Cobalamin X (Methylmalonic Acidemia and Homocysteinemia, cblX Type)
Methylmalonic acidemia and homocysteinemia, cblX type, is an X-linked recessive metabolic disorder characterized by severely delayed psychomotor development apparent in infancy. It is associated with failure to thrive, mental retardation, and intractable epilepsy. Additional features may include microcephaly and choreoathetosis (summary by Yu et al., 2013).
Reference: Organic Acidemia Association