IEMbase 0087: MMAB-related methylmalonic aciduria, cblB type
Scope
| Field | Value |
|---|---|
| IEMbase ID | 87 |
| Nosology | 21.9.15.01 |
| Gene | MMAB |
| External IDs | OMIM:251110 |
| Generated mapping | MAPPED by alias_exact:cblb |
| Candidate DisMech targets | Inborn_Disorder_of_Cobalamin_Metabolism_and_Transport.yaml#cblB |
| Review date | 2026-07-07 |
IEMbase phenotype signal
IEMbase represents this as autosomal recessive MMAB-related methylmalonic aciduria, vitamin B12-responsive cblB type. Treatability is marked yes.
The characteristic clinical rows include acidosis, dehydration, acute encephalopathic crisis, failure to thrive, ketosis, life-threatening illness, and vomiting.
The biochemical panel includes elevated urinary and plasma methylmalonic acid, urinary methylcitric acid, urinary 3-hydroxypropionic acid, C3 propionylcarnitine in blood or plasma, C3 acylcarnitine ratios, ammonia, anion gap, lactate, total plasma homocysteine, and free carnitine in dried blood spot or plasma.
Treatment rows include antibiotics, avoidance of fasting, carnitine, hemodialysis, hydroxycobalamin, liver and/or kidney transplantation, carglumic acid, peritoneal dialysis, protein-defined diet, sick-day management, and sodium benzoate.
DisMech phenotype coverage
The generated mapping to
Inborn_Disorder_of_Cobalamin_Metabolism_and_Transport.yaml#cblB is correct.
DisMech models cblB as an MMAB subtype impairing adenosylcobalamin synthesis and producing isolated methylmalonic acidemia. The cobalamin umbrella covers the adenosylcobalamin branch, impaired methylmalonyl-CoA mutase activity, elevated methylmalonic acid, and hydroxocobalamin-based treatment context.
Methylmalonic_Acidemia.yaml is also relevant secondary coverage. It explicitly
lists MMAB as the cblB complementation group, notes that cblB-type MMA tends to
be more severe than cblA-type, and covers acute decompensation,
propionylcarnitine, methylcitric acid, hyperammonemia, chronic MMA
complications, protein-restricted diet, carnitine, hydroxocobalamin, crisis
management, and transplantation.
Concordance and completeness
Judgement: correct mapping and high concordance.
The direct subtype target is the cobalamin umbrella. The isolated MMA entry is useful for severity and management details. IEMbase adds granular emergency and dialysis rows, plus carglumic acid and sodium benzoate, that are not all enumerated in the local cblB subtype.
Curation actions
- Keep the generated mapping to
Inborn_Disorder_of_Cobalamin_Metabolism_and_Transport.yaml#cblB. - Treat
Methylmalonic_Acidemia.yamlas important secondary context for phenotype and management coverage. - No separate MMAB-only file is needed unless isolated MMA is later split by complementation group.