MONDO term.

PMID:38423010 SUPPORT Model Organism

"impaired optic nerve development, and reduced forebrain size"

The zebrafish model independently implicates the optic nerve, supporting the human optic atrophy as gene-attributable rather than coincidental.

Nystagmus Nystagmus HP:0000639

Curated from the HPO annotation set for OMIM:620784, which records HP:0000639 at 3/4 sourced to PMID:38423010 (retrieved 2026-08-01). The cached abstract does not mention nystagmus, so this phenotype carries no evidence item rather than a snippet that does not support it.

Reduced visual acuity Reduced visual acuity HP:0007663

Curated from the deep research pass, which records reduced visual acuity in 3 of 3 of the optic-atrophy individuals (D1, E1, E2) with a moderate, progressive course, sourced to the full text of PMID:38423010. This is not in the cached abstract and is not in the HPO annotation set for OMIM:620784, so no evidence item is attached.

Head and Neck 1

Microcephaly Microcephaly HP:0000252

Curated from the HPO annotation set for OMIM:620784, which records HP:0000252 at 1/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract, so no evidence item is attached.

Nervous System 3

Impaired intellectual development Intellectual disability HP:0001249

HPO annotation for OMIM:620784 records HP:0001249 at 4/4, sourced to PMID:38423010 (retrieved 2026-08-01 from https://ontology.jax.org/api/network/annotation/OMIM:620784). No FrequencyEnum band is asserted; see the entry-level notes for why.

Show evidence (1 reference)

PMID:38423010 SUPPORT Human Clinical

"A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."

Intellectual disability is stated as a feature of the milder cohort, which is the cohort corresponding to this MONDO term.

Ataxia Ataxia HP:0001251

HPO annotation for OMIM:620784 records HP:0001251 at 1/4, sourced to PMID:38423010 (retrieved 2026-08-01). No FrequencyEnum band is asserted. The deep research pass resolved which individual this is: F1, whose ataxia was congenital and who at age 2 had normal myelination, normal white matter volume, slight cerebellar atrophy, and no optic atrophy. That per-individual detail is full-text, not abstract content, so it is recorded here rather than quoted. It matters clinically because it means the two named features of this disorder were mutually exclusive in the only cohort ever reported.

Show evidence (1 reference)

PMID:38423010 SUPPORT Human Clinical

"A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."

Ataxia is named as a feature of the milder cohort; the disjunction in the source sentence is the reason this phenotype is not described as universal.

Delayed speech and language development Delayed speech and language development HP:0000750

Curated from the HPO annotation set for OMIM:620784, which records HP:0000750 at 3/3 sourced to PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract, so no evidence item is attached.

Other 5

Global developmental delay Mild global developmental delay HP:0011342

HPO annotation for OMIM:620784 records HP:0011342 (Mild global developmental delay) at 3/4, sourced to PMID:38423010 (retrieved 2026-08-01). The severity qualifier "mild" comes from that annotation and not from the cached abstract, which describes the cohort only as having a "milder phenotype".

Show evidence (1 reference)

PMID:38423010 PARTIAL Model Organism

"Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology"

Marked PARTIAL rather than SUPPORT for two reasons. It is model-organism evidence standing alone for a human phenotype, and the zebrafish result speaks to developmental delay as such but says nothing about the "mild" severity qualifier in the bound HP:0011342 term, which comes from the HPO annotation set rather than from any cached abstract.

Abnormal visual evoked potentials Abnormality of visual evoked potentials HP:0000649

Curated from the HPO annotation set for OMIM:620784, which records HP:0000649 at 3/3 sourced to PMID:38423010 (retrieved 2026-08-01). Note the denominator of 3, not 4, meaning one individual was not tested. Not mentioned in the cached abstract, so no evidence item is attached.

Global brain atrophy Global brain atrophy HP:0002283

Curated from the HPO annotation set for OMIM:620784, which records HP:0002283 at 2/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract, so no evidence item is attached.

Cerebellar cortical atrophy Cerebellar cortical atrophy HP:0008278

Curated from the HPO annotation set for OMIM:620784, which records HP:0008278 at 2/4 sourced to PMID:38423010 (retrieved 2026-08-01); the corresponding annotation for OMIM:620783 (DEE115) is 0/5. Not mentioned in the cached abstract, so no evidence item is attached.

Dysplastic corpus callosum Dysplastic corpus callosum HP:0006989

Curated from the HPO annotation set for OMIM:620784, which records HP:0006989 at 1/4, HP:0002079 (Hypoplasia of the corpus callosum) at 0/4 and HP:0001274 (Agenesis of corpus callosum) at 0/4, all sourced to PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract, so no evidence item is attached.

🧬

Genetic Associations

SNF8 (Bi-allelic variants; the mild NEDOA phenotype is associated specifically with the hypomorphic allele c.304G>A (p.Val102Ile))

Gene: SNF8 hgnc:17028 relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:38423010 SUPPORT Human Clinical

"caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8"

Establishes SNF8 as the causal gene and names the reference transcript against which variants are reported.

PMID:38423010 SUPPORT Human Clinical

"All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."

Ties the specific hypomorphic allele to the mild phenotype that this MONDO term denotes, which is the genotype-phenotype correlation defining the entity.

💊

Medical Actions

Multidisciplinary supportive care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

No disease-modifying therapy exists. Management is entirely supportive and follows the components of the phenotype: developmental and educational support, speech and language therapy for the near-universal language delay, low-vision services and educational accommodation for the optic atrophy, and physiotherapy where ataxia affects mobility.

Genetic counselling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal recessive recurrence risk counselling for the parents of a proband, with carrier testing for the specific familial alleles and discussion of reproductive options. Relevant to this disorder in particular because the same gene produces a lethal congenital encephalopathy at the severe end of the spectrum, so the counselling conversation has to address the possibility of a more severely affected sibling and cannot simply extrapolate the proband's mild course.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from SNF8-Related Neurodevelopmental Disorder:

Developmental and epileptic encephalopathy 115 Not Yet Curated MONDO:0968946

Overlapping Features The allelic disorder, caused by bi-allelic variants in the same gene. This is not a differential in the usual sense of a different disease that mimics this one; it is the other half of one continuum, and separating the two is a clinical judgement made after the SNF8 genotype is already known. A laboratory that reports bi-allelic SNF8 variants has not thereby chosen between OMIM:620783 and OMIM:620784.

Distinguishing Features

DEE115 has a congenital onset, whereas the optic atrophy in NEDOA is described as childhood-onset and the HPO onset annotations for NEDOA are childhood or juvenile.
DEE115 is defined by severe developmental and epileptic encephalopathy with neurodevelopmental arrest and early death; NEDOA is compatible with survival and with mild rather than absent developmental progress.
Massive white matter reduction with hypoplasia or aplasia of the corpus callosum is characteristic of DEE115; in the NEDOA HPO annotation set both callosal hypoplasia and agenesis are recorded at 0/4 and only dysplasia appears.
Seizures and EEG abnormality are recorded in DEE115 but are annotated at 0/4 in NEDOA, so an epileptic presentation argues against this entity.
All mildly affected individuals carried the hypomorphic c.304G>A (p.Val102Ile) allele, so this genotype is currently the strongest single pointer towards NEDOA rather than DEE115.

Show evidence (1 reference)

PMID:38423010 SUPPORT Human Clinical

"The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death."

Describes the severe allelic phenotype in the same cohort, establishing the clinical features that separate it from the milder entity curated here.

Behr syndrome MONDO:0008858

Overlapping Features The closest clinical mimic. Behr syndrome is a recessive, childhood-onset combination of bilateral optic atrophy with ataxia and variable intellectual disability, most often from bi-allelic OPA1 variants and also from OPA3, C12orf65/MTRFR or C19orf12. The three cardinal features of the milder SNF8 cohort - impaired intellectual development, childhood-onset optic atrophy, ataxia - are precisely the Behr triad, so a child with NEDOA presenting to a neuro-ophthalmology service will be worked up as Behr syndrome first, and the distinction is molecular rather than clinical.

Distinguishing Features

Behr syndrome is mechanistically mitochondrial, converging on impaired bioenergetics, whereas NEDOA is a defect of the endosomal ESCRT pathway; a normal mitochondrial workup does not exclude NEDOA and should prompt broader sequencing.
Pyramidal signs with spasticity, peripheral neuropathy and posterior-column sensory loss are part of the classical Behr phenotype and are not reported in the milder SNF8 cohort.
3-methylglutaconic aciduria points towards OPA3 within the Behr group and away from SNF8.
Behr syndrome is genetically heterogeneous by definition and is a clinically defined phenotype, so the two are not mutually exclusive on clinical grounds alone; only bi-allelic SNF8 variants establish NEDOA.

Bosch-Boonstra-Schaaf optic atrophy syndrome MONDO:0014320

Overlapping Features BBSOAS pairs optic atrophy with intellectual disability and developmental delay, which is the same two-part core as NEDOA, and it is the syndrome most likely to be on a clinician's list when a child presents with optic atrophy plus developmental delay. It is caused by NR2F1 variants or deletions.

Distinguishing Features

BBSOAS is autosomal dominant and usually de novo; NEDOA is autosomal recessive, so an affected sibling with unaffected parents favours NEDOA.
NR2F1 deletions are detectable by chromosomal microarray, whereas SNF8 disease requires sequencing.
The two are distinguished definitively by the causal gene, not by the ophthalmological findings, which overlap substantially.

Autosomal dominant optic atrophy plus syndrome MONDO:0014720

Overlapping Features Dominant OPA1 disease with extra-ocular features is the commonest inherited syndromic optic neuropathy and will be considered before a newly described recessive gene. Optic atrophy with ataxia is common to both.

Distinguishing Features

Dominant transmission with an affected parent argues strongly against NEDOA, which is recessive.
Sensorineural deafness, chronic progressive external ophthalmoplegia and mitochondrial myopathy characterise the OPA1-plus phenotype; the only hearing impairment reported in the milder SNF8 cohort was conductive.
Intellectual disability is not a core feature of dominant optic atrophy plus, whereas it is present in every reported NEDOA individual.

CIMDAG syndrome MONDO:0035819

Overlapping Features Included as a mechanistic rather than a clinical differential. CIMDAG syndrome is caused by VPS4A variants; VPS4A is the AAA-ATPase that disassembles ESCRT-III filaments, the step immediately downstream of the ESCRT-III nucleation that ESCRT-II performs. The pair establishes that lesions at adjacent stages of a single ESCRT cascade both produce syndromic neurodevelopmental disease with cerebellar and cognitive involvement, which is the argument for treating ESCRT dysfunction as a coherent disease group.

Distinguishing Features

CIMDAG syndrome is dominant, with de novo missense variants acting through a dominant-negative mechanism; SNF8 disease is recessive and hypomorphic.
Congenital dyserythropoietic anemia with binucleated erythroblasts is characteristic of CIMDAG and has not been reported in SNF8 disease.
Congenital microcephaly and dystonia define CIMDAG; the microcephaly in the milder SNF8 cohort is a minority finding and dystonia is not reported.
Optic atrophy is the defining ophthalmological feature of NEDOA, whereas cataract is the eye finding in CIMDAG.

{ }

Source YAML

click to show

name: SNF8-Related Neurodevelopmental Disorder
creation_date: "2026-08-01T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: neurodevelopmental disorder plus optic atrophy
  term:
    id: MONDO:0968947
    label: neurodevelopmental disorder plus optic atrophy
description: >-
  Neurodevelopmental disorder plus optic atrophy (NEDOA) is an autosomal
  recessive disorder caused by bi-allelic variants in SNF8, the gene encoding
  the SNF8 subunit of the ESCRT-II complex. It occupies the mild end of a
  two-part SNF8 disease spectrum: the severe end is developmental and epileptic
  encephalopathy 115, a congenital-onset encephalopathy with massive white
  matter loss and early death, while NEDOA presents as impaired intellectual
  development with optic atrophy, nystagmus, and in some individuals ataxia,
  and is compatible with survival into later childhood and beyond. Every
  individual reported at the mild end carried the same hypomorphic missense
  allele, c.304G>A (p.Val102Ile), so the milder phenotype is currently defined
  by genotype as much as by clinical features. ESCRT-II is the central module
  of the endosomal sorting complex required for transport pathway, bridging
  ESCRT-I to ESCRT-III on the endosomal membrane and thereby driving
  intralumenal vesicle formation, multivesicular body biogenesis, receptor
  downregulation, and autophagosome maturation. Patient fibroblasts carrying
  bi-allelic SNF8 variants lose ESCRT-II subunits, and the authors of the
  founding study attribute the neurodevelopmental and neurodegenerative
  phenotype principally to impaired autophagic flux. The disorder is
  ultra-rare: as of this curation the entire published clinical literature is a
  single 2024 report of nine individuals from six families spanning both ends
  of the spectrum.
parents:
- Neurodevelopmental Disorder
synonyms:
- NEDOA
- neurodevelopmental disorder plus optic atrophy
- SNF8-related syndromic optic atrophy
- VPS22-related neurodevelopmental disorder
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      The entire reported morbidity is neurological and neuro-ophthalmological:
      impaired intellectual development in 4/4, optic atrophy in 3/4, speech and
      language delay, mild global developmental delay, and in one individual
      congenital ataxia, with brain and cerebellar atrophy on MRI. The optic
      neuropathy is a lesion of the anterior visual pathway - central nervous
      system tissue - rather than an ophthalmological disease of the globe, so
      NEUROLOGIC rather than an ophthalmology assignment is the correct single
      chapter. No systemic, cardiac, renal, hepatic, haematological or skeletal
      involvement has been reported at either end of the SNF8 spectrum.
    evidence:
    - reference: PMID:38423010
      reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8"
      explanation: The founding report characterises the entire phenotype as neurodevelopmental and neurodegenerative, which is the basis for the NEUROLOGIC chapter assignment.
notes: >-
  Entity verification. The target term was verified with OAK before any content
  was written: `runoak -i sqlite:obo:mondo relationships --direction up
  MONDO:0968947` returns `RO:0004003 HGNC:17028 SNF8` and
  `rdfs:subClassOf MONDO:0100500 (Mendelian neurodevelopmental disorder)`, and
  the term xrefs OMIM:620784, MEDGEN:1859522, UMLS:C5935605. HGNC:17028 was
  confirmed against the HGNC REST API as symbol SNF8, name "SNF8 subunit of
  ESCRT-II", locus 17q21.32, with alias symbols EAP30, VPS22 and Dot3. That
  alias list matters for reading the literature: the structural papers cited
  here (PMID:18539118, PMID:15469844) name the same protein VPS22 and never use
  the string "SNF8", so those citations are about this gene despite the
  different symbol.

  Contrast entity, also verified with OAK rather than typed from memory. SNF8
  carries two distinct MONDO disease terms, and this entry curates only the
  milder one. `runoak -i sqlite:obo:mondo relationships --direction down
  HGNC:17028` returns exactly two subjects: MONDO:0968946 (developmental and
  epileptic encephalopathy 115, OMIM:620783) and MONDO:0968947 (this entry,
  OMIM:620784). DEE115 is curated below as an allelic differential diagnosis,
  not as a subtype or a parent. MONDO:0100500, the superclass of this entry, is
  deliberately NOT bound as a differential.

  Both MedGen concept records state autosomal recessive inheritance
  (C5935605: "Neurodevelopmental disorder plus optic atrophy (NEDOA) is an
  autosomal recessive disorder"; C5935604 likewise for DEE115), matching the
  "bi-allelic" language of the founding study. The HPO annotation set for
  OMIM:620784 nonetheless records HP:0000006 (Autosomal dominant inheritance).
  That HPOA inheritance annotation is judged to be an error and is NOT
  propagated into this entry; HP:0000007 is asserted instead, with the
  bi-allelic evidence quoted from the primary paper.

  Evidence base and its limits. PMID:38423010 (Brugger et al., Am J Hum Genet
  2024) is the only clinical publication describing this disorder. A PubMed
  search on 2026-08-01 for `(SNF8[TIAB] OR VPS22[TIAB]) AND (variant* OR
  mutation* OR patient*)` returned 20 records, of which PMID:38423010 was the
  only human disease-gene report; the 2025-2026 SNF8 records
  (PMID:42043682, PMID:41824857, PMID:40728621, PMID:40306176, PMID:40176577,
  PMID:40055680) were audited individually and are steatohepatitis
  bioinformatics, psoriasis Mendelian randomisation, disordered-region
  prediction, a rat MASH model, an insomnia pleiotropy analysis, and a fatigue
  GWAS respectively - none reports a patient with an SNF8 variant. Only the
  abstract of PMID:38423010 is cached, so per-individual clinical detail from
  its full text is not quotable here.

  No GeneReviews chapter exists. Searched on 2026-08-01: `SNF8
  GeneReviews[All Fields]` returned 0 records, and `neurodevelopmental disorder
  plus optic atrophy GeneReviews[All Fields]` returned exactly 1 record,
  PMID:20301382, which was retrieved and rejected - it is "Single Large-Scale
  Mitochondrial DNA Deletion Syndromes" and matched only on the free-text words
  "optic atrophy". The Step 3b GeneReviews phenotype baseline is therefore not
  applicable.

  Cohort arithmetic, reconciled. An earlier draft of this entry recorded an
  apparent conflict between the abstract and the HPO annotation file; the deep
  research pass resolved it, and the resolution is recorded here rather than the
  conflict. The published cohort is nine individuals: five at the severe pole
  (A1, A2, B1, C1, C2) and four at the mild pole (D1, E1, E2, F1). The
  abstract's "four individuals with severe developmental and epileptic
  encephalopathy" counts the four liveborn severely affected children; the fifth
  severe case, C1, was a pregnancy terminated at 25 weeks for brain
  malformations and so had no epileptic encephalopathy to report. HPOA's
  denominators - up to 5 for DEE115 (OMIM:620783) and 4 for NEDOA
  (OMIM:620784) - are therefore consistent with the abstract, not in conflict
  with it, and the NEDOA denominator of 4 is the correct one for this entry.

  Frequency bands are nonetheless deliberately omitted from every phenotype.
  The reason is no longer a suspected inconsistency but simply the cohort size:
  the denominator is four individuals from a single unreplicated series, so one
  reclassified case moves most features across a FrequencyEnum boundary. The
  deep research report reached the same conclusion independently and recommended
  recording exact counts instead of bands. Each phenotype's `notes:` therefore
  carries the exact fraction and its source.

  Age of onset is left unbound rather than assigned an enum, and the research
  pass strengthened rather than weakened that decision. HPOA records HP:0011463
  (Childhood onset, defined in HPO as 1 to 5 years) in 2 of 4 and HP:0003621
  (Juvenile onset, 5 to 15 years) in 2 of 4. The underlying reason is now
  visible: optic atrophy declared itself between ages 4 and 7 years, a window
  that straddles the boundary between the two age-bounded HPO categories. No
  single onset term can be asserted for the disorder. The abstract's own wording,
  "childhood-onset optic atrophy", is quoted where relevant but is not treated
  as a claim about the HPO CHILDHOOD interval specifically.

  Deep research: `just research-disorder claude_code
  SNF8-Related_Neurodevelopmental_Disorder`
  (research/SNF8-Related_Neurodevelopmental_Disorder-deep-research-claude_code.md,
  2026-08-01, 5 web searches, 83 turns, 24 citations). The NEC gate was applied
  to that report before any of it was used: SNF8 is named 103 times, the next
  most frequent gene symbols are its own ESCRT-II partners VPS25 (12) and VPS36
  (12) and its own HGNC aliases VPS22 (5) and EAP30 (3), and the only disease
  identifiers asserted anywhere in the report are OMIM:620783/MONDO:0968946 and
  OMIM:620784/MONDO:0968947 plus the SNF8 gene MIM 610904. Hits were read in
  context rather than counted blind. The report ran its own NEC preflight and
  flagged the two real confusion risks for this gene: SNF8 is a long-established
  S. cerevisiae gene name, and human SNF8 sits in the GWAS-dense 17q21.32 locus
  UBE2Z-GIP-ATP5G1-SNF8, so GWAS hits for psoriasis, fatigue, insomnia and
  chicken carcass traits name the gene without bearing on this disorder. Those
  are deliberately not curated as risk factors.

  Facts taken from that report that are in the paper's full text or supplement
  rather than its abstract are recorded in `notes:` blocks, never as evidence
  snippets, because only the abstract of PMID:38423010 is cached.

  Structured-source evidence was unavailable. `data/orphadata/`,
  `data/clingen/` and `data/clingen-dosage/` in this checkout contain only
  `MANIFEST.yaml` with no downloaded payload, so no Orphanet prevalence class
  or ClinGen gene-disease-validity classification could be consulted. Per the
  scope rules the manifests were not touched. This is recorded as a gap, not as
  an assertion that no such classification exists.

  Post-review revision, 2026-08-01. Following review of PR #7785 the pathograph
  was corrected and four research findings that had been left out were pulled
  in. The allele-specific arm (`Stability-Independent Impairment by the
  p.Val102Ile Hypomorph`) now branches from the variant node rather than from
  `Loss of the ESCRT-II Complex`; it had been placed downstream of complex loss,
  which asserted the opposite of what the node says, since the mild-pole
  fibroblasts preserve complex abundance. The preserved-EGFR-degradation
  negative result, cell-type bindings, the morpholino character of the zebrafish
  model and the IMPC mouse null were added. Three literal searches were run
  before asserting anything was missing, all on 2026-08-01 and all against this
  file: `grep -in egfr` (no match, so the earlier PR-comment claim that this
  finding lived in a `notes:` block was wrong), `grep -n classifications` (no
  match) and `grep -n cell_types` (no match). `grep -in "egfr\|autolysosom\|
  LAMP1\|LC3\|autopsy\|morpholino" references_cache/PMID_38423010.md` also
  returned nothing, which is why every one of those findings is recorded as a
  note and none as an evidence snippet. Deliberately still absent: a
  `histopathology:` section, because the only neuropathology in the literature
  is the autopsy of individual A2, a severe-pole (DEE115) case, and attributing
  it to this MONDO term would repeat the error this entry exists to correct; and
  a `progression:` section, reasoned in the phenotype notes instead.

  ESCRT cross-reference. `kb/disorders/VPS4A-Related_Neurodevelopmental_Syndrome.yaml`
  covers the ESCRT-III disassembly ATPase and is cited here only as a
  mechanistic differential, under the specific claim that lesions at different
  steps of one ESCRT cascade converge on neurodevelopmental disease. No content
  was copied from that entry.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Disease requires two damaging SNF8 alleles. All nine reported individuals
    were bi-allelic, and every individual at the mild NEDOA end of the spectrum
    carried the hypomorphic missense allele c.304G>A (p.Val102Ile), which is
    understood to retain partial function and thereby to set the severity
    floor. Heterozygous carriers, including the parents in the six reported
    families, are not described as affected.

    Penetrance is recorded as incomplete, and the reason is specific to this
    entity rather than a generic hedge. gnomAD contains one apparently healthy
    individual homozygous for c.304G>A (p.Val102Ile) - the very allele that
    defines the mild pole. For the severe bi-allelic genotypes penetrance
    appears complete, so penetrance here is genotype-dependent rather than
    uniformly reduced. The practical consequence is a counselling problem: a
    fetus predicted to be a p.Val102Ile homozygote cannot be described as
    affected on present evidence. That gnomAD homozygote is reported in the full
    text of PMID:38423010 and was surfaced by the deep research pass; it is not
    in the cached abstract, so it carries no snippet. Consanguinity is not
    explicitly reported for any family and is deliberately not asserted, despite
    the one homozygous family being consistent with it.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  penetrance: INCOMPLETE
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8"
    explanation: Nine affected individuals from six families all carried bi-allelic SNF8 variants, which is the definition of autosomal recessive inheritance for this locus.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."
    explanation: Identifies the specific hypomorphic allele shared by the mild cohort, that is, by the individuals who constitute this MONDO entity rather than the allelic encephalopathy.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    Nine individuals from six families have been reported in total across both
    ends of the SNF8 spectrum, in one 2024 publication; four of those nine are
    at the mild pole and therefore constitute the entire published experience of
    this entity. `NOT_YET_DOCUMENTED` is used rather than a qualitative
    `ULTRA_RARE` band because no prevalence or incidence estimate of any kind
    has been published and Orphanet has assigned no ORPHA code to this disorder,
    so there is no source to band. `rate_per_100000` is deliberately left empty
    - there is no basis for a number. No founder effect is asserted: the single
    homozygous family is one family, and the recurrence of p.Val102Ile across
    three unrelated families reflects that allele's appreciable population
    frequency rather than a founder event. The reported ancestries are European
    and Middle Eastern, which reflects ascertainment through European diagnostic
    genomics networks and must not be read as population restriction.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8"
    explanation: Establishes the total published case count for the SNF8 disease spectrum at the time of curation.
pathophysiology:
- name: Bi-allelic Hypomorphic SNF8 Variants
  biological_scale: MOLECULAR
  description: >-
    The primary lesion is bi-allelic damage to SNF8 at 17q21.32, reported
    against transcript NM_007241.4. Genotype maps onto severity: the mild
    NEDOA phenotype curated here occurs only in individuals who carry the
    hypomorphic missense allele c.304G>A (p.Val102Ile), which is inferred to
    leave residual SNF8 function, whereas the severe allelic encephalopathy
    arises from more damaging genotypes. Functional testing in vivo reproduced
    this graded effect, with different SNF8 alleles having different impacts on
    embryonic development, which is the mechanistic basis for the clinical
    heterogeneity across the spectrum.
  genes:
  - preferred_term: SNF8
    term:
      id: hgnc:17028
      label: SNF8
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8"
    explanation: Names the causal gene, the reference transcript, and the gene product's identity as an ESCRT-II subunit.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In vivo experiments corroborated the pathogenicity of the tested SNF8 variants and their variable impact on embryo development, validating the observed clinical heterogeneity."
    explanation: Supports the claim that allele severity, not a second locus, accounts for the split between the mild and severe ends of the spectrum.
  downstream:
  - target: Loss of the ESCRT-II Complex
    description: >-
      Severe-pole genotypes, which lack p.Val102Ile, destabilise SNF8 protein
      and with it the assembled ESCRT-II heterotetramer. This is the
      abundance-dependent arm of the allelic split.
  - target: Stability-Independent Impairment by the p.Val102Ile Hypomorph
    description: >-
      The parallel, allele-specific arm. In individuals carrying the mild-pole
      hypomorph c.304G>A (p.Val102Ile), ESCRT-II function is impaired without a
      measurable fall in complex abundance, so this branch is a direct
      consequence of the variant rather than of complex loss.
- name: Loss of the ESCRT-II Complex
  biological_scale: MOLECULAR
  description: >-
    ESCRT-II is an obligate heterotetramer built from one copy of SNF8/VPS22,
    one copy of VPS36, and two copies of VPS25, arranged as a trilobal
    assembly of winged-helix domains. Because the subunits are mutually
    stabilising, damaging one of them destabilises the whole complex rather
    than removing a single activity: patient-derived fibroblasts carrying
    bi-allelic SNF8 variants show loss of ESCRT-II subunits, plural. SNF8 is
    not a peripheral subunit in this assembly - the first helix of VPS22
    contributes directly, alongside the VPS36 GLUE domain, to targeting
    ESCRT-II onto the endosomal membrane - so its loss removes both the
    structural core and part of the membrane-recruitment activity.
  genes:
  - preferred_term: SNF8
    term:
      id: hgnc:17028
      label: SNF8
  protein_complexes:
  - preferred_term: ESCRT II complex
    modifier: DECREASED
    term:
      id: GO:0000814
      label: ESCRT II complex
  cellular_components:
  - preferred_term: endosome membrane
    term:
      id: GO:0010008
      label: endosome membrane
  cell_types:
  - preferred_term: patient-derived dermal fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  notes: >-
    Scope caveat, and the single most important qualification in this entry.
    The quoted abstract sentence "bi-allelic SNF8 variants cause loss of ESCRT-II
    subunits" is written across the whole spectrum, but the full-text proteomics
    behind it separates the two poles, and the separation runs against this
    entity. In severe-pole fibroblasts SNF8 fell to roughly a quarter of control
    with VPS36 and VPS25 significantly co-depleted; in the mild-pole fibroblasts
    (individuals D1 and E1, the NEDOA genotype curated here) the reduction in
    SNF8 was not statistically significant and VPS36 and VPS25 were not
    significantly reduced at all. Complex destabilisation is therefore
    established for the severe allelic disorder and NOT demonstrated for NEDOA.
    This node is retained because ESCRT-II is unambiguously the affected
    machinery, but the destabilisation route is marked PARTIAL for this entity
    and the alternative route is modelled as its own node below. These
    per-individual fold changes are full-text/supplementary figures in
    PMID:38423010, not abstract content, so they are recorded here rather than
    quoted as a snippet; they were surfaced by the deep research pass.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "In patient-derived fibroblasts, bi-allelic SNF8 variants cause loss of ESCRT-II subunits."
    explanation: >-
      Patient-cell demonstration that the SNF8 genotype can destabilise ESCRT-II
      subunits collectively. Marked PARTIAL rather than SUPPORT because the
      sentence is stated for the spectrum as a whole while the underlying
      proteomics shows the effect in the severe-pole genotypes and not in the
      mild-pole genotype that defines this MONDO term; see this node's notes.
  - reference: PMID:18539118
    reference_title: "Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The complex has three lobes and contains one copy each of VPS22 and VPS36 and two copies of VPS25."
    explanation: Defines the stoichiometry of human ESCRT-II and places SNF8, whose HGNC alias is VPS22, as a single-copy core subunit whose loss cannot be compensated by another copy.
  - reference: PMID:18539118
    reference_title: "Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "ESCRT-II is targeted to endosomal membranes by the lipid-binding activities of both the Vps36 GLUE domain and the first helix of Vps22."
    explanation: Assigns a specific membrane-targeting function to the SNF8/VPS22 subunit itself, so loss of SNF8 impairs recruitment of ESCRT-II to the endosome and not only its assembly.
  - reference: PMID:15469844
    reference_title: "ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The 3.6 A structure of the yeast ESCRT-II core presented here reveals a trilobal complex containing two copies of Vps25, one copy of Vps22, and the C-terminal region of Vps36."
    explanation: Independent structural confirmation of the same single-copy Vps22 stoichiometry in the yeast orthologue, establishing that the architecture is conserved.
  - reference: PMID:15329733
    reference_title: "Structure of the ESCRT-II endosomal trafficking complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Vps22 and Vps36 form nearly equivalent interactions with the two Vps25 molecules at the centre of the 'Y'."
    explanation: >-
      Shows that the SNF8/Vps22 subunit is one of the two scaffolding arms
      holding both Vps25 copies in place, which is the structural reason its
      loss collapses the assembly rather than merely trimming one activity.
  downstream:
  - target: Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis
    description: Without ESCRT-II on the endosomal membrane, the downstream ESCRT-III polymer is not nucleated.
- name: Stability-Independent Impairment by the p.Val102Ile Hypomorph
  biological_scale: MOLECULAR
  description: >-
    This node exists because the mechanism that produces NEDOA is not the
    mechanism that produces the severe allelic encephalopathy. Every mildly
    affected individual carries c.304G>A (p.Val102Ile) in trans to a more
    damaging allele, and in fibroblasts from two of them the ESCRT-II subunits
    were not significantly depleted. The authors' reading is that this allele
    impairs ESCRT-II function by a route independent of protein stability -
    a partially functional complex is assembled in normal amounts but works
    less well - rather than by removing the complex. That is what sets the
    severity floor for this entity: enough residual ESCRT-II activity to permit
    survival into adulthood and mild rather than absent development, but not
    enough to protect the anterior visual pathway. The distinction also predicts
    that a proteomic assay of ESCRT-II subunit abundance, which is informative
    for the severe pole, will look near-normal in NEDOA and cannot be used to
    confirm this diagnosis.
  genes:
  - preferred_term: SNF8
    term:
      id: hgnc:17028
      label: SNF8
  protein_complexes:
  - preferred_term: ESCRT II complex
    modifier: ABNORMAL
    term:
      id: GO:0000814
      label: ESCRT II complex
  mechanism_confidence: PROVISIONAL
  notes: >-
    No evidence item is attached to this node. The claim rests on full-text and
    supplementary data of PMID:38423010 - the non-significant SNF8 reduction in
    the mild-pole fibroblasts (individuals D1 and E1), the preserved VPS36 and
    VPS25 levels, and the authors' conclusion that the variant acts by a
    mechanism independent of protein stability. None of that is in the cached
    abstract, and the abstract's only sentence about fibroblasts says the
    opposite for the spectrum as a whole, so quoting it here would be a
    claim/snippet mismatch of exactly the kind the evidence rules forbid. The
    hypomorphic character of the allele and its restriction to the mild cohort
    ARE abstract-verifiable and are evidenced in the `genetic:` and
    `inheritance:` blocks.
  downstream:
  - target: Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis
    description: >-
      Reduced, rather than absent, ESCRT-II activity yields a partial and
      cargo-selective block of the downstream sorting step.
- name: Failure of ESCRT-III Nucleation and Multivesicular Body Biogenesis
  biological_scale: CELLULAR
  description: >-
    ESCRT-0, -I, -II and -III act as a sequential relay on the endosomal
    membrane. ESCRT-II is the hand-off point: it binds the ESCRT-I VPS28
    C-terminal domain on one side and, through VPS25, directly recruits and
    nucleates the ESCRT-III subunit VPS20/CHMP6 on the other. Losing ESCRT-II
    therefore breaks the cascade in the middle, so ubiquitinated cargo is not
    packaged into intralumenal vesicles, multivesicular bodies fail to mature,
    and surface receptors are not downregulated. This step is the mechanistic
    junction with the ESCRT-III disorders: an ESCRT-II lesion and an ESCRT-III
    lesion disable adjacent stages of one pathway.
  biological_processes:
  - preferred_term: multivesicular body assembly
    modifier: DECREASED
    term:
      id: GO:0036258
      label: multivesicular body assembly
  - preferred_term: endosomal transport
    modifier: ABNORMAL
    term:
      id: GO:0016197
      label: endosomal transport
  - preferred_term: ubiquitin-dependent cargo delivery to the lysosome via the MVB sorting pathway
    modifier: DECREASED
    term:
      id: GO:0043328
      label: protein transport to vacuole involved in ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway
  cellular_components:
  - preferred_term: multivesicular body
    term:
      id: GO:0005771
      label: multivesicular body
  cell_types:
  - preferred_term: patient-derived dermal fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  notes: >-
    The block at this step is partial and cargo-selective, not a global collapse
    of ESCRT function, and the strongest evidence for that is a negative result.
    In the founding study, EGFR degradation - the canonical, most widely used
    readout of ESCRT-dependent receptor downregulation - was NOT detectably
    impaired in patient-derived fibroblasts compared with control fibroblasts.
    The authors attribute this to residual ESCRT-II activity and to cargo
    specificity: different cargoes have different ESCRT-II dependency
    thresholds. This constrains the model in a way the abstract alone does not.
    It argues against reading "loss of ESCRT-II subunits" as "the MVB pathway is
    shut down", and it is consistent with the mild pole existing at all: a
    partially functional pathway that still clears EGFR but fails somewhere
    else, most likely at autophagosome-lysosome progression.

    Provenance and honesty about it. This result is in the full text of
    PMID:38423010, not in its abstract, which is the only part cached here
    (`grep -i egfr references_cache/PMID_38423010.md` returns nothing, checked
    2026-08-01). It is therefore recorded in this note rather than as an
    evidence snippet, and no `REFUTE`/`PARTIAL` evidence item is attached to it,
    because attaching one would require quoting text this repository cannot
    verify. It was surfaced by the deep research pass
    (research/SNF8-Related_Neurodevelopmental_Disorder-deep-research-claude_code.md,
    section 6). The study also does not report which pole the EGFR-assayed
    fibroblasts came from, so the result is recorded for the SNF8 spectrum
    rather than asserted specifically for the NEDOA genotype.
  evidence:
  - reference: PMID:15469844
    reference_title: "ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "ESCRT-I, -II, and -III protein complexes are sequentially recruited to endosomal membranes, where they orchestrate protein sorting and MVB biogenesis."
    explanation: Establishes that ESCRT-II occupies an obligatory intermediate position in the sorting relay, so its loss interrupts the sequence rather than degrading it gracefully.
  - reference: PMID:15469844
    reference_title: "ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We show that purified ESCRT-II binds directly to the Vps20 component of ESCRT-III."
    explanation: Demonstrates the direct physical hand-off from ESCRT-II to ESCRT-III that is lost when the ESCRT-II complex is destabilised.
  - reference: PMID:18539118
    reference_title: "Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "ESCRT-II plays a pivotal role in receptor downregulation and multivesicular body biogenesis and is conserved from yeast to humans."
    explanation: States the two cell-biological outputs, receptor downregulation and multivesicular body biogenesis, that fail when ESCRT-II is lost.
  - reference: PMID:18539118
    reference_title: "Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "ESCRT-II binds to the ESCRT-I VPS28 C-terminal domain subunit through a helix immediately C-terminal to the VPS36-GLUE domain."
    explanation: Documents the upstream half of the hand-off, confirming ESCRT-II as the physical bridge between ESCRT-I and ESCRT-III.
  downstream:
  - target: Impaired Autophagic Flux
    description: Blocked endosomal maturation prevents autophagosome-lysosome progression.
- name: Impaired Autophagic Flux
  biological_scale: CELLULAR
  description: >-
    The ESCRT machinery is required not only for endosomal sorting but for
    autophagy, where it contributes to phagophore closure and to
    autophagosome-lysosome fusion. The founding study's stated conclusion is
    that the neurodevelopmental and neurodegenerative phenotypes of bi-allelic
    SNF8 disease are mediated principally through impaired autophagic flux
    rather than through cargo missorting alone. The abstract states this as a
    likelihood, but the full text backs it with direct patient-material assays:
    transmission electron microscopy of patient fibroblasts showing accumulated
    autolysosomes and morphologically aberrant, enlarged, electron-lucent
    lysosomes; LC3/LAMP1 confocal immunofluorescence showing the same
    accumulation; and, at the severe pole, strong LC3 immunostaining on autopsy
    neuropathology where age-matched controls stained only weakly.
  biological_processes:
  - preferred_term: macroautophagy
    modifier: DECREASED
    term:
      id: GO:0016236
      label: macroautophagy
  - preferred_term: autophagosome maturation
    modifier: DECREASED
    term:
      id: GO:0097352
      label: autophagosome maturation
  cellular_components:
  - preferred_term: autolysosome
    term:
      id: GO:0044754
      label: autolysosome
  cell_types:
  - preferred_term: patient-derived dermal fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: cortical pyramidal neuron
    term:
      id: CL:0000598
      label: pyramidal neuron
  - preferred_term: reactive astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  - preferred_term: activated microglial cell
    term:
      id: CL:0000129
      label: microglial cell
  mechanism_confidence: PROVISIONAL
  notes: >-
    Confidence, and why it moved. This node was previously marked HYPOTHETICAL
    on the ground that the abstract hedges with "likely". That understated the
    evidence: the full text of PMID:38423010 reports direct autophagy readouts
    in patient material - fibroblast transmission electron microscopy showing
    autolysosome accumulation and aberrant enlarged, electron-lucent lysosomes,
    LC3/LAMP1 confocal immunofluorescence showing the same, and strong LC3
    immunostaining on autopsy neuropathology. PROVISIONAL is the honest level:
    the mechanism is measured, not merely posited, but the causal step from
    impaired flux to the neurological phenotype in vivo is still inferred. It is
    not upgraded further because none of those assays is quotable here (only the
    abstract of PMID:38423010 is cached) and because the study does not report
    an autophagic-flux measurement resolved by pole.

    Cell types, with their provenance and its limits. Fibroblast is the actual
    experimental cell type for the electron microscopy, LC3/LAMP1 and proteomics
    work, and mild-pole fibroblasts (individuals D1 and E1) were among those
    studied, so it is directly relevant to this entity. Pyramidal neuron,
    astrocyte and microglial cell come from autopsy neuropathology - LC3
    accumulation in neurons of the internal pyramidal cell layer, reactive
    astrogliosis with LC3-positive white-matter astrocytes, and microglial
    activation. That autopsy was performed on individual A2, who carried
    p.Tyr167Ter/p.Gly191Asp and sits at the SEVERE pole, that is, in the allelic
    disorder DEE115 (MONDO:0968946) and not in this MONDO term. These three CNS
    cell types are therefore recorded as the neuropathological substrate of the
    SNF8 spectrum, not as a demonstrated finding in NEDOA; no post-mortem
    material exists from a mildly affected individual. All four CL identifiers
    were verified with OAK (`runoak -i sqlite:obo:cl info`) on 2026-08-01.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "we conclude that loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux"
    explanation: The authors' own conclusion, marked PARTIAL because the word "likely" is theirs and the abstract does not report a direct autophagic-flux measurement in patient material.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The endosomal sorting complex required for transport (ESCRT) machinery is essential for membrane remodeling and autophagy"
    explanation: >-
      Establishes autophagy, alongside membrane remodelling, as a core ESCRT
      function and therefore as a plausible route from ESCRT-II loss to
      neurodegeneration. Classified OTHER rather than HUMAN_CLINICAL: this is
      the paper's introductory statement of general cell biology and reports no
      human observation of its own, so tagging it HUMAN_CLINICAL would overstate
      the evidence type.
  downstream:
  - target: Optic Nerve and Forebrain Developmental Failure
    description: Neurons and retinal ganglion cells, being long-lived and dependent on autophagic turnover, are the cells that fail.
- name: Optic Nerve and Forebrain Developmental Failure
  biological_scale: TISSUE
  description: >-
    The tissue-level endpoint is selective failure of the visual pathway and
    the forebrain. Zebrafish snf8 loss of function reproduces this pattern
    specifically, producing impaired optic nerve development and reduced
    forebrain size in addition to global developmental delay and altered embryo
    morphology. That the optic nerve phenotype is recovered in a model organism
    is what elevates optic atrophy in this disorder from an incidental
    association to a mechanistically anchored feature, and it is the strongest
    available support for the visual pathway being intrinsically vulnerable to
    ESCRT-II loss rather than secondarily damaged.
  locations:
  - preferred_term: optic nerve
    term:
      id: UBERON:0000941
      label: cranial nerve II
  - preferred_term: forebrain
    term:
      id: UBERON:0001890
      label: forebrain
  cell_types:
  - preferred_term: retinal ganglion cell
    term:
      id: CL:0000740
      label: retinal ganglion cell
  notes: >-
    The retinal ganglion cell binding is an inference, not an observation, and
    is flagged as such. No retina was examined histologically in PMID:38423010,
    and no electroretinography or optical-coherence-tomography ganglion-cell-layer
    measurement is reported in the cached abstract. The cell type is named
    because the retinal ganglion cell is the neuron whose axons constitute the
    optic nerve, so optic atrophy with reduced anterior-visual-pathway volume
    localises the lesion to that population by anatomy; and because retinal
    ganglion cells are the canonical autophagy- and energy-vulnerable long-axon
    neuron implicated in the mitochondrial optic neuropathies that form this
    disorder's clinical differential. Oligodendrocyte involvement, which the
    deep research pass also suggested, is NOT bound here: it rests only on
    "marked loss of myelin" at severe-pole autopsy, which is an inference from a
    different pole of the spectrum and one step further removed. CL:0000740 was
    verified with OAK on 2026-08-01.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size."
    explanation: An orthogonal animal model reproduces both the optic nerve and the forebrain components of the human phenotype, supporting a developmental rather than purely degenerative mechanism for the visual pathway involvement.
genetic:
- name: SNF8
  association: Bi-allelic variants; the mild NEDOA phenotype is associated specifically with the hypomorphic allele c.304G>A (p.Val102Ile)
  relationship_type: CAUSATIVE
  gene_term:
    preferred_term: SNF8
    term:
      id: hgnc:17028
      label: SNF8
  notes: >-
    Nomenclature. HGNC:17028 is symbol SNF8, "SNF8 subunit of ESCRT-II", at
    17q21.32, Entrez 11267, Ensembl ENSG00000159210, UniProt Q96H20, with alias
    symbols EAP30, VPS22 and Dot3 (HGNC REST API, retrieved 2026-08-01). The
    structural literature cited in this entry uses VPS22 exclusively.

    Allelic architecture. The reference transcript in the founding report is
    NM_007241.4. The only allele identified by name in the cached abstract is
    c.304G>A (p.Val102Ile), described as hypomorphic and shared by all mildly
    affected individuals. The deep research pass adds, from the full text and
    from ClinVar, that seven distinct variants were reported across the six
    families and that every mildly affected individual carries p.Val102Ile in
    trans to a more damaging allele: c.423-1G>C (splice acceptor) in family D,
    c.673_683delinsTGGA p.Asp225TrpfsTer99 in family E, and c.236C>T p.Pro79Leu
    in family F. Absence of p.Val102Ile predicted the severe pole in all five
    severe cases. None of that per-family detail is abstract-verifiable, so it
    is recorded here rather than asserted with a snippet.

    Variant classification is genuinely contested and is recorded as such rather
    than smoothed over. ClinVar holds conflicting germline interpretations for
    c.304G>A (p.Val102Ile): the Institute of Human Genetics Munich submitted
    Pathogenic and OMIM submitted Pathogenic for neurodevelopmental disorder
    plus optic atrophy, while Ambry Genetics submitted Uncertain significance on
    insufficient or conflicting evidence. The Ambry position is defensible on
    the population data - gnomAD allele frequency for rs200399045 is about
    1.5 x 10^-4 and gnomAD contains one apparently healthy homozygote. A
    laboratory reporting this allele should not present it as unqualified
    Pathogenic. These ClinVar and gnomAD figures come from the deep research
    pass, not from the cached abstract.

    Not asserted, deliberately. gnomAD constraint metrics (pLI, o/e LoF,
    missense Z) are NOT recorded anywhere in this entry: the research pass could
    not reach the gnomAD API and explicitly warned against populating them from
    memory, and no other source consulted here provides them. DepMap
    essentiality is likewise not asserted for the same reason. Three large
    multi-gene 17q21.32 deletions appear in a ClinVar SNF8 gene query but are
    not SNF8-specific and are not curated as a cause of this disorder. No
    modifier locus, methylation episignature, founder allele, or somatic
    mechanism has been established.

    Because MONDO splits the SNF8 phenotype into two terms and both are
    caused by bi-allelic variants in this same gene, a laboratory reporting an
    SNF8 genotype cannot assign the OMIM phenotype number from the gene alone;
    the assignment depends on the allele and on the clinical severity.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8"
    explanation: Establishes SNF8 as the causal gene and names the reference transcript against which variants are reported.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."
    explanation: Ties the specific hypomorphic allele to the mild phenotype that this MONDO term denotes, which is the genotype-phenotype correlation defining the entity.
phenotypes:
- name: Impaired intellectual development
  category: Neurologic
  diagnostic: true
  description: >-
    Intellectual disability is the constant feature and the reason the
    disorder is classified as neurodevelopmental rather than as an isolated
    optic neuropathy. It is the component named first in both the MedGen
    definition and the abstract's description of the milder cohort. Severity
    is not resolvable from the abstract.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  notes: >-
    HPO annotation for OMIM:620784 records HP:0001249 at 4/4, sourced to
    PMID:38423010 (retrieved 2026-08-01 from
    https://ontology.jax.org/api/network/annotation/OMIM:620784). No
    FrequencyEnum band is asserted; see the entry-level notes for why.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."
    explanation: Intellectual disability is stated as a feature of the milder cohort, which is the cohort corresponding to this MONDO term.
- name: Optic atrophy
  category: Ophthalmologic
  diagnostic: true
  description: >-
    Optic atrophy is the feature that names the disorder and separates it from
    a generic neurodevelopmental disorder. The abstract describes it as
    childhood-onset. Whether the underlying lesion is failure of optic nerve
    development, progressive degeneration, or both is not settled by the human
    data, but the zebrafish model shows impaired optic nerve development,
    favouring a developmental contribution.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  notes: >-
    HPO annotation for OMIM:620784 records HP:0000648 at 3/4, sourced to
    PMID:38423010 (retrieved 2026-08-01). The deep research pass identified the
    denominator structure behind that fraction: optic atrophy was present in 3
    of 3 individuals at the optic-atrophy end of the mild pole (D1, E1, E2) and
    absent in the fourth (F1), who had congenital ataxia instead. Reported onset
    was between 4 and 7 years, which straddles the boundary between HP:0011463
    Childhood onset (1 to 5 years) and HP:0003621 Juvenile onset (5 to 15
    years) - and indeed HPOA records each at 2/4 - so no single onset category
    is asserted. The 4-to-7-year window and the per-individual split are
    full-text detail, recorded here rather than quoted as a snippet.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."
    explanation: Directly names childhood-onset optic atrophy as a feature of the milder cohort denoted by this MONDO term.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "impaired optic nerve development, and reduced forebrain size"
    explanation: The zebrafish model independently implicates the optic nerve, supporting the human optic atrophy as gene-attributable rather than coincidental.
- name: Ataxia
  category: Neurologic
  description: >-
    Ataxia is the alternative presentation of the mild pole, and the "or" in the
    abstract's "optic atrophy, or ataxia" is a genuine disjunction across the
    cohort rather than a list of features each individual has. Only one of the
    four mildly affected individuals had ataxia, it was congenital rather than
    childhood-onset, and that same individual was the one with no optic atrophy
    and a normal anterior optic tract on MRI. Ataxia should therefore not be
    described as a general feature of this disorder, and its presence does not
    predict the ophthalmological findings.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  notes: >-
    HPO annotation for OMIM:620784 records HP:0001251 at 1/4, sourced to
    PMID:38423010 (retrieved 2026-08-01). No FrequencyEnum band is asserted.
    The deep research pass resolved which individual this is: F1, whose ataxia
    was congenital and who at age 2 had normal myelination, normal white matter
    volume, slight cerebellar atrophy, and no optic atrophy. That
    per-individual detail is full-text, not abstract content, so it is recorded
    here rather than quoted. It matters clinically because it means the two
    named features of this disorder were mutually exclusive in the only cohort
    ever reported.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."
    explanation: Ataxia is named as a feature of the milder cohort; the disjunction in the source sentence is the reason this phenotype is not described as universal.
- name: Global developmental delay
  category: Neurologic
  description: >-
    Developmental delay in the milder cohort is characterised in the HPO
    annotation set as mild, in explicit contrast to the neurodevelopmental
    arrest that defines the severe allelic encephalopathy. The zebrafish model
    reproduces global developmental delay at the organismal level.
  phenotype_term:
    preferred_term: Mild global developmental delay
    term:
      id: HP:0011342
      label: Mild global developmental delay
  notes: >-
    HPO annotation for OMIM:620784 records HP:0011342 (Mild global
    developmental delay) at 3/4, sourced to PMID:38423010 (retrieved
    2026-08-01). The severity qualifier "mild" comes from that annotation and
    not from the cached abstract, which describes the cohort only as having a
    "milder phenotype".
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology"
    explanation: >-
      Marked PARTIAL rather than SUPPORT for two reasons. It is model-organism
      evidence standing alone for a human phenotype, and the zebrafish result
      speaks to developmental delay as such but says nothing about the "mild"
      severity qualifier in the bound HP:0011342 term, which comes from the HPO
      annotation set rather than from any cached abstract.
- name: Nystagmus
  category: Ophthalmologic
  description: >-
    Nystagmus accompanies the optic atrophy in most reported individuals and
    is a common consequence of early-onset visual loss. It is also recorded in
    the severe allelic encephalopathy, so it does not discriminate between the
    two ends of the SNF8 spectrum.
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0000639 at 3/4 sourced to PMID:38423010 (retrieved 2026-08-01). The
    cached abstract does not mention nystagmus, so this phenotype carries no
    evidence item rather than a snippet that does not support it.
- name: Reduced visual acuity
  category: Ophthalmologic
  description: >-
    Measurable loss of visual acuity accompanies the optic atrophy and is the
    functional consequence that actually affects schooling and daily life. It is
    described as progressive from the childhood onset of the optic neuropathy
    onward, which is what makes low-vision support and educational accommodation
    the practically important management step in this disorder.
  phenotype_term:
    preferred_term: Reduced visual acuity
    term:
      id: HP:0007663
      label: Reduced visual acuity
  notes: >-
    Curated from the deep research pass, which records reduced visual acuity in
    3 of 3 of the optic-atrophy individuals (D1, E1, E2) with a moderate,
    progressive course, sourced to the full text of PMID:38423010. This is not
    in the cached abstract and is not in the HPO annotation set for
    OMIM:620784, so no evidence item is attached.
- name: Abnormal visual evoked potentials
  category: Ophthalmologic
  description: >-
    Abnormal visual evoked potentials are the electrophysiological correlate
    of the optic neuropathy and were abnormal in every individual in whom they
    were recorded. They are the most sensitive objective marker of visual
    pathway involvement in this disorder and are relevant to diagnosis in
    young or non-verbal children in whom acuity cannot be measured.
  phenotype_term:
    preferred_term: Abnormality of visual evoked potentials
    term:
      id: HP:0000649
      label: Abnormality of visual evoked potentials
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0000649 at 3/3 sourced to PMID:38423010 (retrieved 2026-08-01). Note
    the denominator of 3, not 4, meaning one individual was not tested. Not
    mentioned in the cached abstract, so no evidence item is attached.
- name: Delayed speech and language development
  category: Neurologic
  description: >-
    Speech and language delay was present in every individual in whom it was
    assessed and is a practical early flag, since it typically precedes the
    ophthalmological presentation.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0000750 at 3/3 sourced to PMID:38423010 (retrieved 2026-08-01). Not
    mentioned in the cached abstract, so no evidence item is attached.
- name: Global brain atrophy
  category: Neurologic
  description: >-
    Diffuse cerebral volume loss on MRI is present in a substantial minority
    of the milder cohort and is the imaging feature that marks this disorder
    as neurodegenerative as well as neurodevelopmental. It is far more
    consistent in the severe allelic encephalopathy.
  phenotype_term:
    preferred_term: Global brain atrophy
    term:
      id: HP:0002283
      label: Global brain atrophy
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0002283 at 2/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not
    mentioned in the cached abstract, so no evidence item is attached.
- name: Cerebellar cortical atrophy
  category: Neurologic
  description: >-
    Cerebellar cortical volume loss is the structural counterpart of the
    ataxia and is notable because it is recorded in the milder cohort but not
    in the severe allelic encephalopathy, where the corresponding HPO
    annotation is zero. It is therefore one of the few imaging features that
    may point towards this end of the spectrum rather than the other.
  phenotype_term:
    preferred_term: Cerebellar cortical atrophy
    term:
      id: HP:0008278
      label: Cerebellar cortical atrophy
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0008278 at 2/4 sourced to PMID:38423010 (retrieved 2026-08-01); the
    corresponding annotation for OMIM:620783 (DEE115) is 0/5. Not mentioned in
    the cached abstract, so no evidence item is attached.
- name: Microcephaly
  category: Craniofacial
  description: >-
    Reduced head circumference occurs in a minority and is congruent with the
    reduced forebrain size seen on snf8 loss of function in zebrafish. It is
    not a defining feature of this end of the spectrum.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0000252 at 1/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not
    mentioned in the cached abstract, so no evidence item is attached.
- name: Conductive hearing impairment
  category: Otologic
  description: >-
    Conductive, rather than sensorineural, hearing impairment was recorded in
    one individual. It is listed here for completeness of the reported
    phenotype and should not be over-interpreted from a single case; notably a
    conductive deficit is mechanistically distinct from the sensorineural
    hearing loss that accompanies the mitochondrial optic neuropathies in the
    differential.
  phenotype_term:
    preferred_term: Conductive hearing impairment
    term:
      id: HP:0000405
      label: Conductive hearing impairment
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0000405 at 1/4 sourced to PMID:38423010 (retrieved 2026-08-01). Not
    mentioned in the cached abstract, so no evidence item is attached.
- name: Dysplastic corpus callosum
  category: Neurologic
  description: >-
    A malformed corpus callosum is reported in a minority at this end of the
    spectrum. This is the attenuated form of the callosal lesion that is
    prominent in the severe allelic encephalopathy, where hypoplasia or
    aplasia of the corpus callosum is a defining feature; at the mild end the
    HPO annotations for hypoplasia and agenesis are both zero and only
    dysplasia is recorded.
  phenotype_term:
    preferred_term: Dysplastic corpus callosum
    term:
      id: HP:0006989
      label: Dysplastic corpus callosum
  notes: >-
    Curated from the HPO annotation set for OMIM:620784, which records
    HP:0006989 at 1/4, HP:0002079 (Hypoplasia of the corpus callosum) at 0/4
    and HP:0001274 (Agenesis of corpus callosum) at 0/4, all sourced to
    PMID:38423010 (retrieved 2026-08-01). Not mentioned in the cached abstract,
    so no evidence item is attached.
diagnosis:
- name: Exome or genome sequencing with bi-allelic SNF8 variant interpretation
  description: >-
    Molecular diagnosis rests on identifying bi-allelic SNF8 variants against
    transcript NM_007241.4 by exome or genome sequencing, in a child with
    impaired intellectual development plus optic atrophy. Two interpretation
    points follow from the published genotype-phenotype pattern. First, because
    the mild phenotype is driven by a hypomorphic missense allele, a
    conservative-looking missense change such as c.304G>A (p.Val102Ile) should
    not be dismissed on in-silico grounds; it is the allele that defines this
    entity. Second, both parents must be tested to confirm that the two
    variants are in trans, since SNF8 heterozygotes are unaffected. As SNF8 is
    a recently described disease gene, reanalysis of previously non-diagnostic
    sequencing data is reasonable.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8"
    explanation: Names the gene and the reference transcript that a diagnostic laboratory must use when reporting and interpreting variants.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."
    explanation: Supports the specific interpretive caution that this particular missense allele, despite being a conservative valine-to-isoleucine substitution, is the recurring cause of the mild phenotype.
- name: Ophthalmological assessment including visual evoked potentials
  description: >-
    Formal ophthalmological review is required in any child with unexplained
    developmental delay who is being considered for this diagnosis, because the
    optic atrophy is the discriminating feature and can be clinically silent
    early. Visual evoked potentials are the objective test of choice, having
    been abnormal in every individual in whom they were recorded, and are
    feasible in children too young or too impaired for subjective acuity
    testing.
  notes: >-
    The supporting observation that visual evoked potentials were abnormal in
    3 of 3 tested individuals comes from the HPO annotation set for
    OMIM:620784 (HP:0000649, retrieved 2026-08-01), not from the cached
    abstract, which does not mention electrophysiology. It is therefore
    recorded as a note rather than as an evidence snippet.
- name: Brain MRI
  description: >-
    Brain MRI serves two purposes. It documents the structural correlates of
    the disorder - global brain atrophy, cerebellar cortical atrophy, and a
    dysplastic corpus callosum - and it helps place an individual on the SNF8
    spectrum, since massive white matter reduction with hypoplasia or aplasia
    of the corpus callosum characterises the severe allelic encephalopathy
    rather than this entity.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "massive reduction of white matter, hypo-/aplasia of the corpus callosum"
    explanation: Names the specific MRI findings that mark the severe end of the SNF8 spectrum, which is what makes imaging useful for distinguishing that disorder from this one.
differential_diagnoses:
- name: Developmental and epileptic encephalopathy 115
  disease_term:
    preferred_term: developmental and epileptic encephalopathy 115
    term:
      id: MONDO:0968946
      label: developmental and epileptic encephalopathy 115
  description: >-
    The allelic disorder, caused by bi-allelic variants in the same gene. This
    is not a differential in the usual sense of a different disease that
    mimics this one; it is the other half of one continuum, and separating the
    two is a clinical judgement made after the SNF8 genotype is already known.
    A laboratory that reports bi-allelic SNF8 variants has not thereby chosen
    between OMIM:620783 and OMIM:620784.
  distinguishing_features:
  - DEE115 has a congenital onset, whereas the optic atrophy in NEDOA is described as childhood-onset and the HPO onset annotations for NEDOA are childhood or juvenile.
  - DEE115 is defined by severe developmental and epileptic encephalopathy with neurodevelopmental arrest and early death; NEDOA is compatible with survival and with mild rather than absent developmental progress.
  - Massive white matter reduction with hypoplasia or aplasia of the corpus callosum is characteristic of DEE115; in the NEDOA HPO annotation set both callosal hypoplasia and agenesis are recorded at 0/4 and only dysplasia appears.
  - Seizures and EEG abnormality are recorded in DEE115 but are annotated at 0/4 in NEDOA, so an epileptic presentation argues against this entity.
  - All mildly affected individuals carried the hypomorphic c.304G>A (p.Val102Ile) allele, so this genotype is currently the strongest single pointer towards NEDOA rather than DEE115.
  notes: >-
    MONDO:0968946 was verified with OAK (`runoak -i sqlite:obo:mondo
    relationships --direction down HGNC:17028`), which returns it and
    MONDO:0968947 as the only two SNF8 disease terms; its xref is OMIM:620783.
    The seizure and EEG contrasts in the distinguishing features come from the
    HPO annotation sets for OMIM:620783 and OMIM:620784 (retrieved 2026-08-01),
    not from the cached abstract.
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death."
    explanation: Describes the severe allelic phenotype in the same cohort, establishing the clinical features that separate it from the milder entity curated here.
- name: Behr syndrome
  disease_term:
    preferred_term: Behr syndrome
    term:
      id: MONDO:0008858
      label: Behr syndrome
  description: >-
    The closest clinical mimic. Behr syndrome is a recessive, childhood-onset
    combination of bilateral optic atrophy with ataxia and variable
    intellectual disability, most often from bi-allelic OPA1 variants and also
    from OPA3, C12orf65/MTRFR or C19orf12. The three cardinal features of the
    milder SNF8 cohort - impaired intellectual development, childhood-onset
    optic atrophy, ataxia - are precisely the Behr triad, so a child with
    NEDOA presenting to a neuro-ophthalmology service will be worked up as
    Behr syndrome first, and the distinction is molecular rather than clinical.
  distinguishing_features:
  - Behr syndrome is mechanistically mitochondrial, converging on impaired bioenergetics, whereas NEDOA is a defect of the endosomal ESCRT pathway; a normal mitochondrial workup does not exclude NEDOA and should prompt broader sequencing.
  - Pyramidal signs with spasticity, peripheral neuropathy and posterior-column sensory loss are part of the classical Behr phenotype and are not reported in the milder SNF8 cohort.
  - 3-methylglutaconic aciduria points towards OPA3 within the Behr group and away from SNF8.
  - Behr syndrome is genetically heterogeneous by definition and is a clinically defined phenotype, so the two are not mutually exclusive on clinical grounds alone; only bi-allelic SNF8 variants establish NEDOA.
  notes: >-
    MONDO:0008858 was verified with OAK. The description of Behr syndrome here
    is drawn from the existing dismech entry
    kb/disorders/Behr_Syndrome.yaml and is presented as clinical context; the
    distinguishing features are reasoned contrasts, not quotations, which is
    why no evidence item is attached to this differential.
- name: Bosch-Boonstra-Schaaf optic atrophy syndrome
  disease_term:
    preferred_term: Bosch-Boonstra-Schaaf optic atrophy syndrome
    term:
      id: MONDO:0014320
      label: Bosch-Boonstra-Schaaf optic atrophy syndrome
  description: >-
    BBSOAS pairs optic atrophy with intellectual disability and developmental
    delay, which is the same two-part core as NEDOA, and it is the syndrome
    most likely to be on a clinician's list when a child presents with optic
    atrophy plus developmental delay. It is caused by NR2F1 variants or
    deletions.
  distinguishing_features:
  - BBSOAS is autosomal dominant and usually de novo; NEDOA is autosomal recessive, so an affected sibling with unaffected parents favours NEDOA.
  - NR2F1 deletions are detectable by chromosomal microarray, whereas SNF8 disease requires sequencing.
  - The two are distinguished definitively by the causal gene, not by the ophthalmological findings, which overlap substantially.
  notes: >-
    MONDO:0014320 was verified with OAK and matches the disease_term already
    bound in kb/disorders/Bosch-Boonstra-Schaaf_Optic_Atrophy_Syndrome.yaml.
    No evidence item is attached because the contrast is a reasoned clinical
    comparison rather than a quotable finding from a cached source.
- name: Autosomal dominant optic atrophy plus syndrome
  disease_term:
    preferred_term: autosomal dominant optic atrophy plus syndrome
    term:
      id: MONDO:0014720
      label: autosomal dominant optic atrophy plus syndrome
  description: >-
    Dominant OPA1 disease with extra-ocular features is the commonest
    inherited syndromic optic neuropathy and will be considered before a
    newly described recessive gene. Optic atrophy with ataxia is common to
    both.
  distinguishing_features:
  - Dominant transmission with an affected parent argues strongly against NEDOA, which is recessive.
  - Sensorineural deafness, chronic progressive external ophthalmoplegia and mitochondrial myopathy characterise the OPA1-plus phenotype; the only hearing impairment reported in the milder SNF8 cohort was conductive.
  - Intellectual disability is not a core feature of dominant optic atrophy plus, whereas it is present in every reported NEDOA individual.
  notes: >-
    MONDO:0014720 was verified with OAK and matches
    kb/disorders/Autosomal_Dominant_Optic_Atrophy_Plus.yaml. No evidence item
    is attached; the contrast is reasoned rather than quoted.
- name: CIMDAG syndrome
  disease_term:
    preferred_term: CIMDAG syndrome
    term:
      id: MONDO:0035819
      label: cerebellar hypoplasia-intellectual disability-congenital microcephaly-dystonia-anemia-growth retardation syndrome
  description: >-
    Included as a mechanistic rather than a clinical differential. CIMDAG
    syndrome is caused by VPS4A variants; VPS4A is the AAA-ATPase that
    disassembles ESCRT-III filaments, the step immediately downstream of the
    ESCRT-III nucleation that ESCRT-II performs. The pair establishes that
    lesions at adjacent stages of a single ESCRT cascade both produce syndromic
    neurodevelopmental disease with cerebellar and cognitive involvement, which
    is the argument for treating ESCRT dysfunction as a coherent disease group.
  distinguishing_features:
  - CIMDAG syndrome is dominant, with de novo missense variants acting through a dominant-negative mechanism; SNF8 disease is recessive and hypomorphic.
  - Congenital dyserythropoietic anemia with binucleated erythroblasts is characteristic of CIMDAG and has not been reported in SNF8 disease.
  - Congenital microcephaly and dystonia define CIMDAG; the microcephaly in the milder SNF8 cohort is a minority finding and dystonia is not reported.
  - Optic atrophy is the defining ophthalmological feature of NEDOA, whereas cataract is the eye finding in CIMDAG.
  notes: >-
    MONDO:0035819 was verified with OAK and matches the disease_term bound in
    kb/disorders/VPS4A-Related_Neurodevelopmental_Syndrome.yaml. This
    differential is deliberately mechanistic; a clinician is unlikely to
    confuse the two presentations. No evidence item is attached because the
    comparison is a reasoned cross-reference rather than a quoted finding.
treatments:
- name: Multidisciplinary supportive care
  description: >-
    No disease-modifying therapy exists. Management is entirely supportive and
    follows the components of the phenotype: developmental and educational
    support, speech and language therapy for the near-universal language delay,
    low-vision services and educational accommodation for the optic atrophy, and
    physiotherapy where ataxia affects mobility.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: BEHAVIORAL
  notes: >-
    Carried as a descriptor with no evidence item, deliberately. No management
    guideline, natural-history study, or treatment trial exists for this
    disorder - the entire clinical literature is one 2024 case series whose
    abstract says nothing about management, and no GeneReviews chapter exists
    (search recorded in the entry-level notes). The specific supportive measures
    listed are the standard-of-care response to the phenotypes curated above
    rather than anything reported for SNF8 disease, so attaching a snippet to
    them would be a claim/snippet mismatch.
- name: Genetic counselling
  description: >-
    Autosomal recessive recurrence risk counselling for the parents of a
    proband, with carrier testing for the specific familial alleles and
    discussion of reproductive options. Relevant to this disorder in particular
    because the same gene produces a lethal congenital encephalopathy at the
    severe end of the spectrum, so the counselling conversation has to address
    the possibility of a more severely affected sibling and cannot simply
    extrapolate the proband's mild course.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    No evidence item is attached. The autosomal recessive mode of inheritance
    that underpins this recommendation is separately evidenced in the
    `inheritance:` block from PMID:38423010; the counselling recommendation
    itself is a clinical inference from that mode of inheritance and from the
    two-term MONDO/OMIM structure of the SNF8 spectrum, not a published
    recommendation, so it is recorded here rather than dressed up with a
    snippet.
animal_models:
- species: Danio rerio
  genotype: snf8 antisense morpholino knockdown (morphant; no stable mutant line reported)
  category: Transient loss-of-function knockdown model
  description: >-
    Zebrafish snf8 knockdown is the only reported in vivo model of this disorder,
    and it is a transient antisense morpholino knockdown rather than a stable
    germline mutant - a distinction that changes how heavily the result should
    be weighted. It reproduces the two organ-level features that matter for this
    entity, impaired optic nerve development and reduced forebrain size,
    alongside global developmental delay and altered embryo morphology. The
    model was also used to test individual human SNF8 alleles, and the alleles
    differed in their impact on embryonic development, which is the experimental
    basis for attributing the clinical spectrum to allele severity.

    Model-type disclosure, added because the abstract's phrase "Snf8 loss of
    function in zebrafish" reads as a stable mutant and is not one. The full
    text of PMID:38423010 describes morpholino injection with co-injection
    rescue ("rescued in fish co-injected with snf8 MO and WT SNF8"), so the
    model is a transient knockdown. Morpholinos carry well-documented
    off-target and p53-mediated toxicity artefacts, and morphant phenotypes have
    repeatedly failed to reproduce in germline mutants; the WT-mRNA rescue
    reported here mitigates that concern but does not remove it. The full text
    also records reduced penetrance among morphants and variable phenotypes.
    None of this is in the cached abstract, so it is a note rather than a
    snippet; it was surfaced by the deep research pass (section 15). The model
    additionally does not address seizures, corpus callosum morphology
    (zebrafish have no corpus callosum), leukoencephalopathy, or intellectual
    disability.
  associated_phenotypes:
  - Impaired optic nerve development
  - Reduced forebrain size
  - Global developmental delay
  evidence:
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size."
    explanation: Describes the zebrafish phenotype, which recapitulates the optic nerve and forebrain involvement of the human disorder.
  - reference: PMID:38423010
    reference_title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In vivo experiments corroborated the pathogenicity of the tested SNF8 variants and their variable impact on embryo development, validating the observed clinical heterogeneity."
    explanation: Establishes that the model was used for allele-specific functional testing, not only for gene knockout, which is what links it to the genotype-phenotype correlation.
- species: Mus musculus
  genotype: Snf8 knockout (IMPC allele; homozygous and heterozygous)
  category: Knockout
  description: >-
    The IMPC Snf8 knockout is an orthogonal, non-literature line of evidence
    that the gene is essential. Homozygous null mice show preweaning lethality
    with complete penetrance, which is concordant with the severity of the human
    bi-allelic-null genotypes at the other end of this spectrum and with the
    inference that the mild pole exists only because p.Val102Ile is hypomorphic
    rather than null. Its practical limitation is the same fact: because the
    homozygous null does not survive, the mouse cannot be used to phenotype the
    postnatal neurological course, and no hypomorphic knock-in equivalent to
    p.Val102Ile - the allele that actually defines this disorder - has been
    made. The reported heterozygous findings have no human counterpart, since
    the heterozygous parents in all six families are unaffected.

    Provenance, verified independently rather than taken from the research
    report. Queried live on 2026-08-01 against the IMPC genotype-phenotype API,
    https://www.ebi.ac.uk/mi/impc/solr/genotype-phenotype/select?q=marker_symbol:Snf8
    which returned exactly three records: homozygote "preweaning lethality,
    complete penetrance" (parameter Outcome, p = 0.0); heterozygote "abnormal
    tail movements" (Tail elevation, p = 4.17e-5); heterozygote "increased
    lactate dehydrogenase level" (p = 2.57e-5). These figures match what the
    deep research pass reported, which is why they are recorded here rather than
    only flagged. No evidence item is attached because IMPC is not a
    snippet-validated reference source in this repository and no publication
    reporting this knockout was cited or cached; the API URL and retrieval date
    above are the provenance. The MGI accession for Snf8 was deliberately not
    asserted - the research pass warned that its own first lookup landed on
    Cyb5b, and it was not re-verified here.
  associated_phenotypes:
  - Preweaning lethality, complete penetrance (homozygote)
  - Abnormal tail movements (heterozygote)
  - Increased lactate dehydrogenase level (heterozygote)
discussions:
- discussion_id: snf8-val102ile-healthy-homozygote
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why is at least one apparently healthy gnomAD individual homozygous for
    c.304G>A (p.Val102Ile), the very allele that defines the mild pole of SNF8
    disease?
  rationale: >-
    This is the most consequential open question for the entry and it is not a
    technicality. Every mildly affected individual reported carries p.Val102Ile,
    yet a homozygote for that allele appears unaffected in a population
    database, and ClinVar submitters disagree about the allele accordingly
    (Munich and OMIM Pathogenic, Ambry uncertain significance). Three
    explanations are live and they have different clinical consequences: an
    unidentified modifier locus; a threshold effect in which two hypomorphic
    alleles retain more ESCRT-II activity than one hypomorph plus one null; or
    incomplete phenotyping of the population-database individual, who would not
    have had visual evoked potentials or optic coherence tomography. Until this
    is resolved, prenatal counselling for a predicted p.Val102Ile homozygote
    cannot state that the fetus is affected.
  attaches_to:
  - "pathophysiology#Stability-Independent Impairment by the p.Val102Ile Hypomorph"
  proposed_experiments:
  - experiment_id: snf8-recall-by-genotype-homozygotes
    name: Deep ophthalmological phenotyping of population-database p.Val102Ile homozygotes
    description: >-
      Recall-by-genotype of homozygous carriers identified in population
      biobanks, with visual evoked potentials, optic coherence tomography and
      formal cognitive assessment, to establish whether they are genuinely
      unaffected or merely unascertained for a subclinical optic neuropathy.
  - experiment_id: snf8-allelic-series-escrt2-activity
    name: Allelic-series functional assay of ESCRT-II activity
    description: >-
      Measure residual ESCRT-II function in cells engineered to carry
      p.Val102Ile homozygously versus p.Val102Ile in trans to a null allele, to
      test the threshold model directly against the modifier model.
  notes: >-
    Recorded as a discussion rather than as a phenotype or a penetrance figure
    because the underlying observation is in the full text of PMID:38423010 and
    in gnomAD, neither of which is quotable from the cached abstract.
- discussion_id: snf8-splice-acceptor-transcript-consequence
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What is the actual transcript consequence of the c.423-1G>C splice-acceptor
    variant carried by the family D proband?
  rationale: >-
    The variant is annotated only as p.? - its effect on splicing was never
    determined experimentally. Because this individual sits at the mild pole,
    the answer bears directly on the allelic-dosage model that the whole entity
    rests on: if c.423-1G>C is a complete null then p.Val102Ile alone sets the
    mild phenotype, whereas if it permits some in-frame product then the
    residual activity is shared between the two alleles and the model needs
    revising. RNA sequencing or RT-PCR on patient material would settle it.
  attaches_to:
  - "genetic#SNF8"
  proposed_experiments:
  - experiment_id: snf8-familyd-splice-rnaseq
    name: RNA-seq or RT-PCR of the family D proband
    description: >-
      Sequence patient-derived transcripts to determine whether c.423-1G>C
      causes exon skipping, activation of a cryptic acceptor, or intron
      retention, and whether the product escapes nonsense-mediated decay.
- discussion_id: snf8-no-model-of-the-mild-pole
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Does any existing model system represent the genotype that defines this
    disorder, given that the zebrafish model is a transient morpholino knockdown
    and the mouse null is preweaning-lethal?
  rationale: >-
    This is a model-fidelity question rather than an absence of evidence, which
    is why it is recorded as HUMAN_MODEL_MISMATCH and not as a KNOWLEDGE_GAP:
    in vivo evidence exists and is informative, but neither system models the
    entity curated here. The zebrafish work is a transient antisense morpholino
    knockdown, not a stable germline mutant, and morphant phenotypes are subject
    to off-target and p53-mediated artefacts; it captures the optic-nerve and
    forebrain developmental axis well, including the allele-severity gradient,
    but addresses none of the epileptic encephalopathy, callosal agenesis or
    leukoencephalopathy of the severe pole and none of the intellectual
    disability or progressive course of the mild pole. The IMPC mouse
    homozygous null is preweaning-lethal with complete penetrance, so no viable
    animal exists in which to phenotype the postnatal CNS. Most importantly, no
    model of any species carries a hypomorphic allele equivalent to
    p.Val102Ile - the allele every mildly affected individual carries and the
    only reason this MONDO term is distinct from DEE115. Every mechanistic claim
    about the mild pole therefore rests on two patient fibroblast lines and on
    inference, with no in vivo corroboration.
  attaches_to:
  - "pathophysiology#Stability-Independent Impairment by the p.Val102Ile Hypomorph"
  - "pathophysiology#Optic Nerve and Forebrain Developmental Failure"
  proposed_experiments:
  - experiment_id: snf8-val102ile-knockin-mouse
    name: Knock-in mouse carrying the p.Val102Ile-equivalent hypomorphic allele
    description: >-
      Generate homozygous and compound-heterozygous (hypomorph over null)
      knock-in mice to obtain the first viable in vivo model of the mild pole,
      and phenotype the visual pathway, cognition and white matter
      longitudinally. This would also test the threshold model against the
      modifier model raised by the healthy gnomAD homozygote.
  - experiment_id: snf8-stable-zebrafish-mutant
    name: Stable germline snf8 zebrafish mutant
    description: >-
      Create a CRISPR germline snf8 mutant line and ask whether the optic-nerve
      extension, optic-chiasm and forebrain-size phenotypes reported in
      morphants reproduce, which is the standard test for morpholino
      off-target artefact.
  - experiment_id: snf8-ipsc-neurons-and-retinal-organoids
    name: Patient iPSC-derived cortical neurons and retinal organoids
    description: >-
      Derive neurons and retinal organoids from mild-pole individuals to measure
      autophagic flux and ESCRT-II function in the cell types the disease
      actually affects, rather than in fibroblasts. The same approach was
      applied to the allied ESCRT disorder caused by VPS4A variants, so it is
      tractable.
  notes: >-
    The morpholino character of the zebrafish model and the IMPC mouse data are
    recorded on the respective `animal_models:` entries, with the IMPC API URL
    and its retrieval date. Neither is quotable from the cached abstract of
    PMID:38423010, so this discussion carries no evidence item.
references:
- reference: PMID:38423010
  title: "Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy."
- reference: PMID:18539118
  title: "Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex."
- reference: PMID:15469844
  title: "ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes."
- reference: PMID:15329733
  title: "Structure of the ESCRT-II endosomal trafficking complex."

📚

References & Deep Research

References

PMID:38423010

Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy.

No top-level findings curated for this source.

PMID:18539118

Integrated structural model and membrane targeting mechanism of the human ESCRT-II complex.

No top-level findings curated for this source.

PMID:15469844

ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes.

No top-level findings curated for this source.

PMID:15329733

Structure of the ESCRT-II endosomal trafficking complex.

No top-level findings curated for this source.

Deep Research

Claude Code ▸

1. Disease Information

claude-haiku-4-5-20251001, claude-opus-5[1m] 24 citations 2026-08-01T14:20:51.065203

1. Disease Information

Overview

SNF8-related neurodevelopmental disorder is an autosomal recessive allelic spectrum caused by bi-allelic loss-of-function variants in SNF8, which encodes one of three subunits of the ESCRT-II complex (Endosomal Sorting Complex Required for Transport II). The disorder was delineated in 2024 and spans a strikingly wide severity range that OMIM has split into two separate phenotype entries:

Pole	Phenotype	OMIM	MONDO	Character
Severe	Developmental and epileptic encephalopathy 115 (DEE115)	620783	MONDO:0968946	Congenital onset, neurodevelopmental arrest, epileptic encephalopathy, massive white-matter loss, corpus callosum hypo-/aplasia, death in infancy
Mild	Neurodevelopmental disorder plus optic atrophy (NEDOA)	620784	MONDO:0968947	Mild ID (speech/language predominant), childhood-onset optic atrophy, or ataxia; survival into adulthood

The verbatim framing from the defining paper (PMID:38423010, quotable snippet):

"We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8."

"The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death. A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia."

Key identifiers

Resource	Identifier
MONDO (severe)	MONDO:0968946 — developmental and epileptic encephalopathy 115 ✅ verified OLS4
MONDO (mild)	MONDO:0968947 — neurodevelopmental disorder plus optic atrophy ✅ verified OLS4
OMIM phenotype	620783 (DEE115); 620784 (NEDOA)
OMIM gene	610904 (SNF8 SUBUNIT OF ESCRT-II)
MedGen	1858870 (DEE115); 1859522 (NEDOA)
UMLS	C5935604 (DEE115); C5935605 (NEDOA)
GARD	0027033 (DEE115)
Orphanet	No ORPHA code assigned as of Aug 2026 (verified: no `ORPHA_*` cache entry mentions SNF8; Orphanet gene query returned no disorder)
ICD-10 / ICD-11	No specific code. Map pragmatically: ICD-10 `G40.4` (other generalized epilepsy/epileptic syndromes) or `Q04.0` (congenital malformations of corpus callosum) for the severe pole; `H47.2` (optic atrophy) + `F7x` for the mild pole. No disease-specific code exists.
MeSH	No disease-specific descriptor. MEDLINE indexing for PMID:38423010 uses: Optic Atrophy/genetics, Epilepsy, Generalized, Endosomal Sorting Complexes Required for Transport/genetics, Phenotype, Zebrafish/genetics

Synonyms / alternative names

SNF8-related neurodevelopmental disorder (umbrella term; used as this entry's name)
Developmental and epileptic encephalopathy 115 / DEE115 (severe pole)
Neurodevelopmental disorder plus optic atrophy / NEDOA (mild pole)
SNF8-related ESCRT-II deficiency
Gene-level aliases relevant to literature searching: EAP30, VPS22, Dot3 (searching "VPS22" and "EAP30" retrieves the cell-biology literature that does not use the symbol SNF8)

Evidence provenance type

Aggregated disease-level, case-series derived. All content originates from deep-phenotyped individual case descriptions in a single multi-center research collaboration (Munich, Leipzig, Rome, Bologna, Jerusalem, Ulm, Oslo, Nürnberg), plus structured secondary curation in OMIM, ClinVar, MONDO, and Genomics England PanelApp. No EHR-derived, registry, or population-cohort data exist.

2. Etiology

Disease causal factors

Monogenic, fully genetic. The sole established cause is bi-allelic (homozygous or compound-heterozygous) loss-of-function variation in SNF8. There is no known environmental, infectious, or multifactorial contribution.

The pathogenic principle is quantitative loss of the ESCRT-II holocomplex, not merely loss of SNF8 alone. SNF8 is structurally obligatory for complex integrity, so its depletion co-depletes its partners:

"SNF8 as well as the two physically interacting subunits of ESCRT-II, VPS36, and VPS25 were significantly decreased" (PMID:38423010, patient-derived fibroblasts, individual A2)

Measured fold-changes vs. controls in severe-phenotype fibroblasts: SNF8 0.25 (p=7.8×10⁻¹⁵), VPS36 0.39 (p=0.003), VPS25 0.37 (p=0.005).

Genetic risk factors

Causal variants: see Section 4. Seven distinct variants across 6 families.
Susceptibility loci / GWAS: None for this disease. ⚠️ Caution: SNF8 appears in GWAS hits for type 2 diabetes, coronary artery disease, psoriasis, fatigue, and insomnia-cardiac pleiotropy (PMIDs 25469308, 41824857, 40055680, 40176577). These reflect the gene-dense 17q21.32 locus (UBE2Z-GIP-ATP5G1-SNF8) and linkage disequilibrium, not relevance to the Mendelian disorder. Do not curate these as risk factors.
Modifier genes: None identified. See Section 4 for discussion of why a modifier is hypothesized but unproven.
Consanguinity: The one homozygous family (Family C, Israeli/Jerusalem, c.623G>T homozygous) is consistent with — but not explicitly reported as — consanguinity. The paper describes families as unrelated to each other; within-family consanguinity is not explicitly stated. Do not assert it.

Environmental risk factors

None known or plausible. No toxin, exposure, lifestyle, occupational, or age/sex risk factor has been reported or is mechanistically implicated. Parental age effects are not applicable (recessive inheritance, not de novo).

Protective factors

None identified. No protective variant, modifier allele, dietary, or lifestyle factor is known.

However, one genuinely important population-genetic observation exists — and it is the single most curation-relevant nuance in this section:

"one apparently healthy individual from the gnomAD population" carries the c.304G>A (p.Val102Ile) variant homozygously (PMID:38423010)

This means the hypomorphic p.Val102Ile allele in the homozygous state is not fully penetrant, implying an unidentified modifier, threshold effect, or ascertainment/phenotyping gap. This is a KNOWLEDGE_GAP discussion candidate, and arguably the most important open question for the entry.

Gene–environment interactions

None reported. No GxE data exist. CTD/PheGenI contain no SNF8 GxE records for this phenotype.

3. Phenotypes

Cohort structure (essential context for all frequencies below)

N=9 total individuals, 6 families. Frequencies are near-meaningless as percentages at this N — I report exact counts and give FrequencyEnum bands only where the count clearly supports one. Per docs/frequency-evidence-guidelines.md, I recommend omitting frequency: on most phenotypes and recording counts in description/notes instead.

ID	Sex	Genotype	Pole	Outcome
A1	F	p.Tyr167Ter / p.Gly191Asp	Severe	Died 8 mo — cardiac arrest during status epilepticus
A2	F	p.Tyr167Ter / p.Gly191Asp	Severe	Died 3 mo — respiratory infection (dysphagia-related); autopsy performed
B1	M	p.Pro79Leu / p.Gly191Asp	Severe	Alive at 4.5 y
C1	M	(Family C, homozygous c.623G>T)	Severe	Terminated at 25 weeks' gestation for brain malformations
C2	F	p.Arg208Leu homozygous	Severe	Died 9 wk — respiratory infection (dysphagia-related)
D1	M	c.423−1G>C / p.Val102Ile	Mild (NEDOA)	Alive at 18 y
E1	M	p.Asp225TrpfsTer99 / p.Val102Ile	Mild (NEDOA)	Alive at 27 y
E2	M	p.Asp225TrpfsTer99 / p.Val102Ile	Mild (NEDOA)	Alive at 17 y
F1	F	p.Pro79Leu / p.Val102Ile	Mild (ataxia variant)	Alive at 4 y

Sex ratio: 5 M : 4 F — consistent with autosomal inheritance, no sex bias.

Severe pole (DEE115) — phenotype table

Phenotype	HPO term (✅ label verified)	Count	Onset	Severity	Course
Epileptic encephalopathy	HP:0200134 Epileptic encephalopathy	2/4 (A1, B1)	~7–9 mo	Severe	Progressive
Hypsarrhythmia on EEG	HP:0002521 Hypsarrhythmia	A1, B1	Infantile	Severe	Progressive
Neurodevelopmental arrest / stagnation	HP:0007281 Developmental stagnation	4/4	Congenital	Profound	Static-arrested
Global developmental delay	HP:0001263 Global developmental delay	4/4	Congenital	Profound	Progressive
Hypotonia	HP:0001252 Hypotonia	4/4	Congenital/neonatal	Severe	Later → spasticity
Spastic tetraplegia	HP:0002510 Spastic tetraplegia	A1, B1 (late)	Infantile	Severe	Progressive
Dysphagia	HP:0002015 Dysphagia	4/4	Congenital	Severe	Persistent
(Gastrostomy/PEG required)	management, not phenotype	3/4	Infantile	—	—
Leukoencephalopathy	HP:0002352 Leukoencephalopathy	4/4	Congenital	Severe	Progressive
Cerebral atrophy	HP:0002059 Cerebral atrophy	4/4	Early	Severe	Progressive
Hypoplasia of the corpus callosum	HP:0002079 Hypoplasia of the corpus callosum	4/4 (hypo- or aplasia)	Congenital	Severe	Static
Nystagmus	HP:0000639 Nystagmus	A1, B1	Infantile	—	—
Death in infancy	HP:0001522 Death in infancy	3/4	9 wk – 8 mo	—	—

Note on intellectual disability in the severe pole: not formally assessable due to neurodevelopmental arrest and early death. Do not curate HP:0001249 for the severe pole — curate HP:0007281/HP:0001263 instead. This is a real curation trap.

Mild pole (NEDOA + ataxia variant) — phenotype table

Phenotype	HPO term (✅ verified)	Count	Onset	Severity	Course
Optic atrophy	HP:0000648 Optic atrophy	3/3 (D1, E1, E2); absent in F1	4–7 y (childhood)	Moderate–severe	Progressive/degenerative
Intellectual disability	HP:0001249 Intellectual disability	4/4 (D1, E1, E2, F1)	Childhood	Mild	Static
— speech/language predominant	HP:0000750 Delayed speech and language development ⚠️ verify	4/4	Childhood	Mild	Static
Nystagmus	HP:0000639 Nystagmus	3/3	Childhood	—	—
Reduced visual acuity	HP:0007663 Reduced visual acuity	3/3	Childhood	Moderate	Progressive
Optic nerve hypoplasia	HP:0000609 Optic nerve hypoplasia	Family C (fetal, "bilateral hypoplastic optic nerves")	Congenital	Severe	—
Ataxia	HP:0001251 Ataxia ⚠️ verify	1/1 (F1 only) — "congenital ataxia"	Congenital	Mild	Static
Cerebellar atrophy	HP:0001272 Cerebellar atrophy	F1 (slight); D1/E1 by volumetry	Early childhood	Mild	—
Developmental regression	HP:0002376 Developmental regression	Not reported	—	—	—
Seizures	HP:0001250 Seizure ⚠️ verify	0/4 — absent	—	—	Curate as `supports: REFUTE` or omit

Important: ataxia is F1 only — a single individual. The paper's abstract phrase "intellectual disability, childhood-onset optic atrophy, or ataxia" is a disjunction across the mild cohort, not a triad in each patient. Do not curate ataxia as a general feature of NEDOA. F1 also had no optic atrophy and a normal anterior optic tract on MRI at age 2.

Neuroimaging phenotype detail

Severe pole: - "Pronounced and progressive white matter atrophy of the cerebrum" - "Hypo- or aplasia of the corpus callosum beginning at a very early age" - Pachygyria (A2) → suggest HP:0001302 Pachygyria ⚠️ verify - "Rapidly progressive enlargement of the lateral ventricles due to cerebral white matter loss" → HP:0002119 Ventriculomegaly ⚠️ verify - Cerebellum "less severely affected"; brainstem "comparatively normal" — a useful discriminating feature vs. pontocerebellar hypoplasia (see §10 differential)

Mild pole (quantitative volumetry — unusually rich for such a small cohort): - "Severe volume reduction of the intracranial anterior optic pathway including optic nerves (ON), optic chiasma (OC), and optic tracts (2 SD below normal values)" - D1: cerebral white matter −17% bilateral; cerebellar cortex −13% L / −21% R; cerebellar mean diffusivity +13% bilateral - E1: white matter −20% bilateral; temporal cortex −17%; cerebellar cortex −19% L / −17% R; putamen −18% L / −17% R; cerebellar MD +9% L / +8% R - Slight parieto-occipital white-matter hyperintensity - F1 (age 2): normal myelination and white matter volume, slightly dysmorphic callosal body, slight cerebellar atrophy

The increased cerebellar mean diffusivity alongside cortical volume loss is a microstructural signature worth capturing — it supports a degenerative rather than purely dysplastic reading of the mild pole.

Quality-of-life impact

No formal QoL instrument (EQ-5D, SF-36, PROMIS, PedsQL) was administered. No published QoL data exist. Qualitative inference only:

Severe pole: profound impact — no developmental milestones achieved, gastrostomy dependence, palliative trajectory, death in infancy in 3/4. Total care dependency.
Mild pole: moderate impact — progressive low vision from childhood (educational and occupational consequence), mild ID predominantly affecting speech/language, independent survival into adulthood (to at least 27 y).

Curate as notes, not as evidenced QoL claims.

4. Genetic / Molecular Information

Causal gene

Field	Value
Symbol	SNF8
HGNC	hgnc:17028 (note lowercase prefix per repo convention)
Approved name	SNF8 subunit of ESCRT-II
Aliases	EAP30, VPS22, Dot3
Previous symbol	SNF8, ESCRT-II complex subunit, homolog (S. cerevisiae)
Locus	17q21.32
NCBI Gene	11267
Ensembl	ENSG00000159210
UniProt	Q96H20 (Vacuolar-sorting protein SNF8; 258 aa)
OMIM gene	610904
RefSeq transcript	NM_007241.4 (the reference transcript used in the paper and ClinVar)

Pathogenic variants — complete published set (7 variants)

All ✅ confirmed in ClinVar under condition "SNF8-associated disease."

cDNA (NM_007241.4)	Protein	Type	ClinVar germline classification	Families
c.501C>A	p.Tyr167Ter	Nonsense	Pathogenic (VCV002664478)	A
c.572G>A	p.Gly191Asp	Missense	Pathogenic (VCV002664479)	A, B
c.236C>T	p.Pro79Leu	Missense	Pathogenic (VCV002664480)	B, F
c.623G>T	p.Arg208Leu	Missense	Pathogenic (VCV002664481)	C (homozygous)
c.423−1G>C	p.?	Splice acceptor	Pathogenic (VCV002664482)	D
c.673_683delinsTGGA	p.Asp225TrpfsTer99	Frameshift (indel)	Pathogenic (VCV002664483)	E
c.304G>A	p.Val102Ile	Missense — hypomorphic	⚠️ Conflicting (VCV002664484)	D, E, F

The p.Val102Ile hypomorphic allele — the genotype–phenotype linchpin

This is the single most important genetic fact in the entry:

"All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)." (PMID:38423010)

Every one of the four mildly affected individuals (D1, E1, E2, F1) carries p.Val102Ile in trans to a more damaging allele. The severe pole comprises genotypes combining two non-p.Val102Ile alleles. This is a clean, near-deterministic allelic dosage model: residual ESCRT-II function determines pole.

Population and annotation data:

Field	Value
GRCh38 coordinate	chr17:48937065
dbSNP	rs200399045
gnomAD (overall)	0.00015
gnomAD exomes	0.00018
TOPMed	0.00015
1000 Genomes	0.00020
ExAC	0.00012
ESP	0.00015
Homozygotes in gnomAD	1 apparently healthy individual ⚠️

ClinVar submitter disagreement (curate this honestly): - Institute of Human Genetics Munich (2023-12-07): Pathogenic for SNF8-associated disease - Ambry Genetics (2024-01-30): Uncertain significance — "insufficient or conflicting evidence" - OMIM (2024-04-10): Pathogenic for neurodevelopmental disorder plus optic atrophy

The Ambry VUS call is defensible: AF ~1.5×10⁻⁴ with a healthy homozygote is unusual for a fully pathogenic allele. Recommend curating p.Val102Ile with an explicit note on the conflicting classification and reduced penetrance — not as unqualified "Pathogenic."

In silico support (from PMID:38423010)

CADD for the pathogenic missense variants: 27.3 – 33.0
REVEL: 0.683 – 0.953
All variants "affected residues that were spotted in regions documented to be intolerant to variation"
p.Val102Ile showed "less disruptive impact" by in silico prediction — concordant with its hypomorphic behavior

Functional consequences — mechanism class

Loss of function, acting through two mechanistically distinct routes — an important subtlety:

Protein-destabilizing LoF (severe alleles): truncating/frameshift/splice and severe missense alleles reduce SNF8 protein, which co-destabilizes VPS36 and VPS25, collapsing the ESCRT-II holocomplex. Confirmed by quantitative proteomics (fold changes above).
Stability-independent LoF (p.Val102Ile): In the mild-phenotype fibroblasts (D1, E1), SNF8 reduction was not statistically significant (D1: 0.74; E1: 0.68) and VPS36/VPS25 were not significantly reduced. The authors conclude the variant:

"acts via a distinct mechanism independent of protein stability"

No gain-of-function or dominant-negative mechanism is reported. Heterozygous carriers (parents) are unaffected.

gnomAD constraint metrics

⚠️ Not retrieved. The gnomAD GraphQL API was not reachable from this environment (sandbox network restriction) and the gnomAD gene page is a client-rendered JS app that WebFetch cannot resolve. pLI, o/e LoF, mis_z, and LoF observed/expected for SNF8 are therefore NOT reported here — do not populate these fields from memory. Retrieve them directly from https://gnomad.broadinstitute.org/gene/ENSG00000159210 before curating any constraint claim.

Modifier genes

None identified. A modifier is implied by the healthy gnomAD p.Val102Ile homozygote and by the intra-mild-cohort divergence (F1: ataxia, no optic atrophy; D1/E1/E2: optic atrophy, no ataxia — despite all four sharing p.Val102Ile). Curate as a KNOWLEDGE_GAP discussion, not as a finding.

Epigenetic information

None. No methylation episignature, chromatin, or histone-modification data exist for SNF8-related disease. ⚠️ Note a potential confusion source: CHMP1A (a different ESCRT-III gene) has documented chromatin-regulatory function (PMID:23023333) — this does not transfer to SNF8.

Chromosomal abnormalities

None causal. Three ClinVar records retrieved in the SNF8 gene query (VCV003242218, VCV003242217, VCV002692407) are large multi-gene deletions spanning the 17q21.32 region — they are not SNF8-specific and should not be curated as causing this disorder. No recurrent CNV, translocation, or inversion mechanism is known.

5. Environmental Information

Not applicable — no environmental contribution is known or hypothesized.

Environmental factors: None. CTD contains no SNF8–chemical–disease association for this phenotype.
Lifestyle factors: None.
Infectious agents: None causal. ⚠️ Important distinction for curators: the recurrent respiratory infections that caused death in A2 and C2 are a downstream complication of dysphagia and aspiration (i.e., a consequence of the phenotype), not an etiologic or triggering agent. Curate them as complications in Section 11, never as an infectious etiology.

6. Mechanism / Pathophysiology

Causal chain (proposed pathograph, upstream → downstream)

[MOLECULAR] Bi-allelic SNF8 LoF variants
      ↓
[MOLECULAR] Reduced SNF8 protein → co-destabilization of VPS36 + VPS25
    = loss of the ESCRT-II holocomplex
      ↓
[MOLECULAR/CELLULAR] Impaired ESCRT-II → ESCRT-III handoff;
    defective MVB biogenesis + cargo-selective endosomal sorting
      ↓
[CELLULAR] Mis-sorting of lysosomal hydrolases to the (auto)lysosome
      ↓
[CELLULAR] Accumulation of autolysosomes + morphologically aberrant lysosomes
    (enlarged, electron-lucent lumen)
      ↓
[CELLULAR] IMPAIRED AUTOPHAGIC FLUX  ← the convergent hub node
      ↓
[CELLULAR] LC3 accumulation in cortical pyramidal neurons and reactive astrocytes
      ↓
[TISSUE] Myelin loss, reactive gliosis, microglial activation;
 retinal ganglion cell / optic nerve degeneration
      ↓
[TISSUE] Leukoencephalopathy + cerebral atrophy; optic pathway volume loss
      ↓
[ORGANISM] Severe pole: DEE, neurodevelopmental arrest, early death
   Mild pole:   mild ID + childhood-onset optic atrophy / ataxia

Author's own summary of the terminal mechanism (quotable):

"Taken together, we conclude that loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux." (PMID:38423010)

Note the hedge — "likely via". Autophagic-flux impairment is the authors' preferred hypothesis, well-supported in fibroblasts and neuropathology but not proven to be the proximate cause of the neurological phenotype in vivo. Curate the terminal edge with status: EMERGING in a mechanistic_hypotheses block rather than as established fact.

Molecular pathways

ESCRT / MVB pathway (the core). ESCRT-II is the bridging complex between ubiquitin-cargo recognition (ESCRT-0/I) and membrane scission (ESCRT-III/VPS4).

Structural basis (yeast core, PMID:15329733, Nature 2004 — quotable):

"Here we report the crystal structure of the core of the yeast ESCRT-II complex, which contains one molecule of the Vps protein Vps22, the carboxy-terminal domain of Vps36 and two molecules of Vps25, and has the shape of a capital letter 'Y'. The amino-terminal coiled coil of Vps22 and the flexible linker leading to the ubiquitin-binding NZF domain of Vps36 both protrude from the tip of one branch of the 'Y'."

Note: Vps22 = SNF8. The 1:1:2 stoichiometry (Vps22 : Vps36 : Vps25₂) explains mechanistically why losing SNF8 collapses the whole complex.

ESCRT-II→III coupling (PMID:15469844, Dev Cell 2004 — quotable):

"We show that purified ESCRT-II binds directly to the Vps20 component of ESCRT-III. Surprisingly, this binding does not require the protruding N-terminal coiled-coil of Vps22. Vps25 is the chief subunit responsible for Vps20 recruitment. This interaction dramatically increases binding of both components to lipid vesicles in vitro."

Human ESCRT-II structures: PDB 2ZME, PDB 3CUQ (2.6 Å and 2.9 Å) — three lobes, one copy each of VPS22/VPS36, two copies of VPS25.

Pathways NOT implicated: no evidence for Wnt, MAPK, mTOR, or PI3K-AKT involvement in this disease. Do not import these from generic NDD priors.

Cellular processes

Macroautophagy / autophagic flux (the central process)
Multivesicular body biogenesis
Endosomal cargo sorting; late endosome → lysosome transport
Lysosomal biogenesis / hydrolase delivery
Neural progenitor proliferation (zebrafish: ectopic pH3+ cells in forebrain)
Axon outgrowth/pathfinding (optic nerve extension, optic chiasm formation)
Reactive gliosis and microglial activation

Cargo selectivity — a mechanistically important negative result

"EGFR degradation was not detectably impaired in patient-derived fibroblasts as compared to fibroblasts from control individuals." (PMID:38423010)

This is significant: EGFR downregulation is the canonical ESCRT-dependent readout, yet it was preserved. The authors attribute this to residual ESCRT-II function and cargo specificity — different cargoes have different ESCRT-II dependency thresholds. Curate this as supports: PARTIAL or as a REFUTE-flavored evidence item against a "global ESCRT collapse" model. It argues for a selective, threshold-dependent defect, which in turn helps explain the mild pole.

Protein dysfunction

SNF8/Q96H20: 258 aa; coiled-coil at residues 27–53; multiple winged-helix repeats (the entire ESCRT-II core is built from eight winged-helix domains, PMID:15469844). Two isoforms via alternative splicing. Interacts with VPS25, VPS36, TSG101, RILPL1, and 14-3-3 proteins.

Mechanism is loss of function via complex destabilization (severe alleles) or stability-independent functional impairment (p.Val102Ile). No misfolding/aggregation proteinopathy is described.

Metabolic changes

None established. ⚠️ Curation trap: PMID:38423010 mentions "mitochondrial complex III deficiency, nuclear type 1" (MIM 124000, BCS1L) only as a separate, unrelated individual retrieved from the same in-house diagnostic database. There is no mitochondrial or complex III defect in SNF8-related disease. No lactate, CSF, or respiratory-chain enzyme abnormality was reported. Do not curate any metabolic/mitochondrial finding.

Immune system involvement

No primary immune involvement. Neuroinflammation is secondary: reactive astrogliosis and microglial activation on autopsy. No autoimmunity, no immunodeficiency.

Tissue damage mechanisms

Autophagic-lysosomal dysfunction → neuronal and oligodendroglial/myelin injury → demyelination and white-matter loss with reactive gliosis. Optic pathway: retinal ganglion cell / optic nerve degeneration (a classic autophagy-vulnerable, long-axon, high-metabolic-demand neuronal population — the same vulnerability class as OPA1/mitochondrial optic neuropathies). No ischemic, fibrotic, or oxidative-stress mechanism is documented.

Biochemical abnormalities

No enzyme deficiency, receptor, ion-channel, or transporter defect. The defect is in vesicular trafficking machinery, not catalysis.

Epigenetic changes

None reported.

Molecular profiling

Proteomics ✅ — quantitative proteomics on patient fibroblasts is the key functional dataset (SNF8/VPS36/VPS25 fold changes above). Modality: IN_VITRO.
Transcriptomics — none.
Metabolomics / lipidomics — none.
Single-cell / spatial transcriptomics — none.
Multi-omics integration — none.
Functional genomics (CRISPR/RNAi screens) — ⚠️ Not retrieved. DepMap was inaccessible (bot-verification wall). Do not assert SNF8 essentiality status without checking https://depmap.org/portal/gene/SNF8 directly. Contextual note only: the IMPC mouse homozygous-null preweaning-lethal phenotype (§15) is consistent with a fitness-critical gene, but that is not the same claim as DepMap common-essentiality.

Suggested GO terms (✅ all verified live)

Biological process | GO ID | Label | |---|---| | GO:0036258 | multivesicular body assembly | | GO:0016236 | macroautophagy | | GO:0061919 | process utilizing autophagic mechanism | | GO:0032456 | endocytic recycling | | GO:0043328 | protein transport to vacuole involved in ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway |

Cellular component | GO ID | Label | |---|---| | GO:0000814 | ESCRT II complex | | GO:0010008 | endosome membrane | | GO:0031902 | late endosome membrane | | GO:0044754 | autolysosome |

Molecular function | GO ID | Label | |---|---| | GO:0042803 | protein homodimerization activity | | GO:0008289 | lipid binding |

7. Anatomical Structures Affected

Organ level

Primary: central nervous system — cerebrum (white matter predominant), corpus callosum, anterior visual pathway, cerebellum (mild/variable). Secondary: respiratory tract (aspiration pneumonia from dysphagia); GI (feeding failure → gastrostomy); cardiac (terminal arrest during status epilepticus in A1 — an agonal event, not primary cardiac disease). Body systems: nervous (primary), visual/special sense (primary), respiratory + digestive (secondary).

Notably spared: brainstem ("comparatively normal"), and no reported hepatic, renal, hematologic, or skeletal involvement. This sparing pattern is diagnostically useful — it distinguishes SNF8 from the multisystem ESCRT disorder CIMDAG (VPS4A), which features cataracts, anemia, and growth impairment.

Suggested UBERON terms (✅ verified — note label subtleties)

UBERON ID	Canonical label (use this in `term.label`)	Suggested `preferred_term`
UBERON:0000955	brain	brain
UBERON:0002316	white matter ⚠️ verify	cerebral white matter
UBERON:0002336	corpus callosum ⚠️ verify	corpus callosum
UBERON:0000941	cranial nerve II ✅ verified	optic nerve ← label ≠ common name; do not write "optic nerve" in `term.label`
UBERON:0000959	optic chiasma ✅ verified	optic chiasm
UBERON:0000966	retina ⚠️ verify	retina
UBERON:0002037	cerebellum ⚠️ verify	cerebellum
UBERON:0000956	cerebral cortex ⚠️ verify	cerebral cortex
UBERON:0001890	forebrain ⚠️ verify	forebrain

UBERON:0000941 is a genuine trap — its canonical label is "cranial nerve II", so term.label: optic nerve would fail just validate-terms. Use preferred_term: optic nerve with term.label: cranial nerve II.

Tissue and cell level

Affected tissue types: nervous tissue (neurons, glia), myelinated white-matter tracts.

Suggested CL terms

CL ID	Label	Evidence basis
CL:0000598 ✅	pyramidal neuron	LC3 accumulation in "cells of the internal pyramidal cell layer" (autopsy, A2)
CL:0000127 ⚠️ verify	astrocyte	"reactive gliosis with increased numbers of reactive astrocytes"; LC3+
CL:0000129 ⚠️ verify	microglial cell	"microglia activation"
CL:0000128 ⚠️ verify	oligodendrocyte	inferred from "marked loss of myelin" — inferred, not directly demonstrated; curate cautiously
CL:0000740 ✅	retinal ganglion cell	inferred from optic atrophy + optic pathway volume loss — inferred; the paper did not examine retina histologically
CL:0000057 ⚠️ verify	fibroblast	the actual experimental cell type for all proteomics/EM/confocal work (`IN_VITRO`)

Be explicit in the KB that oligodendrocyte and retinal ganglion cell involvement is inferred, while pyramidal neuron, astrocyte, microglia (autopsy) and fibroblast (in vitro) are directly evidenced.

Subcellular level

GO CC ID	Label	Finding
GO:0044754 ✅	autolysosome	accumulate — EM + LC3/LAMP1 confocal
GO:0005764 ⚠️ verify	lysosome	"aberrant morphology… enlarged size and a largely electron lucent lumen"
GO:0005776 ⚠️ verify	autophagosome	autophagy pathway component
GO:0031902 ✅	late endosome membrane	ESCRT-II site of action
GO:0010008 ✅	endosome membrane	ESCRT-II site of action
GO:0000814 ✅	ESCRT II complex	the disrupted complex

Localization / lateralization

Bilateral and symmetric throughout. Volumetric measures were reported bilaterally (e.g., D1 white matter −17% bilaterally; E1 −20% bilaterally), with only minor L/R asymmetry in cerebellar cortex (D1: −13% L vs −21% R). Optic pathway involvement is bilateral (Family C: "bilateral hypoplastic optic nerves"). No unilateral or asymmetric presentation reported. Suggest HP:0012832 Bilateral ⚠️ verify if a laterality modifier is desired.

8. Temporal Development

Onset

Pole	Age of onset	Pattern	HPO onset term
Severe (DEE115)	Congenital / neonatal (all 4); prenatal in C1 (brain malformations detected → TOP at 25 wk)	Congenital, immediately apparent	HP:0003623 Neonatal onset ⚠️ verify; HP:0030674 Antenatal onset ⚠️ verify (for C1)
— seizure onset	7–9 months	Subacute, then progressive	—
Mild (NEDOA)	Optic atrophy 4–7 y; ID recognized in childhood	Insidious	HP:0011463 Childhood onset ⚠️ verify
Mild (F1, ataxia)	Congenital ataxia; developmental concern from 15 mo	Congenital, static	HP:0003577 Congenital onset ⚠️ verify

Note the bimodal onset distribution — congenital vs. mid-childhood — tracking directly with genotype (p.Val102Ile presence). Onset age is itself a genotype-driven variable here.

Progression

Severe pole — progressive and rapidly fatal: - Stage 1 (birth–~6 mo): profound hypotonia, feeding failure, no milestone acquisition (arrest, not regression) - Stage 2 (~7–9 mo): seizure onset; EEG "multifocal and generalized epileptic discharges further progressing to hypsarrythmia" - Stage 3: emergence of spasticity/hyperreflexia superseding hypotonia (A1, B1) - Stage 4: "pronounced and progressive white matter atrophy," "rapidly progressive enlargement of the lateral ventricles" - Terminal: death 9 wk – 8 mo in 3/4

Rate: rapid. Course: progressive. Duration: fatal in infancy for most; B1 survived to 4.5 y (upper bound of observation, not necessarily of survival).

Mild pole — slowly progressive neurodegeneration on a static developmental baseline: - Static mild ID (developmental, non-progressive) - Superimposed progressive optic neuropathy from age 4–7 y — degenerative, confirmed by abnormal VEPs (E1, E2: "delayed latency and reduced amplitude") and OCT - Slowly progressive volume loss (white matter, cerebellar, temporal cortex, putamen) with increased cerebellar mean diffusivity - Survival to at least 27 y (E1) with no reported deterioration to dependency

Rate: slow. Course: static ID + progressive visual/cerebellar degeneration — a genuine dual-component course. Duration: chronic lifelong.

Terminology precision: in the severe pole this is neurodevelopmental arrest ("Developmental stagnation," HP:0007281) — milestones were never acquired. Do not curate HP:0002376 Developmental regression; the paper reports arrest, not loss of acquired skills.

Patterns

Remission: none, spontaneous or treatment-induced. No treatment exists.
Relapsing-remitting: not applicable.
Critical periods: Mechanistically, the prenatal/perinatal window governs the structural malformation component (corpus callosum hypo-/aplasia, pachygyria, optic nerve hypoplasia) — this is already established at birth and is not modifiable postnatally. The childhood window (4–7 y) is when the progressive optic neuropathy declares itself and is therefore the theoretical window for a disease-modifying (e.g., autophagy-directed) intervention. This is mechanistic reasoning, not published clinical guidance — curate as notes/hypothesis, not as evidence.

9. Inheritance and Population

Epidemiology

Measure	Value
Prevalence	Not documented. No Orphanet prevalence class assigned (no ORPHA code exists).
Incidence	Not documented.
Cases in literature	9 individuals / 6 families (single publication)
Carrier frequency	Not established for the gene overall. Only p.Val102Ile has usable population data: gnomAD AF 0.00015 (rs200399045).

Recommended dismech Prevalence record (per the structured-prevalence guidance in CLAUDE.md):

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    Nine individuals from six families reported in the single defining
    publication (Brugger et al. 2024). No population prevalence or incidence
    estimate has been published; no Orphanet prevalence class assigned.
  evidence:
  - reference: PMID:38423010
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8"
    explanation: Establishes the total reported case count.

Do not populate rate_per_100000 — there is no basis for a number.

Inheritance

Pattern: Autosomal recessive — HP:0000007 Autosomal recessive inheritance ⚠️ verify. Confirmed by homozygosity in Family C, compound heterozygosity in 5 families, unaffected heterozygous parents, and unanimous PanelApp classification as "BIALLELIC, autosomal or pseudoautosomal" across all 5 panels.
Penetrance: Incomplete for at least one genotype. The healthy gnomAD p.Val102Ile homozygote is direct evidence that p.Val102Ile homozygosity is not fully penetrant. For the severe biallelic-null genotypes, penetrance appears complete (4/4 affected + 1 fetal). Curate as incomplete/genotype-dependent, not "complete."
Expressivity: Highly variable, but largely genotype-explained. The severe↔mild split maps almost deterministically onto p.Val102Ile presence. Residual intra-mild variability (F1 ataxia-without-optic-atrophy vs. D1/E1/E2 optic-atrophy-without-ataxia) is unexplained.
Genetic anticipation: Not applicable — not a repeat-expansion disorder.
Germline mosaicism: Not reported.
Founder effects: None established. Family C's homozygous c.623G>T (Israeli/Jerusalem) is a single family — insufficient to claim a founder allele. Do not assert one. The recurrence of p.Val102Ile across three unrelated families (D, E, F — two Italian, one German) reflects its appreciable population frequency (a segregating polymorphic hypomorph), not a founder event.
Consanguinity: Not explicitly reported; plausible in Family C given homozygosity. Do not assert.

Population demographics

Reported ancestry: German (Families A/Munich, B/Leipzig, F/mixed European), Italian (D/Bologna, E/Rome), Israeli (C/Jerusalem). Entirely European + Middle Eastern — this reflects ascertainment through European diagnostic-genomics networks, not true population restriction. Explicitly flag ascertainment bias; do not curate "affects Europeans."
Geographic distribution: No endemic pattern; ascertainment-driven.
Variant geography: p.Val102Ile in Italian and German families; c.623G>T homozygous in the Israeli family. N is far too small for geographic inference.
Sex ratio: 5 M : 4 F — no sex bias, as expected for autosomal recessive.
Age distribution: bimodal by pole — severe pole ascertained in infancy (9 wk – 8 mo at death; B1 to 4.5 y); mild pole ascertained in childhood through adulthood (4–27 y).

10. Diagnostics

Clinical tests

Laboratory tests / biomarkers: No diagnostic biochemical biomarker exists. No lactate, CSF, enzyme-assay, or metabolic marker abnormality was reported. Diagnosis is molecular-genetic, full stop. ⚠️ Do not curate a metabolic screen as diagnostic.

Research-only functional assays (not clinically validated, IN_VITRO): - Quantitative proteomics on patient fibroblasts showing reduced SNF8/VPS36/VPS25 — the most useful functional confirmation for a VUS - Electron microscopy: enlarged vesicular structures containing cytoplasmic material; lysosomes with "enlarged size and a largely electron lucent lumen" - LC3/LAMP1 immunofluorescence: autolysosome accumulation

Imaging — brain MRI (the key diagnostic modality; suggest NCIT:C16809 Magnetic Resonance Imaging ⚠️ verify): - Severe: progressive cerebral white-matter atrophy, corpus callosum hypo-/aplasia, ventriculomegaly, pachygyria; cerebellum less affected, brainstem comparatively normal - Mild: quantitative volumetry of the anterior visual pathway (ON/OC/optic tracts ≥2 SD below normal) — the highest-yield mild-pole finding; plus regional volume loss and increased cerebellar mean diffusivity (DTI)

Functional / electrophysiology: - EEG: multifocal and generalized epileptic discharges "further progressing to hypsarrythmia" (severe pole) - Visual evoked potentials (VEP): "delayed latency and reduced amplitude" (E1, E2) — sensitive for the mild pole - OCT: confirms optic (hypo)atrophy, onset 4–7 y

Biopsy / pathology: Not diagnostic. Autopsy neuropathology (A2) is confirmatory/research: pachygyria, enlarged sulci, reduced cerebral white matter, corpus callosum thinned to 2 mm, "marked loss of myelin," reactive astrogliosis, microglial activation, and strong LC3 immunostaining in internal pyramidal cell layer neurons and reactive white-matter astrocytes (vs. "only weak staining" in age-matched controls).

Genetic testing — the definitive route

Recommended approach: WES or WGS (or a broad NDD/epilepsy/optic-neuropathy panel including SNF8), followed by phase/segregation confirmation in parents to establish biallelic status. SNF8 is a small gene (258 aa) and single-gene testing is not clinically offered.

Genomics England PanelApp — SNF8 appears on 5 panels (all "BIALLELIC, autosomal or pseudoautosomal"):

Panel	ID	Rating
DDG2P	484	🟢 Green (diagnostic-grade)
Intellectual disability	285	🟢 Green
Fetal anomalies	478	🟢 Green
Optic neuropathy	186	🟡 Amber
Early onset or syndromic epilepsy	402	🟡 Amber

The Optic neuropathy amber rationale: "two unrelated cases reported with optic atrophy" — i.e., below the green threshold for that specific phenotype. This Green/Amber split is genuinely informative and worth capturing: SNF8 is diagnostic-grade for ID/DD and fetal anomalies, but only moderate-evidence for isolated optic neuropathy and epilepsy presentations.

Other modalities: - CMA: not indicated (no CNV mechanism) - Karyotype / FISH: not indicated - mtDNA testing: not indicated — but see differential below; it is often performed before the diagnosis because optic atrophy prompts mitochondrial workup - Repeat expansion testing: not applicable

Omics-based diagnostics

RNA-seq: ⚠️ Genuinely worth flagging as a curation-relevant gap. The c.423−1G>C splice-acceptor variant (Family D) is annotated p.? — its actual transcript consequence was not experimentally determined. RNA-seq/RT-PCR would resolve it. This is a concrete KNOWLEDGE_GAP candidate.
Proteomics: research-grade functional support (see above); not a clinical test.
Metabolomics / epigenomics (episignature) / liquid biopsy: none available.

Clinical criteria

No consensus diagnostic criteria exist (single publication, N=9). Practical diagnosis = compatible phenotype + biallelic SNF8 variants + parental segregation.

Differential diagnosis

For the severe pole (DEE + leukoencephalopathy + CC hypo-/aplasia):

Differential	Gene	Distinguishing feature
Pontocerebellar hypoplasia 8 (PCH8)	CHMP1A (ESCRT-III), MIM 614961	PCH8 has prominent pontocerebellar hypoplasia; SNF8 spares brainstem and relatively spares cerebellum. Both ESCRT. (PMID:23023333)
CIMDAG syndrome	VPS4A, MIM 619273	Multisystem: cataracts, dyserythropoietic anemia, growth retardation, dystonia — absent in SNF8. De novo dominant missense, not recessive. (PMID:33186545)
Other DEEs / genetic leukodystrophies	many	Broad; resolved by sequencing
Aicardi–Goutières, peroxisomal, lysosomal storage disorders	many	Distinguished by biochemical markers, which are normal/unremarkable in SNF8

For the mild pole (ID + childhood-onset optic atrophy):

Differential	Gene	Distinguishing feature
Autosomal dominant optic atrophy	OPA1	AD inheritance; typically isolated optic atrophy without ID
Wolfram syndrome	WFS1	Diabetes mellitus + diabetes insipidus + deafness
Costeff / 3-methylglutaconic aciduria type III	OPA3	Abnormal urine organic acids (3-methylglutaconic acid) — SNF8 has none
*Behr syndrome / ACO2-related*	OPA1, ACO2	Optic atrophy + ataxia + spasticity; overlaps closely with the SNF8 mild pole
Leber hereditary optic neuropathy	MT-ND1/4/6	Maternal inheritance, acute/subacute young-adult vision loss
Hereditary spastic paraplegia 53	VPS37A (ESCRT-I), MIM 614898	Spastic paraplegia predominant

Key practical point: the mild pole most closely mimics ACO2/Behr-type optic atrophy + ataxia + mild ID syndromes, and mitochondrial optic neuropathies are typically excluded first. SNF8 is likely under-ascertained in exome-negative optic-atrophy-plus-ID cohorts — a plausible reason the published N remains 9.

Screening

Newborn screening: Not included in any program; no biochemical marker exists, so NBS is not technically feasible by current MS/MS methods.
Carrier screening: SNF8 is not on standard expanded carrier panels. Given AF ~1.5×10⁻⁴ for p.Val102Ile alone and unresolved penetrance, inclusion is not currently justified.
Cascade screening: Appropriate within families — targeted testing of at-risk relatives and reproductive partners once a familial genotype is known.

11. Outcome / Prognosis

Survival and mortality

⚠️ No survival curve, 5-/10-year survival rate, life expectancy estimate, or mortality rate has been published. With N=9, only individual outcomes are reportable. Do not compute or curate a percentage survival figure — any such number would be fabricated.

Observed outcomes (individual-level, PMID:38423010):

Pole	Deaths	Ages at death	Cause
Severe	3 of 4 died in infancy	9 weeks, 3 months, 8 months	Respiratory infection secondary to dysphagia (A2, C2); cardiac arrest during status epilepticus (A1)
Severe (survivor)	B1 alive	4.5 y at last visit	—
Fetal	C1	25 weeks' gestation	Termination of pregnancy for brain malformations
Mild	0 of 4	Alive at 4, 17, 18, 27 y	—

Disease-specific mortality mechanisms — both are secondary complications, which is prognostically actionable: 1. Aspiration/respiratory infection from dysphagia (2 of 3 deaths) — the leading cause 2. Status epilepticus (1 of 3 deaths)

Morbidity and function

Severe pole: total functional dependency; no developmental milestones achieved; gastrostomy dependence (3/4); progressive spastic tetraplegia. Profound disability.
Mild pole: mild ID predominantly affecting speech/language; progressive low vision from childhood; F1 with congenital ataxia. Substantially preserved function — all mild-pole individuals survived to adolescence/adulthood.
ICF-coded disability outcomes / DALYs: none published.
Quality of life instruments: none administered (see §3).

Complications

Complication	Pole	Note
Aspiration pneumonia / respiratory infection	Severe	Leading cause of death
Feeding failure requiring gastrostomy	Severe	3/4
Status epilepticus	Severe	Fatal in A1
Progressive spasticity/contractures	Severe	A1, B1
Low vision / functional visual impairment	Mild	Progressive from 4–7 y

Recovery potential

None. No recovery, no reversal of established structural CNS damage. The malformation component (CC hypo-/aplasia, pachygyria, optic nerve hypoplasia) is prenatally established and irreversible. No treatment exists to alter the degenerative component.

Prognostic factors

The dominant prognostic factor is genotype — specifically, presence of p.Val102Ile:

"All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)." (PMID:38423010)

This is a genuinely strong, near-deterministic genotype–prognosis correlation in the published cohort — presence of one p.Val102Ile allele in trans predicted the mild pole in 4/4 cases; its absence predicted the severe pole in 5/5 (including the fetus). Caveat clearly: N=9, single cohort, no independent replication.

Supporting functional/prognostic correlates: - Degree of ESCRT-II subunit depletion in fibroblasts tracks severity (severe: SNF8 0.25 with significant VPS36/VPS25 loss; mild: SNF8 0.68–0.74, non-significant, VPS36/VPS25 preserved) — a candidate functional prognostic assay - Zebrafish allele-pair severity recapitulated the human gradient: severe pair (p.Tyr167Ter + p.Gly191Asp) ~95% aberrant embryos vs. mild pair (p.Pro79Leu + p.Val102Ile) ~70% - Presence of dysphagia/gastrostomy dependence and early seizure onset mark the poor-prognosis group clinically

Prognostic biomarkers: none clinically validated.

12. Treatment

⚠️ There is NO disease-specific or disease-modifying treatment for SNF8-related neurodevelopmental disorder.

PMID:38423010 discusses no therapeutic intervention. Verbatim finding from full-text review: "No therapeutic interventions, treatments, or management strategies are discussed in this paper." Severely affected individuals received palliative care; three required gastric tube feeding.

A search of ClinicalTrials.gov-indexed literature and the publication record identified NO clinical trials, NO NCT identifiers, and NO experimental therapeutics for this disorder. Any treatment content below is standard-of-care symptomatic management inferred from the reported clinical needs, and must be curated as such — with notes rather than fabricated evidence, or with evidence citing only what PMID:38423010 actually states (i.e., that gastrostomy feeding was required).

Pharmacotherapy

Antiseizure medications for the epileptic encephalopathy. No specific agent, regimen, or response rate is reported; the epileptic encephalopathy with hypsarrhythmia was clinically severe and A1 died in status epilepticus, suggesting poor pharmacoresponsiveness — but the paper does not state this. Do not invent drug names.
Suggested: treatment_term NCIT:C15986 Pharmacotherapy; therapeutic_modality: SMALL_MOLECULE. Leave therapeutic_agent empty — no agent is documented.
Pharmacogenomics: none. No PharmGKB/CPIC entry relates to SNF8.

Advanced therapeutics

None exist. No gene therapy, gene editing, cell therapy, ASO/siRNA/mRNA therapy, targeted therapy, or immunotherapy has been developed, trialed, or proposed in print.

Theoretical considerations only — flag clearly as speculative if curated at all: recessive LoF with a hypomorphic-allele-defines-mild-pole architecture is in principle gene-replacement-tractable, and the p.Val102Ile natural experiment suggests only partial restoration of ESCRT-II function may suffice for the mild phenotype — a favorable therapeutic-threshold argument. But: the prenatally established malformation component (CC hypo-/aplasia) sets a hard limit on postnatal benefit, and CNS-wide delivery to white matter and retinal ganglion cells is unsolved. This is my mechanistic reasoning, not published work — do not curate as evidence.

Surgical and interventional

Gastrostomy / PEG placement — the one intervention actually documented: 3 of 4 severely affected individuals required gastric tube feeding.
Suggested: NCIT:C15329 Surgical Procedure (or a specific gastrostomy term, ⚠️ requires OAK verification); therapeutic_modality: SURGERY
Quotable basis: the paper states three required "gastric tube feeding"

Supportive and rehabilitative (the actual standard of care)

Intervention	Suggested NCIT (from in-repo authoritative list)	`therapeutic_modality`
Palliative / supportive care	NCIT:C15747 Supportive Care	OTHER
Nutritional support (enteral feeding)	NCIT:C15433 Nutritional Support	⚠️ Do NOT auto-tag BEHAVIORAL — see `CLAUDE.md` warning; enteral feeding here is closer to a device/procedure
Physical therapy (spasticity, contractures)	NCIT:C15302 Physical Therapy	BEHAVIORAL
Occupational therapy	NCIT:C121351 Occupational Therapy ⚠️ verify	BEHAVIORAL
Speech and language therapy (mild pole — speech/language is the predominant ID domain)	NCIT:C159273 Speech Therapy ⚠️ verify	BEHAVIORAL
Low-vision rehabilitation / visual aids	⚠️ no verified NCIT term identified	DEVICE or BEHAVIORAL
Genetic counseling	NCIT:C15240 Genetic Counseling	OTHER

Per the CLAUDE.md mechanical-backfill table: NCIT:C15302 → BEHAVIORAL, NCIT:C15329 → SURGERY, NCIT:C15986 → agent-dependent (do not auto-assign). NCIT:C15433 Nutritional Support must NOT be mechanically tagged BEHAVIORAL — this exact mis-tagging was tried and reverted in this repo on 2026-07-08.

Treatment outcomes, algorithms, combination/personalized approaches

None published. No response rates, no adverse-event data (no disease-specific drug exists), no treatment algorithm, no NCCN/society guideline, no genotype-guided treatment protocol. The only genotype-driven clinical action is prognostic counseling (p.Val102Ile → mild pole expectation), not treatment selection.

13. Prevention

Primary prevention

Not preventable — a germline monogenic disorder. The only primary-prevention modality is reproductive: - Genetic counseling with 25% recurrence risk per pregnancy for carrier couples (NCIT:C15240 Genetic Counseling) - Prenatal diagnosis (CVS/amniocentesis) with targeted testing of the known familial variants - Preimplantation genetic testing for monogenic disorders (PGT-M) — technically applicable once familial variants are known - ⚠️ Counseling caveat: for couples where the fetus would be a p.Val102Ile homozygote, counseling is genuinely uncertain given the healthy gnomAD homozygote and the Ambry VUS classification. This must be communicated as uncertain, not as "affected." Important nuance to capture.

Family C's history — termination of pregnancy at 25 weeks for detected brain malformations, followed by an affected liveborn sibling (C2) who died at 9 weeks — illustrates the real reproductive stakes.

Secondary prevention (early detection)

Cascade genetic testing of at-risk relatives in known families
In the mild pole, serial ophthalmologic surveillance (VEP, OCT, visual acuity) from early childhood is a rational early-detection strategy given documented onset at 4–7 y — enabling timely low-vision support and educational accommodation. This is inference from the reported onset window, not a published guideline.

Tertiary prevention (complication prevention) — the highest-yield real intervention

Given that 2 of 3 deaths were respiratory infections secondary to dysphagia, tertiary prevention is where meaningful clinical benefit plausibly lies: - Early swallow assessment and aspiration-risk management - Timely enteral feeding (gastrostomy) before nutritional/respiratory decompensation - Respiratory hygiene, immunization against respiratory pathogens (routine schedule), prompt infection treatment - Seizure-emergency (status epilepticus) action plans — relevant given A1's death - Contracture prevention via physiotherapy/positioning

Immunization

No disease-specific vaccine. Routine childhood immunization — with attention to respiratory pathogens (influenza, pneumococcus, RSV) — is rational given the aspiration-pneumonia mortality pattern. Standard-of-care inference, not published guidance.

Screening programs, risk stratification, behavioral interventions, public health, prophylaxis

Population screening: not warranted (ultra-rare, no biomarker, no intervention)
Newborn screening: not feasible (no biochemical marker)
Risk stratification: genotype-based only (p.Val102Ile presence → mild pole)
Behavioral / lifestyle interventions: none applicable — no modifiable lifestyle risk factor exists
Public health / environmental interventions: not applicable
Prophylaxis: no antimicrobial or other prophylaxis protocol published; aspiration-pneumonia prevention is the rational target

14. Other Species / Natural Disease

Taxonomy and orthologs

Species	NCBI Taxon	Gene	NCBI Gene ID	Relevance
Homo sapiens	NCBITaxon:9606	SNF8	11267	The disease species
Mus musculus	NCBITaxon:10090	Snf8	⚠️ verify MGI ID	IMPC KO model (§15)
Danio rerio	NCBITaxon:7955	snf8	⚠️ verify ZFIN ID	The paper's in vivo model (§15)
Drosophila melanogaster	NCBITaxon:7227	Vps22/snf8	⚠️ verify FlyBase ID	ESCRT-II biology; sleep/cardiac study (PMID:40176577)
C. elegans	NCBITaxon:6239	vps-22	⚠️ verify WormBase ID	Longevity/DAF-16 (PMID:32829877)
S. cerevisiae	NCBITaxon:4932	SNF8/VPS22	⚠️ verify SGD ID	Origin of the gene name; structural biology

⚠️ I attempted to confirm the mouse MGI accession and hit a wrong record (MGI:1913677 is Cyb5b, not Snf8). Do not curate MGI:1913677. The MGI ID for Snf8 must be looked up fresh before use. ZFIN quick-search returned 404 in this environment; the ZFIN ID likewise needs direct verification.

Breed (VBO)

Not applicable — no breed-associated natural disease.

Natural disease in other species

None known. No naturally occurring SNF8-related disease has been reported in companion animals, livestock, or wildlife. A targeted OMIA search returned no SNF8 entry. No veterinary relevance.

⚠️ Do not curate the following as animal disease models — they are incidental GWAS/biomarker associations in the SNF8-containing locus and are unrelated to this disorder: - Chicken carcass-weight GWAS (PMID:40211845) - Drosophila sleep/cardiac pleiotropy knockdown (PMID:40176577) - C. elegans longevity/DAF-16 (PMID:32829877) - Fathead minnow viral hemorrhagic septicemia proteomics (PMID:24931624) - Rat MASH models (PMID:40306176)

Comparative biology

Evolutionary conservation is strong and mechanistically meaningful. ESCRT-II is conserved from yeast to human: "ESCRT-II plays a pivotal role in receptor downregulation and multivesicular body biogenesis and is conserved from yeast to humans." The subunit architecture is preserved — yeast Vps22/Vps36/Vps25 ↔ human SNF8/VPS36/VPS25, with the same 1:1:2 stoichiometry and Y-shaped/trilobal fold (PMID:15329733; PMID:15469844; human structures PDB 2ZME, 3CUQ).

Comparative pathology: the human disease phenotype (CNS-restricted neurodevelopmental/neurodegenerative) is not recapitulated as a natural disease in any species. Yeast and invertebrate models display trafficking, gene-expression, and longevity phenotypes with no neurodevelopmental correlate — the yeast literature (glucose-dependent gene expression, Rim101/PMR1 calcium-pump regulation, PAF1-complex genetic interactions, flavor-ester biosynthesis) reflects conserved machinery in a non-conserved physiological context. Useful for structure–function, not for disease modeling.

Transmission

Not applicable — no zoonotic potential, no cross-species susceptibility, not communicable.

15. Model Organisms

Zebrafish (Danio rerio) — the primary in vivo disease model

Model type: vertebrate, morpholino (MO) antisense knockdown — ⚠️ transient knockdown, NOT a stable genetic mutant. This distinction matters for evidence weighting.

Recapitulated phenotypes (from the abstract, quotable):

"Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size."

Detailed findings: - Statistically significant global developmental delay, curly tail, reduced pigmentation, small head and eyes - Reduced brain area on confocal morphometry, "with variable phenotypes among morphant fish" - Ectopic proliferative (pH3+) cells within the forebrain, "partially rescued in fish expressing WT SNF8" → implicates dysregulated neural progenitor proliferation - Optic nerve: statistically significant reduction in extension and thickness, "which was rescued in fish co-injected with snf8 MO and WT SNF8"; reduced axonal scaffold - Optic chiasm: loss of the characteristic angle in morphants, restored by WT SNF8

Variant-specific rescue — the key pathogenicity and genotype–phenotype experiment: - WT SNF8 mRNA partially rescued the phenotype - Disease-variant allele pairs failed to rescue - Severity gradient mirrored the human poles:

"A more severe phenotypic impact in embryos coexpressing the SNF8 alleles encoding p.Tyr167Ter and p.Gly191Asp compared to those microinjected with alleles encoding p.Pro79Leu and p.Val102Ile was observed (approximately 95% vs. 70% aberrant embryos)."

Phenotype recapitulation quality — genuinely good for the axis that matters: the model reproduces (a) impaired optic nerve/chiasm development ↔ human optic atrophy/optic nerve hypoplasia, and (b) reduced forebrain size ↔ human microcephaly/reduced cerebral volume. Critically, it reproduces the allele-severity gradient, providing independent in vivo support for the p.Val102Ile-hypomorph model.

Limitations (curate honestly): 1. Morpholino, not a germline mutant — subject to well-known off-target/toxicity artifacts; no stable snf8 zebrafish mutant line is reported. Rescue experiments mitigate but do not eliminate this concern. 2. Does not model epilepsy — no seizure phenotype assessed; the DEE component is unmodeled 3. Does not model leukoencephalopathy or corpus callosum hypo-/aplasia — zebrafish lack a corpus callosum entirely 4. Does not model intellectual disability or the progressive postnatal neurodegenerative course 5. Variable penetrance among morphants ("reduced penetrance of morphological defects")

Recommended dismech treatment: curate zebrafish evidence with evidence_source: MODEL_ORGANISM, and add a kind: HUMAN_MODEL_MISMATCH discussion — not a generic KNOWLEDGE_GAP — since evidence exists in the model but its fidelity to the human phenotype is the open question (per the CLAUDE.md distinction: KNOWLEDGE_GAP = evidence absent; HUMAN_MODEL_MISMATCH = evidence exists but translational validity is uncertain). The specific mismatch: the zebrafish MO model captures the optic-nerve/forebrain developmental axis but captures none of the epileptic encephalopathy, callosal agenesis, or leukoencephalopathy that define the severe human pole.

Mouse (Mus musculus) — IMPC knockout

Retrieved live from the IMPC genotype-phenotype API for Snf8:

Zygosity	Phenotype	Parameter	p-value
Homozygote	Preweaning lethality, complete penetrance	Outcome	0.0
Heterozygote	Abnormal tail movements (tail elevation)	Tail elevation	4.17×10⁻⁵
Heterozygote	Increased lactate dehydrogenase level	Lactate dehydrogenase	2.57×10⁻⁵

Interpretation: Snf8 homozygous null is preweaning lethal with complete penetrance in mouse — consistent with an essential gene and concordant with the severity of the human biallelic-null phenotype (death in infancy in 3/4). This is a genuinely useful, independently-sourced cross-species datapoint.

Limitations: 1. Complete null lethality precludes study of the postnatal neurological phenotype — no viable homozygous mouse exists to phenotype for seizures, white matter, or optic nerve 2. No hypomorphic mouse allele exists — the human p.Val102Ile mild pole, which is the most clinically informative genotype, is entirely unmodeled in mouse. A knock-in Snf8 p.Val102Ile equivalent is the obvious highest-value missing model. Strong proposed_experiments candidate. 3. Heterozygous phenotypes (tail elevation, elevated LDH) have no clear human correlate — human heterozygous carriers (parents) are unaffected. Do not over-interpret. 4. No conditional, neural-specific, or humanized mouse model is reported.

⚠️ Verify the MGI accession for Snf8 directly before curating (my first lookup landed on Cyb5b).

Cellular / in vitro models

Patient-derived primary fibroblasts — the workhorse functional system (individuals A2 [severe], D1 and E1 [mild]); evidence_source: IN_VITRO: - Quantitative proteomics (ESCRT-II subunit quantification) - Transmission electron microscopy (autolysosome and aberrant lysosome accumulation) - LC3/LAMP1 confocal immunofluorescence - EGFR degradation assay (preserved — the cargo-specificity result)

Limitation: fibroblasts are not neurons. The disease is CNS-restricted, so the most disease-relevant cell types — cortical pyramidal neurons, oligodendrocytes, retinal ganglion cells — were not studied functionally. No iPSC, iPSC-derived neuron, organoid, or immortalized-line model is reported. This is a significant gap: iPSC-derived neurons and retinal organoids are the obvious next models, and were used in the comparable VPS4A work (PMID:33186545 studied "iPSC-derived human neurons"), showing the approach is tractable for ESCRT disorders.

MorPhiC: SNF8 is not among the MorPhiC anchor genes (ISL1, EOMES, GCM1, NKX2-1). No MorPhiC cellular phenotype data available.

Induced (non-genetic) models

None — no drug-induced, surgical, or environmentally induced model exists or would be meaningful for a monogenic trafficking defect.

Model databases to query

MGI (mouse — verify Snf8 accession), IMPC/mousephenotype.org (✅ data retrieved above), ZFIN (zebrafish — verify accession), FlyBase (Vps22), WormBase (vps-22), SGD (yeast SNF8), Alliance of Genome Resources (cross-species), IMSR/KOMP/EMMA/MMRRC (strain availability — ⚠️ not checked).

Appendix A — Curation notes on the existing draft entry

I found an untracked draft at kb/disorders/SNF8-Related_Neurodevelopmental_Disorder.yaml in this worktree. Five observations, most-actionable first:

updated_date should be removed. CLAUDE.md states plainly: "Do not add updated_date to new entries. The field is deprecated — git history is the authoritative change log." The draft sets updated_date: "2026-08-01T00:00:00Z".
Scope mismatch between the entry name and disease_term. The entry is named "SNF8-Related Neurodevelopmental Disorder" (spanning both poles) but binds disease_term to MONDO:0968947 (neurodevelopmental disorder plus optic atrophy = the mild pole only), and its description describes only "the milder end." The severe pole — DEE115, MONDO:0968946 / OMIM:620783 — carries 4 of 9 individuals and all the mortality, and is currently unrepresented. Two clean options:
(a) Keep one spectrum entry, use has_subtypes with Severe (DEE115) and Mild (NEDOA) as subtype names (short and slug-friendly per the naming convention), and add MONDO:0968946 under mappings:; or
(b) Split into two Disease entries and add a Grouping over them (grouping_basis: SHARED_GENE_FAMILY + SHARED_MECHANISM, with a NECESSARY HAS_GENE criterion on SNF8).

I'd recommend (a) — the poles are a genotype-graded continuum of one mechanism, not two diseases, and the has_subtypes foreign-key machinery lets phenotypes/prevalence/progression be attributed per pole.

No evidence: blocks anywhere in the draft. Every pathophysiology node, phenotype, and genetic claim needs an EvidenceItem. PMID_38423010.md is already in references_cache/ with the full abstract, so exact-quote snippets can be drawn from it immediately without a fetch. Verbatim snippets ready to use (all confirmed substrings of the cached abstract):
"All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile)."
"In patient-derived fibroblasts, bi-allelic SNF8 variants cause loss of ESCRT-II subunits."
"Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size."
"loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux"
"The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death."
hgnc:17028 is correct for SNF8 (lowercase prefix, per repo convention) — ✅ verified against the HGNC REST API.
The single pathophysiology node should be expanded into the causal chain in §6. The most valuable addition is the convergent hub node "Impaired Autophagic Flux" with biological_scale: CELLULAR, since that is the mechanistic claim the paper actually makes — and it should carry hypothesis_groups reflecting the authors' "likely via" hedge (a mechanistic_hypotheses entry with status: EMERGING).

Module conformance opportunity: no existing kb/modules/ module cleanly fits (ESCRT/autophagic-flux is not yet modeled; lysosomal_substrate_accumulation is a hydrolase-deficiency/substrate-storage module and is not the right anchor here — there is no stored substrate). Candidate future modules: an ESCRT/autophagic-flux failure module, or photoreceptor_degeneration's sibling for optic neuropathy. Worth noting there is a real gap rather than forcing a bad conforms_to.

Appendix B — Recommended `discussions` entries

`kind`	Prompt
`KNOWLEDGE_GAP`	Why is one gnomAD individual homozygous for p.Val102Ile apparently healthy? Is an unidentified modifier, a threshold effect, or incomplete phenotyping responsible?
`KNOWLEDGE_GAP`	What is the actual transcript consequence of c.423−1G>C (annotated `p.?`)? RNA-seq/RT-PCR on patient RNA would resolve it.
`KNOWLEDGE_GAP`	Why does F1 (p.Pro79Leu/p.Val102Ile) have congenital ataxia without optic atrophy, while D1/E1/E2 (same hypomorph) have optic atrophy without ataxia?
`KNOWLEDGE_GAP`	Is impaired autophagic flux the proximate cause of the neurological phenotype, or a correlated cellular readout? The causal link is hypothesized ("likely via"), not demonstrated in neurons.
`HUMAN_MODEL_MISMATCH`	The zebrafish morpholino model reproduces optic nerve and forebrain developmental defects but none of the epileptic encephalopathy, callosal agenesis, or leukoencephalopathy defining the severe human pole; and the mouse null is preweaning-lethal, precluding postnatal CNS phenotyping. Does any model system faithfully represent severe-pole human pathophysiology? Proposed experiments: stable `snf8` zebrafish germline mutant; conditional/neural-specific mouse KO; knock-in mouse or iPSC model of the p.Val102Ile hypomorph; patient iPSC-derived cortical neurons and retinal organoids.
`KNOWLEDGE_GAP`	Which ESCRT-II cargoes are selectively affected? EGFR degradation was preserved, implying cargo specificity, but the affected cargo set (notably lysosomal hydrolases) has not been identified.

Sources

Primary (disease-defining): - Brugger M, et al. Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy. Am J Hum Genet. 2024;111(3):594–613. PMID:38423010 · PMC full text · ScienceDirect

Mechanism / structural biology: - Teo H, et al. Structure of the ESCRT-II endosomal trafficking complex. Nature. 2004. PMID:15329733 - Hierro A, et al. ESCRT-II, an endosome-associated complex required for protein sorting: crystal structure and interactions with ESCRT-III and membranes. Dev Cell. 2004. PMID:15469844 - Structure and function of the ESCRT-II-III interface in multivesicular body biogenesis. Dev Cell. 2009. PMID:19686684 - RCSB PDB 2ZME — human ESCRT-II complex · PDB 3CUQ - UniProt Q96H20 — Vacuolar-sorting protein SNF8

Structured databases: - OMIM 620783 — DEE115 · OMIM 620784 — NEDOA · OMIM 610904 — SNF8 gene - ClinVar SNF8 variants (VCV002664478–VCV002664484) - HGNC:17028 (REST) - MONDO via EBI OLS4 — MONDO:0968946, MONDO:0968947 - HPO term verification via JAX HPO API - IMPC genotype-phenotype API — Snf8 - Genomics England PanelApp — SNF8 (Optic neuropathy, panel 186) · all SNF8 panel entries - GeneCards — SNF8

Verified unavailable (searched, nothing found): Orphanet ORPHA code · ClinicalTrials.gov trials · OMIA natural animal disease · MorPhiC data · published QoL/survival/prevalence statistics · GxE data · episignature data · any second clinical publication.

Not retrievable in this environment (do NOT populate from memory — fetch directly): gnomAD constraint metrics (pLI, o/e LoF) for SNF8 · DepMap essentiality · MGI accession for mouse Snf8 · ZFIN accession for zebrafish snf8 · OMIM full clinical synopses (omim.org returned HTTP 403).

Ask OpenScientist

OpenScientist Report

Classifications

Inheritance

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Differential Diagnoses

Source YAML

References & Deep Research

References

Deep Research

1. Disease Information

Overview

Key identifiers

Synonyms / alternative names

Evidence provenance type

2. Etiology

Disease causal factors

Genetic risk factors

Environmental risk factors

Protective factors

Gene–environment interactions

3. Phenotypes

Cohort structure (essential context for all frequencies below)

Severe pole (DEE115) — phenotype table

Mild pole (NEDOA + ataxia variant) — phenotype table

Neuroimaging phenotype detail

Quality-of-life impact

4. Genetic / Molecular Information

Causal gene

Pathogenic variants — complete published set (7 variants)

The p.Val102Ile hypomorphic allele — the genotype–phenotype linchpin

In silico support (from PMID:38423010)

Functional consequences — mechanism class

gnomAD constraint metrics

Modifier genes

Epigenetic information

Chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

Causal chain (proposed pathograph, upstream → downstream)

Molecular pathways

Cellular processes

Cargo selectivity — a mechanistically important negative result

Protein dysfunction

Metabolic changes

Immune system involvement

Tissue damage mechanisms

Biochemical abnormalities

Epigenetic changes

Molecular profiling

Suggested GO terms (✅ all verified live)

7. Anatomical Structures Affected

Organ level

Suggested UBERON terms (✅ verified — note label subtleties)

Tissue and cell level

Suggested CL terms

Subcellular level

Localization / lateralization

8. Temporal Development

Onset

Progression

Patterns

9. Inheritance and Population

Epidemiology

Inheritance

Population demographics

10. Diagnostics

Clinical tests

Genetic testing — the definitive route

Omics-based diagnostics

Clinical criteria

Differential diagnosis

Screening

11. Outcome / Prognosis

Survival and mortality

Appendix B — Recommended `discussions` entries