Complementation studies in cells from patients affected by trichothiodystrophy with normal or enhanced UV photosensitivity.

A normal level of UV-induced DNA-repair synthesis (UDS) was observed in fibroblasts from a patient affected by trichothiodystrophy (TTD) without photosensitivity. This finding indicates that the hypersensitivity to UV light and the reduced UDS due to the presence of xeroderma pigmentosum complementation group D mutation (XP-D), described in photosensitive TTD patients, are not constantly associated with TTD. Complementation analysis in heterokaryons, obtained by fusion of repair-proficient with repair-deficient TTD cells, demonstrates that cells from the patient showing normal photosensitivity are able to restore UDS in UV-hypersensitive TTD cells.