[Sulfite oxidase deficiency presenting as Leigh syndrome]

An enzyme deficiency can be demonstrated in 15 to 20% of cases of Leigh syndrome. A case of isolated sulphite oxidase deficiency is reported in a girl presenting with Leigh syndrome.

An 8 month-old girl was admitted suffering from hypotonia and slow increase of head circumference (-1 SD). Examination showed spastic quadriplegia, dyskinesia, axial hypotonia and difficulties in swallowing. The patient had a coarse face, broad nasal bridge, long philtrum and ectopia lentis. Brain CT scan showed bilateral hypodensity of lenticular nuclei and moderate cortical atrophy. Amino acid chromatography showed accumulation of S sulfocysteine and low levels of cysteine. The sulphite test was positive. Sulphite oxidase activity in fibroblasts and liver was undetectable contrasting with a normal activity of xanthine oxidase. Progressive brain damage led to death at 1 year of age. Prenatal diagnosis of sulphite oxidase deficiency was made in two further pregnancies.

The search for sulphite oxidase deficiency must be included in discussing the etiology of Leigh syndrome; the sulphite test is a simple method of screening such cases.