Xeroderma pigmentosum.

Xeroderma pigmentosum is a rare, recessively transmitted disease associated with increased sensitivity to ultraviolet radiation in wavelengths found in sunlight, development of cancers in sun-exposed areas of the body in much larger numbers and much earlier in life than in normal individuals, and in some patients, neurologic deficiencies unrelated to sun exposure. Extensive cellular, biochemical, and molecular genetic studies in numerous laboratories have revealed that cells derived from patients with this disease have defective repair of ultraviolet-light-induced damage in cellular DNA, and that extensive genetic heterogeneity and numerous distinct genes are involved in the genetics of this disease and the etiopathogenesis of its associated changes. A number of these genes and gene products are now being, or have been, cloned, and their gene products characterized.