To identify the disease-causing mutations in a cohort of 120 Brazilian women fulfilling criteria for HBOC, we carried out a comprehensive screening of BRCA1/2, TP53 R337H, CHEK2 1100delC, followed by an analysis of copy number variations in 14 additional breast cancer susceptibility genes (PTEN, ATM, NBN, RAD50, RAD51, BRIP1, PALB2, MLH1, MSH2, MSH6, TP53, CDKN2A, CDH1 and CTNNB1). The gene discussed is ATM; the disease is breast cancer.