Genes are made of DNA. Each chromosome contains about 20,000 to 25,000 genes. Every person has two copies of each gene – one copy from each parent. Human genes are nearly identical for all humans with less than one percent being slightly different. These slightly different genes are called alleles and they contribute to each person’s unique physical appearance. Genes contain instructions for making proteins. Each cell requires thousands of proteins to work together in order for that cell to function properly. Genetic mutations cause proteins to malfunction or be missing entirely which causes the cell to malfunction. Sometimes when a cell malfunctions it can grow and reproduce at a very rapid and uncontrolled rate creating a tumor, better known as cancer.
Some genes are tumor suppressor genes. They produce proteins that repair damaged, broken, or mutated DNA, thereby preventing a tumor from forming. Examples of tumor suppressor genes are the BRCA1 and BRCA2 genes. When mutations occur in these genes, they do not repair damaged DNA and tumors may develop. Mutations in the BRCA1/2 genes are associated with breast, ovarian, pancreatic, and other cancers, and because our genes come from our parents, BRCA mutations are inherited. Not everyone who inherits a BRCA mutation will develop cancer because other factors such as other genetic factors, environment, and lifestyle contribute to the risk of developing cancer.
Risk factors for having a harmful BRCA mutation can be personal or family-related. Personal risk factors include breast cancer at an early age (below 50), history of breast and/or ovarian cancer, cancer in both breasts, breast cancer AND one or more relatives diagnosed with breast cancer below 50, one relative diagnosed with ovarian cancer or two or more relatives diagnosed with breast or pancreatic cancer, and Ashkenazi Jewish heritage with at least one close relative diagnosed with breast, ovarian, or pancreatic cancer. Family risk factors include two or more relatives diagnosed with breast cancer below 50, a male relative with breast cancer, a relative with breast and ovarian cancer or with cancer in both breasts, a relative with ovarian cancer, and a relative with a BRCA1/2 mutation.
So far researchers have identified over 1,800 BRCA1 mutations. Because there are so many mutations, BRCA1/2 testing can be problematic. For example, a person with a negative test result and a personal or family history that suggests that he or she might be at risk for a mutation but no close relatives have been identified as having such a mutation, he or she might still have a mutation that was not identified by the test and that mutation has not yet been identified as being harmful. Likewise, a person with an uncertain test result means that that person has a mutation but that mutation has not yet been identified as contributing to cancer risk.
As you can see, the interpretation of gene mutation testing can be complicated. For this reason, a consultation with a genetic specialist is usually recommended, especially for those with a negative test result but positive personal or family history.
For more information go to www.ghr.nlm.nih.gov/gene?initial=b or www.cancer.gov/types/breast/hp/breast-ovarian-genetics-pdq
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