Classical Homocystinuria in a Juvenile Patient.

Classical homocystinuria, also known as cystathionine beta synthase deficiency, is a rare disorder of methionine metabolism, leading to an abnormal accumulation of homocysteine and its metabolites in blood and urine. A young child with homocystinuria is discussed, who presented with behavioral abnormalities, involuntary movement, mental retardation, and decreased vision since birth. The diagnosis of homocystinuria was not made at initial presentation.