What is Methylmalonic Aciduria and Homocystinuria, cblC Type?

Methylmalonic aciduria and homocystinuria, cblC type is a metabolic disorder that affects the body's ability to process a protein called cobalamin. Cobalamin is also known as vitamin B12. The most well-described form of methylmalonic aciduria and homocystinuria is type cblC, or methylmalonic aciduria and homocystinuria, cblC type; it is also the most common of these disorders.

The age of initial presentation of cblC ranges from (1) newborns who can be small for gestational age with unusually small head size; to (2) infants who can have poor feeding, failure to thrive, and neurologic/developmental abnormalities; to (3) toddlers who can have failure to thrive, poor head growth, developmental delay, low muscle tone, and seizures; and to (4) young adults/adults who may develop confusion, mental illness, cognitive decline, and anemia.

How common is Methylmalonic Aciduria and Homocystinuria, cblC Type?

The estimated incidence is estimated to be approximately 1 in 100,000 births.

How is Methylmalonic Aciduria and Homocystinuria, cblC Type treated?

Currently, there is no treatment that cures or alleviates all the symptoms of methylmalonic aciduria and homocystinuria, cblC type. Critically ill individuals must be stabilized, preferably in consultation with a metabolic specialist, by treating their metabolic disease. Dietary modifications may improve symptoms and gastrostomy tube placement for feeding is often required. Seizures are treated using standard protocols. Medications have proven effective in some cases.

During the first year of life, infants may need to be evaluated once or twice a month. Routine medical care should include special attention to growth and development; neurologic evaluation for early signs of delay, behavioral disturbances, and seizures; and ophthalmologic evaluation for retinal and optic nerve changes. Prolonged fasting and excessive dietary protein intake should be limited.

What is the prognosis for a person with Methylmalonic Aciduria and Homocystinuria, cblC Type?

Some affected individuals have early and severe symptoms, while others reach adulthood without evidence of ongoing disease progression. In some cases, severe neurologic symptoms and/or cognitive impairment persist. It is difficult to discern whether or not such impairments are due to the disease progression prior to treatment or ongoing neurological decline.

Other names for
methylmalonic aciduria and homocystinuria, cblC type

  • Disorders of intracellular cobalamin metabolism
  • Methylmalonic aciduria (cobalamin deficiency) cblC type, with homocystinuria
  • cblC


  • Bell et al., 2011, Sci Transl Med, 3(65):65, PMID: 21228398
  • Berg et al., 2013, Genet Med, 15(1):36-44, PMID: 22995991
  • Carrillo-Carrasco, 2013, http://www.ncbi.nlm.nih.gov/books/NBK1328/
  • Enns et al., 1999, J Inherit Metab Dis, 22(5):599-607, PMID: 10399092
  • Huemer et al., 2005, J Pediatr, 147(4):469-72, PMID: 16227032
  • Lerner-Ellis et al., 2006, Nat Genet, 38(1):93-100, PMID: 16311595
  • Liu et al., 2010, J Hum Genet, 55(9):621-6, PMID: 20631720
  • Patton et al., 2000, Ophthalmic Genet, 21(3):151-4, PMID: 11035547
  • Richard et al., 2009, Hum Mutat, 30(11):1558-66, PMID: 19760748
  • Smith et al., 2006, Mol Genet Metab, 88(2):138-45, PMID: 16574454