An HPLC assay for detection of elevated urinary S ‐sulphocysteine, a metabolic marker of sulphite oxidase deficiency

Summary Sulphite oxidase deficiency occurs in man in two forms, as the isolated deficiency and as a syndrome of combined molybdoenzyme deficiency. This latter pleiotropic condition has as its underlying cause a defect in the synthesis of the molybdenum cofactor required for the activity of all molybdoenzymes in humans. Difficulties in diagnosis of sulphite oxidase deficiency are often encountered. A new method for detection of a key diagnostic metabolite, S ‐sulphocysteine, is outlined. The procedure is based on precolumn derivatization of urinary amino acids with dimethylaminoazobenzene sulphonyl chloride (Dabsyl‐Cl) and resolution of the modified S ‐sulphocysteine by reversed‐phase HPLC. A number of affected patients and control individuals with similar clinical symptoms have been studied, and a clear demarcation between the two groups has been noted.