Follow-up study on a susceptibility locus for schizophrenia on chromosome 6q

TAAR6variation effect on clinic presentation and outcome in a sample of schizophrenic in-patients: An open label study

We recently reported an association betweenTAAR6(trace amine associated receptor 6 gene) variations and schizophrenia (SZ). We now report an association of a set ofTAAR6variations and clinical presentation and outcome in a sample of 240 SZ Korean patients. Patients were selected by a Structured Clinical Interview, DSM-IV Axis I disorders – Clinical Version (SCID-CV). Other psychiatric or neurologic disorders, as well as medical diseases, were exclusion criteria. To assess symptom severity, patients were administered the CGI scale and the PANSS at baseline and at the moment of discharge, 1 month later on average.TAAR6variations rs6903874, rs7452939, rs8192625 and rs4305745 were investigated; rs6903874, rs7452939 and rs8192625 entered the statistical investigation after LD analysis. Rs8192625 G/G homozygosis was found to be significantly associated both with a worse clinical presentation at PANSS total and positive scores and with a shorter period of illness before hospitalization. No haplotype significant findings were found. The present study stands for a role of theTAAR6in the clinical presentation of SZ. Moreover, our results show that this genetic effect may be counteracted by a correct treatment. Haplotype analysis was not informative in our sample, probably also because of the incomplete SNPs' coverage of the gene we performed. Further studies in this direction are warranted.

Differential Dorsolateral Prefrontal Cortex Proteomic Profiles of Suicide Victims with Mood Disorders

Suicide is a major public health concern; nevertheless, its neurobiology remains unknown. An area of interest in suicide research is the dorsolateral prefrontal cortex (DLPFC). We aimed to identify altered proteins and potential biological pathways in the DLPFC of individuals who died by suicide employing mass spectrometry-based untargeted proteomics. Postmortem DLPFC from age-matched male suicide mood disorder cases (n = 5) and non-suicide mood disorder cases (n = 5) were compared. The proteins that differed between groups at false discovery rate (FDR) adjusted p-values (Benjamini-Hochberg-Yekutieli) <0.3 and Log2 fold change (FC) >|0.4| were considered statistically significant and were subjected to pathway analysis by Qiagen Ingenuity software. Thirty-three of the 5162 detected proteins showed significantly altered expression levels in the suicide cases and two of them after adjustment for body mass index. The top differentially expressed protein was potassium voltage-gated channel subfamily Q member 3 (KCNQ3) (Log2FC = -0.481, p = 2.10 × 10-09, FDR = 5.93 × 10-06), which also showed a trend to downregulation in Western blot (p = 0.045, Bonferroni adjusted p = 0.090). The most notably enriched pathway was the GABA receptor signaling pathway (p < 0.001). Here, we report a reduction trend of KCNQ3 levels in the DLPFC of male suicide victims with mood disorders. Further studies with a larger sample size and equal sex representation are needed.

Molecular Variants in Human Trace Amine-Associated Receptors and Their Implications in Mental and Metabolic Disorders

We provide a comprehensive review of the available evidence on the pathophysiological implications of genetic variants in the human trace amine-associated receptor (TAAR) superfamily. Genes coding for trace amine-associated receptors (taars) represent a multigene family of G-protein-coupled receptors, clustered to a small genomic region of 108 kb located in chromosome 6q23, which has been consistently identified by linkage analyses as a susceptibility locus for schizophrenia and affective disorders. Most TAARs are expressed in brain areas involved in emotions, reward and cognition. TAARs are activated by endogenous trace amines and thyronamines, and evidence for a modulatory action on other monaminergic systems has been reported. Therefore, linkage analyses were followed by fine mapping association studies in schizophrenia and affective disorders. However, none of these reports has received sufficient universal replication, so their status remains uncertain. Single nucleotide polymorphisms in taars have emerged as susceptibility loci from genome-wide association studies investigating migraine and brain development, but none of the detected variants reached the threshold for genome-wide significance. In the last decade, technological advances enabled single-gene or whole-exome sequencing, thus allowing the detection of rare genetic variants, which may have a greater impact on the risk of complex disorders. Using these approaches, several taars (especially taar1) variants have been detected in patients with mental and metabolic disorders, and in some cases, defective receptor function has been demonstrated in vitro. Finally, with the use of transcriptomic and peptidomic techniques, dysregulations of TAARs (especially TAAR6) have been identified in brain disorders characterized by cognitive impairment.

Genetic Evaluation of Schizophrenia Using the Illumina HumanExome Chip

INTRODUCTION

Schizophrenia is a genetically heterogeneous disorder that is associated with several common and rare genetic variants. As technology involved, cost advantages of chip based genotyping was combined with information about rare variants, resulting in the Infinium HumanExome Beadchip. Using this chip, a sample of 493 patients with schizophrenia or schizoaffective disorder and 484 healthy controls was genotyped.

RESULTS

From the initial 242901 SNVs, 88306 had at least one minor allele and passed quality control. No variant reached genomewide-significant results (p<10(-8)). The SNP with the lowest p-value was rs1230345 in WISP3 (p = 3.05*10(-6)), followed by rs9311525 in CACNA2D3 (p = 1.03*10(-5)) and rs1558557 (p = 3.85*10(-05)) on chromosome 7. At the gene level, 3 genes were of interest: WISP3, on chromosome 6q21, a signally protein from the extracellular matrix. A second candidate gene is CACNA2D3, a regulator of the intracerebral calcium pathway. A third gene is TNFSF10, associated with p53 mediated apoptosis.

Genetic assessment of additional endophenotypes from the Consortium on the Genetics of Schizophrenia Family Study

The Consortium on the Genetics of Schizophrenia Family Study (COGS-1) has previously reported our efforts to characterize the genetic architecture of 12 primary endophenotypes for schizophrenia. We now report the characterization of 13 additional measures derived from the same endophenotype test paradigms in the COGS-1 families. Nine of the measures were found to discriminate between schizophrenia patients and controls, were significantly heritable (31 to 62%), and were sufficiently independent of previously assessed endophenotypes, demonstrating utility as additional endophenotypes. Genotyping via a custom array of 1536 SNPs from 94 candidate genes identified associations for CTNNA2, ERBB4, GRID1, GRID2, GRIK3, GRIK4, GRIN2B, NOS1AP, NRG1, and RELN across multiple endophenotypes. An experiment-wide p value of 0.003 suggested that the associations across all SNPs and endophenotypes collectively exceeded chance. Linkage analyses performed using a genome-wide SNP array further identified significant or suggestive linkage for six of the candidate endophenotypes, with several genes of interest located beneath the linkage peaks (e.g., CSMD1, DISC1, DLGAP2, GRIK2, GRIN3A, and SLC6A3). While the partial convergence of the association and linkage likely reflects differences in density of gene coverage provided by the distinct genotyping platforms, it is also likely an indication of the differential contribution of rare and common variants for some genes and methodological differences in detection ability. Still, many of the genes implicated by COGS through endophenotypes have been identified by independent studies of common, rare, and de novo variation in schizophrenia, all converging on a functional genetic network related to glutamatergic neurotransmission that warrants further investigation.

The influence of AHI1 variants on the diagnosis and treatment outcome in schizophrenia

The present study aimed to explore whether four single nucleotide polymorphisms (SNPs) within the AHI1 gene could be associated with schizophrenia (SCZ) and whether they could predict the clinical outcomes in SCZ patients treated with antipsychotics. Four hundred twenty-six (426) in-patients with SCZ and 345 controls were genotyped for four AHI1 SNPs (rs11154801, rs7750586, rs9647635 and rs9321501). Baseline and clinical measures for SCZ patients were assessed through the Positive and Negative Syndrome Scale (PANSS). Allelic and genotypic frequencies in SCZ subjects were compared with those of controls using the χ² statistics. The repeated-measure ANOVA was used for the assessment of treatment outcomes measured by PANSS changes. The case-control analysis did not show any difference in the genotypic distribution of the SNPs, while in the allelic analysis, a weak association was found between the rs9647635 A allele and SCZ. Furthermore, in the haplotype analysis, three haplotypes resulted in being associated with SCZ. On the other hand, two SNPs (rs7750586 and rs9647635) were associated with clinical improvement of negative symptoms in the allelic analysis, although in the genotypic analysis, only trends of association were found for the same SNPs. Our findings suggest a possible influence of AHI1 variants on SCZ susceptibility and antipsychotic response, particularly concerning negative symptomatology. Subsequent well-designed studies would be mandatory to confirm our results due to the methodological shortcomings of the present study.

Transcriptome study of differential expression in schizophrenia

Schizophrenia genome-wide association studies (GWAS) have identified common SNPs, rare copy number variants (CNVs) and a large polygenic contribution to illness risk, but biological mechanisms remain unclear. Bioinformatic analyses of significantly associated genetic variants point to a large role for regulatory variants. To identify gene expression abnormalities in schizophrenia, we generated whole-genome gene expression profiles using microarrays on lymphoblastoid cell lines (LCLs) from 413 cases and 446 controls. Regression analysis identified 95 transcripts differentially expressed by affection status at a genome-wide false discovery rate (FDR) of 0.05, while simultaneously controlling for confounding effects. These transcripts represented 89 genes with functions such as neurotransmission, gene regulation, cell cycle progression, differentiation, apoptosis, microRNA (miRNA) processing and immunity. This functional diversity is consistent with schizophrenia's likely significant pathophysiological heterogeneity. The overall enrichment of immune-related genes among those differentially expressed by affection status is consistent with hypothesized immune contributions to schizophrenia risk. The observed differential expression of extended major histocompatibility complex (xMHC) region histones (HIST1H2BD, HIST1H2BC, HIST1H2BH, HIST1H2BG and HIST1H4K) converges with the genetic evidence from GWAS, which find the xMHC to be the most significant susceptibility locus. Among the differentially expressed immune-related genes, B3GNT2 is implicated in autoimmune disorders previously tied to schizophrenia risk (rheumatoid arthritis and Graves' disease), and DICER1 is pivotal in miRNA processing potentially linking to miRNA alterations in schizophrenia (e.g. MIR137, the second strongest GWAS finding). Our analysis provides novel candidate genes for further study to assess their potential contribution to schizophrenia.

Toward a modern search for schizophrenia genes

Genetic epidemiology has provided consistent evidence that schizophrenia has a genetic component It is now clear that this genetic component is complex and polygenic, with several genes interacting in epistasis. Although molecular studies have failed to identify any DNA variant that clearly contributes to vulnerability to schizophrenia, several regions have been implicated by linkage studies. To overcome the difficulties in the search for schizophrenia genes, it is necessary (i) to use methods of analysis that are appropriate for complex multifactorial disorders; (ii) to gather large enough clinical samples; and (iii) in the absence of genetic validity of the diagnostic classification currently used, to apply new strategies in order to better define the affected phenotypes. For this purpose, we describe here two strategies: (i) the candidate symptom approach, which concerns affected subjects and uses proband characteristics as the affected phenotype, such as age at onset, severity, and negative/positive symptoms; and (ii) the endophenotypic approach, which concerns unaffected relatives and has already provided positive findings with phenotypes, such as P50 inhibitory gating or eye-movement dysfunctions.

Fine mapping of AHI1 as a schizophrenia susceptibility gene: from association to evolutionary evidence

In previous studies, we identified a locus for schizophrenia on 6q23.3 and proposed the Abelson helper integration site 1 (AHI1) as the candidate gene. AHI1 is expressed in the brain and plays a key role in neurodevelopment, is involved in Joubert syndrome, and has been recently associated with autism. The neurodevelopmental role of AHI1 fits with etiological hypotheses of schizophrenia. To definitively confirm our hypothesis, we searched for associations using a dense map of the region. Our strongest findings lay within the AHI1 gene: single-nucleotide polymorphisms rs11154801 and rs7759971 showed significant associations (P=6.23E-06; P=0.84E-06) and haplotypes gave P values in the 10E-8 to 10E-10 range. The second highest significant region maps close to AHI1 and includes the intergenic region between BC040979 and PDE7B (rs2038549 at P=9.70E-06 and rs1475069 at P=6.97E-06), and PDE7B and MAP7. Using a sample of Palestinian Arab families to confirm these findings, we found isolated signals. While these results did not retain their significance after correction for multiple testing, the joint analysis across the 2 samples supports the role of AHI1, despite the presence of heterogeneity. Given the hypothesis of positive selection of schizophrenia genes, we resequenced a 11 kb region within AHI1 in ethnically defined populations and found evidence for a selective sweep. Network analysis indicates 2 haplotype clades, with schizophrenia-susceptibility haplotypes clustering within the major clade. In conclusion, our data support the role of AHI1 as a susceptibility gene for schizophrenia and confirm it has been subjected to positive selection, also shedding light on new possible candidate genes, MAP7 and PDE7B.

A large replication study and meta-analysis in European samples provides further support for association of AHI1 markers with schizophrenia

The Abelson helper integration site 1 (AHI1) gene locus on chromosome 6q23 is among a group of candidate loci for schizophrenia susceptibility that were initially identified by linkage followed by linkage disequilibrium mapping, and subsequent replication of the association in an independent sample. Here, we present results of a replication study of AHI1 locus markers, previously implicated in schizophrenia, in a large European sample (in total 3907 affected and 7429 controls). Furthermore, we perform a meta-analysis of the implicated markers in 4496 affected and 18,920 controls. Both the replication study of new samples and the meta-analysis show evidence for significant overrepresentation of all tested alleles in patients compared with controls (meta-analysis; P = 8.2 x 10(-5)-1.7 x 10(-3), common OR = 1.09-1.11). The region contains two genes, AHI1 and C6orf217, and both genes-as well as the neighbouring phosphodiesterase 7B (PDE7B)-may be considered candidates for involvement in the genetic aetiology of schizophrenia.

Influence of TAAR6 polymorphisms on response to aripiprazole

BACKGROUND

There is some evidence suggesting a role of TAAR6 in schizophrenia. The aim of the present study is to investigate possible influences of a panel of markers in TAAR6 (rs8192625, rs4305745, rs4305746, rs6903874, rs6937506) on clinical outcomes and side effects in a sample of Korean schizophrenic aripiprazole treated patients.

METHODS

Efficacy was assessed at baseline and weeks 1, 2, 4, 6, 8 using CGI-S, CGI-I, BPRS and SANS. Side effects were evaluated through SAS, BAS and AIMS. Multivariate analysis of covariance (MANCOVA) was used to test possible influences of single SNPs on clinical and safety scores. Tests for associations using multi-marker haplotypes were performed using the statistics environment "R".

RESULTS

A significant time per genotype interaction was found between rs4305746 in repeated measures of ANOVA on BPRS scores (F=2.45, df=10,365, p=0.008). In particular G/A and A/A genotype patients were more likely to improve over time as compared to carriers of the G/G genotype. Permutation analysis confirmed a significant effect of rs4305746 on course of BPRS scores over time (p=0.007). Haplotype analysis did not reveal any significant association with clinical and safety scores at any time.

CONCLUSION

A possible association could exist between some genotypes in TAAR6 and response to aripiprazole. However, several limitations characterize the present work, such as small sample size, the finding related to a single scale and the possibility of false positive findings, thus further investigation is required.

Decreased expression of Fyn protein and disbalanced alternative splicing patterns in platelets from patients with schizophrenia

Fyn, a Src-family kinase, is highly expressed in brain tissue and blood cells. In the mouse brain, Fyn participates in brain development, synaptic transmission through the phosphorylation of N-methyl-d-aspartate (NMDA) receptor subunits, and the regulation of emotional behavior. Recently, we found that Fyn is required for the signal transduction in striatal neurons that is initiated by haloperidol, an antipsychotic drug. To determine whether Fyn abnormalities are present in patients with schizophrenia, we analyzed Fyn expression in platelet samples from 110 patients with schizophrenia, 75 of the patients' first-degree relatives, and 130 control subjects. A Western blot analysis revealed significantly lower levels of Fyn protein among the patients with schizophrenia and their relatives, compared with the level in the control group. At the mRNA level, the splicing patterns of fyn were altered in the patients and their relatives; specifically, the ratio of fynDelta7, in which exon 7 is absent, was elevated. An expression study in HEK293T cells revealed that FynDelta7 had a dominant-negative effect on the phosphorylation of Fyn's substrate. These results suggest novel deficits in Fyn function, manifested as the downregulation of Fyn protein or the altered transcription of the fyn gene, in patients with schizophrenia.

No association found between the promoter variations of QKI and schizophrenia in the Chinese population

BACKGROUND

Schizophrenia is a chronic psychiatric disorder with a strong genetic component. Several recent published studies have reported that the mRNA expression level of quaking homolog, KH domain RNA binding (QKI) is down regulated in individuals diagnosed with schizophrenia.

METHODS

We were interested in the genetic variants around the promoter region of QKI and selected seven variants in this region, namely rs4263561, rs3904720, rs387504, rs3763197, rs7772756, rs7758706 and rs4709716. For the study we recruited 288 individuals diagnosed with schizophrenia and 288 control subjects. All the recruits were from Shanghai and were Han Chinese in origin.

RESULTS

No individual SNP nor any haplotype was found to be associated with schizophrenia.

CONCLUSIONS

These results suggest that the variants within the promoter region of QKI gene are unlikely to play a major role in susceptibility to schizophrenia in the Chinese population.

Cannabinoid receptors in brain: pharmacogenetics, neuropharmacology, neurotoxicology, and potential therapeutic applications

Much progress has been achieved in cannabinoid research. A major breakthrough in marijuana-cannabinoid research has been the discovery of a previously unknown but elaborate endogenous endocannabinoid system (ECS), complete with endocannabinoids and enzymes for their biosynthesis and degradation with genes encoding two distinct cannabinoid (CB1 and CB2) receptors (CBRs) that are activated by endocannabinoids, cannabinoids, and marijuana use. Physical and genetic localization of the CBR genes CNR1 and CNR2 have been mapped to chromosome 6 and 1, respectively. A number of variations in CBR genes have been associated with human disorders including osteoporosis, attention deficit hyperactivity disorder (ADHD), posttraumatic stress disorder (PTSD), drug dependency, obesity, and depression. Other family of lipid receptors including vanilloid (VR1) and lysophosphatidic acid (LPA) receptors appear to be related to the CBRs at the phylogenetic level. The ubiquitous abundance and differential distribution of the ECS in the human body and brain along with the coupling to many signal transduction pathways may explain the effects in most biological system and the myriad behavioral effects associated with smoking marijuana. The neuropharmacological and neuroprotective features of phytocannabinoids and endocannabinoid associated neurogenesis have revealed roles for the use of cannabinoids in neurodegenerative pathologies with less neurotoxicity. The remarkable progress in understanding the biological actions of marijuana and cannabinoids have provided much richer results than previously appreciated cannabinoid genomics and raised a number of critical issues on the molecular mechanisms of cannabinoid induced behavioral and biochemical alterations. These advances will allow specific therapeutic targeting of the different components of the ECS in health and disease. This review focuses on these recent advances in cannabinoid genomics and the surprising new fundamental roles that the ECS plays in the retrograde signaling associated with cannabinoid inhibition of neurotransmitter release to the genetic basis of the effects of marijuana use and pharmacotherpeutic applications and limitations. Much evidence is provided for the complex CNR1 and CNR2 gene structures and their associated regulatory elements. Thus, understanding the ECS in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

Association of common variants in the Joubert syndrome gene (AHI1) with autism

It has been suggested that autism, like other complex genetic disorders, may benefit from the study of rare or Mendelian variants associated with syndromic or non-syndromic forms of the disease. However, there are few examples in which common variation in genes causing a Mendelian neuropsychiatric disorder has been shown to contribute to disease susceptibility in an allied common condition. Joubert syndrome (JS) is a rare recessively inherited disorder, with mutations reported at several loci including the gene Abelson's Helper Integration 1 (AHI1). A significant proportion of patients with JS, in some studies up to 40%, have been diagnosed with autism spectrum disorder (ASD) and several linkage studies in ASD have nominally implicated the region on 6q where AHI1 resides. To evaluate AHI1 in ASD, we performed a three-stage analysis of AHI1 as an a priori candidate gene for autism. Re-sequencing was first used to screen AHI1, followed by two subsequent association studies, one limited and one covering the gene more completely, in Autism Genetic Resource Exchange (AGRE) families. In stage 3, we found evidence of an associated haplotype in AHI1 with ASD after correction for multiple comparisons, in a region of the gene that had been previously associated with schizophrenia. These data suggest a role for AHI1 in common disorders affecting human cognition and behavior.

Initial association of NR2E1 with bipolar disorder and identification of candidate mutations in bipolar disorder, schizophrenia, and aggression through resequencing

Nuclear receptor 2E1 gene (NR2E1) resides within a 6q21-22 locus for bipolar disorder and schizophrenia. Mice deleted for Nr2e1 show altered neurogenesis, cortical and limbic abnormalities, aggression, hyperexcitability, and cognitive impairment. NR2E1 is therefore a positional and functional candidate for involvement in mental illness. We performed association analyses in 394 patients with bipolar disorder, 396 with schizophrenia, and 479 controls using six common markers and haplotypes. We also performed a comprehensive mutation screen of NR2E1, resequencing its entire coding region, complete 5' and 3' untranslated regions, consensus splice-sites, and evolutionarily conserved regions in 126 humans with bipolar disorder, schizophrenia, or aggressive disorders. NR2E1 was associated with bipolar disorder I and II [odds ratio (OR = 0.77, P = 0.013), bipolar disorder I (OR = 0.77, P = 0.015), bipolar disorder in females (OR = 0.72, P = 0.009), and with age at onset < or = 25 years (OR = 0.67, P = 0.006)], all of which remained significant after correcting for multiple comparisons. We identified eight novel candidate mutations that were absent in 325 controls; four of these were predicted to alter known neural transcription factor binding sites. Analyses of NR2E1 mRNA in human brain revealed forebrain-specific transcription. The data presented support the hypothesis that genetic variation at NR2E1 may be associated with susceptibility to brain-behavior disorders.

Susceptibility of schizophrenia and affective disorder not associated with loci on chromosome 6q in Han Chinese population

Background

Several linkage studies across multiple population groups provide convergent support for susceptibility loci for schizophrenia – and, more recently, for affective disorder – on chromosome 6q. We explore whether schizophrenia and affective disorder have common susceptibility gene on 6q in Han Chinese population.

Methods

In the present study, we genotyped 45 family trios from Han Chinese population with mixed family history of schizophrenia and affective disorder. Twelve short tandem repeat (STRs) markers were selected, which covered 102.19 cM on chromosome 6q with average spacing 9.29 cM and heterozygosity 0.78. The transmission disequilibrium test (TDT) was performed to search for susceptibility loci to schizophrenia and affective disorder.

Results

The results showed STRs D6S257, D6S460, D6S1021, D6S292 and D6S1581 were associated with susceptibility to psychotic disorders. When families were grouped into schizophrenia and affective disorder group, D6S257, D6S460 and D6S1021, which map closely to the centromere of chromosome 6q, were associated with susceptibility to schizophrenia. Meanwhile, D6S1581, which maps closely to the telomere, was associated with susceptibility to affective disorder. But after correction of multiple test, all above association were changed into no significance (P > 0.05).

Conclusion

These results suggest that susceptibility of schizophrenia and affective disorder not associated with loci on chromosome 6q in Han Chinese population.

Increased familial risk and genomewide significant linkage for Alzheimer's disease with psychosis

Psychotic symptoms are common in Alzheimer's disease (AD) and are associated with increased cognitive impairment and earlier institutionalization. One study has suggested that they are genetically modified and two genome screens have been performed to search for susceptibility loci for AD with psychosis (AD + P). The aim of this study was to further investigate the familial aggregation of AD + P and perform a genome screen for AD, conditioning on the presence or absence of psychotic symptoms. Samples from the UK and US were combined, providing data from 374 families in which at least two members met criteria for AD and had complete data regarding psychotic symptoms. Generalized estimating equations (GEE) were used to assess the relationship of psychotic symptoms between siblings. A total of 321 affected relative pairs (ARPs) were genotyped for linkage. There was a significant association between proband psychosis status and the occurrence of AD + P in siblings in the UK (OR = 4.17, P = 0.002) and US (OR = 3.2, P < 0.001) samples. Chromosomewide and genomewide significant linkage peaks were observed on chromosomes 7 (LOD = 2.84) and 15 (LOD = 3.16), respectively, with the strongest evidence coming from pairs concordant for AD without psychosis. A LOD score of 2.98 was observed close to a previously reported AD + P linkage region on chromosome 6, however the increase in LOD attributable to psychosis was not significant. These findings support the hypothesis that psychotic symptoms in AD are genetically modified and that a gene/s implicated in their aetiology may be located on chromosome 7 and 15.

Significant correlation in linkage signals from genome-wide scans of schizophrenia and schizotypy

Prior family and adoption studies have suggested a genetic relationship between schizophrenia and schizotypy. However, this has never been verified using linkage methods. We therefore attempted to test for a correlation in linkage signals from genome-wide scans of schizophrenia and schizotypy. The Irish study of high-density schizophrenia families comprises 270 families with at least two members with schizophrenia or poor-outcome schizoaffective disorder (n=637). Non-psychotic relatives were assessed using the structured interview for schizotypy (n=746). A 10-cM multipoint, non-parametric, autosomal genome-wide scan of schizophrenia was performed in Merlin. A scan of a quantitative trait comprising ratings of DSM-III-R criteria for schizotypal personality disorder in non-psychotic relatives was also performed. Schizotypy logarithm of the odds (LOD) scores were regressed onto schizophrenia LOD scores at all loci, with adjustment for spatial autocorrelation. To assess empirical significance, this was also carried out using 1000 null scans of schizotypy. The number of jointly linked loci in the real data was compared to distribution of jointly linked loci in the null scans. No markers were suggestively linked to schizotypy based on strict Lander-Kruglyak criteria. Schizotypy LODs predicted schizophrenia LODs above chance expectation genome wide (empirical P=0.04). Two and four loci yielded nonparametric LOD (NPLs) >1.0 and >0.75, respectively, for both schizophrenia and schizotypy (genome-wide empirical P=0.04 and 0.02, respectively). These results suggest that at least a subset of schizophrenia susceptibility genes also affects schizotypy in non-psychotic relatives. Power may therefore be increased in molecular genetic studies of schizophrenia if they incorporate measures of schizotypy in non-psychotic relatives.

A genome-wide scan for modifier loci in schizophrenia

The purpose of this study was to detect genetic loci that influence clinical features of, but not necessarily susceptibility to, psychotic illness. In the Irish Study of High-Density Schizophrenia Families (n = 270 families, n = 1,408 individuals), subjects with non-affective psychosis were rated using the Operational Criteria Checklist for Psychotic Illness. Factor analysis identified hallucinations, delusions, and negative, manic, and depressive symptom factors. We performed autosomal genome-wide multipoint non-parametric quantitative trait locus linkage analysis, in affected individuals only, using these five factors, as well as age at onset, and course of illness. Determination of empirical significance and correction for multiple testing was implemented using 200 simulated genome scans. We also tested for pleiotropic loci by examining the sums of -log(10)'s of the empirical P values of multiple traits in selected regions. LODs of 2.42 and 2.35 were obtained near D9S934 (9q33.1) and D14S587 (14q24.2), respectively, for course of illness, and of 2.26 between D6S1040-D6S2420 (6q23.1-25.1) and age at onset. No other regions met criteria for suggestive linkage to any one trait. No loci were significant after correction for multiple testing. On 6q, however, the joint linkage of age of onset, course, delusions, and depressive symptoms resulted in a genome-wide P = 0.06. We conclude that genes located near 9q33.1 and 14q24.2 may modify the clinical course and severity of schizophrenia. A gene in 6q may affect several clinical features of illness.

Support for involvement of the AHI1 locus in schizophrenia

Recently, markers in the Abelson Helper Integration Site 1 (AHI1) region were shown to be associated with schizophrenia in a family sample of Israeli-Arabs. Here, we report a study evaluating the relevance of the AHI1 region to schizophrenia in an Icelandic sample. Seven markers shown to confer risk in the previous report were typed in 608 patients diagnosed with broad schizophrenia and 1,504 controls. Odds ratios for the overtransmitted alleles in the Israeli-Arab families ranged from 1.15 to 1.29 in the Icelandic sample. After Bonferroni correction for the seven markers tested, two markers were significantly associated with schizophrenia. Thus, our results are in general agreement with the previous report, with the strongest association signal observed in a region upstream of the AHI1 gene.

Evidence of linkage to psychosis on chromosome 5q33-34 in pedigrees ascertained for bipolar disorder

It is hypothesized that the presence of psychotic features may define a subtype of bipolar disorder that is more homogeneous in its genetic predisposition than bipolar disorder as a whole. We used psychosis as an alternative phenotype definition in a re-analysis of the NIMH Bipolar Genetics Initiative data sets. In this analysis we selected only those families in which at least two members were diagnosed with bipolar disorder type 1 with psychotic features. This analysis identified a linkage signal on chromosome 5q33-q34, a region previously implicated in independent linkage studies of schizophrenia and of psychosis, broadly defined. This finding is consistent with the hypothesis that susceptibility to psychosis may characterize at least a subtype of bipolar disorder.

Ion channel functional candidate genes in multigenic neuropsychiatric disease

Scores of monogenic Mendelian ion channel diseases serve to anchor the pathophysiology of the channelopathies, but there are also now clear examples of environmental, pharmacogenetic, and acquired channelopathy mechanisms. The cardinal feature of heritable ion channel disease is a periodic disturbance of rhythmic function in constitutionally hyperexcitable tissue. While the complexity of neuroanatomy obscures functional analysis of mutations causing monogenic seizure, ataxia, or migraine syndromes, extrapolation from the cardiac (Long QT [LQT]) and muscle (Periodic Paralysis) channelopathy syndromes provides a simplified predictive framework of molecular pathology: electrically stabilizing potassium ion (K(+)) and chloride ion (Cl(-)) channels, likely having lesions that diminish their current, and excitatory Na(+) channels, likely having gain-of-function lesions. The voltage-gated calcium channel gene family that contains CACNA1C, the newest LQT locus, causing Timothy Syndrome with a phenotype including autism, has proven to be particularly informative for its members' ability to tie the various central nervous system (CNS) phenotypes together in an interpretable fashion, now including direct extension to the classically multigenic neuropsychiatric phenotypes. Features of a promising ion channel candidate gene arise from its broad locus, gene family, nature of alleles, physiology and pharmacology, tissue expression profile, and phenotype in model organisms. KCNN3 is explored as a paradigm to consider.

AHI1, a pivotal neurodevelopmental gene, and C6orf217 are associated with susceptibility to schizophrenia

Schizophrenia, a severe neuropsychiatric disorder, is believed to involve multiple genetic factors. A significant body of evidence supports a pivotal role for abnormalities of brain development in the disorder. Linkage signals for schizophrenia map to human chromosome 6q. To obtain a finer localization, we genotyped 180 single nucleotide polymorphisms (SNPs) in a young, inbred Arab-Israeli family sample with a limited number of founders. The SNPs were mostly within a approximately 7 Mb region around the strong linkage peak at 136.2 Mb that we had previously mapped. The most significant genetic association with schizophrenia for single SNPs and haplotypes was within a 500 kb genomic region of high linkage disequilibrium (LD) at 135.85 Mb. In a different, outbred, nuclear family sample that was not appropriate for linkage analysis, under-transmitted haplotypes incorporating the same SNPs (but not the individual SNPs) were significantly associated with schizophrenia. The implicated genomic region harbors the Abelson Helper Integration Site 1 (AHI1) gene, which showed the strongest association signal, and an adjacent, primate-specific gene, C6orf217. Mutations in human AHI1 underlie the autosomal recessive Joubert Syndrome with brain malformation and mental retardation. Previous comparative genomic analysis has suggested accelerated evolution of AHI1 in the human lineage. C6orf217 has multiple splice isoforms and is expressed in brain but does not seem to encode a functional protein. The two genes appear in opposite orientations and their regulatory upstream regions overlap, which might affect their expression. Both, AHI1 and C6orf217 appear to be highly relevant candidate genes for schizophrenia.

Family-based association studies of the TCP1 gene and schizophrenia in the Chinese Han population

A previous case-control study by Yang et al. indicated that the TCP1 gene in 6q25 was associated with schizophrenia in the Han population. To replicate this result, we selected eight SNPs (rs2273828, rs3818298, rs1547094, rs1547093, rs2295898, rs2295899, rs4832, rs15982) spanning the whole gene and performed a family-based study using 325 trios samples. Our transmission disequilibrium test showed neither allele nor haplotype association with schizophrenia, and suggests that the TCP1 locus is not associated with schizophrenia in the Chinese population. Since 6q25 has consistently been found to be a susceptible region for schizophrenia, we suggest that other genes within this region should be the focus of attention.

Human QKI, a new candidate gene for schizophrenia involved in myelination

We have previously shown that chromosome 6q25-6q27 includes a susceptibility locus for schizophrenia in a large pedigree from northern Sweden. In this study, we fine-mapped a 10.7 Mb region, included in this locus, using 42 microsatellites or SNP markers. We found a 0.5 Mb haplotype, likely to be inherited identical by decent, within the large family that is shared among the majority of the patients (69%). A gamete competition test of this haplotype in 176 unrelated nuclear families from the same geographical area as the large family showed association to schizophrenia (empirical P-value 0.041). The only gene located in the region, the quaking homolog, KH domain RNA binding (mouse) (QKI), was investigated in human brain autopsies from 55 cases and 55 controls using a high-resolution mRNA expression analysis. Relative mRNA expression levels of two QKI splice variants were clearly downregulated in schizophrenic patients (P-value 0.0004 and 0.03, respectively). The function of QKI has not been studied in humans, but the mouse homolog is involved in neural development and myelination. In conclusion, we present evidence from three unrelated sample-sets that propose the involvement of the QKI gene in schizophrenia. The two family based studies suggest that there may be functional variants of the QKI gene that increase the susceptibility of schizophrenia in northern Sweden, whereas the case-control study suggest that splicing of the gene may be disturbed in schizophrenic patients from other geographical origins. Taken together, we propose QKI as a possible target for functional studies related to the role of myelination in schizophrenia.

Excitement and confusion on chromosome 6q: the challenges of neuropsychiatric genetics in microcosm

The search for genes that are implicated in the pathogenesis of schizophrenia (SCZ), bipolar disorder (BPD) and other complex neuropsychiatric phenotypes has yielded a plethora of positive findings, but has also engendered a substantial degree of confusion. Exciting findings include positive linkage results in a number of chromosomal regions and the identification of several genes that have been associated with SCZ and to a lesser extent with BPD. Confusing aspects include the difference between studies in localization of linkage peaks in the same chromosomal regions, raising the possibility that these regions may harbor more than one gene, the fact that positive linkage findings as well as associated genes appear in several cases to be shared by more than one disorder, and the failure to identify thus far the precise pathogenic variants in associated genes. Recent findings of linkage and association studies on chromosome 6q illustrate the current status of neuropsychiatric genetics in intriguing microcosm. Positive findings from linkage and association studies are reviewed in order to identify approaches that may help to settle apparent contradictions and allow an interpretation of the results that may prove useful in application to findings from other chromosomal regions. Not only SCZ and BPD but also other psychiatric and neurological phenotypes are considered. Taking a topographic approach, we identify five foci of positive findings on chromosome 6q and suggest that each may harbor gene(s) that confer susceptibility to SCZ or BPD or may modify their onset or clinical course. We further suggest that in searching for these genes the possibility that they may be implicated in more than one disorder should be taken into account. We also discuss the potential contribution of rare genetic variants identified in homogeneous, isolated populations to the subsequent identification of common variants in the same gene that contribute to disease susceptibility in outbred populations.

Failure to find association between TRAR4 and schizophrenia in the Chinese Han population

The TRAR4 gene locates in SCZD5 (MIM 603175), which a number of studies have linked with schizophrenia. One recent study suggested that three TRAR4 variants (M1: rs4305745, P=0.0014; M2: rs6903874, P=0.0026; M3: rs6937506, P=0.0052) in the 3'-UTR were associated with schizophrenia. To replicate these findings, we conducted a family-based association study within a sample of 235 Chinese Han trios. However, we didn't find significant evidence of preferential transmission of the three variants across all the trios (all P values>0.2). Thus, we conclude that TRAR4 is not a major or independent determinant in the occurrence of schizophrenia in the Chinese Han population.

[Lack of association between the G681C polimorphism in the 5-HT1D(beta) autoreceptor gene and schizophrenia]

A major role of the serotonergic system has been hypothesized in the pathogenesis of schizophrenia, mostly based on the evidence of action of atypical antipsychotics. Disturbances of serotonergic pathways have been implicated in the etiology of schizophrenia. The aim of this study was to investigate the association between schizophrenia and the G861C polymorphism in the 5-HT1D(beta) autoreceptor gene. There was conducted a case-control analysis in a sample of 196 schizophrenic patients and 143 gender, age and ethnic matched controls. No statistically differences were found in allelic or genotypic distributions between cases and controls. Thus, the results do not support an association of the G861C polymorphism in the 5-HT1D(beta) autoreceptor gene with schizophrenia in the studied sample.

Queensland Centre for Mental Health Research: the first 17 years

OBJECTIVE

To reflect on the establishment and evolution of the Queensland Centre for Mental Health Research.

METHOD

Narrative historical review.

RESULTS

First established as an inpatient research unit in December 1987, the focus of the Centre evolved in concert with the skills of the staff. After the structure was revised in 1996 and 1999, the Centre has evolved into a group with four main research streams--epidemiology, developmental neurobiology, genetics and policy and economics. Although the group maintains a strong focus on serious mental disorders such as schizophrenia, our policy and economic work has a wider perspective. The Queensland Centre for Mental Health Research is based in an historic mental health service, with laboratories in collaborating universities and institutes. Key lessons learnt by the group along the way relate to the importance of focusing on a restricted range of research topics in order to build a critical mass.

CONCLUSIONS

Given a facilitating environment, hospital-based research groups can prosper. Over the last 17 years, a cost-efficient, focused and productive research group has evolved that has made contributions to international research.

Fine mapping of a schizophrenia susceptibility locus at chromosome 6q23: increased evidence for linkage and reduced linkage interval

We previously reported an autosomal scan for schizophrenia susceptibility loci in a systematically recruited sample of Arab Israeli families. The scan detected significant evidence for linkage at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) and a multipoint parametric LOD score of 4.16. In order to refine this finding we typed 42 additional microsatellite markers on chromosome 6q between D6S1570 (99.01 cM from the pter) and D6S281 (190.14 from the pter) in the same sample (average intermarker distance approximately 1.7 cM). In the 23 cM region between D6S1715 and D6S311, markers were more closely spaced ( approximately 1.1 cM). Multipoint nonparametric and parametric and single point linkage analyses were performed. The peak NPL rose to 4.98 (P=0.00000058) at D6S1626 (136.97 cM), immediately adjacent to D6S292 (NPL 4.98, P=0.00000068), the marker that gave the highest NPL in the original genome scan, under the broad diagnostic category. The putative susceptibility region (NPL-1) was reduced from 12.0 to 4.96 cM. The peak multipoint parametric LOD score was 4.63 at D6S1626 under a dominant genetic model, core diagnostic category and the LOD-1 interval was 2.10 cM. The maximum single point LOD score (3.55, theta=0.01) was also at D6S1626 (dominant model, core diagnostic category). Increased evidence for linkage in the same sample as in the original genome scan and consistent localization of the linkage peak add further support for the presence of a schizophrenia susceptibility locus at chromosome 6q23. Moreover, the markedly reduced linkage interval greatly improves prospects for identifying a schizophrenia susceptibility gene within the implicated region.

Complexities in psychiatric genetics

A substantial contribution of genetic factors to the risk of psychiatric disorders such as schizophrenia, bipolar disorder, autism, and drug and alcohol dependence has already been established. However, the familial transmission of these disorders cannot be explained by simple Mendelian models of inheritance, and non-genetic factors must also play a substantial role in their etiologies. Furthermore, the prevalence of any major psychiatric disorder is a great deal higher than that of Mendelian disorders. It has been suggested that evolutionary forces would rapidly eliminate large gene effects, which would suggest that mental disorders, which are highly prevalent, are associated with minor gene effects (Risch, 1994). The current paradigm is that genes with small interacting genetic effects, in conjunction with environmental factors, affect the risk for psychiatric disease. New laboratory and statistical methodology and database tools, and the availability of large clinical samples for the study of linkage and association sustain optimism that genes involved with these diseases will be characterized in the near future. This accomplishment should in turn lead not only to a better understanding of the primary molecular pathophysiology and to more specific and effective therapies, but also to a better understanding of non-genetic risk factors that could be targets for preventive strategies.

Human cannabinoid receptor 1: 5' exons, candidate regulatory regions, polymorphisms, haplotypes and association with polysubstance abuse

A number of lines of evidence make the gene that encodes the G-protein-coupled CB1/Cnr1 receptor a strong candidate to harbor variants that might contribute to individual differences in human addiction vulnerability. The CB1/Cnr1 receptor is the major brain site at which cannabinoid marijuana constituents are psychoactive as well as the principal brain receptor for endogenous anandamide ligands. It is densely expressed in brain circuits likely to be important for both the reward and mnemonic processes important for addiction. Altered drug effects in CB1/Cnr1 knockout mice and initial association studies also make variants at the CB1/Cnr1 locus candidates for roles in human vulnerabilities to addictions. However, many features of this gene's structure, regulation and variation remain poorly defined. This poor definition has limited the ability of previous association studies to adequately sample variation at this locus. We now report improved definition of the human CB1/Cnr1 locus and its variants. Novel exons 1-3, splice variant and candidate promoter region sequences add to the richness of the CB1/Cnr1 locus. Candidate promoter region sequences confer reporter gene expression in cells that express CB1/Cnr1. Common polymorphisms reveal patterns of linkage disequilibrium in European- and in African-American individuals. A 5' CB1/Cnr1 "TAG" haplotype displays significant allelic frequency differences between substance abusers and controls in European-American, African-American and Japanese samples. Post-mortem brain samples of heterozygous individuals contain less mRNA transcribed from the TAG alleles than from other CB1/Cnr1 haplotypes. CB1/ Cnr1 genomic variation thus appears to play roles in human addiction vulnerability.

Polymorphisms in the trace amine receptor 4 (TRAR4) gene on chromosome 6q23.2 are associated with susceptibility to schizophrenia

Several linkage studies across multiple population groups provide convergent support for a susceptibility locus for schizophrenia--and, more recently, for bipolar disorder--on chromosome 6q13-q26. We genotyped 192 European-ancestry and African American (AA) pedigrees with schizophrenia from samples that previously showed linkage evidence to 6q13-q26, focusing on the MOXD1-STX7-TRARs gene cluster at 6q23.2, which contains a number of prime candidate genes for schizophrenia. Thirty-one screening single-nucleotide polymorphisms (SNPs) were selected, providing a minimum coverage of at least 1 SNP/20 kb. The association observed with rs4305745 (P=.0014) within the TRAR4 (trace amine receptor 4) gene remained significant after correction for multiple testing. Evidence for association was proportionally stronger in the smaller AA sample. We performed database searches and sequenced genomic DNA in a 30-proband subsample to obtain a high-density map of 23 SNPs spanning 21.6 kb of this gene. Single-SNP analyses and also haplotype analyses revealed that rs4305745 and/or two other polymorphisms in perfect linkage disequilibrium (LD) with rs4305745 appear to be the most likely variants underlying the association of the TRAR4 region with schizophrenia. Comparative genomic analyses further revealed that rs4305745 and/or the associated polymorphisms in complete LD with rs4305745 could potentially affect gene expression. Moreover, RT-PCR studies of various human tissues, including brain, confirm that TRAR4 is preferentially expressed in those brain regions that have been implicated in the pathophysiology of schizophrenia. These data provide strong preliminary evidence that TRAR4 is a candidate gene for schizophrenia; replication is currently being attempted in additional clinical samples.

Maternal transmission disequilibrium of the glutamate receptor GRIK2 in schizophrenia

Schizophrenia is characterized by thought disorders, hallucinations and delusions. Genetic studies have shown a high linkage at chromosome 6q16-21. Among the genes located in this region is the glutamate receptor ionotropic kainate 2 gene (GRIK2 or GLUR6), a functional candidate for susceptibility to schizophrenia. In this study, transmission of GRIK2 was evaluated in 356 schizophrenic patients from three different clinical centers. Whereas paternal transmission shows equilibrium, we observed maternal transmission disequilibrium of GRIK2 in the largest population (p=0.03), which was still significant when all populations were added (p=0.05). These results are similar to the maternal GRIK2 transmission disequilibrium previously reported for autism, and support the presence of a susceptibility gene for schizophrenia at 6q16.

Lack of association or linkage disequilibrium between schizophrenia and polymorphisms in the 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes: family-based association study

Genetic factors play a major role in the etiology of schizophrenia and disturbances of serotonergic pathways have been implicated in this disorder. The aim of the present study was to examine genetic association between schizophrenia and polymorphisms in the 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) autoreceptor genes in ninety trios from Portugal. No association or linkage disequilibrium was obtained between schizophrenia and 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes with both haplotype relative risk (HRR) and transmission disequilibrium test (TDT). Concerning 5-HT1Dbeta autoreceptor gene, also negative results was obtained in the analysis of the haplotypes with transmit. Thus, our data provide no support for the hypothesis that polymorphisms at 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) genes contributes to susceptibility to schizophrenia in the Portuguese population.

Linkage of eye movement dysfunction to chromosome 6p in schizophrenia: additional evidence

Establishing the genetics of physiological traits associated with schizophrenia may be an important first step in building a neurobiological bridge between the disease phenotype and its genetic underpinnings. One of the best known of the traits associated with schizophrenia is a disorder of smooth pursuit eye tracking (ETD), which is present in 50-80% of schizophrenia patients. ETD is more than three times more prevalent in the families of a schizophrenia patient than is schizophrenia itself. Arolt et al. [1999] estimated LOD scores for ETD of 2.85 for D6S282 and 3.70 for D6S271, two markers on 6p21.1, as well as obtaining an indication of possible linkage for schizophrenia. Our sample comprised two large families in Denmark. Markers in the region that was implicated by the study of Arolt et al. [1996, 1999] were analyzed as part of a genome scan using the "latent trait (L.T.) model" for the co-transmission of schizophrenia and ETD that we had previously fitted to segregation analysis data from Norway. We obtained a LOD score of 2.05 for D6S1017, a marker within 3 cM of the positive markers obtained by Arolt et al. [1996, 1999]. We regard our results as independent evidence supporting the findings of Arolt et al. [1996, 1999] and also as support for the L.T. model as a way of combining the traits ETD and schizophrenia.

The molecular genetics of schizophrenia: new findings promise new insights

The high heritability of schizophrenia has stimulated much work aimed at identifying susceptibility genes using positional genetics. However, difficulties in obtaining clear replicated linkages have led to the scepticism that such approaches would ever be successful. Fortunately, there are now signs of real progress. Several strong and well-established linkages have emerged. Three of the best-supported regions are 6p24-22, 1q21-22 and 13q32-34. In these cases, single studies achieved genome-wide significance at P<0.05 and suggestive positive findings have also been reported in other samples. The other promising regions include 8p21-22, 6q21-25, 22q11-12, 5q21-q33, 10p15-p11 and 1q42. The study of chromosomal abnormalities in schizophrenia has also added to the evidence for susceptibility loci at 22q11 and 1q42. Recently, evidence implicating individual genes within some of the linked regions has been reported and more importantly replicated. The weight of evidence now favours NRG1 and DTNBP1 as susceptibility loci, though work remains before we understand precisely how genetic variation at each locus confers susceptibility and protection. The evidence for catechol-O-methyl transferase, RGS4 and G72 is promising but not yet persuasive. While further replications remain the top priority, the respective contributions of each gene, relationships with aspects of the phenotype, the possibility of epistatic interactions between genes and functional interactions between the gene products will all need investigation. The ability of positional genetics to implicate novel genes and pathways will open up new vistas for neurobiological research, and all the signs are that it is now poised to deliver crucial insights into the nature of schizophrenia.

Linkage studies of schizophrenia

The study of schizophrenia genetics has revealed much about the disease but none of the essential secrets of its etiology, so far, for numerous reasons. First, schizophrenia is a complex trait, influenced by both genes and environment. Second, it appears to be a highly heterogeneous disease, with locus and allelic heterogeneity both between and within families likely. Third, since it is common, it is likely that the genetic liability variants are common, and so are found with relatively high frequency in the general population. Fourth, linkage methods, which deliver rapid coverage of the genome, have great power to identify single genes causing Mendelian disorders but are poorly suited to the genetic architecture of complex traits. Although association methods are undeniably more powerful in such situations, affordable technologies to deliver the much higher density whole genome coverage required are not yet available and candidate gene studies of schizophrenia have not produced robust and replicable results. In spite of these limitations, there are now sufficient data to support several conclusions. Numerous regions of the human genome give consistent, though by no means unanimous, support for linkage. The precise nature of these signals is not yet understood, and power to position the effects is poor, but metanalyses show the co-occurrence is unlikely to be due to chance. Combined approaches utilizing linkage for rapid genome coverage and association for fine-scale follow-up have identified several promising candidate genes. Although the definition of replication in a complex trait is itself complex, a number of these candidates have been supported by numerous studies. These converging lines of evidence suggest that the genetics of schizophrenia, long considered a most intractable problem, are at last beginning to be unraveled.

A systematic genomewide linkage study in 353 sib pairs with schizophrenia

We undertook a genomewide linkage study in a total of 353 affected sib pairs (ASPs) with schizophrenia. Our sample consisted of 179 ASPs from the United Kingdom, 134 from Sweden, and 40 from the United States. We typed 372 microsatellite markers at approximately 10-cM intervals. Our strongest finding was a LOD score of 3.87 on chromosome 10q25.3-q26.3, with positive results being contributed by all three samples and a LOD-1 interval of 15 cM. This finding achieved genomewide significance (P<.05), on the basis of simulation studies. We also found two regions, 17p11.2-q25.1 (maximum LOD score [MLS] = 3.35) and 22q11 (MLS = 2.29), in which the evidence for linkage was highly suggestive. Linkage to all of these regions has been supported by other studies. Moreover, we found strong evidence for linkage (genomewide P<.02) to 17p11.2-q25.1 in a single pedigree with schizophrenia. In our view, the evidence is now sufficiently compelling to undertake detailed mapping studies of these three regions.

From genomics to proteomics: new directions in molecular neuropsychiatry

Neuropsychiatry, like many other biomedical sciences, has been revolutionized by the advances in genomic technologies over the years. The advent of PCR (polymerase chain reaction) and the sequencing of the human genome have provided invaluable insights into the molecular genetics of the various psychiatric disorders through the study of candidate genes and linkage analyses. However, biological phenotype is dictated by protein expression, which has been shown to stray from the genetic blueprint designated by the genome. Consequently, the field of proteomics has recently emerged as a powerful means of exploring protein structure, function, and expression patterns. The ability to study disease at the gene and protein levels presents a tremendous opportunity for neuropsychiatric research, particularly in terms of the potential for developing therapeutic agents for novel protein targets.

Recent advances in the genetics of schizophrenia

The high heritability of schizophrenia has stimulated much work aimed at identifying susceptibility genes using positional genetics. As a result, several strong and well-established linkages have emerged. Three of the best-supported regions are 6p24-22, 1q21-22 and 13q32-34 where single studies have achieved genome-wide significance at P<0.05 and suggestive positive findings have also been reported in other samples. Other promising regions include 8p21-22, 6q21-25, 22q11-12, 5q21-q33, 10p15-p11 and 1q42. Recently, evidence implicating individual genes within some of the linked regions has been reported and more importantly replicated. Currently, the weight of evidence supports NRG1 and DTNBP1 as schizophrenia susceptibility loci, though work remains before we understand precisely how genetic variation at each locus confers susceptibility and protection. The evidence for COMT, RGS4 and G72 is promising but not yet persuasive. While it is essential that further replications are established, the respective contributions of each gene, relationships with aspects of the phenotype, the possibility of epistatic interactions between genes and functional interactions between the gene products will all need investigation. The ability of positional genetics to implicate novel genes and pathways will open up new vistas for neurobiological research, and all the signs are that genetic research is poised to deliver crucial insights into the nature of schizophrenia.

Psychiatric genetics in Australia

Australian research in psychiatric genetics covers molecular genetic studies of depression, anxiety, alcohol dependence, Alzheimer's disease, bipolar disorder, schizophrenia, autism, and attention deficit hyperactivity disorder. For each disorder, a variety of clinical cohorts have been recruited including affected sib pair families, trios, case/controls, and twins from a large population-based twin registry. These studies are taking place both independently and in collaboration with international groups. Microarray studies now complement DNA investigations, while animal models are in development. An Australian government genome facility provides a high throughput genotyping and mutation detection service to the Australian scientific community, enhancing the contribution of Australian psychiatric genetics groups to gene discovery.

Initial genome-wide scan for linkage with schizophrenia in the Japanese Schizophrenia Sib-Pair Linkage Group (JSSLG) families

To determine if there are common genes that contribute to the susceptibility for schizophrenia, first-stage genome-wide scan was carried out by genotyping 417 short-tandem repeat (STR) markers in 338 individuals from 130 families with 148 affected sib-pairs identified at 16 sites nationwide in Japan. Data was from the Japanese Schizophrenia Sib-pair Linkage Group (JSSLG), which is a multi-site collaborative study group established to create a national resource for genetic studies of schizophrenia in Japan. All subjects were Japanese, and the probands and their siblings had schizophrenia. Multipoint non-parametric linkage analysis and exclusion mapping were performed with GENEHUNTER software. Simulation studies suggested that in the absence of linkage we could expect one multipoint maximum LOD score (MLS) of 1.9 per genome scan. An MLS of 3.7 would be expected only once in every 20 genome scans and thus corresponds to a genome-wide significance of 0.05. No loci in the initial screen fulfilled the criteria for significant or suggestive evidence for linkage. Ten chromosomes (1, 2, 3, 4, 5, 8, 9, 14, 17, and 20) had at least one region with a nominal P value < 0.05. Susceptibility genes with lambdas of 3 and 2 were excluded from 98 and 70% of the genome, respectively. Our results suggest that common genes that contribute significantly to susceptibility for schizophrenia are unlikely to exist in the Japanese population.

beta-1,3-Glucuronyltransferase-1 gene implicated as a candidate for a schizophrenia-like psychosis through molecular analysis of a balanced translocation

We have mapped and sequenced both chromosome breakpoints of a balanced t(6;11)(q14.2;q25) chromosome translocation that segregates with a schizophrenia-like psychosis. Bioinformatics analysis of the regions revealed a number of confirmed and predicted transcripts. No confirmed transcripts are disrupted by either breakpoint. The chromosome 6 breakpoint region is gene poor, the closest transcript being the serotonin receptor 1E (HTR1E) at 625 kb telomeric to the breakpoint. The chromosome 11 breakpoint is situated close to the telomere. The closest gene, beta-1,3-glucuronyltransferase (B3GAT1 or GlcAT-P), is 299 kb centromeric to the breakpoint. B3GAT1 is the key enzyme during the biosynthesis of the carbohydrate epitope HNK-1, which is present on a number of cell adhesion molecules important in neurodevelopment. Mice deleted for the B3GAT1 gene show defects in hippocampal long-term potentiation and in spatial memory formation. We propose that the translocation causes a positional effect on B3GAT1, affecting expression levels and making it a plausible candidate for the psychosis found in this family. More generally, regions close to telomeres are highly polymorphic in both sequence and length in the general population and several studies have implicated subtelomeric deletions as a common cause of idiopathic mental retardation. This leads us to the hypothesis that polymorphic or other variation of the 11q telomere may affect the activity of B3GAT1 and be a risk factor for schizophrenia and related psychoses in the general population.

Genome scan meta-analysis of schizophrenia and bipolar disorder, part II: Schizophrenia

Schizophrenia is a common disorder with high heritability and a 10-fold increase in risk to siblings of probands. Replication has been inconsistent for reports of significant genetic linkage. To assess evidence for linkage across studies, rank-based genome scan meta-analysis (GSMA) was applied to data from 20 schizophrenia genome scans. Each marker for each scan was assigned to 1 of 120 30-cM bins, with the bins ranked by linkage scores (1 = most significant) and the ranks averaged across studies (R(avg)) and then weighted for sample size (N(sqrt)[affected casess]). A permutation test was used to compute the probability of observing, by chance, each bin's average rank (P(AvgRnk)) or of observing it for a bin with the same place (first, second, etc.) in the order of average ranks in each permutation (P(ord)). The GSMA produced significant genomewide evidence for linkage on chromosome 2q (PAvgRnk<.000417). Two aggregate criteria for linkage were also met (clusters of nominally significant P values that did not occur in 1,000 replicates of the entire data set with no linkage present): 12 consecutive bins with both P(AvgRnk) and P(ord)<.05, including regions of chromosomes 5q, 3p, 11q, 6p, 1q, 22q, 8p, 20q, and 14p, and 19 consecutive bins with P(ord)<.05, additionally including regions of chromosomes 16q, 18q, 10p, 15q, 6q, and 17q. There is greater consistency of linkage results across studies than has been previously recognized. The results suggest that some or all of these regions contain loci that increase susceptibility to schizophrenia in diverse populations.

No genetic association between polymorphisms in the Fyn kinase gene and age of schizophrenic onset

Since the mRNA level of Fyn, a neurodevelopmental molecule, expression had been reported to be increased in postmortem schizophrenic prefrontal cortex and showed a strong correlation with age of disease onset, we investigated whether the three polymorphisms of the Fyn gene on genomic DNA (-93A/G, IVS10+37T/C and Ex12+894T/G) also had an effect on clinical onset in 139 unrelated schizophrenics. A comparison of the age of onset among the groups classified by polymorphisms showed no significant difference. Moreover, all allelic combinations also failed to show significant differences in age of onset among the groups. The present study reports that there is no indication that the three polymorphisms in the Fyn gene are associated with the age of schizophrenic onset.

Genome scan of Arab Israeli families maps a schizophrenia susceptibility gene to chromosome 6q23 and supports a locus at chromosome 10q24

Schizophrenia is a complex neuropsychiatric disorder to which an as-yet-unknown number of genes contribute, interacting with each other and the environment. Linkage analyses have implicated several chromosomal regions as harboring schizophrenia susceptibility loci although rarely at levels commensurate with proposed thresholds for genome-wide significance. We systematically recruited Arab Israeli families multiply affected with schizophrenia from the catchment area of a Regional Mental Health Center. Clinical diagnoses were established by semistructured interviews and all other available sources of information under narrow, core and broad categories. Using 350 microsatellite markers, spaced at an average of 10.3 cM, we performed an autosomal scan in 155 subjects from 21 families. Linkage analysis employed affects only, multipoint, nonparametric (model-free) and also parametric (dominant and recessive) approaches. We detected significant evidence for a schizophrenia susceptibility gene at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) under the broad diagnostic category and a parametric LOD score of 3.33 (dominant model). Under the core diagnostic category the NPL was 4.29 (P=0.00001) and the LOD score 4.16 (dominant model). We also detected suggestive evidence for linkage at chromosome 10q24 under the broad diagnostic category (NPL 3.24, P=0.0008; heterogeneity LOD score, dominant model 2.65, alpha=0.82). Additionally, NPL scores >2.0 were observed at chromosome 2q37, 4p15-16, 7p22, 9q21-22 and 14q11.1-11.2. The linkage we detected at chromosome 6q23 fulfills the criteria for genome-wide significance and is located approximately midway between loci suggested by a previous significant report at chromosome 6q25 and findings located more centromerically at 6q21-22.