Decreased repair of x-ray induced DNA single-strand breaks in lymphocytes in Down's syndrome.

Gamma-ray irradiation introduces single and/or double strand breaks into the DNA molecule of the cells. In the case of mammalian cells, these breaks are being repaired in general during the first hr following exposure to ionizing radiation. The article reports on the results obtained from testing the ability of cultured lymphocytes from patients with Down's syndrome to repair radiation-induced DNA single-strand breaks. The ability to repair was deduced from the study of the DNA sedimentation profiles in alkaline sucrose gradients. It was found that lymphocytes from Down's syndrome patients are less efficient in repairing single-strand DNA breaks than are lymphocytes from normal individuals. This significantly increased fraction of unrepaired DNA strand breaks might be associated with the unusually high level of radiation-induced chromosome aberrations as compared with normals.