Studies in this laboratory are designed to elucidate the role of DNA repair processes in human diseases and in carcinogenesis and in normal and abnormal aging. Most studies have been conducted with cells from patients with xeroderma pigmentosum (XP) who have defective DNA repair plus multiple cutaneous malignancies and premature aging of sun-exposed skin and of the nervous system. Cells from patients with diseases with abnormal cell growth and differentiation, and with primary neuronal, muscular, and retinal degenerations are also being studied. These diseases include ataxia telangiectasia, Alzheimer disease, Parkinson disease, Hungtinton disease, Duchenne muscular dystrophy, retinitis pigmentosa, and Cockayne syndrome. These studies are designed to elucidate the pathogenesis of these disorders. We assess the biological effectiveness of DNA repair primarily by in vitro assays of cell survival after treatment of the cells with the DNA damaging agents. We search for DNA damage by extracting the DNA and having it subjected to analysis by capillary gas chromatography-mass spectrometry.