Dietary therapy in two patients with a mild form of sulphite oxidase deficiency. Evidence for clinical and biological improvement.

We report an attempt at dietetic therapy in two unrelated patients with isolated sulphite oxidase deficiency, with a mild clinical course and late onset of symptoms. In case 1, disease started at 15 months with an acute crisis of agitation, unexplained crying and restlessness following otitis. Case 2 was diagnosed at 10 months when she presented with slight motor delay and dislocation of lenses. In both cases, sulphite oxidase activity measured in fibroblasts was undetectable. Therapy consisted of a diet low in protein from natural foods (daily methionine intake 130-150 mg) and a synthetic amino acid mixture (50 g per day) without cystine and methionine (Xmet, Cys Maxamaid, SHS International Ltd). A comparison of clinical and biochemical parameters was made between the period before treatment and after 2 years of treatment. Restriction in protein and sulphur amino acids brought about a dramatic decrease of urinary thiosulphate and S-sulphocysteine. It also brought about a generalized hypoaminoacidaemia with a low plasma methionine and cystine in both patients. Furthermore, both patients grew normally with no signs of neurological deterioration, and there was evidence of progress in psychomotor development.