This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Methylmalonic acidemia and homocysteinemia type cblX, is an inborn error of vitamin B12 (cobalamin) metabolism in which the body is unable to break down (metabolize) certain proteins and fats properly. It is characterized by severe delays of motor (movement) and neurological (brain) development starting in infancy. Defects in cobalamin metabolism are characterized by a buildup of methylmalonic acid and/or homocysteine in the blood and urine. There are several other types of combined methylmalonic acidemia and homocysteinemia disorders, including cblC, cblD, cblF and cblJ.
Signs and symptoms of methylmalonic acidemia and homocysteinemia type cblX may include difficulties with weight gain (failure to thrive), intellectual disability, and intractable (uncontrolled) epilepsy. Additional features may include a very small head (microcephaly), brain malformations, and movement disorders. This condition is caused by mutations in the HCFC1 gene, is inherited in an X-linked recessive manner, and is usually seen in males. Mutations within the HCFC1 gene affect another gene known as MMACHC, which is related to the most common defect of cobalamin disorder, cblC. There is no cure for this condition. In general, individuals with methylmalonic acidemia and homocystinuria may respond to a combined treatment strategy including supplementation of nutrients, such as a hydroxycobalamin, betaine, folic acid, vitamin B6 and L-carnitine.
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