PSORALEN-DNA CROSS-LINKING PHOTOADDUCTS IN DYSKERATOSIS CONGENITA - DELAY IN EXCISION AND PROMOTION OF SISTER CHROMATID EXCHANGE

Dyskeratosis congenita is a rare X-linked recessive disease, characterized by mucosal leukokeratosis, nail dystrophy, telangiectasia, reticulated hyperpigmentation, pancytopenia, and a heightened susceptibility to infection and malignancy. We exposed cultured fibrobasts and peripheral leukocytes from normal persons and from 2 unrelated young adult men with dyskeratosis congenita to 4,5'8-trimethylpsoralen and ultraviolent light. We then compared certain of their responses. Labeled DNA from fibroblasts exposed to 4,5',8-trimethylpsoralen and ultraviolet light showed fast-sedimenting DNA, a pattern we interpreted as evidence that cross-linking, psoralen-DNA photoadducts had been formed by the treatment. Fast-sedimenting DNA persisted for 24 hr in dyskeratosis congenita cells but disappeared from normal cells during a 24-hr repair period. Cultured peripheral blood leukocytes from persons with this syndrome similarly exposed to 4,5',8-trimethylpsoralen and ultraviolet light developed more sister chromatid exchanges than did cells from normal persons. These data suggest that a heightened susceptibility to DNA cross-links may be of fundamental importance in the etiology of dyskeratosis congenita.