Jolie explained that she is a carrier of what she calls a "faulty" BRCA1 gene, which puts her at increased risk for breast cancer. "Those with a defect in BRCA1 have a 65 percent risk of getting it, on average," penned Jolie.
In Jolie's case, her doctors estimated that she had an 87 percent risk of breast cancer. According to the National Cancer Institute, about 12 percent of women in the general population will develop breast cancer in their lifetime.
But what exactly is a BRCA1 gene? According to the National Cancer Institute, BRCA1 (and BRCA2) is in a class of genes known as tumor suppressors. BRCA stands for Breast Cancer susceptibility gene. In normal cells, these genes help prevented uncontrolled cell growth.
The National Cancer Institute states, "A woman's risk of developing breast and/or ovarian cancer is greatly increased if she inherits a deleterious (harmful) BRCA1 or BRCA2 mutation. Men with these mutations also have an increased risk of breast cancer. Both men and women who have harmful BRCA1 or BRCA2 mutations may be at increased risk of other cancers."
There are genetic tests available to test for mutations on these genes.