Adebayo Anjorin

Collaborative genome-wide association analysis supports a role for ANK3 and CACNA1C in bipolar disorder

To identify susceptibility loci for bipolar disorder, we tested 1.8 million variants in 4,387 cases and 6,209 controls and identified a region of strong association (rs10994336, P = 9.1 × 10−9) in ANK3 (ankyrin G). We also found further support for the previously reported CACNA1C (alpha 1C subunit of the L-type voltage-gated calcium channel; combined P = 7.0 × 10−8, rs1006737). Our results suggest that ion channelopathies may be involved in the pathogenesis of bipolar disorder.

Whole-genome association study of bipolar disorder

We performed a genome-wide association scan in 1461 patients with bipolar (BP) 1 disorder, 2008 controls drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder and the University College London sample collections with successful genotyping for 372 193 single nucleotide polymorphisms (SNPs). Our strongest single SNP results are found in myosin5B (MYO5B; P=1.66 × 10−7) and tetraspanin-8 (TSPAN8; P=6.11 × 10−7). Haplotype analysis further supported single SNP results highlighting MYO5B, TSPAN8 and the epidermal growth factor receptor (MYO5B; P=2.04 × 10−8, TSPAN8; P=7.57 × 10−7 and EGFR; P=8.36 × 10−8). For replication, we genotyped 304 SNPs in family-based NIMH samples (n=409 trios) and University of Edinburgh case–control samples (n=365 cases, 351 controls) that did not provide independent replication after correction for multiple testing. A comparison of our strongest associations with the genome-wide scan of 1868 patients with BP disorder and 2938 controls who completed the scan as part of the Wellcome Trust Case–Control Consortium indicates concordant signals for SNPs within the voltage-dependent calcium channel, L-type, alpha 1C subunit (CACNA1C) gene. Given the heritability of BP disorder, the lack of agreement between studies emphasizes that susceptibility alleles are likely to be modest in effect size and require even larger samples for detection.

DISC1 association, heterogeneity and interplay in schizophrenia and bipolar disorder.

Disrupted in schizophrenia 1 (DISC1) has been associated with risk of schizophrenia, schizoaffective disorder, bipolar disorder, major depression, autism and Asperger syndrome, but apart from in the original translocation family, true causal variants have yet to be confirmed. Here we report a harmonized association study for DISC1 in European cohorts of schizophrenia and bipolar disorder. We identify regions of significant association, demonstrate allele frequency heterogeneity and provide preliminary evidence for modifying interplay between variants. Whereas no associations survived permutation analysis in the combined data set, significant corrected associations were observed for bipolar disorder at rs1538979 in the Finnish cohorts (uncorrected P=0.00020; corrected P=0.016; odds ratio=2.73±95% confidence interval (CI) 1.42–5.27) and at rs821577 in the London cohort (uncorrected P=0.00070; corrected P=0.040; odds ratio=1.64±95% CI 1.23–2.19). The rs821577 single nucleotide polymorphism (SNP) showed evidence for increased risk within the combined European cohorts (odds ratio=1.27±95% CI 1.07–1.51), even though significant corrected association was not detected (uncorrected P=0.0058; corrected P=0.28). After conditioning the European data set on the two risk alleles, reanalysis revealed a third significant SNP association (uncorrected P=0.00050; corrected P=0.025). This SNP showed evidence for interplay, either increasing or decreasing risk, dependent upon the presence or absence of rs1538979 or rs821577. These findings provide further support for the role of DISC1 in psychiatric illness and demonstrate the presence of locus heterogeneity, with the effect that clinically relevant genetic variants may go undetected by standard analysis of combined cohorts.

Case-case genome-wide association analysis shows markers differentially associated with schizophrenia and bipolar disorder and implicates calcium channel genes

Objective There are theoretical reasons why comparing marker allele frequencies between cases of different diseases, rather than with controls, may offer benefits. The samples may be better matched, especially for background risk factors common to both diseases. Genetic loci may also be detected which influence which of the two diseases occurs if common risk factors are present. Method We used samples of UK bipolar and schizophrenic cases that had earlier been subject to genome-wide association studies and compared marker allele frequencies between the two samples. When these differed for a marker, we compared the case sample allele frequencies with those of a control sample. Results Eight markers were significant at P value of less than 10−5. Of these, the most interesting finding was for rs17645023, which was significant at P value of less than 10−6 and which lies 36 kb from CACNG5. Control allele frequencies for this marker were intermediate between those for bipolar and schizophrenic cases. Conclusion The application of this approach suggests that it does have some merits. The finding for CACNG5, taken together with the earlier implication of CACNA1C and CACNA1B, strongly suggests a key role for voltage-dependent calcium channel genes in the susceptibility to bipolar disorder and/or schizophrenia.

Analysis of genetic deletions and duplications in the University College London bipolar disorder case control sample.

Genetic deletions and duplications known as copy number variants have been strongly implicated in genetic susceptibility to schizophrenia, autism, attention deficit hyperactivity disorder and epilepsy. The overall rate of copy number variants in the University College London (UCL) bipolar disorder sample was found to be slightly lower than the rate in controls. This finding confirms the results from other studies that have also shown no increased rate of copy number variants in bipolar disorder. However, some rare duplications and deletions were observed only in bipolar disorder cases and not in controls, these included some that had previously been detected only in rare cases of bipolar disorder. We conclude that copy-number variant analysis shows no obvious sharing of the same genetic susceptibility between schizophrenia and bipolar disorder. Copy number variants do not seem to have an important role in susceptibility to bipolar disorder, they may, however, still represent a rare cause of the disease, although the evidence for this is far from clear.

Confirmation of prior evidence of genetic susceptibility to alcoholism in a genome-wide association study of comorbid alcoholism and bipolar disorder.

Objectives Alcoholism and affective disorders are both strongly comorbid and heritable. We have investigated the genetic comorbidity between bipolar affective disorder and alcoholism. Methods A genome-wide allelic association study of 506 patients from the University College London bipolar disorder case–control sample and 510 ancestrally matched supernormal controls. One hundred forty-three of the bipolar patients fulfilled the Research Diagnostic Criteria diagnosis of alcoholism. A total of 372 193 single nucleotide polymorphisms (SNPs) were genotyped. Genes previously shown to be associated with alcoholism and addiction phenotypes were then tested for association in the bipolar alcoholic sample using gene-wise permutation tests of all SNPs genotyped within a 50-kb region flanking each gene. Results Several central nervous system genes showed significant (P<0.05) gene-wise evidence of association with bipolar alcoholism. The genes implicated, which replicated genes previously shown to be associated with alcoholism were: cadherin 11, collagen type 11 &agr;2, neuromedin U receptor 2, exportin7, and semaphorin-associated protein 5A. The SNPs most strongly implicated in bipolar alcoholism, but, which did not meet conventional genome-wide significance criteria were the insulin-like growth factor-binding protein 7, carboxypeptidase O, cerebellin 2, and the cadherin 12 genes. Conclusion We have confirmed the role of some genes previously shown to be associated with alcoholism in the comorbid bipolar alcoholism subgroup. In this subgroup, bipolar disorder may lower the threshold for the phenotypic expression of these alcoholism susceptibility genes. We also show that some genes may independently increase susceptibility to affective disorder and alcoholism.

No evidence for excess runs of homozygosity in bipolar disorder.

Background Recent studies have reported large common regions of homozygosity (ROHs) that are the result of autozygosity, that is, the cooccurrence within individuals of long haplotypes that have a high frequency in the population. A recent study reports that such regions are found more commonly in individuals with schizophrenia compared with controls, and identified nine ‘risk ROHs’ that were individually more common in cases. Of these, four contained or neighboured genes associated with schizophrenia (NOS1AP/UHMK1, ATF2, NSF and PIK3C3). Methods We have applied the same methodology to a UK sample of 506 cases with bipolar disorder and 510 controls. Results There was no overall excess of common ROHs among bipolar individuals. With one exception, the haplotypes accounting for the ROHs appeared to be distributed according to the Hardy–Weinberg equilibrium. One ROH was individually more common among cases (uncorrected P = 0.0003). This ROH spanned the chromosome 2p23.3 gene ITSN2 (the gene for intersectin 2 isoform 2). However, inspection of the homozygous haplotypes and haplotype-based tests for association failed to provide a clearer understanding of why this ROH was occurring more commonly. Conclusion Overall, we conclude that, in contrast with schizophrenia, common ROHs are rarely associated with susceptibility to bipolar disorder. This supports the idea that predominantly different genes are increasing susceptibility to schizophrenia and bipolar affective disorders.

Analysis of ANK3 and CACNA1C variants identified in bipolar disorder whole genome sequence data.

Genetic markers in the genes encoding ankyrin 3 (ANK3) and the α‐calcium channel subunit (CACNA1C) are associated with bipolar disorder (BP). The associated variants in the CACNA1C gene are mainly within intron 3 of the gene. ANK3 BP‐associated variants are in two distinct clusters at the ends of the gene, indicating disease allele heterogeneity.

The functional GRM3 Kozak sequence variant rs148754219 affects the risk of schizophrenia and alcohol dependence as well as bipolar disorder

We previously reported that a Kozak sequence variant in the metabotropic glutamate receptor 3 gene (GRM3), rs148754219, is associated with bipolar disorder (BP) and affects gene transcription and translation (Kandaswamy et al., 2013). A marker near GRM3, rs12704290, is one of the top hits and reached genome-wide significance in a recently reported genome-wide association study of schizophrenia (SZ) (Ripke et al., 2014), and markers for GRM3 have also been reported to demonstrate association with alcohol dependence syndrome (ADS) (Levey et al., 2014). In our original sample, considering patients successfully genotyped for rs148754219, 19 out of 1062 BP cases and only four out of 932 controls were heterozygous [odds ratio (OR)=4.2 (1.4–12.3), P=0.005]. We have genotyped this variant in additional controls and cases diagnosed with BP, SZ and ADS with the same ancestry. Patients were assessed by trained clinicians as described previously (Kandaswamy et al., 2013; Way et al., 2014). Allele counts were compared and significance was tested using Fisher’s exact test. Thirteen out of 934 additional BP cases and three out of 377 additional controls were heterozygous [OR=1.8 (0.49–6.2), P=not significant]. Combined with the originally reported results (Kandaswamy et al., 2013), 32 out of 1964 BP cases and seven out of 1309 controls were heterozygous [OR=3.0 (1.3–6.8), P=0.003]. Out of 1235 SZ cases 16 were heterozygous and were compared with the total control sample [OR=2.4 (0.99–5.8), P=0.03]. Out of 1514 ADS cases 18 were heterozygous and one was homozygous for the variant allele [OR=2.5 (1.0–5.9), P=0.03]. If all case cohorts (BP, SZ and ADS) are combined together, there would be one homozygote and 66 heterozygotes out of 4971 cases compared with the seven heterozygotes out of 1309 controls [OR=2.7 (1.2–5.8), P=0.004]. Previous work has supported the view that some genetic risk factors may be common to different psychiatric diagnoses (Lydall et al., 2011; Lee et al., 2013). Although the individual results are of questionable significance, the magnitude and direction of effect are consistent across all the cohorts and thus suggest the possibility that this rare variant may have a direct, functional effect on the risk of developing any of these three disorders. Because of its rarity, large sample sizes would be needed to confirm these results. Doing this would be worthwhile because if this finding is confirmed it could provide molecular insight into a mechanism involving GRM3 leading to increased risk of mental disorders and could provide a basis for further functional and therapeutic studies.

Genetic association and sequencing of the insulin-like growth factor 1 gene in bipolar affective disorder.

Insulin‐like growth factor 1 (IGF1) has been shown to have an important role in brain development and function. Studies of IGF1 administration in rodents have shown that it has an anxiolytic and antidepressant effect. A genome‐wide association study (GWAS) of the first University College London (UCL) cohort of 506 bipolar affective disorder subjects and 510 controls was carried out. The exons and flanking regions of IGF1 were resequenced, any new polymorphisms found were genotyped in an enlarged UCL sample of 937 cases and 941 controls. GWAS data gave good evidence of allelic and haplotypic association between multiple IGF1 SNPs and bipolar disorder (BD). New polymorphisms were found by resequencing IGF1 region. Data from GWAS and the new markers showed that twelve out of 43 SNPs showed association with BD with the four most significant SNPs having values of 3.7 × 10−5, 8.4 × 10−4, 2.6 × 10−4, and 2.5 × 10−4. A 5′ promoter microsatellite polymorphism previously correlated with plasma lipoprotein concentration was also associated with BD (P = 0.013). Haplotypic association confirmed association with BD with significance values similar to the single marker SNP values. The marker rs12426318 has also been found to be associated with BD in a second sample. A test of gene wide significance with permutation testing for all markers genotyped at IGF1 was also significant. These data implicate IGF1 as a candidate gene to cause genetic susceptibility to BD.