Breast cancer affects about one woman at 10. But in some families with a genetic predisposition, this risk is much higher. Patients with a family history and / or unusually young age therefore have to diagnose genetic research for key genes involved in hereditary breast cancer (BRCA1 and BRCA2). Identification of a disease-causing mutation is in fact important to detect a genetic risk in family members. However, it takes at less than 20% of the examined families, a mutation, and in a small number of patients whose clinical significance of genetic variants to be found is not clear. That leads to uncertainty. In this project work the University Hospital of Ghent, Leuven and Brussels to identify other causative mutations using new techniques in patients with a clear family history of breast cancer, in which a BRCA1 or BRCA2 mutation was excluded. The university will also develop functional testing centers for genetic variants of uncertain significance. This project will ensure that more families are unraveling the genetic basis of breast cancer. This leads to better treatment and prevention.