IEMbase 0083: AMN-related amnionless deficiency
Scope
| Field | Value |
|---|---|
| IEMbase ID | 83 |
| Nosology | 21.9.03.01 |
| Gene | AMN |
| External IDs | OMIM:261100 |
| Generated mapping | UNMAPPED |
| Candidate DisMech targets | Best fuzzy candidate Hereditary_Orotic_Aciduria.yaml#Type III |
| Review date | 2026-07-07 |
IEMbase phenotype signal
IEMbase represents this as autosomal recessive AMN-related amnionless deficiency, with alternate labels Najman-Imerslund-Grasbeck syndrome due to AMN, megaloblastic anemia-1 Norwegian type, and IGS. The prevalence field records about 1:200,000 in Finland and Norway. Treatability is marked yes.
The characteristic biochemical signal includes low plasma vitamin B12, elevated plasma and urinary methylmalonic acid, urinary homocysteine, and elevated total plasma homocysteine. Additional rows include total plasma protein.
Characteristic clinical rows include megaloblastic anemia, anorexia, apathy, psychotic behavior, dementia, failure to thrive, and irritability.
The treatment row is cobalamin.
DisMech phenotype coverage
No standalone DisMech entry for Imerslund-Grasbeck syndrome, amnionless deficiency, or AMN-related inherited cobalamin malabsorption was found.
Hereditary_Intrinsic_Factor_Deficiency.yaml includes differential context for
AMN: it distinguishes CUBN or AMN receptor defects causing
Imerslund-Grasbeck syndrome from CBLIF/GIF intrinsic factor deficiency. This is
not sufficient to count as disease coverage for AMN deficiency.
The best fuzzy candidate, Hereditary_Orotic_Aciduria.yaml#Type III, is a false
positive. The shared features are megaloblastic anemia and failure to thrive,
but the mechanisms and diagnostic biochemical signatures are different.
Concordance and completeness
Judgement: true local gap.
This record should be handled together with the CUBN IGS record. AMN also collides textually with "adrenomyeloneuropathy" in unrelated X-linked adrenoleukodystrophy content, so future mapping should key on AMN as the gene and Imerslund-Grasbeck as the disease context.
Curation actions
- Keep this IEMbase record unmapped for now.
- Add a future Imerslund-Grasbeck syndrome entry or grouping with AMN and CUBN subtype coverage.
- Include cobalamin treatment and the cobalamin-malabsorption biochemical panel when the entry is curated.