Genetic complementation analysis of ataxia telangiectasia by somatic cell fusion.

After cells from patients with ataxia telangiectasia (AT) have been exposed to ionizing radiation, the rate of semiconservative DNA replication is inhibited to a significantly lesser extent than in cells from normal individuals. This diminished inhibition of DNA synthesis is a general characteristic of irradiated AT cell strains, irrespective of their capacity to perform repair DNA synthesis after treatment with gamma-rays. Using the abnormal regulation of DNA replication in AT cells as a parameter, a procedure was developed that allows genetic complementation analysis of AT. The five AT cell strains that were investigated in this respect could be assigned to three complementation groups. The results show that an extensive genetic heterogeneity exists in the AT syndrome.