Variant forms of ataxia telangiectasia

Two ataxia telangiectasia patients with unusual clinical and cellular features are described. Cultured fibroblasts and PHA stimulated lymphocytes from these two patients showed a smaller increase of radiosensitivity than cells from other A-T patients, as measured by colony forming ability or induced chromosome damage respectively, after exposure to ionising radiation. The response of DNA synthesis to irradiation of these cells was, however, the same as for other A-T patients. Cells from a third patient with some clinical features of A-T but with a very protracted course also showed low levels of radiation induced chromosome damage, but colony forming ability and the response of DNA synthesis after irradiation were no different from cells of normal subjects. There was, however, an increased level of translocations and unstable chromosomal rearrangements in this patient's lymphocytes.

Effects of the DNA strand-cleaving antitumor agent, streptonigrin, on ataxia telangiectasia cells

Cells from patients with ataxia telangiectasia (A-T) were shown to be more sensitive to streptonigrin than were cells from normal individuals. A linear dose-dependent cell survival was observed for both normal and A-T cells exposed to streptonigrin (up to 1.5 ng/ml) for 3-hr, with the A-T cells being about twice as sensitive as were the normal cells (Do approximately 0.25 ng compared with Do approximately 0.5 ng). The extreme toxicity of streptonigrin is also seen in the response of DNA synthesis which is inhibited sharply in both A-T and normal cells using doses of up to 125 ng/ml, although the effect was less pronounced in A-T cells. A greater amount of time was needed for recovery of DNA synthesis in normal cells compared with that of A-T cells. Finally, chromosomes from both A-T lymphocytes and fibroblasts show about a doubling of breakage rate following exposure to streptonigrin. The increased sensitivity of A-T cells to streptonigrin appears to be fairly comparable to the sensitivity to ionizing radiation, bleomycin, or neocarzinostatin and provides further evidence that perhaps A-T cells are deficient in some form of DNA strand repair.