An assessment of the radiosensitivity of ataxia-telangiectasia heterozygotes.

Heterozygotes of ataxia-telangiectasia (AT) can, in certain parts of the world, represent a significant proportion of the population. Epidemiological studies suggest that they are more cancer prone than normal individuals. Fibroblasts of five AT heterozygotes are significantly more sensitive to gamma irradiation (mean D0 = 1.18 Gy) than five normals (mean D0 = 1.49 Gy) although some overlap in response is observed. Experiments designed to maximize differences in survival by allowing a period for the repair of potentially lethal damage (PLD) showed that only one out of five AT heterozygotes was defective in the repair of PLD. This technique does not, therefore, permit an improved discrimination of AT heterozygotes. Two AT heterozygotes were tested for their ability to repair lesions that give rise to micronuclei. Both, like the homozygote, were seen to be defective in this capacity. Defects in the repair of chromosome damage may permit a cellular discrimination of the heterozygotes.