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Vitamin B12-unresponsive methylmalonic acidemia type mut-

Synonym(s) Partial deficiency of methylmalonyl-CoA mutase
Vitamin B12-unresponsive methylmalonic aciduria type mut-
Prevalence Unknown
Inheritance Autosomal recessive
Age of onset Infancy
  • E71.1
MeSH -
MedDRA -


Disease definition

Vitamin B12-unresponsive methylmalonic acidemia type mut- is an inborn error of metabolism characterized by recurrent ketoacidotic comas or transient vomiting, dehydration, hypotonia and intellectual deficit, which does not respond to administration of vitamin B12.


Prevalence of this form of the disorder is not known. More than 450 cases have been reported to date.

Clinical description

The disease typically presents very early in life (<1 to 4 weeks), although later onset cases have been observed, with features including lethargy, failure to thrive, recurrent vomiting, dehydration, respiratory distress, muscle hypotonia, developmental delay, intellectual deficit, hepatomegaly and coma. Patients may show signs of anemia. They may also have potentially life-threatening ketoacidosis and/or hyperammonemia, renal and neurological complications, metabolic stroke and cardiomyopathy. mut- is generally less severe than vitamin B12-unresponsive methylmalonic acidemia type mut0 (see this term) and may in some cases respond to vitamin B12 therapy. Long term complications include metabolic stroke and development of end stage renal failure. These complications are more frequent in mut0 than in mut-.


The disease is caused by partial deficiency in the activity of the mitochondrial vitamin B12-dependent enzyme methylmalonyl-CoA mutase which is a result of mutations in the MUT gene (6p21).

Genetic counseling

It is transmitted as an autosomal recessive trait.

Expert reviewer(s)

  • Dr David WATKINS

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