Lavinia Athanasiu

Gene variants associated with schizophrenia in a Norwegian genome-wide study are replicated in a large European cohort

We have performed a genome-wide association study (GWAS) of schizophrenia in a Norwegian discovery sample of 201 cases and 305 controls (TOP study) with a focused replication analysis in a larger European sample of 2663 cases and 13,780 control subjects (SGENE-plus study). Firstly, the discovery sample was genotyped with Affymetrix Genome-Wide Human SNP Array 6.0 and 572,888 markers were tested for schizophrenia association. No SNPs in the discovery sample attained genome-wide significance (P<8.7 x 10(-8)). Secondly, based on the GWAS data, we selected 1000 markers with the lowest P values in the discovery TOP sample, and tested these (or HapMap-based surrogates) for association in the replication sample. Sixteen loci were associated with schizophrenia (nominal P value<0.05 and concurring OR) in the replication sample. As a next step, we performed a combined analysis of the findings from these two studies, and the strongest evidence for association with schizophrenia was provided for markers rs7045881 on 9p21, rs433598 on 16p12 and rs10761482 on 10q21. The markers are located in PLAA, ACSM1 and ANK3, respectively. PLAA has not previously been described as a susceptibility gene, but 9p21 is implied as a schizophrenia linkage region. ACSM1 has been identified as a susceptibility gene in a previous schizophrenia GWAS study. The association of ANK3 with schizophrenia is intriguing in light of recent associations of ANK3 with bipolar disorder, thereby supporting the hypothesis of an overlap in genetic susceptibility between these psychopathological entities.

Expanding the range of ZNF804A variants conferring risk of psychosis

A trio of genome-wide association studies recently reported sequence variants at three loci to be significantly associated with schizophrenia. No sequence polymorphism had been unequivocally (P<5 × 10−8) associated with schizophrenia earlier. However, one variant, rs1344706[T], had come very close. This polymorphism, located in an intron of ZNF804A, was reported to associate with schizophrenia with a P-value of 1.6 × 10−7, and with psychosis (schizophrenia plus bipolar disorder) with a P-value of 1.0 × 10−8. In this study, using 5164 schizophrenia cases and 20 709 controls, we replicated the association with schizophrenia (odds ratio OR=1.08, P=0.0029) and, by adding bipolar disorder patients, we also confirmed the association with psychosis (added N=609, OR=1.09, P=0.00065). Furthermore, as it has been proposed that variants such as rs1344706[T]—common and with low relative risk—may also serve to identify regions harboring less common, higher-risk susceptibility alleles, we searched ZNF804A for large copy number variants (CNVs) in 4235 psychosis patients, 1173 patients with other psychiatric disorders and 39 481 controls. We identified two CNVs including at least part of ZNF804A in psychosis patients and no ZNF804A CNVs in controls (P=0.013 for association with psychosis). In addition, we found a ZNF804A CNV in an anxiety patient (P=0.0016 for association with the larger set of psychiatric disorders).

Sex-dependent association of common variants of microcephaly genes with brain structure

Loss-of-function mutations in the genes associated with primary microcephaly (MCPH) reduce human brain size by about two-thirds, without producing gross abnormalities in brain organization or physiology and leaving other organs largely unaffected [Woods CG, et al. (2005) Am J Hum Genet 76:717–728]. There is also evidence suggesting that MCPH genes have evolved rapidly in primates and humans and have been subjected to selection in recent human evolution [Vallender EJ, et al. (2008) Trends Neurosci 31:637–644]. Here, we show that common variants of MCPH genes account for some of the common variation in brain structure in humans, independently of disease status. We investigated the correlations of SNPs from four MCPH genes with brain morphometry phenotypes obtained with MRI. We found significant, sex-specific associations between common, nonexonic, SNPs of the genes CDK5RAP2, MCPH1, and ASPM, with brain volume or cortical surface area in an ethnically homogenous Norwegian discovery sample (n = 287), including patients with mental illness. The most strongly associated SNP findings were replicated in an independent North American sample (n = 656), which included patients with dementia. These results are consistent with the view that common variation in brain structure is associated with genetic variants located in nonexonic, presumably regulatory, regions.

A genome-wide association study of bipolar disorder in Norwegian individuals, followed by replication in Icelandic sample

BACKGROUND In the present study we investigated genetic variants associated with bipolar disorder in a homogenous Norwegian sample, and potential genetic overlap with schizophrenia, using the Affymetrix 6.0 array. METHODS We carried out a genome-wide association study (GWAS) by genotyping 620 390 single-nucleotide polymorphisms (SNPs) in a case-control sample of Norwegian origin (the TOP study) including bipolar disorder (n=194), healthy controls (n=336) and schizophrenia (n=230), followed by replication and combined analysis in a genetically concordant Icelandic sample of bipolar disorder (n=435), and healthy controls (n=10,258). RESULTS We selected 1000 markers with the lowest P values in the TOP discovery GWAS and tested these (or their surrogates) for association in the Icelandic replication sample. Polymorphisms on 35 loci were confirmed associated with bipolar disorder (nominal P value<0.05; not corrected for multiple testing) in the replication sample. The most significant markers were located in DLEU2, GUCY1B2, PKIA, CCL2, CNTNAP5, DPP10, and FBN1. The combined group of schizophrenia and bipolar disorder compared to controls did not provide additional significant findings. LIMITATIONS Relatively small number of samples. CONCLUSIONS We detected weak but reproducible association with markers in several genes, in proximity to susceptibility loci found in previous GWAS studies of bipolar disorder. Further work is required to study their localization, expression, and regulation and international meta-analytic efforts will help to further elucidate their role.

BDNF val66met modulates the association between childhood trauma, cognitive and brain abnormalities in psychoses

OBJECTIVE Brain derived neurotrophic factor (BDNF) is important for brain development and plasticity, and here we tested if the functional BDNF val66met variant modulates the association between high levels of childhood abuse, cognitive function, and brain abnormalities in psychoses. METHOD 249 patients with a broad DSM-IV schizophrenia spectrum disorder or bipolar disorder were consecutively recruited to the TOP research study (mean±age: 30.7±10.9; gender: 49% males). History of childhood trauma was obtained using the Childhood Trauma Questionnaire. Cognitive function was assessed through a standardized neuropsychological test battery. BDNF val66met was genotyped using standardized procedures. A sub-sample of n=106 Caucasians with a broad DSM-IV schizophrenia spectrum disorder or bipolar disorder (mean±age: 32.67±10.85; 49% males) had data on sMRI. RESULTS Carriers of the Methionine (met) allele exposed to high level of childhood abuse demonstrated significantly poorer cognitive functioning compared to homozygotic Valine (val/val) carriers. Taking in consideration multiple testing, using a more conservative p value, this was still shown for physical abuse and emotional abuse, as well as a trend level for sexual abuse. Further, met carriers exposed to high level of childhood sexual abuse showed reduced right hippocampal volume (r(2)=0.43; p=0.008), and larger right and left lateral ventricles (r(2)=0.37; p=0.002, and r(2)=0.27; p=0.009, respectively). Our findings were independent of age, gender, diagnosis and intracranial volume. CONCLUSION Our data demonstrate that in patients with psychoses, met carriers of the BDNF val66met with high level of childhood abuse have more cognitive and brain abnormalities than all other groups.

Serotonin Transporter Gene Polymorphism, Childhood Trauma, and Cognition in Patients With Psychotic Disorders

OBJECTIVE The functional polymorphism in the promoter region of the SLC6A4/5-HTT serotonin transporter gene (5-HTTLPR) has been linked to altered stress response. Carriers of the short (s-) allele have increased negative psychological reactions and stress hormone release compared with carriers of the long (l-) allele, interacting with severe life events including childhood trauma. High stress levels are associated with cognitive impairments in a variety of clinical and experimental studies. Patients with psychotic disorders are characterized both by more childhood traumatic events and abnormal stress responses and by significant but highly variable cognitive dysfunction. We hypothesize that 5-HTTLPR variations and long-term effects of childhood trauma interact and contribute to some of the variation in cognitive dysfunction seen in patients with psychotic disorders. METHODS Patients with psychotic disorders (schizophrenia and affective spectrums) were recruited from a catchment area-based treatment organization. History of childhood abuse was obtained by the Childhood Trauma Questionnaire. Cognitive function was assessed through a comprehensive, standardized neuropsychological test battery. 5-HTTLPR genotypes were analyzed using standard polymerase chain reaction. RESULTS We observed a significant interaction between 5-HTTLPR variants and childhood trauma across cognitive domains; here, homozygotic s-carriers exposed to high levels of childhood trauma (physical neglect and abuse) had significantly poorer cognitive functioning than all other groups. CONCLUSIONS Our results need replication but underline the importance of investigating childhood trauma and its interaction with genetic markers when studying cognitive dysfunction in patients with psychotic disorders.

TCF4 sequence variants and mRNA levels are associated with neurodevelopmental characteristics in psychotic disorders.

TCF4 is involved in neurodevelopment, and intergenic and intronic variants in or close to the TCF4 gene have been associated with susceptibility to schizophrenia. However, the functional role of TCF4 at the level of gene expression and relationship to severity of core psychotic phenotypes are not known. TCF4 mRNA expression level in peripheral blood was determined in a large sample of patients with psychosis spectrum disorders (n=596) and healthy controls (n=385). The previously identified TCF4 risk variants (rs12966547 (G), rs9960767 (C), rs4309482 (A), rs2958182 (T) and rs17512836 (C)) were tested for association with characteristic psychosis phenotypes, including neurocognitive traits, psychotic symptoms and structural magnetic resonance imaging brain morphometric measures, using a linear regression model. Further, we explored the association of additional 59 single nucleotide polymorphisms (SNPs) covering the TCF4 gene to these phenotypes. The rs12966547 and rs4309482 risk variants were associated with poorer verbal fluency in the total sample. There were significant associations of other TCF4 SNPs with negative symptoms, verbal learning, executive functioning and age at onset in psychotic patients and brain abnormalities in total sample. The TCF4 mRNA expression level was significantly increased in psychosis patients compared with controls and positively correlated with positive- and negative-symptom levels. The increase in TCF4 mRNA expression level in psychosis patients and the association of TCF4 SNPs with core psychotic phenotypes across clinical, cognitive and brain morphological domains support that common TCF4 variants are involved in psychosis pathology, probably related to abnormal neurodevelopment.

Interplay between childhood trauma and BDNF val66met variants on blood BDNF mRNA levels and on hippocampus subfields volumes in schizophrenia spectrum and bipolar disorders

OBJECTIVE Here we investigated a two hit gene environment model in relation to functional genomic factors (BDNF mRNA), and volume of hippocampal subfields in schizophrenia spectrum and bipolar disorders, focusing on both an environmental (childhood trauma) and genetic risk factor (BDNF val66met). METHOD A total of 323 patients with a broad DSM-IV schizophrenia spectrum disorder or bipolar disorder were consecutively recruited. A history of childhood trauma was obtained using the Childhood Trauma Questionnaire. BDNF DNA and RNA were analyzed using standardized procedures. A subsample of n = 108 underwent MRI scanning, and the FreeSurfer was used to obtain measures of hippocampal subfield. All MRI data were corrected for age and gender, with post-hoc analysis correcting for ICV. RESULTS A history of childhood trauma or being a met carrier of the BDNF val66met was associated with significantly reduced BDNF mRNA level. Additive effects were observed between a history of childhood trauma and BDNF val66met, in the direction of met carriers with high levels of childhood trauma having the lowest BDNF mRNA levels. Lastly, met carriers reporting high levels of childhood trauma (specifically sexual or physical abuse) had significantly reduced hippocampal subfield volumes CA2/3 and CA4 dentate gyrus. CONCLUSION The current findings demonstrate that the reduced BDNF mRNA levels found in psychosis may be associated with both a history of childhood trauma and BDNF val66met variants. Further, our study supports a two hit model including a history of childhood trauma as well as genetic vulnerability (met carriers of the BDNF val66met) behind reduced volume of hippocampal subfields in psychosis. This was specifically found for areas important for neurogenesis, the CA2/3 and the CA4 DG.

Catechol O-methyltransferase variants and cognitive performance in schizophrenia and bipolar disorder versus controls.

BACKGROUND The gene encoding Catechol O-methyltransferase (COMT), a dopamine catabolic enzyme, is an important candidate gene in several psychiatric disorders. Several studies have shown an association between the functional Val(158)Met polymorphism and cognitive performance. However, the results have been inconsistent and there are few studies addressing other COMT single nucleotide polymorphisms (SNPs). METHODS We investigated SNPs across the whole COMT gene, including the Val(158)Met polymorphism, for a putative effect on working memory, executive function and IQ in 315 patients with schizophrenia or bipolar disorder and 340 healthy controls. RESULTS We replicated the association between the Val(158)Met variant and working memory performance, and found a significant interaction between this SNP and diagnosis, with patients with schizophrenia showing a specific, reduced performance on the 2-back test. Several other COMT SNPs were associated with different cognitive functions, but did not remain significant after controlling for multiple testing. We also found significant interaction effects between the SNP variants and gender. CONCLUSIONS The present study replicates earlier findings showing an association between the functional Val(158)Met polymorphism and working memory performance, with schizophrenia subjects particularly vulnerable. Furthermore, our findings suggest that other parts of the COMT gene seem to affect several related cognitive domains, which further support the notion that COMT is a modifier gene in prefrontal dopamine functioning.

Genome-Wide Analysis of Attention Deficit Hyperactivity Disorder in Norway

Background Attention deficit hyperactivity disorder (ADHD) is a highly heritable neuropsychiatric condition, but it has been difficult to identify genes underlying this disorder. This study aimed to explore genetics of ADHD in an ethnically homogeneous Norwegian population by means of a genome-wide association (GWA) analysis followed by examination of candidate loci. Materials and Methods Participants were recruited through Norwegian medical and birth registries as well as the general population. Presence of ADHD was defined according to DSM-IV criteria. Genotyping was performed using Illumina Human OmniExpress-12v1 microarrays. Statistical analyses were divided into several steps: (1) genome-wide association in the form of logistic regression in PLINK and follow-up pathway analyses performed in DAPPLE and INRICH softwares, (2) SNP-heritability calculated using genome-wide complex trait analysis (GCTA) tool, (3) gene-based association tests carried out in JAG software, and (4) evaluation of previously reported genome-wide signals and candidate genes of ADHD. Results In total, 1.358 individuals (478 cases and 880 controls) and 598.384 autosomal SNPs were subjected to GWA analysis. No single polymorphism reached genome-wide significance. The strongest signal was observed at rs9949006 in the ENSG00000263745 gene (OR=1.51, 95% CI 1.28–1.79, p=1.38E-06). Pathway analyses of the top SNPs implicated genes involved in the regulation of gene expression, cell adhesion and inflammation. Among previously identified ADHD candidate genes, prominent association signals were observed for SLC9A9 (rs1393072, OR=1.46, 95% CI = 1.21–1.77, p=9.95E-05) and TPH2 (rs17110690, OR = 1.38, 95% CI = 1.14–1.66, p=8.31E-04). Conclusion This study confirms the complexity and heterogeneity of ADHD etiology. Taken together with previous findings, our results point to a spectrum of biological mechanisms underlying the symptoms of ADHD, providing targets for further genetic exploration of this complex disorder.