Increased breast cancer risk in ATM heterozygote mutation carriers has been previously reported in studies that either inferred obligate carriership (Swift et al, 1987; Pippard et al, 1988) or directly tested for gene mutations (Athma et al, 1996; Stancovic et al, 1998; Inskip et al, 1999; Janin et al, 1999; Olsen et al, 2001). Here, ATM is linked to breast carcinoma.