Methylmalonic acidemia (MMA) is the most common organic acidemia in Asian cases. We report a 14-year-old boy who was admitted to psychiatric clinic with affective symptoms. MMA was diagnosed after extensive laboratory tests. This emphasizes that even a typical psychiatric disorder can actually represent part of the spectrum of an underlying systemic disorder. MMA is an autosomal-recessive inborn error of metabolism. The incidence might be as high as 1 in 25,000. It is believed that this disease is more prevalent in the Middle East because of consanguineous marriages. MMA usually presents clinically with nonspecific symptoms such as seizure, poor feeding, loss of consciousness, psychomotor retardation. As a consequence, patients often undergo extensive work-up before the correct diagnosis is made. MMA is usually diagnosed in the first year of life. however, this report deals with a patient whose disease could not be diagnosed until the age fourteen.

The most common phenotype features appear during infancy. Rare patients may present as adolescents or adults with CNS disease. Our patient had episodes of confusion and mood lability which could be related to metabolic decompensation episodes. When a patient has been labeled as having a psychiatric illness, other general medical conditions (especially rare diseases) might be ignored. This emphasizes that even a typical psychiatric disorder can actually represent part of the spectrum of an underlying systemic disorder.