BRCA1 - Mutations and Cancer Risk

Mutations and Cancer Risk

Certain variations of the BRCA1 gene lead to an increased risk for breast cancer as part of a hereditary breast-ovarian cancer syndrome. Researchers have identified hundreds of mutations in the BRCA1 gene, many of which are associated with an increased risk of cancer. Women with an abnormal BRCA1 or BRCA2 gene have up to a 60% risk of developing breast cancer by age 90; increased risk of developing ovarian cancer is about 55% for women with BRCA1 mutations and about 25% for women with BRCA2 mutations.

These mutations can be changes in one or a small number of DNA base pairs (the building-blocks of DNA). Those mutations can be identified with PCR and DNA sequencing.

In some cases, large segments of DNA are rearranged. Those large segments, also called large rearrangements, can be a deletion or a duplication of one or several exons in the gene. Classical methods for mutations detection (sequencing) are unable to reveal those mutations. Other methods are proposed: Q-PCR, Multiplex Ligation-dependent Probe Amplification (MLPA), and Quantitative Multiplex PCR of Shorts Fluorescents Fragments (QMPSF). New methods have been recently proposed: heteroduplex analysis (HDA) by multi-capillary electrophoresis or also dedicated oligonucleotides array based on comparative genomic hybridization (array-CGH).

Some results suggest that hypermethylation of the BRCA1 promoter, which has been reported in some cancers, could be considered as an inactivating mechanism for BRCA1 expression.

A mutated BRCA1 gene usually makes a protein that does not function properly because it is abnormally short. Researchers believe that the defective BRCA1 protein is unable to help fix mutations that occur in other genes. These defects accumulate and may allow cells to grow and divide uncontrollably to form a tumor.

BRCA1 mRNA 3' UTR can be bound by an miRNA, Mir-17 microRNA. It has been suggested that variations in this miRNA along with Mir-30 microRNA could confer susceptibility to breast cancer.

In addition to breast cancer, mutations in the BRCA1 gene also increase the risk of ovarian, fallopian tube, and prostate cancers. Moreover, precancerous lesions (dysplasia) within the Fallopian tube have been linked to BRCA1 gene mutations. Pathogenic mutations anywhere in a model pathway containing BRCA1 and BRCA2 greatly increase risks for a subset of leukemias and lymphomas.

Women having inherited a defective BRCA1 or BRCA2 gene have risks for breast and ovarian cancer that are so high and seem so selective that many mutation carriers choose to have prophylactic surgery. There has been much conjecture to explain such apparently striking tissue specificity. Major determinants of where BRCA1/2 hereditary cancers occur are related to tissue specificity of the cancer pathogen, the agent that causes chronic inflammation or the carcinogen. The target tissue may have receptors for the pathogen, become selectively exposed to an inflammatory process or to a carcinogen. An innate genomic deficit in a tumor suppressor gene impairs normal responses and exacerbates the susceptibility to disease in organ targets. This theory also fits data for several tumor suppressors beyond BRCA1 or BRCA2. A major advantage of this model is that it suggests there may be some options in addition to prophylactic surgery.