Manic-depressive Psychosis as the Initial Symptom in Adult Siblings with Late-onset Combined Methylmalonic Aciduria and Homocystinemia, Cobalamin C Type

Methylmalonic aciduria (MMA) is an autosomal recessive disorder of cobalamin (cbl) metabolism. Cobalamin C (cblC) disease is the most common type of MMA and is characteristically concurrent with homocystinemia (HCY) due to impaired synthesis of two active forms of cbl, namely adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). The estimated worldwide incidence of MMA ranges between 1:48,000 and 1:250,000.[1] Mutations of the MMA and HCY type C protein (MMACHC) gene are responsible for cblC disease and were first identified by Lerner‐Ellis et al. in 2006.[2] By the year 2016, more than 82 different MMACHC gene mutations have been reported (http:// www.hgmd.cf.ac.uk/ac/index.php). Among these mutations, c.609G>A (p.W203X) was reported to be the most frequent cblC mutation in Chinese patients.[3]