Xeroderma pigmentosum complementation group G associated with Cockayne's syndrome.

Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are two rare inherited disorders with a clinical and cellular hypersensitivity to the UV component of the sunlight spectrum. Although the two traits are generally considered as clinically and genetically distinct entities, on the biochemical level a defect in the nucleotide excision-repair (NER) pathway is involved in both. Classical CS patients are primarily deficient in the preferential repair of DNA damage in actively transcribed genes, whereas in most XP patients the genetic defect affects both "preferential" and "overall" NER modalities. Here we report a genetic study of two unrelated, severely affected patients with the clinical characteristics of CS but with a biochemical defect typical of XP. By complementation analysis, using somatic cell fusion and nuclear microinjection of clo