Stewart W. Morris

Association of Neuregulin 1 with schizophrenia and bipolar disorder in a second cohort from the Scottish population.

Neuregulin 1 (NRG1) is a strong candidate for involvement in the aetiology of schizophrenia. A haplotype, initially identified as showing association in the Icelandic and Scottish populations, has shown a consistent effect size in multiple European populations. Additionally, NRG1 has been implicated in susceptibility to bipolar disorder. In this first study to select markers systematically on the basis of linkage disequilibrium across the entire NRG1 gene, we used haplotype-tagging single-nucleotide polymorphisms to identify single markers and haplotypes associated with schizophrenia and bipolar disorder in an independently ascertained Scottish population. Haplotypes in two regions met an experiment-wide significance threshold of P=0.0016 (Nyholts SpD) and were permuted to correct for multiple testing. Region A overlaps with the Icelandic haplotype and shows nominal association with schizophrenia (P=0.00032), bipolar disorder (P=0.0011), and the combined case group (P=0.0017). This region includes the 5′ exon of the NRG1 GGF2 isoform and overlaps the expressed sequence tag (EST) cluster Hs.97362. However, no haplotype in Region A remains significant after permutation analysis (P>0.05). Region B contains a haplotype associated with both schizophrenia (P=0.00014), and the combined case group (P=0.000062), although it does not meet Nyholts threshold in bipolar disorder alone (P=0.0022). This haplotype remained significant after permutation analysis in both the schizophrenia and combined case groups (P=0.024 and P=0.016, respectively). It spans a ∼136 kb region that includes the coding sequence of the sensory and motor neuron derived factor (SMDF) isoform and 3′ exons of all other known NRG1 isoforms. Our study identifies a new of NRG1 region involved in schizophrenia and bipolar disorder in the Scottish population.

Cytogenetic and genetic evidence supports a role for the kainate-type glutamate receptor gene, GRIK4, in schizophrenia and bipolar disorder

In the search for the biological causes of schizophrenia and bipolar disorder, glutamate neurotransmission has emerged as one of a number of candidate processes and pathways where underlying gene deficits may be present. The analysis of chromosomal rearrangements in individuals diagnosed with neuropsychiatric disorders is an established route to candidate gene identification in both Mendelian and complex disorders. Here we describe a set of genes disrupted by, or proximal to, chromosomal breakpoints (2p12, 2q31.3, 2q21.2, 11q23.3 and 11q24.2) in a patient where chronic schizophrenia coexists with mild learning disability (US: mental retardation). Of these disrupted genes, the most promising candidate is a member of the kainate-type ionotropic glutamate receptor family, GRIK4 (KA1). A subsequent systematic case–control association study on GRIK4 assessed its contribution to psychiatric illness in the karyotypically normal population. This identified two discrete regions of disease risk within the GRIK4 locus: three single single nucleotide polymorphism (SNP) markers with a corresponding underlying haplotype associated with susceptibility to schizophrenia (P=0.0005, odds ratio (OR) of 1.453, 95% CI 1.182–1.787) and two single SNP markers and a haplotype associated with a protective effect against bipolar disorder (P=0.0002, OR of 0.624, 95% CI 0.485–0.802). After permutation analysis to correct for multiple testing, schizophrenia and bipolar disorder haplotypes remained significant (P=0.0430, s.e. 0.0064 and P=0.0190, s.e. 0.0043, respectively). We propose that these convergent cytogenetic and genetic findings provide molecular evidence for common aetiologies for different psychiatric conditions and further support the ‘glutamate hypothesis’ of psychotic illness.

Interacting haplotypes at the NPAS3 locus alter risk of schizophrenia and bipolar disorder

The neuronal PAS domain 3 (NPAS3) gene encodes a neuronal transcription factor that is implicated in psychiatric disorders by the identification of a human chromosomal translocation associated with schizophrenia and a mouse knockout model with behavioural and hippocampal neurogenesis defects. To determine its contribution to the risk of psychiatric illness in the general population, we genotyped 70 single-nucleotide polymorphisms across the NPAS3 gene in 368 individuals with bipolar disorder, 386 individuals with schizophrenia and 455 controls. Modestly significant single-marker and global and individual haplotypes were identified in four discrete regions of the gene. The presence of both risk and protective haplotypes at each of these four regions indicated locus and allelic heterogeneity within NPAS3 and suggested a model whereby interactions between variants across the gene might contribute to susceptibility to illness. This was supported by predicting the most likely haplotype for each individual at each associated region and then calculating an NPAS3-mediated ‘net genetic load’ value. This value differed significantly from controls for both bipolar disorder (P=0.0000010) and schizophrenia (P=0.0000012). Logistic regression analysis also confirmed the combinatorial action of the four associated regions on disease risk. In addition, sensitivity/specificity plots showed that the extremes of the genetic loading distribution possess the greatest predictive power—a feature suggesting multiplicative allele interaction. These data add to recent evidence that the combinatorial analysis of a number of relatively small effect size haplotypes may have significant power to predict an individuals risk of a complex genetic disorder such as psychiatric illness.

The PDE4B gene confers sex-specific protection against schizophrenia

Background Phosphodiesterase 4B (PDE4B) is a candidate gene for schizophrenia and affective disorders through its disruption by a chromosomal translocation in an individual with schizophrenia, its inhibition by the antidepressant rolipram, and its physical interaction with another key candidate, Disrupted in Schizophrenia (DISC1). Objective To determine the contribution made by PDE4B to the population risk of schizophrenia and bipolar disorder by carrying out a case–control association study. Methods Twenty-six tagging single nucleotide polymorphisms were selected across the PDE4B gene and genotyped in DNA samples from 386 schizophrenia cases, 368 bipolar disorder cases and 455 controls. Main results Single single nucleotide polymorphisms and a resulting haplotype conferred a protective effect against schizophrenia in the female population. The haplotype result remained significant after correction for multiple testing (P=0.012). Conclusion The observation that a PDE4B haplotype alters the genetic risk of schizophrenia in the Scottish population complements the known participation of this gene in biological processes associated with mental illness. Further studies are needed to replicate this finding and identify underlying sequence variants.

A study of chromosome 4p markers and dopamine D5 receptor gene in schizophrenia and bipolar disorder

There are several lines of evidence which suggest that chromosome 4p may contain a major susceptibility locus for the functional psychoses. We previously reported a family (family 50) with cases of schizophrenia and schizoaffective disorder which gave maximum lod scores of 1.96 and 1.84 respectively with the markers D4S403 and a microsatellite near to DRD5 (DRD5-M). More recently Blackwood and co-workers described a family segregating bipolar and unipolar affective disorders which gives a maximum lod score of 4.1 with the marker D4S394, which lies 10 cM from D4S403. They obtained a combined maximum lod of 3.3 in their total sample of 12 bipolar families and found significant evidence of heterogeneity (χ2 = 18.8, df = 2, P = 0.00008). Here we report the results of a linkage study of chromosome 4p markers in a sample of 24 multiply affected families with schizophrenia and related disorders. We obtained an overall maximum lod of 1.12 with D4S403 under both dominant and recessive modes of transmission, with no statistical support for heterogeneity within our sample. Examination of family by family data shows that only family 50 appears to show linkage at this locus. However, a discrepancy exists since our study examined families fulfilling criteria for a linkage study of schizophrenia while Blackwood et al examined families included in a genetic linkage study of bipolar disorder. This may be explained by the clinical features displayed by members of family 50, which show that all the affected members have some affective symptoms. It is therefore possible that a broad phenotype including unipolar depression, bipolar disorder, schizoaffective disorder and schizophrenia when accompanied by significant affective symptoms can result from mutations within a gene in this region. The dopamine D5 receptor gene lies within the region identified by the linkage studies and is therefore a major candidate for the putative disease gene. In family 50 we have looked for mutations of DRD5 by sequence analysis of the coding region and single stranded conformational polymorphism (SSCP) analysis of the promoter. SSCP analysis of the coding and promoter regions have also been carried out in unrelated cases of DSM-IIIR schizophrenia. Finally association studies of the (TC)n repeat in the promoter and schizophrenia, and DRD5-M and bipolar disorder were performed. These studies provided no further evidence supporting the possibility that mutations in DRD5 give rise to the linkage findings or are acting as susceptibility loci in schizophrenia or bipolar disorder.

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 528 kb 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.

Association analysis of the chromosome 4p15–p16 candidate region for bipolar disorder and schizophrenia

Several independent linkage studies have identified chromosome 4p15–p16 as a putative region of susceptibility for bipolar disorder (BP), schizophrenia (SCZ) and related phenotypes. Previously, we identified two subregions (B and D) of the 4p15–p16 region that are shared by three of four 4p-linked families examined. Here, we describe a large-scale association analysis of regions B and D (3.8 and 4.5 Mb, respectively). We selected 408 haplotype-tagging single nucleotide polymorphisms (SNPs) on a block-by-block basis from the International HapMap project and tested them in 368 BP, 386 SCZ and 458 control individuals. Nominal significance thresholds were determined using principal component analysis as implemented in the program SNPSpD. In region B, overlapping SNPs and haplotypes met the region-wide threshold (P⩽0.0005) at the global and individual haplotype test level and clustered in two regions. In region D, no individual SNPs were nominally significant, but multiple global and individual haplotypes were associated with BP and/or SCZ (region-wide threshold, P⩽0.0003). These overlapping haplotypes fell into two regions. Within each of these four clusters, at least one globally significant haplotype withstood permutation testing (Pgp⩽0.05). Five predicted genes were found within these associated regions, while Known/RefSeq genes, including KIAA0746 and PPARGC1A, mapped nearby. There were also nine other clusters within regions B and D with nominally significant haplotypes, but only at the individual haplotype level. KIAA0746, PPARGC1A, GPR125, CCKAR and DKFZp761B107 overlapped with these regions. This study has identified significant associations between BP and SCZ within the chromosome 4p linkage region, resulting in candidate regions worthy of further investigation.

Haplotype Analysis and a Novel Allele-Sharing Method Refines a Chromosome 4p Locus Linked to Bipolar Affective Disorder

BACKGROUND Bipolar affective disorder (BPAD) and schizophrenia (SCZ) are common conditions. Their causes are unknown, but they include a substantial genetic component. Previously, we described significant linkage of BPAD to a chromosome 4p locus within a large pedigree (F22). Others subsequently have found evidence for linkage of BPAD and SCZ to this region. METHODS We constructed high-resolution haplotypes for four linked families, calculated logarithm of the odds (LOD) scores, and developed a novel method to assess the extent of allele sharing within genes between the families. RESULTS We describe an increase in the F22 LOD score for this region. Definition and comparison of the linked haplotypes allowed us to prioritize two subregions of 3.8 and 4.4 Mb. Analysis of the extent of allele sharing within these subregions identified 200 kb that shows increased allele sharing between families. CONCLUSIONS Linkage of BPAD to chromosome 4p has been strengthened. Haplotype analysis in the additional linked families refined the 20-Mb linkage region. Development of a novel allele-sharing method allowed us to bridge the gap between conventional linkage and association studies. Description of a 200-kb region of increased allele sharing prioritizes this region, which contains two functional candidate genes for BPAD, SLC2A9, and WDR1, for subsequent studies.

Convergence of linkage, association and GWAS findings for a candidate region for bipolar disorder and schizophrenia on chromosome 4p

Convergence of linkage, association and GWAS findings for a candidate region for bipolar disorder and schizophrenia on chromosome 4p

Hereditary multi-infarct dementia unlinked to chromosome 19q12 in a large Scottish pedigree: evidence of probable locus heterogeneity.

Hereditary multi-infarct dementia is a rare autosomal dominant disorder that predominantly affects the cerebral white matter. A locus was recently mapped in French pedigrees to chromosome 19q12. We have examined a large Scottish pedigree with neuropathologically confirmed hereditary multi-infarct dementia using polymorphic DNA markers spanning the 19q12 region and found no evidence of linkage. This suggests that, as in familial Alzheimers disease, there is more than one locus.