Identification of ataxia telangiectasia heterozygotes, a cancer-prone population, using the single-cell gel electrophoresis (Comet) assay

Heterozygotes of ataxia telangiectasia (AT) may comprise up to 1% of the general population. Because these individuals have no clinical expression of AT but may be highly radiosensitive and strongly predisposed for several forms of cancer, identification of AT carriers represents a considerable interest in cancer epidemiology and radiotherapy. We report a new approach for the in vitro identification of AT-heterozygotes based on the evaluation of the radiosensitivity and DNA damage repair ability of peripheral blood mononuclear cells using the single-cell gel electrophoresis (Comet) assay. The assay was performed on cells isolated from four different groups of individuals: (1) apparently healthy donors (n = 10); (2) patients with breast cancer showing a normal reaction to radiotherapy (n = 10); (3) a group of obligate AT carriers (parents of AT-homozygotes, n = 20); and (4) AT-homozygotes (n = 4). Cells irradiated with 3 Gy of x-rays were assayed for three parameters: (1) the initial and (2) residual DNA damage and (3) the kinetics of DNA damage repair. Both AT-heterozygotes' and AT-homozygotes' cells were found to be highly sensitive to x-irradiation. Quantitative evaluation of the single-cell electrophoregrams revealed that the average initial DNA damage in AT-heterozygous and AT-homozygous cells was almost three times higher than that in control non-AT cells. In addition, the DNA repair process in irradiated AT carrier cells was almost three times slower, and the extent of irreparable DNA damage in these cells was three times greater than in controls. Simultaneous assessment of the three parameters enabled correct identification of all tested AT carriers. This method seems to be a sensitive and useful tool for populational studies as a rapid prescreening test for a mutated AT status. The approach can also be extended for prediction of the in vivo radiosensitivity, which would enable optimization of individual radiotherapy schedules.