Unusual sensitivity of ataxia telangiectasia cells to bleomycin

Peripheral blood lymphocytes from four patients with ataxia telangiectasia (AT), an inherited disorder showing, among other features, radiosensitivity and a high frequency of cancers, were shown to be cytogenetically more sensitive to bleomycin than were lymphocytes from both normal individuals and a single patient with xeroderma pigmentosum. With cell survival techniques, a biphasic dose-response curve was seen for both normal and AT fibroblasts, although the AT cells showed a much lower survival. The increased sensitivity to bleomycin in AT cells might be expected since it is a radiomimetic drug, but more importantly the known action of bleomycin in producing DNA strand scission suggests that AT cells might be defective in rejoining a proportion of DNA strand breaks.