Enzyme defects in xeroderma pigmentosum.

Fibroblast strains were obtained from 12 patients with xeroderma pigmentosum of various clinical types. Repair replication of UV-damaged DNA in the fibroblasts was studied by 3H-thymidine labeling and radioautography. DNA repair replication was found decreased in all xeroderma pigmentosum fibroblasts compared with control cells obtained from normal donors. Repair activities in patients cells ranged from nearly 0% in three infant cases and two cases of De Sanctis-Cacchione syndrome to approximately 100% in an adult moderate case. There was, however, no correlation between the level of repair replication and the severity of clinical symptoms. Since three cases which showed a lack of repair DNA replication were infants, it is assumed that these cases may develop De Sanctis-Cacchione syndrome in the future. A genetic analysis of xeroderma pigmentosum cells, was performed with cell fusion methods using irradiated HVJ virus in order to determine the type of the complementation group. XP-1, XP-3, XP-4, XP-6 and XP-9 may be classified into group D; XP-2, XP-7, XP-8, XP-11 and XP-12 into group A; and XP-5 into the group E.