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Bipolar disorder (BD) is a heritable mental illness with complex etiology. We performed a genome-wide association study (GWAS) of 41,917 BD cases and 371,549 controls of European ancestry, which identified 64 associated genomic loci. BD risk alleles were enriched in genes in synaptic signaling pathways and brain-expressed genes, particularly those with high specificity of expression in neurons of the prefrontal cortex and hippocampus. Significant signal enrichment was found in genes encoding targets of antipsychotics, calcium channel blockers, antiepileptics, and anesthetics. Integrating eQTL data implicated 15 genes robustly linked to BD via gene expression, encoding druggable targets such as HTR6, MCHR1, DCLK3 and FURIN. Analyses of BD subtypes indicated high but imperfect genetic correlation between BD type I and II and identified additional associated loci. Together, these results advance our understanding of the biological etiology of BD, identify novel therapeutic leads, and prioritize genes for functional follow-up studies.

Schizophrenia and bipolar disorder are two distinct diagnoses that share symptomology. Understanding the genetic factors contributing to the shared and disorder-specific symptoms will be crucial for improving diagnosis and treatment. In genetic data consisting of 53,555 cases (20,129 bipolar disorder [BD], 33,426 schizophrenia [SCZ]) and 54,065 controls, we identified 114 genome-wide significant loci implicating synaptic and neuronal pathways shared between disorders. Comparing SCZ to BD (23,585 SCZ, 15,270 BD) identified four genomic regions including one with disorder-independent causal variants and potassium ion response genes as contributing to differences in biology between the disorders. Polygenic risk score (PRS) analyses identified several significant correlations within case-only phenotypes including SCZ PRS with psychotic features and age of onset in BD. For the first time, we discover specific loci that distinguish between BD and SCZ and identify polygenic components underlying multiple symptom dimensions. These results point to the utility of genetics to inform symptomology and potential treatment.

Substantial evidence supports a role for dysfunction of brain serotonergic (5-HT) systems in the pathogenesis of major affective disorder, both unipolar (recurrent major depression) and bipolar. 1 Modification of serotonergic neurotransmission is pivotally implicated in the mechanism of action of antidepressant drugs 2 and also in the action of mood stabilizing agents, particularly lithium carbonate. 3 Accordingly, genes that code for the multiple subtypes of serotonin receptors that have been cloned and are expressed in brain, 4 are strong candidates for a role in the genetic etiology of affective illness. We examined a structural variant of the serotonin 2C (5-HT2C) receptor gene (HTR2C) that gives rise to a cysteine to serine substitution in the N terminal extracellular domain of the receptor protein (cys23ser), 5 in 513 patients with recurrent major depression (MDD-R), 649 patients with bipolar (BP) affective disorder and 901 normal controls. The subjects were drawn from nine European countries participating in the European Collaborative Project on Affective Disorders. There was significant variation in the frequency of the HT2CR ser23 allele among the 10 population groups included in the sample (from 24.6% in Greek control subjects to 9.2% in Scots, 2 = 20.9, df 9, P = 0.01). Logistic regression analysis demonstrated that over and above this interpopulation variability, there was a significant excess of HT2CR ser23 allele carriers in patients compared to normal controls that was demonstrable for both the MDD ( 2 = 7.34, df 1, P = 0.006) and BP ( 2 = 5.45, df 1, P = 0.02) patients. These findings support a possible role for genetically based structural variation in 5-HT2C receptors in the pathogenesis of major affective disorder. Molecular Psychiatry (2001) 6, 579-585.It is widely accepted that the genetic basis of affective disorders, both unipolar (recurrent major depression) and bipolar (manic depressive illness) is complex and is likely to involve several genes and also environmental factors. 6,7 A principal aim of the European Collaborative Project on Affective Disorders (ECPAD) is to harness the statistical power potentially provided by the large numbers of subjects who can be recruited by the participating centers in order to elucidate the role of candidate genes and environmental factors in the pathogenesis of affective illness. 8 In the course of the project a very large sample has been recruited and clinically evaluated, with blood samples obtained for DNA extraction. The method of recruitment of patients has been described in detail by Souery et al 8 and is summarized below in the Methods section. Subjects were genotyped for the HT2CR cys23ser polymorphism in the participating laboratories according to a standardized protocol (see below). Clinical and genotype data were centralized in the ECPAD database in Brussels and were electronically transferred to BL and FM for statistical analysis. After removal of subjects whose geographical origin was unclear, whose genotype data were ambiguous or contrad...