D. H. R. Blackwood

Genome-wide association for major depressive disorder: a possible role for the presynaptic protein piccolo

Major depressive disorder (MDD) is a common complex trait with enormous public health significance. As part of the Genetic Association Information Network initiative of the US Foundation for the National Institutes of Health, we conducted a genome-wide association study of 435u2009291 single nucleotide polymorphisms (SNPs) genotyped in 1738 MDD cases and 1802 controls selected to be at low liability for MDD. Of the top 200, 11 signals localized to a 167u2009kb region overlapping the gene piccolo (PCLO, whose protein product localizes to the cytomatrix of the presynaptic active zone and is important in monoaminergic neurotransmission in the brain) with P-values of 7.7 × 10−7 for rs2715148 and 1.2 × 10−6 for rs2522833. We undertook replication of SNPs in this region in five independent samples (6079 MDD independent cases and 5893 controls) but no SNP exceeded the replication significance threshold when all replication samples were analyzed together. However, there was heterogeneity in the replication samples, and secondary analysis of the original sample with the sample of greatest similarity yielded P=6.4 × 10−8 for the nonsynonymous SNP rs2522833 that gives rise to a serine to alanine substitution near a C2 calcium-binding domain of the PCLO protein. With the integrated replication effort, we present a specific hypothesis for further studies.

Genome-wide association study of major depressive disorder: new results, meta-analysis, and lessons learned

Major depressive disorder (MDD) is a common complex disorder with a partly genetic etiology. We conducted a genome-wide association study of the MDD2000+ sample (2431 cases, 3673 screened controls and >1u2009M imputed single-nucleotide polymorphisms (SNPs)). No SNPs achieved genome-wide significance either in the MDD2000+ study, or in meta-analysis with two other studies totaling 5763 cases and 6901 controls. These results imply that common variants of intermediate or large effect do not have main effects in the genetic architecture of MDD. Suggestive but notable results were (a) gene-based tests suggesting roles for adenylate cyclase 3 (ADCY3, 2p23.3) and galanin (GAL, 11q13.3); published functional evidence relates both of these to MDD and serotonergic signaling; (b) support for the bipolar disorder risk variant SNP rs1006737 in CACNA1C (P=0.020, odds ratio=1.10); and (c) lack of support for rs2251219, a SNP identified in a meta-analysis of affective disorder studies (P=0.51). We estimate that sample sizes 1.8- to 2.4-fold greater are needed for association studies of MDD compared with those for schizophrenia to detect variants that explain the same proportion of total variance in liability. Larger study cohorts characterized for genetic and environmental risk factors accumulated prospectively are likely to be needed to dissect more fully the etiology of MDD.

Meta-Analysis of Genome-Wide Association Data of Bipolar Disorder and Major Depressive Disorder

Meta-analysis of genome-wide association data of bipolar disorder and major depressive disorder

GWA study data mining and independent replication identify cardiomyopathy-associated 5 (CMYA5) as a risk gene for schizophrenia

We conducted data-mining analyses using the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) and molecular genetics of schizophrenia genome-wide association study supported by the genetic association information network (MGS-GAIN) schizophrenia data sets and performed bioinformatic prioritization for all the markers with P-values ⩽0.05 in both data sets. In this process, we found that in the CMYA5 gene, there were two non-synonymous markers, rs3828611 and rs10043986, showing nominal significance in both the CATIE and MGS-GAIN samples. In a combined analysis of both the CATIE and MGS-GAIN samples, rs4704591 was identified as the most significant marker in the gene. Linkage disequilibrium analyses indicated that these markers were in low LD (3u2009828u2009611–rs10043986, r2=0.008; rs10043986–rs4704591, r2=0.204). In addition, CMYA5 was reported to be physically interacting with the DTNBP1 gene, a promising candidate for schizophrenia, suggesting that CMYA5 may be involved in the same biological pathway and process. On the basis of this information, we performed replication studies for these three single-nucleotide polymorphisms. The rs3828611 was found to have conflicting results in our Irish samples and was dropped out without further investigation. The other two markers were verified in 23 other independent data sets. In a meta-analysis of all 23 replication samples (family samples, 912 families with 4160 subjects; case–control samples, 11u2009380 cases and 15u2009021 controls), we found that both markers are significantly associated with schizophrenia (rs10043986, odds ratio (OR)=1.11, 95% confidence interval (CI)=1.04–1.18, P=8.2 × 10−4 and rs4704591, OR=1.07, 95% CI=1.03–1.11, P=3.0 × 10−4). The results were also significant for the 22 Caucasian replication samples (rs10043986, OR=1.11, 95% CI=1.03–1.17, P=0.0026 and rs4704591, OR=1.07, 95% CI=1.02–1.11, P=0.0015). Furthermore, haplotype conditioned analyses indicated that the association signals observed at these two markers are independent. On the basis of these results, we concluded that CMYA5 is associated with schizophrenia and further investigation of the gene is warranted.

A common variant in the 3′UTR of the GRIK4 glutamate receptor gene affects transcript abundance and protects against bipolar disorder

Underactivity of the glutamatergic system is an attractive model for the pathophysiology of several major mental illnesses. We previously described a chromosome abnormality disrupting the kainate class ionotropic glutamate receptor gene, GRIK4/KA1, in an individual with schizophrenia and learning disability (mental retardation). We also demonstrated in a case-control study that two physically separated haplotypes within this gene were significantly associated with increased risk of schizophrenia and decreased risk of bipolar disorder, respectively. The latter protective haplotype was located at the 3′ end of the gene. We now report the identification from carriers of the protective haplotype of a deletion variant within the 3′ untranslated region of the gene. The deletion allele also was found to be negatively associated with bipolar disorder in both initial (P = 0.00000019) and replication (P = 0.0107) case-control studies. Expression studies indicated that deletion-carrying mRNA transcripts were relatively more abundant. We postulate that this may be a direct consequence of the differences in the RNA secondary structures predicted for the insertion and deletion alleles. These data suggest a mechanism whereby the genetic protective effect is mediated through increased kainate receptor expression.

708 Common and 2010 rare DISC1 locus variants identified in 1542 subjects: analysis for association with psychiatric disorder and cognitive traits.

A balanced t(1;11) translocation that transects the Disrupted in schizophrenia 1 (DISC1) gene shows genome-wide significant linkage for schizophrenia and recurrent major depressive disorder (rMDD) in a single large Scottish family, but genome-wide and exome sequencing-based association studies have not supported a role for DISC1 in psychiatric illness. To explore DISC1 in more detail, we sequenced 528u2009kb of the DISC1 locus in 653 cases and 889 controls. We report 2718 validated single-nucleotide polymorphisms (SNPs) of which 2010 have a minor allele frequency of <1%. Only 38% of these variants are reported in the 1000 Genomes Project European subset. This suggests that many DISC1 SNPs remain undiscovered and are essentially private. Rare coding variants identified exclusively in patients were found in likely functional protein domains. Significant region-wide association was observed between rs16856199 and rMDD (P=0.026, unadjusted P=6.3 × 10−5, OR=3.48). This was not replicated in additional recurrent major depression samples (replication P=0.11). Combined analysis of both the original and replication set supported the original association (P=0.0058, OR=1.46). Evidence for segregation of this variant with disease in families was limited to those of rMDD individuals referred from primary care. Burden analysis for coding and non-coding variants gave nominal associations with diagnosis and measures of mood and cognition. Together, these observations are likely to generalise to other candidate genes for major mental illness and may thus provide guidelines for the design of future studies.

A transmission disequilibrium and linkage analysis of D22S278 marker alleles in 574 families: further support for a susceptibility locus for schizophrenia at 22q12

Patients with schizophrenia rarely develop rheumatoid arthritis, an autoimmune disease that exhibits genetic association with the HLA DRB1*04 gene. We previously investigated the hypothesis that schizophrenia is negatively associated with DRB1*04, and found that only half the expected number of schizophrenic patients had this gene when compared with controls. We now report the results of DRB1*04 genotyping in pedigrees multiply affected with schizophrenia. Polymerase chain reaction amplification and sequence-specific oligonucleotide probes were used to determine the DRB1 genotypes of the 187 members of 23 pedigrees multiply affected with RDC schizophrenia. DQA1, DQB1 and DPB1 genotypes were similarly determined. We analysed data using the extended transmission/disequilibrium test and found a trend for the preferential non-transmission of DRB1*04 alleles from heterozygous parents to their schizophrenic offspring (16 of 23 alleles not transmitted, chi 2 = 3.5, p = 0.06). We found no evidence for a gene of major effect using GENEHUNTER for parametric and non-parametric linkage analysis. The results from this small sample need to be interpreted with caution, but they are in keeping with previous reports and suggest that HLA DRB1*04 alleles may be associated with a reduced risk of schizophrenia.Previously, a combined analysis by the Chromosome 22 Collaborative Linkage Group (1996; Am. J. Med Genet. 67, 40-45) used an affected sib-pair analysis of a single marker (D22S278) in 574 families multiply affected by schizophrenia and found some evidence for linkage (chi 2 = 9.35, 1 df, p = 0.001), suggesting the presence of a disease locus nearby on chromosome 22q12. In order to further investigate the importance of this result, we have performed the transmission disequilibrium test (TDT) and additional parametric and non-parametric linkage analysis of the same data. The most positive result obtained was an admixture lod score of 0.9 under the assumption of locus heterogeneity and dominant transmission. The result of the TDT analysis was significant at p = 0.015 (allele-wise; chi 2 = 22, 10 df) and p = 0.00016 (genotype-wise; chi 2 = 66.2, 30 df, empirical p value = 0.0009). Overall, these results further strengthen the notion that there is a susceptibility locus for schizophrenia close to D22S278.

Bridging the translational divide: identical cognitive touchscreen testing in mice and humans carrying mutations in a disease-relevant homologous gene.

Development of effective therapies for brain disorders has been hampered by a lack of translational cognitive testing methods. We present the first example of using the identical touchscreen-based cognitive test to assess mice and humans carrying disease-related genetic mutations. This new paradigm has significant implications for improving how we measure and model cognitive dysfunction in human disorders in animals, thus bridging the gap towards effective translation to the clinic.

Cognitive brain potentials and psychological deficits in Alzheimer's dementia and Korsakoff's amnesic syndrome.

Auditory-event-related potentials, including the P300 response, were recorded from 20 patients with Alzheimer-type dementia (ATD), 17 patients with Korsakoffs syndrome (KS) and 23 age-matched control subjects. Each of the subjects was assessed using a version of the Luria Neuropsychological Investigation. Prolonged P300 latency and reduced P300 latency and reduced P300 amplitude, which are features of normal ageing and which also occur, to a greater degree, in ATD, correlated significantly with degree of impairment of language ability in both Alzheimer patients and controls. On the other hand, the association between P300 latency changes and various tests of memory was not consistent across the three subject groups; there was a significant negative correlation between P300 latency and visual memory in ATD and a significant positive correlation in KS, whereas in controls no significant correlation was found. By contrast, P300 latency and memory for words were significantly negatively correlated in controls, but in neither of the patient groups. Detailed studies of language function may further elucidate the complex relationships between neuropsychological measures and P300 changes in normal ageing and dementia.

Genetic survival analysis of age-at-onset of bipolar disorder: evidence for anticipation or cohort effect in families

Age-at-onset (AAO) in a number of extended families ascertained for bipolar disorder was analysed using survival analysis techniques, fitting proportional hazards models to estimate the fixed effects of sex, year of birth, and generation, and a random polygenic genetic effect. Data comprised the AAO (for 171 affecteds) or age when last seen (ALS) for 327 unaffecteds, on 498 individuals in 27 families. ALS was treated as the censored time in the statistical analyses. The majority of individuals classified as affected were diagnosed with bipolar I and II (nu2005 =u2005103) or recurrent major depressive disorder (nu2005 =u200568). In addition to the significant effects of sex and year of birth, a fitted ‘generation’ effect was highly significant, which could be interpreted as evidence for an anticipation effect. The risk of developing bipolar or unipolar disorder increased twofold with each generation descended from the oldest founder. However, although information from both affected and unaffected individuals was used to estimate the relative risk of subsequent generations, it is possible that the results are biased because of the ‘Penrose effect’. Females had a twofold increased risk in developing depressive disorder relative to males. The risk of developing bipolar or unipolar disorder increased by approximately 4% per year of birth. A polygenic component of variance was estimated, resulting in a ‘heritability’ of AAO of approximately 0.52. In a family showing strong evidence of linkage to chromosome 4p (family 22), the ‘affected haplotype’ increased the relative risk of being affected by a factor of 46. In this family, there was strong evidence of a time trend in the AAO. When either year of birth or generation was fitted in the model, these effects were highly significant, but neither was significant in the presence of the other. For this family, there was no increase in trinucleotide repeats measured by the repeat expansion detection method in affected individuals compared with control subjects. Proportional hazard models appear appropriate to analyse AAO data, and the methodology will be extended to map quantitative trait loci (QTL) for AAO.