Because of the complex pattern of genetic transmission, it is expected that multiple genes will contribute to susceptibility to bipolar disorder. It is possible that combinations of genes will be stronger risk factors for developing bipolar disorder than individual genes, so we are examining gene-gene interactions (genetic epistasis) throughout the genome to identify genes which, in concert, may increase susceptibility. This analysis has led to the identification of multiple such interacting regions, and the group is now seeking to identify the specific genes involved in these interactions.