Hypersensitivity of cells from a new chromosomal-breakage syndrome to DNA-damaging agents

Cells derived from a patient with severe chromosomal breakage, immunodeficiency, and growth retardation were found to resemble those from individuals with ataxia telangiectasia (A-T) in terms of their sensitivity to cell killing and the induction of cytogenic abnormalities by X-rays. Their response to other DNA-damaging agents, including 254-nm UV light, mitomycin C, MNNG, and bleomycin was also A-T-like. In contrast to classical A-T, however, X-irradiated cells exhibited a G₁ block after release from density inhibition of growth that was not significantly different from that of normal controls.