Screening breast cancer patients for Norwegian ATM mutations

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Heterozygosity for Ataxia Telangiectasia (AT), a cancerprone recessive syndrome, has been associated with an increased risk of breast cancer. In the present study, 483 Norwegian breast cancer patients were screened for carrier status of six different ATM mutations found in Norwegian AT patients. One breast cancer patient carried the Norwegian founder mutation, giving a point estimate of the frequency of 0.2% (95% CI 0.01-1.2%). Assuming a 0.5% carrier frequency, the present results are consistent with a maximum 2.4-fold increased lifetime risk of breast cancer in ATM heterozygotes. The study had 95% power to detect a 4.6-fold elevated lifetime risk, and a 9-fold elevated risk in women below age 55.