In view of extensive linkage disequilibrium in the 3p21.1 region, encompassing more than 30 genes, we could not identify the causal locus. Genome-wide significant association to the 3p21.1 region has previously been reported in GWAS of samples overlapping with ours at rs1042779 (12 kb from our peak SNP) for bipolar disorder,28 rs736408 (2 kb) for a combined bipolar disorder and schizophrenia phenotype,7 and rs2251219 (248 kb) for a combined major depressive and bipolar disorder phenotype.29 Reanalysis of this last combined dataset suggested that the signal was largely attributable to the group with bipolar disorder.30 Furthermore, the association evidence for our peak chromosome 3 SNP rs2535629 was genome-wide significant in a joint analysis of bipolar disorder and schizophrenia samples done by the PGC schizophrenia group (p=7·8×10−9).6
