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. Subtle phenotypic features with developmental delay and MRI brain finding of bilateral medially dislocated lens, eventually provided the first indication at five years of age. Laboratory screening with plasma amino acid profile by ion exchange chromatography (IEC) showed elevated homocystine and methionine, and low cystine in plasma in the absence of vitamin B12, and folate deficiency; giving the diagnosis of classical homocysteinuria.