Familial breast cancer risk assessment.

A family, with a strong history of dominant breast and ovarian cancer, is described. Using highly polymorphic microsatellite markers within the BRCA1 breast cancer gene on chromosome 17q21; three affected sisters, their father and a paternal second cousin once removed, are shown to share the same "abnormal" haplotype. Because of this informative linkage, the carrier status of the unaffected siblings can be established by determining whether they inherited their father's "normal" or "abnormal" haplotype. Presymptomatic diagnosis is important in decisions regarding prophylactic surgery or follow-up care. However, the widespread general population presymptomatic DNA testing of breast cancer is currently not recommended because of inherent problems in the sensitivity and specificity of DNA testing.