complete bipolar disorder and control data-set (at GABRB1) and found the signal to be maximal within the RDC schizoaffective disorder, bipolar type subset of participants. Testing of independent SNPs within genes encoding gamma amniobutyric acid (GABA)A receptors showed this set of individuals to have significant system-wide association with variation across the set of SNPs at these receptors (P = 6.6×10–5)36 with gene-wide evidence for association at GABRB1, GABRA4, GABRB3, GABRA5 and GABRR1. This is consistent with the current analysis of the same data-set in which we observe a signal at P<0.00001 at GABRB1 (Table 2), and multiple associated SNPs at these other genes within our set of nominally significant associations (online Table DS2). The strongest association signal within the RDC schizoaffective disorder, bipolar type data-set (P = 2.32×10–7) occurred on chromosome 21 with SNPs within the gene B3GALT5, a member of the beta-1,3-galactosyltransferase (beta3GalT) gene family which encode type II membrane-bound glycoproteins with diverse enzymatic functions. To our knowledge, these specific proteins have not been previously implicated in pathophysiology of mood or psychotic illness. The strong association we observe at chromosome 16p13.3 is of interest because it lies within the gene A2BP1, encoding ataxin 2-binding protein 1 isoform 4, a
