Sulfite oxidase deficiency. Biochemical and clinical investigations of a hereditary metabolic disorder in sulfur metabolism.

Study of a 4 1/2-year-old boy with the unusual combination of acute infantile hemiplegia, ectopia lentis and the absence of homocystinuria showed large amounts of abnormal sulfur-containing metabolites (sulfite, thiosulfate and S-sulfocysteine) in the urine. Sulfite and S-sulfocysteine were also present in the plasma. His inorganic sulfate excretion was only 50 per cent of total sulfur, as compared with 75 to 95 per cent by controls. Loading with L-cysteine hydrochloride and L-methionine further increased the excretion of sulfite and thiosulfate, but not inorganic sulfate excretion. Sulfite oxidase activity in skin fibroblasts average 1.07 nmol of cytochrome d reduced per milligram of protein per minute in control lines; it was not detectable (less than 5 per cent) in the patient. Activity was reduced in both parents (0.50 in the father and 0.32 in the mother)--compatible with autosomal recessive inheritance. Good biochemical responses to a low sulfur amino acid diet suggest that early treatment may benefit the patient.