Clinical, genetic and DNA repair studies on a consecutive series of patients with xeroderma pigmentosum.

We report clinical, genetic and biochemical findings in 13 families with the photosensitive genodermatosis, xeroderma pigmentosum. All patients had a defect in repair of DNA damage provoked by ultraviolet radiation. Eleven patients and their three affected sibs were defective in the excision repair of UVR induced DNA lesions while the other two were defective in post-replication repair. One in the former group was diagnosed prior to the development of permanent skin abnormalities and preventive measures succeeded for almost five years in maintaining a normal appearing skin. In addition, two cases were diagnosed prenatally and aborted therapeutically. Some patients' parents showed slightly reduced repair of UVR induced DNA damage. In xeroderma pigmentosum (XP), the defect in the excision of DNA lesions appears to be due to homozygosity for one of at least seven different mutations and, accordingly, XP patients can be assigned to seven so-called complementation groups, A to G. Of these, groups A, C and D are the most common. Somatic cell fusion allowed three of the families reported here to be assigned to group A, four to group C and four to group D. Fibroblasts of patients from these three groups were shown to differ not only in the degree and kinetics of their residual DNA repair but also in the kinetics with which their defect is complemented by fusion with normal or XP cells of other groups. This confirms that mutations of different genes play a role in XP and provides a basis for understanding how such genes interact to secure repair of DNA lesions in normal cells. We discuss the phenotype of XP from different complementation groups in relation to the severe neurological abnormalities which may develop and must be considered in genetic counselling. We also discuss the biochemical anomalies of XP and the cellular effects of physical and chemical agents which damage DNA. In the practical management of XP, the importance of early differential diagnosis and prompt initiation of treatment is emphasized. Lastly we review the relationship between DNA repair and skin cancer in XP.