His laboratory focuses on identifying genetic variants that alter an individual's risk of developing specific conditions. These variants fall roughly into two categories. Some are associated with a very high risk of developing a disease; variants of this type, such as those in known breast cancer-linked genes, are of great medical importance. The second category of variants is associated with more modest risk. The medical significance of variants in the latter group is not yet known, but their isolation and identification can lend insight into the mechanism of complex conditions.