Hugh Gurling

Letter abstract - Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's Disease

We undertook a two-stage genome-wide association study (GWAS) of Alzheimers disease (AD) involving over 16,000 individuals, the most powerful AD GWAS to date. In stage 1 (3,941 cases and 7,848 controls), we replicated the established association with the apolipoprotein E (APOE) locus (most significant SNP, rs2075650, P = 1.8 × 10−157) and observed genome-wide significant association with SNPs at two loci not previously associated with the disease: at the CLU (also known as APOJ) gene (rs11136000, P = 1.4 × 10−9) and 5′ to the PICALM gene (rs3851179, P = 1.9 × 10−8). These associations were replicated in stage 2 (2,023 cases and 2,340 controls), producing compelling evidence for association with Alzheimers disease in the combined dataset (rs11136000, P = 8.5 × 10−10, odds ratio = 0.86; rs3851179, P = 1.3 × 10−9, odds ratio = 0.86).

Genetic evidence implicates the immune system and cholesterol metabolism in the aetiology of Alzheimer's disease.

Background Late Onset Alzheimers disease (LOAD) is the leading cause of dementia. Recent large genome-wide association studies (GWAS) identified the first strongly supported LOAD susceptibility genes since the discovery of the involvement of APOE in the early 1990s. We have now exploited these GWAS datasets to uncover key LOAD pathophysiological processes. Methodology We applied a recently developed tool for mining GWAS data for biologically meaningful information to a LOAD GWAS dataset. The principal findings were then tested in an independent GWAS dataset. Principal Findings We found a significant overrepresentation of association signals in pathways related to cholesterol metabolism and the immune response in both of the two largest genome-wide association studies for LOAD. Significance Processes related to cholesterol metabolism and the innate immune response have previously been implicated by pathological and epidemiological studies of Alzheimers disease, but it has been unclear whether those findings reflected primary aetiological events or consequences of the disease process. Our independent evidence from two large studies now demonstrates that these processes are aetiologically relevant, and suggests that they may be suitable targets for novel and existing therapeutic approaches.

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.

A microarray gene expression study of the molecular pharmacology of lithium carbonate on mouse brain mRNA to understand the neurobiology of mood stabilization and treatment of bipolar affective disorder.

Objectives Lithium is the most widely prescribed and effective mood-stabilizing drug used for the treatment of bipolar affective disorder. To understand how lithium produces changes in the brain, we studied brain mRNA from 10 mice after treatment with lithium and compared them with 10 untreated controls. Methods We used the MAS 5.0, Smudge miner, GC-RMA and FDR-AME packages of software (Bioconductor, Seattle, Washington, USA) to determine gene expression changes using Affymetrix MOE430E 2.0 microarrays after 2 weeks of lithium treatment. Results We used both a false discovery rate (FDR-AME) assessment of significance and the Bonferroni method to correct for the possibility of false-positive changes in gene expression among the 39 000 genes present in each array. Our primary method of analysis was to use t-tests on normalized gene expression intensities. By using a Bonferroni correction of P<1.28×10−6, we found that 121 genes showed significant changes in expression. The three genes with the most changed mRNA expression were alanine-glyoxylate aminotransferase 2-like 1 (Agxt2l1), c-mer proto-oncogene tyrosine kinase (Mertk) and sulfotransferase family 1A phenol-preferring member 1 (Sult1a1). Also among the group of 121 genes with significant changes in gene expression that survived Bonferroni correction (Table 2) were the genes encoding the Per2 period gene (Per2 P=1.33×10−8, 2.47-fold change), the metabotropic glutamate receptor (Grm3, P=9.48×10−7, 0.7-fold change) and secretogranin II (Scg2, P=9.48×10−7, 1.28-fold change) as well as several myelin-related genes and protein phosphatases. By taking a significance value of P<0.05 without Bonferroni or FDR-AME correction, we identified a total of 4474 genes showing changed mRNA expression in response to lithium. FDR-AME analysis showed that 1027 out of these 4474 genes were significantly changed in expression. Among the mRNAs that were significantly changed with t-tests and FDR-AME were several that had already been implicated in response to lithium such as increased brain-derived neurotrophic factor mRNA ( t-test P=0.0008–0.0005, FDR-AME P=0.0396–0.0393, 1.44-fold change) &bgr;-phosphatidylinositol transfer protein (Pitpnb, t-test P<0.0000, FDR-AME P=0.003, 1.26-fold change) and inositol (myo)-1(or 4)-monophosphatase 1(Impa1, t test P<0.0000, FDR-AME P=0.004, 1.22-fold change). Of interest in relation to the side effect of hypothyroidism, which is caused by long-term lithium treatment was the fact that we observed changes in mRNA expression in five genes related to thyroxine metabolism. These included deiodinase (Dio2 t-test P=0.000003–0.004, FDR-AME P=0.0048–0.061, 1.53-fold change) and thyroid hormone receptor interactor 12 (Trip12, t-test P=0.003, FDR-AME P=0.075, 1.19-fold change). Of relevance to multiple sclerosis was the observed upregulation of the long isoform of myelin basic protein (t-test P=0.00013, FDR-AME P=0.0169). Changes in mRNA expression were found in 45 genes related to phosphatidylinositol metabolism using uncorrected t-tests but only 13 genes after FDR-AME. Thus, our work confirms the considerable previous research implicating this system. Gene ontology analysis showed that lithium significantly affected a cluster of processes associated with nucleotide and nucleoside metabolism. The analysis showed that there were 170 genes expressing RNA described as having ATP-binding or ATPase activity that had changed mRNA expression. The changes found have been discussed in relation to previous experimental work on the pharmacology of lithium.

A Genomewide Association Study of Response to Lithium for Prevention of Recurrence in Bipolar Disorder

OBJECTIVE Lithium remains a first-line treatment for bipolar disorder, but the mechanisms by which it prevents the recurrence of mood episodes are not known. The authors utilized data from a genomewide association study to examine associations between single nucleotide polymorphisms (SNPs) and the outcome of lithium treatment in two cohorts of patients with bipolar I disorder or bipolar II disorder. METHOD The hazard for mood episode recurrence was examined among 1,177 patients with bipolar I disorder or bipolar II disorder, including 458 individuals treated with lithium carbonate or citrate, who were participants in the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) cohort. SNPs showing the greatest evidence of association in Cox regression models were then examined for association with positive lithium response among 359 bipolar I or II disorder patients treated with lithium carbonate or citrate in a second cohort from the University College London. RESULTS The strongest association in the STEP-BD cohort (minimum p=5.5 x 10(-7)) was identified for a region on chromosome 10p15 (rs10795189). Of the regions showing suggestive evidence (p<5 x 10(-4)) of association with lithium response, five were further associated with positive lithium response in the University College London cohort, including SNPs in a region on chromosome 4q32 spanning a gene coding for the glutamate/alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionate (AMPA) receptor GRIA2. CONCLUSIONS Multiple novel loci merit further examination for association with lithium response in bipolar disorder patients, including one region that spans the GRIA2 gene, for which expression has been shown to be regulated by lithium treatment.

Genome-wide association study of suicide attempts in mood disorder patients

OBJECTIVE Family and twin studies suggest that liability for suicide attempts is heritable and distinct from mood disorder susceptibility. The authors therefore examined the association between common genomewide variation and lifetime suicide attempts. METHOD The authors analyzed data on lifetime suicide attempts from genomewide association studies of bipolar I and II disorder as well as major depressive disorder. Bipolar disorder subjects were drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder cohort, the Wellcome Trust Case Control Consortium bipolar cohort, and the University College London cohort. Replication was pursued in the NIMH Genetic Association Information Network bipolar disorder project and a German clinical cohort. Depression subjects were drawn from the Sequential Treatment Alternatives to Relieve Depression cohort, with replication in the Netherlands Study of Depression and Anxiety/Netherlands Twin Register depression cohort. RESULTS Strongest evidence of association for suicide attempt in bipolar disorder was observed in a region without identified genes (rs1466846); five loci also showed suggestive evidence of association. In major depression, strongest evidence of association was observed for a single nucleotide polymorphism in ABI3BP, with six loci also showing suggestive association. Replication cohorts did not provide further support for these loci. However, meta-analysis incorporating approximately 8,700 mood disorder subjects identified four additional regions that met the threshold for suggestive association, including the locus containing the gene coding for protein kinase C-epsilon, previously implicated in models of mood and anxiety. CONCLUSIONS The results suggest that inherited risk for suicide among mood disorder patients is unlikely to be the result of individual common variants of large effect. They nonetheless provide suggestive evidence for multiple loci, which merit further investigation.

Maternally derived microduplications at 15q11-q13: implication of imprinted genes in psychotic illness

OBJECTIVE Rare copy number variants have been implicated in different neurodevelopmental disorders, with the same copy number variants often increasing risk of more than one of these phenotypes. In a discovery sample of 22 schizophrenia patients with an early onset of illness (10-15 years of age), the authors observed in one patient a maternally derived 15q11-q13 duplication overlapping the Prader-Willi/Angelman syndrome critical region. This prompted investigation of the role of 15q11-q13 duplications in psychotic illness. METHOD The authors scanned 7,582 patients with schizophrenia or schizoaffective disorder and 41,370 comparison subjects without known psychiatric illness for copy number variants at 15q11-q13 and determined the parental origin of duplications using methylation-sensitive Southern hybridization analysis. RESULTS Duplications were found in four case patients and five comparison subjects. All four case patients had maternally derived duplications (0.05%), while only three of the five comparison duplications were maternally derived (0.007%), resulting in a significant excess of maternally derived duplications in case patients (odds ratio=7.3). This excess is compatible with earlier observations that risk for psychosis in people with Prader-Willi syndrome caused by maternal uniparental disomy is much higher than in those caused by deletion of the paternal chromosome. CONCLUSIONS These findings suggest that the presence of two maternal copies of a fragment of chromosome 15q11.2-q13.1 that overlaps with the Prader-Willi/Angelman syndrome critical region may be a rare risk factor for schizophrenia and other psychoses. Given that maternal duplications of this region are among the most consistent cytogenetic observations in autism, the findings provide further support for a shared genetic etiology between autism and psychosis.

Fine mapping of a susceptibility locus for bipolar and genetically related unipolar affective disorders, to a region containing the C21ORF29 and TRPM2 genes on chromosome 21q22.3

Linkage analyses of bipolar families have confirmed that there is a susceptibility locus near the telomere on chromosome 21q. To fine map this locus we carried out tests of allelic association using 30 genetic markers near the telomere at 21q22.3 in 600 bipolar research subjects and 450 ancestrally matched supernormal control subjects. We found significant allelic association with the microsatellite markers D21S171 (P=0.016) and two closely linked single-nucleotide polymorphisms, rs1556314 (P=0.008) and rs1785467 (P=0.025). A test of association with a three locus haplotype across the susceptibility region was significant with a permutation test of P=0.011. A two SNP haplotype was also significantly associated with bipolar disorder (P=0.01). Only two brain expressed genes, TRPM2 and C21ORF29 (TSPEAR), are present in the associated region. TRPM2 encodes a calcium channel receptor and TSPEAR encodes a peptide with repeats associated with epilepsy in the mouse. DNA from subjects who had inherited the associated marker alleles was sequenced. A base pair change (rs1556314) in exon 11 of TRPM2, which caused a change from an aspartic acid to a glutamic acid at peptide position 543 was found. This SNP showed the strongest association with bipolar disorder (P=0.008). Deletion of exon 11 of TRPM2 is known to cause dysregulation of cellular calcium homeostasis in response to oxidative stress. A second nonconservative change from arginine to cysteine at position 755 in TRPM2 (ss48297761) was also detected. A third nonconservative change from histidine to glutamic acid was found in exon 8 of TSPEAR. These changes need further investigation to establish any aetiological role in bipolar disorder.

NK1 (TACR1) receptor gene 'knockout' mouse phenotype predicts genetic association with ADHD

Mice with functional genetic ablation of the Tacr1 (substance P-preferring receptor) gene (NK1R−/−) are hyperactive. Here, we investigated whether this is mimicked by NK1R antagonism and whether dopaminergic transmission is disrupted in brain regions that govern motor performance. The locomotor activity of NK1R−/− and wild-type mice was compared after treatment with an NK1R antagonist and/or psychostimulant (d-amphetamine or methylphenidate). The inactivation of NK1R (by gene mutation or receptor antagonism) induced hyperactivity in mice, which was prevented by both psychostimulants. Using in vivo microdialysis, we then compared the regulation of extracellular dopamine in the prefrontal cortex (PFC) and striatum in the two genotypes. A lack of functional NK1R reduced (>50%) spontaneous dopamine efflux in the prefrontal cortex and abolished the striatal dopamine response to d-amphetamine. These behavioural and neurochemical abnormalities in NK1R−/− mice, together with their atypical response to psychostimulants, echo attention deficit hyperactivity disorder (ADHD) in humans. These findings prompted genetic studies on the TACR1 gene (the human equivalent of NK1R) in ADHD patients in a case—control study of 450 ADHD patients and 600 screened supernormal controls. Four single-nucleotide polymorphisms (rs3771829, rs3771833, rs3771856, and rs1701137) at the TACR1 gene, previously known to be associated with bipolar disorder or alcoholism, were strongly associated with ADHD. In conclusion, our proposal that NK1R−/− mice offer a mouse model of ADHD was borne out by our human studies, which suggest that DNA sequence changes in and around the TACR1 gene increase susceptibility to this disorder.

Twin and adoption studies. How good is the evidence for a genetic role

Research into the possibility that heredity may influence drinking habits is still in its infancy, and the conclusions that can be reached from a number of the available twin and adoption studies are limited by their methodological deficiencies. Nevertheless, the balance of evidence suggests a modest genetic effect on both normal drinking and alcoholism in men, though similar evidence for women is so far lacking. Further studies are required to assess the significance of the genetic contribution, to elucidate exactly what is inherited, and to examine the nature of gene-environment interactions.