BRCA2 and BRCA1 are normally expressed in the cells of breast and other tissue, where they help repair damaged DNA or destroy cells if DNA cannot be repaired. They are involved in the repair of chromosomal damage with an important role in the error-free repair of DNA double strand breaks. If BRCA1 or BRCA2 itself is damaged by a BRCA mutation, damaged DNA is not repaired properly, and this increases the risk for breast cancer. "BRCA1" and "BRCA2" have been described as "breast cancer susceptibility genes" and "breast cancer susceptibility proteins". The predominant allele has a normal tumor suppressive function whereas high penetrance mutations in these genes cause a loss of tumor suppressive function, which correlates with an increased risk of breast cancer.