BRCA mutation

A BRCA mutation is a mutation in either of the BRCA1 and BRCA2 genes, which are tumour suppressor genes. Hundreds of different types of mutations in these genes have been identified, some of which have been determined to be harmful, while others have no proven impact. Harmful mutations in these genes may produce a hereditary breast-ovarian cancer syndrome in affected persons. Only 5-10% of breast cancer cases in women are attributed to BRCA1 and BRCA2 mutations (with BRCA1 mutations being slightly more common than BRCA2 mutations), but the impact on women with the gene mutation is more profound. Women with harmful mutations in either BRCA1 or BRCA2 have a risk of breast cancer that is about five times the normal risk, and a risk of ovarian cancer that is about ten to thirty times normal. The risk of breast and ovarian cancer is higher for women with a high-risk BRCA1 mutation than with a BRCA2 mutation. Having a high-risk mutation does not guarantee that the woman will develop any type of cancer, or imply that any cancer that appears was actually caused by the mutation, rather than some other factor.

High-risk mutations, which disable an important error-free DNA repair process (homology directed repair), significantly increase the person's risk of developing breast cancer, ovarian cancer and certain other cancers. Why BRCA1 and BRCA2 mutations lead preferentially to cancers of the breast and ovary is not known, but lack of BRCA1 function seems to lead to non-functional X-chromosome inactivation. Not all mutations are high-risk; some appear to be harmless variations. The cancer risk associated with any given mutation varies significantly and depends on the exact type and location of the mutation and possibly other individual factors.

Mutations can be inherited from either parent and may be passed on to both sons and daughters. Each child of a genetic carrier, regardless of sex, has a 50% chance of inheriting the mutated gene from the parent who carries the mutation. As a result, half of the people with BRCA gene mutations are male, who would then pass the mutation on to 50% of their offspring, male or female. The risk of BRCA-related breast cancers for men with the mutation is higher than for other men, but still low. However, BRCA mutations can increase the risk of other cancers, such as colon cancer, pancreatic cancer, and prostate cancer.