Ana Pereira

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.

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.

A threonine to isoleucine missense mutation in the pericentriolar material 1 gene is strongly associated with schizophrenia

Markers at the pericentriolar material 1 gene (PCM1) have shown genetic association with schizophrenia in both a University College London (UCL) and a USA-based case–control sample. In this paper we report a statistically significant replication of the PCM1 association in a large Scottish case–control sample from Aberdeen. Resequencing of the genomic DNA from research volunteers who had inherited haplotypes associated with schizophrenia showed a threonine to isoleucine missense mutation in exon 24 which was likely to change the structure and function of PCM1 (rs370429). This mutation was found only as a heterozygote in 98 schizophrenic research subjects and controls out of 2246 case and control research subjects. Among the 98 carriers of rs370429, 67 were affected with schizophrenia. The same alleles and haplotypes were associated with schizophrenia in both the London and Aberdeen samples. Another potential aetiological base pair change in PCM1 was rs445422, which altered a splice site signal. A further mutation, rs208747, was shown by electrophoretic mobility shift assays to create or destroy a promoter transcription factor site. Five further non-synonymous changes in exons were also found. Genotyping of the new variants discovered in the UCL case–control sample strengthened the evidence for allelic and haplotypic association (P=0.02–0.0002). Given the number and identity of the haplotypes associated with schizophrenia, further aetiological base pair changes must exist within and around the PCM1 gene. PCM1 protein has been shown to interact directly with the disrupted-in-schizophrenia 1 (DISC1) protein, Bardet-Biedl syndrome 4, and Huntingtin-associated protein 1, and is important in neuronal cell growth. In a separate study we found that clozapine but not haloperidol downregulated PCM1 expression in the mouse brain. We hypothesize that mutant PCM1 may be responsible for causing a subtype of schizophrenia through abnormal cell division and abnormal regeneration in dividing cells in the central nervous system. This is supported by our previous finding of orbitofrontal volumetric deficits in PCM1-associated schizophrenia patients as opposed to temporal pole deficits in non-PCM1-associated schizophrenia patients. Caution needs to be exercised in interpreting the actual biological effects of the mutations we have found without further cell biology. However, the DNA changes we have found deserve widespread genotyping in multiple case–control populations.

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.

Support of association between BRD1 and both schizophrenia and bipolar affective disorder

A recent study published by our group implicated the bromodomain containing protein 1 (BRD1) gene located at chromosome 22q13.33 with schizophrenia (SZ) and bipolar affective disorder (BPD) susceptibility and provided evidence suggesting a possible role for BRD1 in neurodevelopment. The present study reports an association analysis of BRD1 and the neighboring gene ZBED4 using a Caucasian case–control sample from Denmark and England (UK/DK sample: 490 patients with BPD, 527 patients with SZ, and 601 control individuals), and genotypes obtained from a BPD genome wide association (GWA) study of an overlapping English sample comprising 506 patients with BPD and 510 control individuals (UCL sample). In the UK/DK sample we genotyped 11 SNPs in the BRD1 region, of which six showed association with SZ (minimal single marker P‐values of 0.0014), including two SNPs that previously showed association in a Scottish population [Severinsen et al. (2006); Mol Psychiatry 11(12): 1126–1138]. Haplotype analysis revealed specific risk as well as protective haplotypes with a minimal P‐value of 0.0027. None of the 11 SNPs showed association with BPD. However, analyzing seven BRD1 SNPs obtained from the BPD GWA study, positive associations with BPD was observed with all markers (minimal P‐value of 0.0014). The associations reported add further support for the implication of BRD1 with SZ and BPD susceptibility.

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 Pu2009=u20090.0003). 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.

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 3.7u2009×u200910−5, 8.4u2009×u200910−4, 2.6u2009×u200910−4, and 2.5u2009×u200910−4. A 5′ promoter microsatellite polymorphism previously correlated with plasma lipoprotein concentration was also associated with BD (Pu2009=u20090.013). 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.

PW01-232 - Connectivity genes in comorbid alcoholism and bipolar disorder

Introduction Bipolar disorder (BPD) and alcoholism are strongly comorbid and both have significant genetic influences but no consistent genetic vulnerability has been found. We aimed to find bipolar-alcoholism vulnerability genes. Method A genome-wide association study (GWAS) of 510 patients with bipolar disorder (BPD), of whom 143 met Research Diagnostic Criteria (RDC) alcoholism diagnoses, and 506 ancestrally matched supernormal controls. We genotyped 372K genetic markers on an Affymetrix 500K-array. Chi-square analysis of allelic association using PLINK, and permutation testing for gene-wise association of genes previously associated with alcoholism-related phenotypes using COMBASSOC, were performed. Results No marker met genomewide significance. Gene-wise analyses of markers clustering near genes already implicated in alcoholism, but which were not associated in non-alcoholic BPD, were: Cadherin-11 (CDH11, p = 6 × 10-4), Exportin 7 (XPO7), neuromedin-U receptor 2 (NMUR2), collagen type XI-alpha 2 (COL11A2) and Semaphorin-5A (SEMA5A). Discussion These genes replicated prior genetic reports implicating “connectivity” (adhesion, migration and neuronal signalling) genes in addictions and comorbid BPD. Connectivity genes regulate neuronal connections during development and play roles in later neuroadaptive and mnemonic processes. These processes may influence addiction vulnerability, as seen clinically in denial, cognitive impairment, and repetitive substance misuse and relapse behaviour. We propose that we have identified genes i) increasing susceptibility to alcoholism that could be unmasked or released by the presence of bipolar affective disorder; ii) and genes increasing susceptibility to affective disorder that also predispose to secondary alcoholism. We were limited by small sample size. Larger future studies are needed.