DNA synthesis in ataxia telangiectasia

After the discovery that cultured cells from AT patients are hypersensitive to ionizing radiation the suggestion was made that AT-could be the 1 X-ray-analogue 1 of xeroderma pigmentosum. The latter syndrome (XP) is characterized by hypersensitivity to short-wave UV-radiation, caused by a reduced ability to properly remove UV-induced DNA damage. The evidence for a DNA repair defect in AT cells is not as strong as in the case of XP (see section 2.2.5 of this thesis). Different XP patients vary in their clinical and cellular UV-sensitivity, and this variability roughly correlates with the capacity to repair the UV damage in the DNA. in AT apparent differences in gamma-ray induced repair DNA synthesis contrast with a rather uniform pattern of radiohypersensitivity. The rate of DNA replication is affected by low doses of ionizing or non-ionizing radiation. ln 1977 it was shown that UV-induced inhibition of DNA synthesis is persistent in highly UV-sensitive XP cell strains; whereas less UV-sensitive cells showed recovery from this inhibition. [n the hope to find a consistent biochemical defect in AT cells, it was decided to study the effect ~f ionizing radiation on the rate of DNA synthesis in AT cells.