Xeroderma pigmentosum (XP) is an autosomal recessive photosensitive disorde
r with an extremely high incidence of UV-related skin cancers associated wi
th impaired ability to repair UV-induced DNA damage. There are seven nucleo
tide excision repair (NER) complementation groups (A through G) and an MER
proficient form (XP variant). XPA, B, D and G patients may also develop XP
neurological disease. The laboratory diagnosis of XP can be performed by au
toradiography. Recently, the isolation and characterization of the genes re
sponsible for XP have made it possible to use molecular biological techniqu
es to diagnose XP patients, for carrier detection and for prenatal diagnosi
s, especially in Japanese XPA patients. These techniques include polymerase
chain reaction (PCR) and plasmid host cell reactivation assays with cloned
XP genes. DNA damage is not repaired by the NER system equally throughout
the genome. There are two DNA repair pathways: 1) transcription-coupled rep
air, and 2) global genome repair. Many factors involved in these pathways a
re related to the pathogenesis of XP and a related photosensitive disease,
Cockayne syndrome. Clinical management consists of early diagnosis followed
by a rigorous program of sun protection including avoidance of unnecessary
UV exposure, wearing UV blocking clothing, and use of sunblocks on the ski
n. Although there is no cure for XP, the efficacy of oral retinoids for the
prevention of new skin cancers, local injection of interferon, and the ext
ernal use of a prokaryotic DNA repair enzyme have been reported.