Homocystinuria: Studies on cystathionine β‐synthase,S‐adenosylmethionine synthetase and cystathionase activities in skin fibroblasts

Cystathionine β‐synthase,S‐adenosylmethionine synthetase and cystathionase activities were assayed in skin fibroblast cultures from five pyridoxine responsive and five pyridoxine non‐responsive homocystinurics, six obligate heterozygotes for homocystinuria and ten normal control subjects. The specific deficiency in cystathionine β‐synthase activity was confirmed in nine of the homocystinuric cultures. However, in one pyridoxine responsive case the level of cystathionine β‐synthase activity was found to be comparable with those of the heterozygotes. A negative correlation appeared to exist between the level of residual enzyme activity and the pre‐treatment severity of clinical symptoms.