Low levels of photoreactivating enzyme in xeroderma pigmentosum variants.

Abstract

XERODERMA pigmentosum (XP) is a recessive, hereditary disease in which patients develop malignancies on areas of skin exposed to sunlight1. Although fibroblasts from most XP individuals are deficient in excision repair of damage to DNA (classical XP), those from a few individuals (XP variants) having the usual clinical signs of XP seem to have normal excision capacity2. Photoreactivation is a DNA repair process in which the photoreactivating enzyme (PRE) monomerises pyrimidine dimers induced by ultraviolet light3. As PRE is present in normal human cells4, but only at reduced levels in classical XP cells5, we thought that the XP variants may also be defective in PRE activity. We therefore measured this activity in fibroblasts from four XP variants (Table 1) and found that Variants XP30RO, XP4BE, XP13BE, and XP7TA have 56, 11, 9, and 4% of the normal level of PRE activity, respectively.