Genetic alterations in hereditary breast cancer.
Genetic linkage studies have led to the identification of highly penetrant genes as the possible cause of inherited cancer risk in many cancer-prone families. Most women with a family history of breast/ovarian cancer have tumors characterized by alterations in particular genes, mainly BRCA1 and BRCA2, but also CHK2, ATM, STK11 and others. This paper examines the BRCA1 and BRCA2 genes, focusing on the Italian pattern of mutations. The function of these two genes, classified as tumor suppressors, is linked with key metabolic mechanisms such as DNA damage repair, regulation of gene expression and cell cycle control. The pathological BRCA allelic variants may cause alteration of protein function, transcriptional activity and DNA repair; accumulation of the defects leads to widespread chromosome instability that may be directly responsible for cancer formation. In fact, mutations in BRCA1 and BRCA2, conferring a highly increased susceptibility to breast and ovarian cancer, do not lead to cancer by themselves. The current consensus is that these are 'caretaker' genes, which, when inactivated, allow other genetic defects to accumulate. The nature of these other molecular events may define the pathway through which BRCA1 and BRCA2 act. The BRCA mutation spectrum is complex, and the significance of most nucleotide alterations is difficult to understand. Moreover, the mutation pattern seems to be related to ethnicity. The Italian Consortium of Hereditary Breast and Ovarian Cancer has reviewed 1758 families; 23% have been found to be carriers of pathogenetic mutations in BRCA1 or BRCA2. Founder mutations have been described in geographically restricted areas of Italy; a regional founder effect has been demonstrated in Italy for the mutations BRCA1 5083del19 and BRCA2 8765delAG, and a probable new founder mutation has been characterized in Tuscany. The presence of founder mutations has practical implications for genetic testing.