About 10% of cases are associated with inherited defects in two genes, BRCA1 and BRCA2 . Human BRCA1 and BRCA2 are large proteins (1,834 and 3,418 amino acid residues, respectively) that interact with a wide range of other proteins involved in transcription, chromosome maintenance, DNA repair, and control of the cell cycle. Women with defects in either the BRCA1 or BRCA2 gene have a greater than 80% chance of developing breast cancer.