Do we know the cause of xeroderma pigmentosum?

DNA repair in mammals consists of a large family of genes that encode a variety of mutually interacting gene products. These gene products coordinately locate and prepare damaged sites in chromatin for eventual excision and replacement and interact with transcriptionally active and replicating regions. Subsets of repair genes are represented by the complementation groups of xeroderma pigmentosum (XP), Cockayne syndrome, trichothiodystrophy and the ERCC series, which overlap one another to varying degrees. Cloned DNA sequences or whole chromosomes correct the UV-sensitive phenotype of XP by only 6-50%, which may be informative for the precise mechanisms of complementation and repair and for the relative importance of various UV photoproducts. Repair deficiencies in vivo are associated with increases in the toxic effects of UV damage and chronic expression of damage-inducible genes, with consequent implications for viability, development, neurological and immunological function, and carcinogenesis.