Defect in repair of IR-induced chromosome damage in

ATM mutant B-CLLs. Percentage of cells showing induced chromatid type aberrations (gaps, breaks, and interchanges) in G2 at 4 hours following exposure to 1 Gy x-rays in B-CLL tumors 1, 33, and 39 (n = 100), with mutant ATM, and in B-CLLs 51 and 56 with wild-type ATM/TP53 (n = 60). The proportion of unirradiated cells with damage is also indicated with n = 65 and 55, respectively.