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Start free with EleplanVitamin B12-unresponsive methylmalonic acidemia
ORPHA:27Disease
Also called Methylmalonyl-CoA mutase deficiency · Methylmalonyl-Coenzyme A mutase deficiency · Vitamin B12-unresponsive methylmalonic aciduria
What it is
Vitamin B12-unresponsive methylmalonic acidemia is an inborn error of vitamin B12 (cobalamin) metabolism characterized by recurrent ketoacidotic crises or transient vomiting, dehydration, hypotonia and intellectual deficit, which does not respond to administration of vitamin B12. There are two types of vitamin B12-unresponsive methylmalonic acidemia: mut0 and mut-.
Key facts
- Age of onset
- Childhood, Infancy, Neonatal
- Inheritance
- Autosomal recessive
- Classified as
- Disease
Recorded for the broader condition
- Prevalence
- 1-9 / 100 000 (Europe)Methylmalonic acidemia without homocystinuria
Orphanet records these for the broader condition rather than for this specific form. They are a starting point, not a figure for this subtype — subtypes often differ, and some are defined by being rarer than the condition they sit under.
Signs and symptoms
Common30–79%
6Sometimes5–29%
14- Abnormality of speech or vocalization
- Anemia
- Ataxia
- Cardiomyopathy
- Choreoathetosis
- Hyperammonemia
- Immunodeficiency
- Macrocytic anemia
and 6 more in this range
These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
Genes reported in subtypes
Orphanet records this gene on 2 more specific entries under this disorder, not on this entry itself:
A well-studied disease is usually split into subtypes, and the gene is curated on whichever one the evidence belongs to. Open a subtype to see which gene goes with it.
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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