Detection of ataxia telangiectasia heterozygous cell lines by postirradiation cumulative labeling index: measurements with coded samples.

Coded skin fibroblast cell strains from ataxia telangiectasia (AT) families and apparently normal individuals were obtained from two different sources. AT homozygous strains were clearly identified on the basis of marked hypersensitivity to cell killing by X-irradiation. AT heterozygotes were intermediate in their cytotoxic response between AT homozygotes and five normal reference cell strains. When density-inhibited cultures were X-irradiated and immediately subcultured to low density, a large fraction of AT heterozygous cells were irreversibly blocked in G1 as determined by cumulative labeling indices following incubation with [3H]thymidine. No such block occurred in four reference normal or AT homozygous strains. Three coded cell strains from apparently normal individuals resembled AT heterozygotes in their response; two of these strains were heterozygous for lysosomal storage disease. Thus, although the phenotype associated with the cellular response of AT heterozygous cells to X-irradiation is not specific to this disorder, the cumulative labeling indices assay may be a useful method for the detection of AT heterozygotes in kindreds with known AT.