IEMbase 0036: ABAT-related GABA transaminase deficiency
Scope
| Field | Value |
|---|---|
| IEMbase ID | 36 |
| Nosology | 23.2.05.01 |
| Gene | ABAT |
| External IDs | OMIM:137150; OMIM:613163 |
| Generated mapping | UNMAPPED; best fuzzy candidate Generalized_Epilepsy_with_Febrile_Seizures_Plus.yaml |
| Candidate DisMech targets | none currently valid |
| Review date | 2026-07-07 |
IEMbase phenotype signal
IEMbase represents ABAT deficiency as a GABA-catabolism disorder upstream of succinic semialdehyde dehydrogenase. Biochemical markers include increased GABA by MRS, increased free CSF GABA, increased CSF beta-alanine, increased CSF homocarnosine, and increased growth hormone.
The clinical signal is a severe developmental and epileptic encephalopathy: psychomotor delay, seizures, feeding difficulties, hypotonia, lethargy, high-pitched cry, spasticity, increased tendon reflexes, accelerated growth, and diffusion restriction in the internal capsule, external capsule, and subcortical white matter on MRI. IEMbase lists flumazenil as a pharmacologic intervention.
DisMech phenotype coverage
There is no current DisMech entry or subtype for ABAT-related GABA transaminase
deficiency. The generated fuzzy candidate,
Generalized_Epilepsy_with_Febrile_Seizures_Plus.yaml, should be rejected.
GEFS+ is a familial epilepsy/channelopathy spectrum involving sodium-channel,
GABA-A receptor subunit, and synaptic genes such as GABRD; it is not an ABAT
enzyme defect.
Succinic_Semialdehyde_Dehydrogenase_Deficiency.yaml is a pathway neighbor in
GABA catabolism, but it is not the same disease. SSADH deficiency is caused by
ALDH5A1 and has GHB/4-hydroxybutyrate accumulation as a core diagnostic signal,
whereas ABAT deficiency is anchored by GABA transaminase loss and elevated GABA,
homocarnosine, beta-alanine, and growth hormone.
Concordance and completeness
Judgement: generated unmapped status is correct. The GEFS+ candidate is a misleading GABA-related lexical/pathway match, not a disease-entity match.
IEMbase provides a strong future curation outline for ABAT deficiency, including the distinctive biochemical panel, growth phenotype, and early MRI diffusion restriction pattern. DisMech currently lacks valid local phenotype coverage for this disease.
Curation actions
- Do not map this record to GEFS+ or to SSADH deficiency.
- Consider ABAT deficiency as a future GABA-catabolism curation target adjacent to, but separate from, SSADH deficiency.
- If curated, preserve the flumazenil treatment note and the growth hormone / accelerated-growth signal because these help distinguish ABAT deficiency from other epilepsy-metabolism disorders.