Identification of germline missense mutations and rare allelic variants in the ATM gene in early‐onset breast cancer

Epidemiological studies have shown an increased risk of breast cancer in obligate ataxia telangiectasia (A‐T) heterozygotes. We analyzed 100 samples from young breast cancer patients for mutations in ataxia‐telangiectasia mutated (ATM), the gene responsible for the autosomal recessive condition, A‐T, to determine whether A‐T heterozygosity predisposes such individuals to develop breast cancer. These patients were selected from families with a moderate or absent family history of breast cancer and included a subset of 16 radiosensitive patients. Forty‐four germline sequence variants were detected by fluorescent chemical cleavage of mismatch of RT‐PCR products. These included seven rare variants found in nine patients (three described for the first time), but no truncating mutations. Although three variants were detected in the radiosensitive subset, this was not statistically significant compared to the nonradiosensitive group. One variant, G2765S, is likely to be a missense mutation, but the other six variants probably represent rare polymorphisms. However, five of the seven rare germline variants detected showed loss of heterozygosity of the wild‐type ATM allele for one or more markers close to the ATM locus in matched tumor DNA. This high rate of somatic inactivation of ATM may indicate either that these rare variants play a role in breast cancer development or alternatively that a neighboring tumor suppressor gene is important for tumorigenesis. We found germline truncating ATM mutations to be rare in these young breast cancer patients and therefore they are unlikely to play a role in the etiology of their disease. Genes Chromosomes Cancer 26:286–294, 1999. © 1999 Wiley‐Liss, Inc.