Simultaneous measurement, using flow cytometry, of radiosensitivity and defective mitogen response in ataxia telangiectasia and related syndromes.

In a retrospective study, peripheral blood mononuclear cells from 13 patients with known ataxia telangiectasia (AT) (Louis Bar syndrome, McKusick #20890) were irradiated with different doses of X-rays prior to stimulation with phytohaemagglutinin. Mitogen response and cell cycle progression were assessed by two-parameter 5-bromo-2'-deoxyuridine/Hoechst--ethidium bromide flow cytometry. Compared to age-matched controls, AT cells show a severely defective mitogen response in both unirradiated and irradiated cells. Following irradiation with 1.5 Gy, AT cells exhibit significantly greater accumulations of cells in the G2 phase of the first cell cycle than controls. The ratio between the number of cells accumulated in the first cycle G2 phase and the growth fraction provides a clear distinction between AT and control cultures. In addition, two patients with microcephaly, normal intelligence, immunodeficiency, chromosomal instability and risk for lymphoreticular malignancies (Seemanová syndrome) and two patients with the Nijmegen breakage syndrome (both syndromes are listed as McKusick #25126) also exhibit very poor mitogen response and moderately increased G2 phase accumulations after X-irradiation. The simultaneous assessment of radiosensitivity and mitogen response in a single cell kinetic assay provides a speedy and accurate classification of cells of AT and AT-related syndromes.