Family-based association studies of impact, a candidate gene for bipolar disorder on chromosome 18q12, in ashkenazi bipolar family samples

Bipolar disorders are common disorders of mood with an estimated prevalence of 0.4. Evidence from family, twin and adoption studies suggest there is a genetic component to susceptibility. Linkage studies of bipolar disorders suggest susceptibility loci likely exist on chromosomes 4p, 10q, 12q, 18p, and 21q. Positive linkage studies on chromosome 18 have suggested increased evidence of a parent-of origin effect and imprinting (Nothen et al., 1999). Recently, Kosaki et al., 2001, cloned IMPACT, the human homolog of the mouse imprinted gene Impact (human chromosome 18cen) and suggested that it or an adjacent gene in the imprinted region represents a candidate for bipolar disorders. We have undertaken family-based association studies of two informative SNPs, one CTT insertion/deletion, and one CA-repeat polymorphism in the IMPACT gene. Transmission Disequilibrium Testing (TDT) was implemented with the S.A.G.E. TDTExact software for a sample of 172 Ashkenazi Jewish Bipolar parent/child triads from the United States which were typed. Our results do not implicate a role for IMPACT in the susceptibility to Bipolar disorder when looking at allele transmission in this population.