What is Methylmalonic Aciduria and Homocystinuria, cblC Type? Methylmalonic aciduria and homocystinuria is a metabolic disorder that affects the body's ability to process a protein called cobalamin (also known as vitamin B12). The most well-described and common form of the condition is type cblC. Type cblC is caused by harmful genetic changes (variants) in the MMACHC gene. Methylmalonic aciduria and homocystinuria, cblC type typically presents in newborns, though symptoms can develop at any age. Heart problems (such as dilated cardiomyopathy or congenital heart defects), a buildup of excess fluid in the body and tissues (hydrops fetalis), and poor fetal growth (IUGR) may present prenatally. Infants and children may have a small head size (microcephaly), poor feeding and growth (failure to thrive), anemia, low muscle tone (hypotonia), eye abnormalities, and seizures. Developmental delays and intellectual disability are also common in younger individuals. Individuals who present with symptoms later in life, such as adolescents and adults, may develop confusion, mental illness, cognitive decline, and anemia. How common is Methylmalonic Aciduria and Homocystinuria, cblC Type? The incidence of methylmalonic aciduria and homocystinuria, cblC type in the population is 1 in 100,000 births. How is Methylmalonic Aciduria and Homocystinuria, cblC Type treated? There is no cure for methylmalonic aciduria and homocystinuria, cblC type. Individuals experiencing a severe episode of illness (metabolic crisis) should be stabilized and seen by a metabolic specialist. 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 frequently (at least 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 an individual 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. Treatment may improve but not prevent symptoms of the disease. Benefits of methylmalonic aciduria and homocystinuria, cblC type Carrier Screening (Genetic Testing) Carrier screening is an important form of genetic testing for those who may be at risk of passing methylmalonic aciduria and homocystinuria, cblc type to their baby. Carrier Screening for methylmalonic aciduria and homocystinuria, cblc type can help in identifying that risk. The Foresight® Carrier Screen helps clinicians guide care and empowers patients to take action to make the best decision for their families. Learn more about the Foresight® Carrier Screen} by Myriad Genetics. Other names formethylmalonic aciduria and homocystinuria, cblC type Disorders of intracellular cobalamin metabolism Methylmalonic aciduria (cobalamin deficiency) cblC type, with homocystinuria cblC References 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