Skip to
  1. Homepage
  2. Rare diseases
  3. Search
Simple search

Simple search

(*) mandatory field


Other search option(s)

Methylmalonic acidemia with homocystinuria, type cblC

Synonym(s) CblC defect
Cobalamin C defect
Combined defect in adenosylcobalamin and methylcobalamin synthesis, type cblC
Methylmalonic aciduria with homocystinuria, type cblC
Prevalence Unknown
Inheritance Autosomal recessive
Age of onset All ages
  • E72.1
MeSH -
MedDRA -


Disease definition

cblC type methylmalonic acidemia with homocystinuria is a form of methylmalonic acidemia with homocystinuria (see this term), an inborn error of vitamin B12 (cobalamin) metabolism characterized by megaloblastic anemia, lethargy, failure to thrive, developmental delay, intellectual deficit and seizures.


To date, over 500 cases of cblC have been reported, making it the most frequent type of methylmalonic acidemia with homocystinuria.

Clinical description

The disease typically presents with failure to thrive, acute neurological deterioration, intellectual deficit, lethargy, seizures, microcephaly, a salt-and-pepper retinopathy, and signs of megaloblastic anemia (pallor, fatigue, anorexia). Severe brain abnormalities including hydrocephalus, white matter abnormalities, cerebral atrophy, and unusual basal ganglia lesions are common. Onset of the disorder can be early (infantile) or late (juvenile or adult), with the late-onset form characterized by ataxia, dementia and psychosis.


cblC type methylmalonic acidemia with homocystinuria is caused by mutations in the MMACHC gene (1p36.3) and is transmitted in an autosomal recessive manner.

Expert reviewer(s)

  • Dr David WATKINS

(*) Required fields.

Attention: Only comments seeking to improve the quality and accuracy of information on the Orphanet website are accepted. For all other comments, please send your remarks via contact us. Only comments written in English can be processed.

Captcha image

Detailed information

Clinical practice guidelines
Article for general public
Clinical genetics review
Get Acrobat Reader
The documents contained in this web site are presented for information purposes only. The material is in no way intended to replace professional medical care by a qualified specialist and should not be used as a basis for diagnosis or treatment.