Gene set enrichment analysis and expression pattern exploration implicate an involvement of neurodevelopmental processes in bipolar disorder.

BACKGROUND: Bipolar disorder (BD) is a common and highly heritable disorder of mood. Genome-wide association studies (GWAS) have identified several independent susceptibility loci. In order to extract more biological information from GWAS data, multi-locus approaches represent powerful tools since they utilize knowledge about biological processes to integrate functional sets of genes at strongly to moderately associated loci. METHODS: We conducted gene set enrichment analyses (GSEA) using 2.3 million single-nucleotide polymorphisms, 397 Reactome pathways and 24,025 patients with BD and controls. RNA expression of implicated individual genes and gene sets were examined in post-mortem brains across lifespan. RESULTS: Two pathways showed a significant enrichment after correction for multiple comparisons in the GSEA: GRB2 events in ERBB2 signaling, for which 6 of 21 genes were BD associated (PFDR = 0.0377), and NCAM signaling for neurite out-growth, for which 11 out of 62 genes were BD associated (PFDR = 0.0451). Most pathway genes showed peaks of RNA co-expression during fetal development and infancy and mapped to neocortical areas and parts of the limbic system. LIMITATIONS: Pathway associations were technically reproduced by two methods, although they were not formally replicated in independent samples. Gene expression was explored in controls but not in patients. CONCLUSIONS: Pathway analysis in large GWAS data of BD and follow-up of gene expression patterns in healthy brains provide support for an involvement of neurodevelopmental processes in the etiology of this neuropsychiatric disease. Future studies are required to further evaluate the relevance of the implicated genes on pathway functioning and clinical aspects of BD.

Identification of shared risk loci and pathways for bipolar disorder and schizophrenia.

Bipolar disorder (BD) is a highly heritable neuropsychiatric disease characterized by recurrent episodes of mania and depression. BD shows substantial clinical and genetic overlap with other psychiatric disorders, in particular schizophrenia (SCZ). The genes underlying this etiological overlap remain largely unknown. A recent SCZ genome wide association study (GWAS) by the Psychiatric Genomics Consortium identified 128 independent genome-wide significant single nucleotide polymorphisms (SNPs). The present study investigated whether these SCZ-associated SNPs also contribute to BD development through the performance of association testing in a large BD GWAS dataset (9747 patients, 14278 controls). After re-imputation and correction for sample overlap, 22 of 107 investigated SCZ SNPs showed nominal association with BD. The number of shared SCZ-BD SNPs was significantly higher than expected (p = 1.46x10-8). This provides further evidence that SCZ-associated loci contribute to the development of BD. Two SNPs remained significant after Bonferroni correction. The most strongly associated SNP was located near TRANK1, which is a reported genome-wide significant risk gene for BD. Pathway analyses for all shared SCZ-BD SNPs revealed 25 nominally enriched gene-sets, which showed partial overlap in terms of the underlying genes. The enriched gene-sets included calcium- and glutamate signaling, neuropathic pain signaling in dorsal horn neurons, and calmodulin binding. The present data provide further insights into shared risk loci and disease-associated pathways for BD and SCZ. This may suggest new research directions for the treatment and prevention of these two major psychiatric disorders.

Genome-wide association study reveals two new risk loci for bipolar disorder.

Bipolar disorder (BD) is a common and highly heritable mental illness and genome-wide association studies (GWAS) have robustly identified the first common genetic variants involved in disease aetiology. The data also provide strong evidence for the presence of multiple additional risk loci, each contributing a relatively small effect to BD susceptibility. Large samples are necessary to detect these risk loci. Here we present results from the largest BD GWAS to date by investigating 2.3 million single-nucleotide polymorphisms (SNPs) in a sample of 24,025 patients and controls. We detect 56 genome-wide significant SNPs in five chromosomal regions including previously reported risk loci ANK3, ODZ4 and TRANK1, as well as the risk locus ADCY2 (5p15.31) and a region between MIR2113 and POU3F2 (6q16.1). ADCY2 is a key enzyme in cAMP signalling and our finding provides new insights into the biological mechanisms involved in the development of BD.

Replication study and meta-analysis in European samples supports association of the 3p21.1 locus with bipolar disorder.

BACKGROUND: Common genetic polymorphisms at chromosome 3p21.1, including rs2251219 in polybromo 1 (PBRM1), have been implicated in susceptibility to bipolar affective disorder (BP) through genome-wide association studies. Subsequent studies have suggested that this is also a risk locus for other psychiatric phenotypes, including major depression and schizophrenia. METHODS: To replicate the association, we studied 2562 cases with BP and 25,439 control subjects collected from seven cohorts with either genome-wide association or individual genotyping of rs2251219 and tagging single nucleotide polymorphisms across the PBRM1 gene. Results from the different case-control groups were combined with the inverse variance weighting method. RESULTS: In our dataset, rs2251219 was associated with BP (odds ratio [OR] = .89, p = .003), and meta-analysis of previously published data with our nonoverlapping new data confirmed genome-wide significant association (OR = .875, p = 2.68 × 10(-9)). Genotypic data from the SGENE-plus consortium were used to examine the association of the same variant with schizophrenia in an overall sample of 8794 cases and 25,457 control subjects, but this was not statistically significant (OR = .97, p = .21). CONCLUSIONS: There is strong evidence of association of rs2251219 with BP. However, our data do not support association of this marker with schizophrenia. Because the region of association has high linkage disequilibrium, forming a large haplotype block across many genes, it is not clear which gene is causally implicated in the disorder.

Assessment of the contribution of CFH and chromosome 10q26 AMD susceptibility loci in a Russian population isolate.

BACKGROUND/AIMS: A strong association has been confirmed between age-related macular degeneration (AMD) and variants at two independent loci including Tyr402His in the complement factor H (CFH) on 1q32 and Ser69Ala at LOC387715, a hypothetical gene on chromosome 10q26. The contribution of both loci to AMD was investigated in an isolated north-west Russian population. METHODS: Together with a PLEKHA1 variant at 10q26, the CFH Tyr402His and LOC387715 Ser69Ala polymorphisms were genotyped in 155 patients with AMD and 151 age-matched controls. chi(2) and Mantel-Haenszel (M-H) score tests were used to test for association. Sex-adjusted ORs were calculated. RESULTS: The frequency of the Tyr402His C allele was significantly higher in patients with AMD compared with controls (p(M-H)=0.0035). The increased risk observed in patients homozygous for the C allele (OR(HOM)=2.71, 95% CI 1.25 to 5.90) in this indigenous Russian population was considerably lower than that observed in previous western Caucasian populations. A significant increase in the frequency of the LOC387715 variant was observed in patients with late-stage AMD compared with controls (p(M-H)=0.007), with a homozygous OR of 3.47 (95% CI 1.01 to 11.9), although this association was not seen with early-stage AMD. CONCLUSION: The CFH gene contributes to AMD in this Russian population, although the risk conferred is considerably lower in this population than that found in other Western populations. A contribution of LOC387715 to disease in this population is also likely to be of weak effect.