DNA repair deficiencies and cellular senescence are unrelated in xeroderma pigmentosum cell lines.

Senescence of skin fibroblast cultures from normal individuals occurred after 23.9 +/- 6.3 (S.D.) passages; senescence in DNA repair-deficient cell lines from xeroderma pigmentosum patients occurred at 22.9 +/- 5.5 passages. Cells from xeroderma pigmentosum variant and Cockayne syndrome patients reached senescence at similar passage numbers. Xeroderma pigmentosum patients contract skin cancer as a consequence of their repair deficiencies but show no symptoms of premature ageing; neither do their cells age prematurely in vitro. The clinical spectrum and the life-span of fibroblasts in culture therefore lend no support for a correlation between ageing and the DNA repair or DNA replication deficiencies found in xeroderma pigmentosum and Cockayne syndrome cells.