Mutations in the familial early-onset breast cancer gene (BRCA1) account for approximately 2-5% of all breast cancer cases (Easton et al., 1993). Since the isolation of the BRCA1 gene in 1994, many mutations have been identified. We report here a total of 254 BRCA1 mutations, 132 (52%) of which are unique. These represent mutations entered into a database established by the Breast Cancer Information Core (BIC), which have appeared in the literature or have been submitted by BIC members and other contributors prior to publication. A total of 221 (87%) of all mutations or 107 (81%) of the unique mutations are small deletions, insertions, nonsense point mutations, splice variants, and regulatory mutations that result in truncation or absence of the BRCA1 protein. A total of 11 disease-associated missense mutations (5 unique), and 21 variants (19 unique) as yet unclassified as either missense mutations or polymorphisms have been detected. Thirty-five independent benign polymorphisms are also described. The most common mutations are 185delAG and 5382insC, which account for 30 (11.7%) and 26 (10.1%), respectively, of all mutations shown. The biological and clinical relevance of these BRCA1 mutations is discussed.
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