ABSTRACT
Linkage analysis was used to pinpoint the first breast cancer gene (BRCA1) on chromosome 17q21. A total of 146 cases of breast cancer from 23 extended families were studied by linkage analysis of 183 polymorphic markers. LOD scores (logarithms of odds ratios) were calculated using a multilocus autosomal-dominant model, and strong linkage (106:1) for a highly polymorphic marker (D17S74) on chromosome 17q was found for early-onset families. In contrast, no increased risk was associated with this marker in late-onset families, indicating heterogeneity of risk and the likely existence of other breast cancer genes. Subsequent work led to the discovery of the first breast cancer gene (BRCA1).
