Defective DNA excision repair in cells of patients with homocystinuria.

Fibroblasts obtained from biopsied material and lymphocytes from patients with homocystinuria were studied for repair activity using the criterion of repair of DNA breaks induced by 4-nitroquinoline 1-oxide and gamma-irradiation and criteria of reactivation and induced mutagenesis of vaccinia virus. Lymphocytes showed defective DNA repair for all these criteria. In fibroblast cultures, the inhibition of cell-repair activity for the gamma-type was retained. The number of spontaneous and gamma-induced virus mutations increased as passaging of fibroblasts proceeded.