Fibroblasts from ataxia telangiectasia (AT) and AT heterozygotes show an enhanced level of residual DNA double-strand breaks after low dose-rate γ-irradiation as assayed by pulsed field gel electrophoresis

Skin fibroblasts from ataxia telangiectasia (AT) patients, obligate AT heterozygotes (ATH) and normal individuals were studied for colony-forming ability and repair of DNA double-strand breaks (dsb) after γ-irradiation. AT cells were three to four times more radiosensitive than normal cells at high and low dose-rate exposures; ATH cells, however, showed a marginally increased radiosensitivity after high dose-rate γ-irradiation and an intermediate response after low dose-rate exposure. The repair of DNA dsb was studied by pulsed field gel electrophoresis. After high dose-rate γ-irradiation the repair time constant (t1/2) was around 1h for normal, ATH and AT cells. After low dose-rate γ-irradiation the fraction of residual dsb was 1.4% for normal, 2.1% for ATH and 5.2% for AT cells, demonstrating a deficiency in the repair of a small fraction of dsb in AT. (author)