Xeroderma pigmentosum complementation group G--report of two cases.

Genetic complementation studies allowed assignment of a brother (XP124LO) and sister (XP 125LO), aged 14 and 12 years respectively, to the rare complementation group of classical xeroderma pigmentosum (XP), XP-G. Both patients manifested only mild cutaneous changes, with no UV-induced skin tumours, although abnormal sensitivity to UVB wavelengths was demonstrated by irradiation monochromator skin testing. Physical and neurological development was normal. Measurement of UV-induced unscheduled DNA synthesis in cultured fibroblasts showed reduction of repair synthesis to 14% and 16% of normal in XP124LO and XP125LO, respectively. This contrasts with a reduction to 5% of normal in previously described group G patients, XP2BI and XP3BR, who had correspondingly severe cutaneous and neurological manifestations.