Sulphite oxidase deficiency--a report of two siblings.

Isolated sulphite oxidase deficiency is a rare metabolic disorder characterised by neurological abnormalities, lens subluxation and seizures. Inheritance is autosomal recessive. We report two siblings with onset of clinical symptoms at 6 months of age, progressing to severe mental retardation, spasticity and seizures which were difficult to control. One of the siblings had lens subluxation. Diagnosis is made upon the increased levels of urinary sulphite, and high plasma S-sulphocysteine and thiosulphate levels. No treatment is known to be of help. Prenatal diagnosis is possible from the analysis of uncultured chorionic villus material for sulphite oxidase.