Genomewide genetic linkage analysis confirms the presence of susceptibility loci for schizophrenia, on chromosomes 1q32.2, 5q33.2, and 8p21-22 and provides support for linkage to schizophrenia, on chromosomes 11q23.3-24 and 20q12.1-11.23

A reanalysis of 409 European-Ancestry and African American schizophrenia pedigrees reveals significant linkage to 8p23.3 with evidence of locus heterogeneity

The detection and replication of schizophrenia risk loci can require substantial sample sizes, which has prompted various collaborative efforts for combining multiple samples. However, pooled samples may comprise sub-samples with substantial population genetic differences, including allele frequency differences. We investigated the impact of population differences via linkage reanalysis of Molecular Genetics of Schizophrenia 1 (MGS1) affected sibling-pair data, comprising two samples of distinct ancestral origin: European (EA: 263 pedigrees) and African-American (AA: 146 pedigrees). To exploit the linkage information contained within these distinct continental samples, we performed separate analyses of the individual samples, allowing for within-sample locus heterogeneity, and the pooled sample, allowing for both within-sample and between-sample heterogeneity. Significance levels, corrected for the multiple tests, were determined empirically. For all suggestive peaks, stronger linkage evidence was obtained in either the EA or AA sample than the combined sample, regardless of how heterogeneity was modeled for the latter. Notably, we report genomewide significant linkage of schizophrenia to 8p23.3 and evidence for a second, independent susceptibility locus, reaching suggestive linkage, 29 cM away on 8p21.3. We also detected suggestive linkage on chromosomes 5p13.3 and 7q36.2. Many regions showed pronounced differences in the extent of linkage between the EA and AA samples. This reanalysis highlights the potential impact of population differences upon linkage evidence in pooled data and demonstrates a useful approach for the analysis of samples drawn from distinct continental groups.

Association of RGS4 variants with schizotypy and cognitive endophenotypes at the population level

Background

While association studies on schizophrenia show conflicting results regarding the importance of the regulator of the G-protein signaling 4 (RGS4) gene, recent work suggests that RGS4 may impact on the structural and functional integrity of the prefrontal cortex. We aimed to study associations of common RGS4 variants with prefrontal dependent cognitive performance and schizotypy endophenotypes at the population level.

Methods

Four RGS4 single nucleotide polymorphisms (SNP1 [rs10917670], SNP4 [rs951436], SNP7 [rs951439], and SNP18 [rs2661319]) and their haplotypes were selected. Their associations with self-rated schizotypy (SPQ), vigilance, verbal, spatial working memory and antisaccade eye performance were tested with regressions in a representative population of 2,243 young male military conscripts.

Results

SNP4 was associated with negative schizotypy (higher SPQ negative factor for common T allele, p = 0.009; p = 0.031 for differences across genotypes) and a similar trend was seen also for common A allele of SNP18 (p = 0.039 for allele-load model; but p = 0.12 for genotype differences). Haplotype analyses showed a similar pattern with a dose-response for the most common haplotype (GGGG) on the negative schizotypy score with or without adjustment for age, IQ and their interaction (p = 0.011 and p = 0.024, respectively). There was no clear evidence for any association of the RGS4 variants with cognitive endophenotypes, except for an isolated effect of SNP18 on antisaccade error rate (p = 0.028 for allele-load model).

Conclusion

Common RGS4 variants were associated with negative schizotypal personality traits amongst a large cohort of young healthy individuals. In accordance with recent findings, this may suggest that RGS4 variants impact on the functional integrity of the prefrontal cortex, thus increasing susceptibility for psychotic spectrum disorders.

Biomarker discovery in psychiatric disorders

Schizophrenia is a multifaceted neuropsychiatric disorder. Its onset is the result of complex interactions between genetic, developmental and environmental factors. It almost certainly presents a heterogeneous group of aetiologies which may not be reflected in the symptomatic/clinical presentation of patients. Therefore, a better molecular understanding of the disease onset and progression is urgently needed. The high complexity of the disorder and the heterogeneity of patient populations account for the slow progress of biomarker discovery approaches. Multi-omics profiling approaches can be employed to investigate large numbers of patient and control samples in a single experiment. These large scale experiments are required to identify disease intrinsic molecular signatures as well as patient subgroups with potentially distinct biochemical pathways underpinning their symptoms. In this overview, we describe some of the most important challenges for biomarker discovery for psychiatric disorders and emphasize how these problems contribute to the requirement of large sample numbers. Results of MS-based protein profiling studies in schizophrenia research are reviewed and technical advantages and difficulties of the methodologies described. We outline recent technological advances that generated impressive results in other areas of research and point to their applicability for biomarker discovery in psychiatric disorders.

Large recurrent microdeletions associated with schizophrenia

Reduced fecundity, associated with severe mental disorders, places negative selection pressure on risk alleles and may explain, in part, why common variants have not been found that confer risk of disorders such as autism, schizophrenia and mental retardation. Thus, rare variants may account for a larger fraction of the overall genetic risk than previously assumed. In contrast to rare single nucleotide mutations, rare copy number variations (CNVs) can be detected using genome-wide single nucleotide polymorphism arrays. This has led to the identification of CNVs associated with mental retardation and autism. In a genome-wide search for CNVs associating with schizophrenia, we used a population-based sample to identify de novo CNVs by analysing 9,878 transmissions from parents to offspring. The 66 de novo CNVs identified were tested for association in a sample of 1,433 schizophrenia cases and 33,250 controls. Three deletions at 1q21.1, 15q11.2 and 15q13.3 showing nominal association with schizophrenia in the first sample (phase I) were followed up in a second sample of 3,285 cases and 7,951 controls (phase II). All three deletions significantly associate with schizophrenia and related psychoses in the combined sample. The identification of these rare, recurrent risk variants, having occurred independently in multiple founders and being subject to negative selection, is important in itself. CNV analysis may also point the way to the identification of additional and more prevalent risk variants in genes and pathways involved in schizophrenia.

A genome screen for quantitative trait loci influencing schizophrenia and neurocognitive phenotypes

OBJECTIVE

Deficits in neurocognitive function have been demonstrated in individuals with schizophrenia and in the unaffected family members of these individuals. Genetic studies of such complementary traits, along with traditional analyses of diagnosis, may help to elucidate the biological pathways underlying familial liability to schizophrenia and related disorders. The authors conducted a multiplex, multigenerational family study using a genome-wide screen for schizophrenia and related neurocognitive phenotypes.

METHOD

Participants were 1) 676 European American individuals from 43 families, ascertained through an individual with schizophrenia, and 2) 236 healthy comparison subjects. Participants were evaluated clinically and examined through the use of a computerized neurocognitive test battery that provided measures of accuracy and speed on the cognitive domains of abstraction and mental flexibility; attention; verbal, face, and spatial memory; language and reasoning; spatial and emotion processing; and sensorimotor dexterity. A genome-wide linkage screen was also performed. Healthy comparison subjects were included in order to obtain normative phenotypic data but were not genotyped.

RESULTS

Significant evidence for linkage of schizophrenia to chromosome 19q was observed. Analysis of cognitive traits revealed significant linkage to chromosome 5q for the domains of abstraction and mental flexibility. A variety of other neurocognitive traits also showed nominal evidence of linkage to the 5q region. Joint analyses with diagnosis suggested that this quantitative trait locus may also influence schizophrenia.

CONCLUSIONS

Although chromosome 5 has been implicated in previous linkage studies of schizophrenia, the identification of the chromosome 19 quantitative trait locus is a novel finding. The identification of the chromosome 5 quantitative trait locus through linkage to neurocognitive phenotypes in the present study may inform functional hypotheses pertaining to how genotypes are connected to disease.

Genetic association between 5'-upstream single-nucleotide polymorphisms of PDGFRB and schizophrenia in a Korean population

PDGFRB is located on chromosome 5q31-q32, a chromosomal region identified by linkage analyses to contain a susceptibility gene for schizophrenia (SCZ). Recent research has focused on the role of the N-methyl-d-aspartate (NMDA) receptor in the pathogenesis of SCZ. D4 dopamine receptor-mediated transactivation of the gene encoding platelet-derived growth factor receptor beta (PDGFRB) has immediate effects on synaptic neurotransmission via calcium-dependent inactivation of NMDA receptors. In this study, we investigate the association between the PDGFRB gene and SCZ in a Korean population. We screened 6 single-nucleotide polymorphisms (SNPs) in the 5'-upstream region of PDGFRB and conducted a case-control study of 381 SCZ patients and 752 controls. The genotype and haplotype frequencies of 3 of the 6 SNPs [SNP1 (g.-1924T>C, rs3756314), SNP3 (g.-1772A>G, rs3756312) and SNP4 (rs3756311, g.-1658G>A)] were significantly associated with SCZ [SNP1, corrected p=0.012 (co-dominant model), 0.002 (Dominant model), and 0.506 (Recessive model); SNP3 and 4, corrected p=0.003, 0.009, and 0.049]. Haplotype analysis also revealed that ht1 (CGG) and ht2 (TAA) were significantly associated with SCZ (ht1, corrected p=0.018, 0.340, and 0.010; ht2, corrected p=0.002, 0.009, and 0.016). Transient transfection in neuronal cells revealed that ht1 had higher luciferase activity than the vector alone. Furthermore, Pdgfrb expression was increased in the frontal cortex and hippocampus in a mouse model of SCZ induced by MK801. We conclude that SNPs of the 5'-upstream region of PDGFRB are associated with SCZ in a Korean population. These are weak positives that require future studies to confirm these results.

Rare chromosomal deletions and duplications increase risk of schizophrenia

Schizophrenia is a severe mental disorder marked by hallucinations, delusions, cognitive deficits and apathy, with a heritability estimated at 73-90% (ref. 1). Inheritance patterns are complex, and the number and type of genetic variants involved are not understood. Copy number variants (CNVs) have been identified in individual patients with schizophrenia and also in neurodevelopmental disorders, but large-scale genome-wide surveys have not been performed. Here we report a genome-wide survey of rare CNVs in 3,391 patients with schizophrenia and 3,181 ancestrally matched controls, using high-density microarrays. For CNVs that were observed in less than 1% of the sample and were more than 100 kilobases in length, the total burden is increased 1.15-fold in patients with schizophrenia in comparison with controls. This effect was more pronounced for rarer, single-occurrence CNVs and for those that involved genes as opposed to those that did not. As expected, deletions were found within the region critical for velo-cardio-facial syndrome, which includes psychotic symptoms in 30% of patients. Associations with schizophrenia were also found for large deletions on chromosome 15q13.3 and 1q21.1. These associations have not previously been reported, and they remained significant after genome-wide correction. Our results provide strong support for a model of schizophrenia pathogenesis that includes the effects of multiple rare structural variants, both genome-wide and at specific loci.

Chitinase-3-like 1 (CHI3L1) gene and schizophrenia: genetic association and a potential functional mechanism

BACKGROUND

Gene expression data and association analyses in two Chinese samples implicate chitinase 3-like 1 (CHI3L1), a cellular survival gene, in schizophrenia susceptibility.

METHODS

We tested whether the association data are robust to replication in a Caucasian schizophrenia sample and performed a comprehensive investigation of common genetic variation at the locus.

RESULTS

In a sample of 375 case and 812 control subjects we identified significant association with the same risk allele at the promoter single nucleotide polymorphism (SNP) associated in the original study (rs10399805; p = .018) and with another SNP at intron 7 of CHI3L1 (rs2275351; p = .008). The rs10399805 SNP is located at position -247 and disrupts the C/EBP-AML-1 binding site in the gene promoter; the risk allele is predicted to increase CHI3L1 expression, as has been reported in several postmortem schizophrenia studies. Carriers of the risk variant presented with fewer positive symptoms and relatively spared cognitive performance compared with other schizophrenia patients.

CONCLUSIONS

These findings support a functional mechanism for involvement of CHI3L1 in schizophrenia susceptibility, possibly contributing to a less severe illness. The associated variants in this study are not well tagged by all Whole-Genome Association (WGA) platforms, suggesting additional genotyping may be necessary despite the imminent availability of WGA data from large SZ samples. Because CHI3L1 may be involved in transmission of stress-induced cellular responses, studies of interaction with known environmental risk factors may also be warranted.

Analysis of protocadherin alpha gene enhancer polymorphism in bipolar disorder and schizophrenia

Cadherins and protocadherins are cell adhesion proteins that play an important role in neuronal migration, differentiation and synaptogenesis, properties that make them targets to consider in schizophrenia (SZ) and bipolar disorder (BD) pathogenesis. Consequently, allelic variation occurring in protocadherin and cadherin encoding genes that map to regions of the genome targeted in SZ and BD linkage studies are particularly strong candidates to consider. One such set of candidate genes is the 5q31-linked PCDH family, which consists of more than 50 exons encoding three related, though distinct family members--alpha, beta, and gamma--which can generate thousands of different protocadherin proteins through alternative promoter usage and cis-alternative splicing. In this study, we focused on a SNP, rs31745, which is located in a putative PCDHalpha enhancer mapped by ChIP-chip using antibodies to covalently modified histone H3. A striking increase in homozygotes for the minor allele at this locus was detected in patients with BD. Molecular analysis revealed that the SNP causes allele-specific changes in binding to a brain protein. The findings suggest that the 5q31-linked PCDH locus should be more thoroughly considered as a disease-susceptibility locus in psychiatric disorders.

Mice lacking the immediate early gene Egr3 respond to the anti-aggressive effects of clozapine yet are relatively resistant to its sedating effects

Immediate early genes (IEGs) of the early growth response gene (Egr) family are activated in the brain in response to stress, social stimuli, and administration of psycho-active medications. However, little is known about the role of these genes in the biological or behavioral response to these stimuli. Here we show that mice lacking the IEG transcription factor Egr3 (Egr3-/- mice) display increased aggression, and a decreased latency to attack, in response to the stressful social stimulus of a foreign intruder. Together with our findings of persistent and intrusive olfactory-mediated social investigation of conspecifics, these results suggest increased impulsivity in Egr3-/- mice. We also show that the aggression of Egr3-/- mice is significantly inhibited with chronic administration of the antipsychotic medication clozapine. Despite their sensitivity to this therapeutic effect of clozapine, Egr3-/- mice display a marked resistance to the sedating effects of acute clozapine compared with WT littermate controls. This indicates that the therapeutic, anti-aggressive action of clozapine is separable from its sedating activity, and that the biological abnormality resulting from loss of Egr3 distinguishes these different mechanisms. Thus Egr3-/- mice may provide an important tool for elucidating the mechanism of action of clozapine, as well as for understanding the biology underlying aggressive behavior. Notably, schizophrenia patients display a similar decreased susceptibility to the side effects of antipsychotic medications compared to non-psychiatric controls, despite the medications producing a therapeutic response. This suggests the possibility that Egr3-/- mice may provide insight into the neurobiological abnormalities underlying schizophrenia.

Association of RGS2 and RGS5 variants with schizophrenia symptom severity

BACKGROUND

Several lines of evidence indicate that Regulator of G Protein Signaling 4 (RGS4) contributes to schizophrenia vulnerability. RGS4 is one of a family of molecules that modulate signaling via G-protein coupled receptors. Five genes encoding members of this family (RGS2, RGS4, RGS5, RGS8 and RGS16) map to chromosome 1q23.3-1q31. Due to overlapping cellular functions and chromosomal proximity, we hypothesized that multiple RGS genes may contribute to schizophrenia severity and treatment responsiveness.

METHODS

Subjects were 750 individuals with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Inferred ancestries were: 221 (30%) 'Africa only', 422 (56%) 'Europe only' and 107 (14%) 'Other'. Fifty-nine single nucleotide polymorphisms (SNPs) in or near the RGS5, RGS16, RGS8 and RGS2 genes were genotyped. Multiple linear regression was used to analyze association of markers with Positive and Negative Symptoms Scale (PANSS) total scores at baseline and throughout antipsychotic treatment.

RESULTS

RGS5 marker rs10799902 was associated with altered baseline PANSS total score in both the Africa only (P=0.0440) and Europe only (P=0.0143) strata, although neither association survived multiple comparisons correction. A common five-marker haplotype of the RGS2 gene was associated with more severe baseline PANSS total score in the Europe only strata (global P=0.0254; haplotype-specific P=0.0196). In contrast to RGS4, none of the markers showed association with antipsychotic treatment response.

CONCLUSIONS

RGS2 and RGS5 genotypes predicted severity of baseline symptoms in schizophrenia. Although these analyses are exploratory and replication is required, these data suggest a possible role for multiple RGS proteins in schizophrenia.

NOS1AP in schizophrenia

NOS1AP is an attractive candidate gene for schizophrenia susceptibility. Linkage and association studies from multiple samples drawn from different populations indicate that a schizophrenia susceptibility gene is located in the region of chromosome 1 containing NOS1AP. Increased NOS1AP expression is observed in postmortem samples from individuals with schizophrenia. NOS1AP binds to neuronal nitric oxide synthase and synapsin, other candidate genes for schizophrenia, and may disrupt signal transduction through the N-methyl d-aspartate receptor complex, leading to hypofunctioning of that system. In this review, I present the evidence supporting NOS1AP as a schizophrenia susceptibility gene, with a focus on explaining the strengths and weaknesses of the evidence obtained from each type of study that has been conducted.

Genomic structural variation and schizophrenia

It has recently been demonstrated that a large amount of structural variation exists in the human genome. Since 2004, when two landmark studies reported polymorphic levels of copy number variation in phenotypically normal individuals, our understanding of genome-wide levels of copy number variation has grown. This has inspired hypotheses about this class of variation's contribution to complex genetic phenotypes, including the specific hypothesis that structural variation is associated with psychiatric illness. The technology to accurately and efficiently detect polymorphic structural variants is still largely under development, but some examples of genomic imbalance contributing to schizophrenia and bipolar disorder already have been identified. Although much optimism surrounds this burgeoning field, the technical challenges in reliably identifying structural variation mean recent literature should be approached with caution.

Phenomic, convergent functional genomic, and biomarker studies in a stress-reactive genetic animal model of bipolar disorder and co-morbid alcoholism

We had previously identified the clock gene D-box binding protein (Dbp) as a potential candidate gene for bipolar disorder and for alcoholism, using a Convergent Functional Genomics (CFG) approach. Here we report that mice with a homozygous deletion of DBP have lower locomotor activity, blunted responses to stimulants, and gain less weight over time. In response to a chronic stress paradigm, these mice exhibit a diametric switch in these phenotypes. DBP knockout mice are also activated by sleep deprivation, similar to bipolar patients, and that activation is prevented by treatment with the mood stabilizer drug valproate. Moreover, these mice show increased alcohol intake following exposure to stress. Microarray studies of brain and blood reveal a pattern of gene expression changes that may explain the observed phenotypes. CFG analysis of the gene expression changes identified a series of novel candidate genes and blood biomarkers for bipolar disorder, alcoholism, and stress reactivity.

Differential RNA expression between schizophrenic patients and controls of the dystrobrevin binding protein 1 and neuregulin 1 genes in immortalized lymphocytes

The dystrobrevin binding protein 1 (DTNBP1) and neuregulin 1 (NRG1) genes have been related to schizophrenia (SZ) and bipolar disorder (BP) by several whole-genome linkage and associations studies. Few expression studies in post-mortem brains have also reported a lower or a higher expression of DTNBP1 and NRG1, respectively, in SZ. Since the difficulty to access post-mortem brains, we evaluated RNA expression of DTNBP1 and NRG1 in immortalized lymphocytes of SZ patients and unrelated-family controls. An antipsychotic stimulation was also used to challenge the genetic background of the subjects and enhance differential expression. Immortalized lymphocytes of twelve SZ and twelve controls were grown individually in the presence or not of the antipsychotic olanzapine (Zyprexa; EliLilly). RNA was extracted and pooled in four groups of three SZ and four groups of three controls, and used to probe Agilent 18K microchips. Mean gene expression values were contrasted between SZ and control groups using a T-test. For DTNBP1, RNA expression was lower in SZ than in controls before (-28%; p=0.02) and after (-30%; p=0.01) olanzapine stimulation. Similarly, NRG1 GGF2 isoform showed a lower expression in SZ before (-29%; p=0.04) and after (-33%; p=0.02) olanzapine stimulation. In contrast, NRG1 GGF isoform showed no significant difference between SZ and controls (-7%; p=0.61, +3%; p=0.86, respectively), but was slightly repressed by olanzapine in controls (-8%; p=0.008) but not in SZ (+1%; p=0.91). These results are in agreement with those observed in post-mortem brain when the isoforms involved are considered.

The myelin-pathogenesis puzzle in schizophrenia: a literature review

Schizophrenia is a serious and disabling mental disorder with symptoms such as auditory hallucinations, disordered thinking and delusions, avolition, anhedonia, blunted affect and apathy. In this review article we seek to present the current scientific findings from linkage studies and susceptible genes and the pathophysiology of white matter in schizophrenia. The article has been reviewed in two parts. The first part deals with the linkage studies and susceptible genes in schizophrenia in order to have a clear-cut picture of the involvement of chromosomes and their genes in schizophrenia. The genetic linkage results seem to be replicated in some cases but in others are not. From these results, we cannot draw a fine map to a single locus or gene, leading to the conclusion that schizophrenia is not caused by a single factor/gene. In the second part of the article we present the oligodendrocyte-related genes that are associated with schizophrenia, as we hypothesize a potential role of oligodendrocyte-related genes in the pathology of the disorder.

Association study in the 5q31-32 linkage region for schizophrenia using pooled DNA genotyping

BACKGROUND

Several linkage studies suggest that chromosome 5q31-32 might contain risk loci for schizophrenia (SZ). We wanted to identify susceptibility genes for schizophrenia within this region.

METHODS

We saturated the interval between markers D5S666 and D5S436 with 90 polymorphic microsatellite markers and genotyped two sets of DNA pools consisting of 300 SZ patients of Bulgarian origin and their 600 parents. Positive associations were followed-up with SNP genotyping.

RESULTS

Nominally significant evidence for association (p < 0.05) was found for seven markers (D5S0023i, IL9, RH60252, 5Q3133_33, D5S2017, D5S1481, D5S0711i) which were then individually genotyped in the trios. The predicted associations were confirmed for two of the markers: D5S2017, localised in the SPRY4-FGF1 locus (p = 0.004) and IL9, localized within the IL9 gene (p = 0.014). Fine mapping was performed using single nucleotide polymorphisms (SNPs) around D5S2017 and IL9. In each region four SNPs were chosen and individually genotyped in our full sample of 615 SZ trios. Two SNPs showed significant evidence for association: rs7715300 (p = 0.001) and rs6897690 (p = 0.032). Rs7715300 is localised between the TGFBI and SMAD5 genes and rs6897690 is within the SPRY4 gene.

CONCLUSION

Our screening of 5q31-32 implicates three potential candidate genes for SZ: SMAD5, TGFBI and SPRY4.

Genetic examination of the PLXNA2 gene in Japanese and Chinese people with schizophrenia

Aberrant neuronal development is one of the integrative theories for the etiology of schizophrenia. The plexin A2 (PLXNA2) gene is one of the receptor genes for axonal guidance factors. Recently, four single nucleotide polymorphisms (SNPs), rs841865, rs752016, rs1327175 and rs2498028, from the PLXNA2 genomic interval have been reported to be associated with schizophrenia in samples from European Americans, Latin Americans and Asian Americans. We tested these four SNPs for association with disease in two Asian populations: 1140 case-control Japanese samples and 293 Chinese pedigrees (1163 samples). In the Japanese samples, significant differences in the allelic frequency and genotypic distribution of rs841865 (p=0.019 and 0.020, respectively) were observed between cases and controls. Haplotype analysis also revealed a significant association of the gene with the disease (global p=0.028). In contrast, there was no genetic contribution of PLXNA2 to Chinese schizophrenia, either by linkage analysis or association tests (allelic and haplotypic transmission disequilibrium tests). These findings suggest that PLXNA2 confers a varying genetic risk for schizophrenia among different populations.

Positive association between PDLIM5 and schizophrenia in the Chinese Han population

The PDZ and LIM domain 5 protein (PDLIM5) contains one PDZ (post-synaptic density-95/discs large/zone occludens-1) domain and three LIM (Lin-11, Isl-1, and Mec-3) domains, and is also known as Enigma homologue LIM domain (ENH) protein or LIM protein. DNA microarray analysis of post-mortem brains of schizophrenics has indicated up-regulation of the mRNA level of PDLIM5, and Horiuchi and colleagues reported two single nucleotide polymorphisms (SNPs) (rs2433320 and rs2433322) in the 5' region of the PDZ and LIM domain 5 gene (PDLIM5) to be significantly associated with schizophrenia in the Japanese population. On the other hand, no association with schizophrenia was observed by Kato and colleagues in a different sample of the Japanese population. In this study, we genotyped six SNPs (including rs2433320 and rs2433322) covering PDLIM5 in 507 schizophrenia patients and 530 normal controls recruited from Jiangxi Province, China. Although rs2433320 was negative in our samples, rs2433322 showed significantly different frequencies between cases and controls (P=0.000010). In addition, high linkage disequilibrium was observed between rs2433320 and rs2433322 (D'=0.880), and haplotypes constructed from the two SNPs were significantly associated with schizophrenia (global P=0.00019, even after strict Bonferroni correction). Our results provide further evidence to support PDLIM5 as a potential susceptible gene for schizophrenia.

Ethnic stratification of the association of RGS4 variants with antipsychotic treatment response in schizophrenia

BACKGROUND

Genetic association studies, including a large meta-analysis, report association of regulator of G protein signaling 4 (RGS4) with schizophrenia in the context of heterogeneity. The central role of RGS4 in regulating signaling via Gi/o coupled neurotransmitter receptors led us to hypothesize that there may be RGS4 genotypes predictive of specific disease phenotypes and antipsychotic treatment responses.

METHODS

Subjects were 678 individuals with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Among the 678 subjects, the inferred ancestries were 198 (29%) "Africa only," 397 (59%) "Europe only," and 83 (12%) "Other." Eight single nucleotide polymorphisms (SNPs) spanning RGS4 were genotyped. Multiple linear regression was used to analyze association of RGS4 markers with Positive and Negative Symptoms Scale (PANSS) scores at baseline and throughout antipsychotic treatment.

RESULTS

Two consecutive markers within RGS4, rs2661319 and rs2842030, were associated with more severe baseline PANSS total score. Treatment with perphenazine was more effective than treatment with quetiapine (p = .010) or ziprasidone (p = .002) in individuals of inferred African ancestry and homozygous for the rs951439 C allele.

CONCLUSIONS

RGS4 genotypes predicted both the severity of baseline symptoms and relative responsiveness to antipsychotic treatment. Although these analyses are exploratory and replication is required, these data provide support for RGS4 in schizophrenia pathogenesis and suggest a functional role for RGS4 in differential antipsychotic treatment efficacy of schizophrenia.

Evidence of missense mutations on the neuregulin 1 gene affecting function of prepulse inhibition

BACKGROUND

Neuregulin 1 (NRG1) is one of the leading candidate genes in schizophrenia. Rodents with NRG1 knock-out showed significantly impaired prepulse inhibition (PPI) in the original report linking NRG1 to schizophrenia. A widely used surrogate measure of psychosis in animal models, PPI is considered a schizophrenia endophenotype. We hypothesized that if NRG1 influences PPI in rodents, then it should have a similar effect on PPI in humans.

METHODS

We examined the potential neurophysiological effects of two nonsynonymous single nucleotide polymorphisms located on NRG1 (rs3924999 and rs10503929) on PPI. Genotyping was completed in 430 unrelated individuals, including 244 schizophrenia cases and 186 controls. PPI was available in a subgroup of 113 cases and 63 controls.

RESULTS

Rs3924999 genotype was significantly associated with PPI (p = .003): PPI was lowest in the subjects who were homozygous for the minor allele A/A carriers, intermediate in A/G carriers, and highest in homozygous major alleles G/G carriers. The associations persisted within cases (p = .02) and controls (p = .02) analyzed separately. An additive model suggested that rs3924999 alone contributes to 7.9% of the PPI variance. In contrast, rs10503929 genotype was not associated with PPI (p = .85). Schizophrenia patients had reduced PPI compared to control subjects (p = .04). Neither single nucleotide polymorphism was associated with schizophrenia (all p > .37). However, schizophrenia patients with abnormal PPI may be associated with rs3924999 (p = .05).

CONCLUSIONS

A missense mutation on rs3924999 of the neuregulin 1 gene may have a functional effect on prepulse inhibition in both schizophrenia and healthy control populations.

Association of the gene encoding neurogranin with schizophrenia in males

The neurogranin (NRGN) gene produces a postsynaptic brain-specific protein that regulates calmodulin-Ca(2+) availability in neurons. Acting downstream of the NMDA receptor and upstream of calcineurin and other proteins implicated in schizophrenia, NRGN is a good candidate for association studies in schizophrenia. NRGN expression is regulated during development and is modulated by thyroid hormones and retinoids, molecules essential for the proper development of the central nervous system. Given the genetic complexity of schizophrenia and the potential genetic heterogeneity in different populations, we studied a possible association of NRGN with schizophrenia in 73 Azorean proband-parent triads and in two independent case-control samples from the Portuguese-mainland (244 schizophrenic and 210 controls) and Brazil (69 schizophrenic and 85 mentally healthy individuals). Genotype distribution showed association of the rs7113041 SNP with schizophrenia in males of Portuguese origin, which was confirmed by the analysis of the proband-parent triads. This evidence, implicating NRGN in schizophrenia, introduces another player into the glutamatergic hypothesis of schizophrenia.

More evidence supports the association of PPP3CC with schizophrenia

Calcineurin is a calcium/calmodulin-dependent protein phosphatase composed of two subunits, a regulatory subunit of calcineurin B (CNB) and a catalytic subunit of calcineurin A (CNA). PPP3CC is the gamma isoform of CNA located at the chromosome 8p21.3 region. To evaluate the association between PPP3CC and schizophrenia in the Taiwanese population, 10 single nucleotide polymorphism (SNP) markers across the gene were genotyped by the method of MALDI-TOF in 218 schizophrenia families with at least two affected siblings. One SNP (rs2272080) located around the exon 1 untranslated region was nominally associated with schizophrenia (P=0.024) and significantly associated with the expression of PPP3CC in lymphoblast cell line; the TT and TG genotype had significantly higher relative expression levels than the GG genotype (P=0.0012 and 0.015, respectively). In further endophenotype stratification, the single locus of rs2272080 and the haplotypes of both two-SNP haplotype (rs7833266-rs2272080) and seven-SNP haplotype (rs2461491-rs2469758-rs2461489-rs2469770-rs2449340-rs1482337-rs2252471) showed significant associations with the subgroup of schizophrenia with deficits of the sustained attention as tested by the continuous performance test (CPT, P<0.05) and the executive functioning as tested by the Wisconsin Card Sorting Test (WCST, P<0.05). The results suggest that PPP3CC gene may be a true susceptibility gene for schizophrenia.

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.

NCAM1 association study of bipolar disorder and schizophrenia: polymorphisms and alternatively spliced isoforms lead to similarities and differences

OBJECTIVE

The neural cell adhesion molecule (NCAM1) is a multifunction transmembrane protein involved in synaptic plasticity, neurodevelopment, and neurogenesis. Multiple NCAM1 proteins were differentially altered in bipolar disorder and schizophrenia. Single nucleotide polymorphisms (SNPs) in the NCAM1 gene were significantly associated with bipolar disorder in the Japanese population. Bipolar disorder and schizophrenia may share common vulnerability or susceptibility risk factors for shared features in each disorder.

METHODS

Both SNPs and splice variants in the NCAM1 gene were analysed in bipolar disorder and schizophrenia. A case-control study design for association of SNPs and differential exon expression in the NCAM1 gene was used.

RESULTS

A genotypic association between bipolar disorder and SNP b (rs2303377 near mini-exon b) and a suggestive association between schizophrenia and SNP 9 (rs646558) were found. Three of the two marker haplotypes for SNP 9 and SNP b showed varying frequencies between bipolar and controls (P<0.0001) as well as between schizophrenia and controls (P<0.0001). There were nine NCAM1 transcripts present in postmortem brain samples that involve alternative splicing of NCAM1 mini-exons (a, b, c) and the secreted (SEC) exon. Significant differences in the amounts of four alternatively spliced isoforms were found between NCAM1 SNP genotypes. In exploratory analysis, the c-SEC alternative spliced isoform was significantly decreased in bipolar disorder compared to controls for NCAM1 SNP b heterozygotes (P=0.013).

CONCLUSIONS

Diverse NCAM1 transcripts were found with possibly different functions. The results suggest that SNPs within NCAM1 contribute differential risk for both bipolar disorder and schizophrenia possibly by alternative splicing of the gene.

Failure to confirm allelic and haplotypic association between markers at the chromosome 6p22.3 dystrobrevin-binding protein 1 (DTNBP1) locus and schizophrenia

Background

Previous linkage and association studies may have implicated the Dystrobrevin-binding protein 1 (DTNBP1) gene locus or a gene in linkage disequilibrium with DTNBP1 on chromosome 6p22.3 in genetic susceptibility to schizophrenia.

Methods

We used the case control design to test for of allelic and haplotypic association with schizophrenia in a sample of four hundred and fifty research subjects with schizophrenia and four hundred and fifty ancestrally matched supernormal controls. We genotyped the SNP markers previously found to be significantly associated with schizophrenia in the original study and also other markers found to be positive in subsequent studies.

Results

We could find no evidence of allelic, genotypic or haplotypic association with schizophrenia in our UK sample.

Conclusion

The results suggest that the DTNBP1 gene contribution to schizophrenia must be rare or absent in our sample. The discrepant allelic association results in previous studies of association between DTNBP1 and schizophrenia could be due population admixture. However, even positive studies of European populations do not show any consistent DTNBP1 alleles or haplotypes associated with schizophrenia. Further research is needed to resolve these issues. The possible confounding of linkage with association in family samples already showing linkage at 6p22.3 might be revealed by testing genes closely linked to DTNBP1 for allelic association and by restricting family based tests of association to only one case per family.

Genome-wide scan of bipolar disorder and investigation of population stratification effects on linkage: support for susceptibility loci at 4q21, 7q36, 9p21, 12q24, 14q24, and 16p13

Bipolar disorder (BPD) is a complex genetic disorder with cycling symptoms of depression and mania. Despite the extreme complexity of this psychiatric disorder, attempts to localize genes which confer vulnerability to the disorder have had some success. Chromosomal regions including 4p16, 12q24, 18p11, 18q22, and 21q21 have been repeatedly linked to BPD in different populations. Here we present the results of a whole genome scan for linkage to BPD in an Irish population. Our most significant result was at 14q24 which yielded a non-parametric LOD (NPL) score of 3.27 at the D14S588 marker with a nominal P-value of 0.0006 under a narrow (bipolar type I only) model of affection. We previously reported linkage to 14q22-24 in a subset of the families tested in this analysis. We also obtained suggestive evidence for linkage at 4q21, 9p21, 12q24, and 16p13, chromosomal regions that have all been previously linked to BPD. Additionally, we report on a novel approach to linkage analysis, STRUCTURE-Guided Linkage Analysis (SGLA), which is designed to reduce genetic heterogeneity and increase the power to detect linkage. Application of this technique resulted in more highly significant evidence for linkage of BPD to three regions including 16p13, a locus that has been repeatedly linked to numerous psychiatric disorders.

Molecular analysis of a chromosome 4 inversion segregating in a large schizophrenia kindred from Hong Kong

The present study looks at a paracentric inversion on chromosome 4 [inv(4)(q13;q25)] in members of a large schizophrenia kindred from Hong Kong, and the possibility of a susceptibility gene for schizophrenia at one of the inversion breakpoints. Fluorescence in situ hybridization with BAC and fosmid clones was used to determine the location of the 4q13 and 4q25 breakpoints, however bioinformatic analysis indicated that no known genes are directly disrupted by the breakpoints. We identified several putative genes and expressed sequence tags (ESTs) from around the breakpoint regions, and have characterized them further in order to determine whether they may represent full-length mRNAs that are disrupted by the inversion. Overall, it appears that, while no known genes are disrupted, an as yet undiscovered gene, or indeed, a known gene, may be present near one of the breakpoints and may be disrupted by position effect. We hypothesized that either the 4q13 or 4q25 breakpoint region may contain a common susceptibility gene for schizophrenia. We genotyped 117 schizophrenia families for several short tandem repeat polymorphisms close to the breakpoints. Family based association testing showed no association at the 4q13 breakpoint region, but showed significant allelic association for marker D4S2989 at the 4q25 breakpoint region (p=0.016). This study suggests that the 4q breakpoint regions may harbour a gene that contributes to the illness in the large Hong Kong pedigree, and this 4q25 region should be examined further in other schizophrenia samples.

Case-control association study of Disrupted-in-Schizophrenia-1 (DISC1) gene and schizophrenia in the Chinese population

Disrupted-in-Schizophrenia-1 (DISC1) has first been identified as a candidate gene for schizophrenia through study of a Scottish family with a balanced (1; 11) (q42.1; q14.3) translocation. Lots of linkage and association studies supported DISC1 as a risk factor for schizophrenia. In this study, we genotyped three SNPs in DISC1 using a set of Han Chinese samples of 560 schizophrenics and 576 controls. No positive association was detected in the whole samples but analysis of allele frequencies in female samples showed weak association between SNP rs2295959 and the disease (chi(2)=6.188, P=0.0135, OR=0.728, 95% CI=0.567-0.935). Our results provide further evidence for sex difference for the effect of the gene on the aetiology of schizophrenia. Our findings also would encourage further studies, particularly family-based association studies with larger samples, to analyze the association between DISC1 and schizophrenia.

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.

Homozygosity of the interleukin-10 receptor 1 G330R allele is associated with schizophrenia

Infections of unknown origin and an altered immune response have been hypothesized to play a role in the pathogenesis of schizophrenia. We have previously identified two single nucleotide polymorphisms (SNPs) of the IL-10 receptor 1 (IL-10R1) causing a substitution of glycine 330 to arginine (G330R) and of serine 138 to glycine (S138G). A possible association between these IL-10R1 variants and schizophrenia has been investigated in the present study. DNA of 101 unrelated Austrian patients with a DSM-III-R (Diagnostic and Statistical Manual of Mental Disorders) consensus diagnosis of schizophrenia (n = 70) or schizoaffective disorder (n = 31) and DNA of 121 German schizophrenic patients (DSM-III-R) was analyzed for the presence of S138G and G330R by allele-specific multiplex PCRs. Data from patients were compared with 250 unrelated, psychiatric healthy controls. No difference in allele frequency was detected between patients and controls (G330R: 34.0% vs. 30.0%, P = 0.208; S138G: 19.7% vs. 16.6%, P = 0.235; by Fisher's exact test). However, there was a significant difference in genotype distribution (wt/wt, wt/mut, mut/mut) for G330R between patients (46.8%, 38.3%, 14.9%) and controls (47.6%, 44.8%, 7.6%; Fisher's test P = 0.032). No such difference was seen for S138G. Our results suggest that homozygosity of the IL-10R1 G330R allele is associated with schizophrenia and may contribute to the expression of disease phenotype in susceptible individuals.

Linkage of schizophrenia with chromosome 1q32 in Korean multiplex families

Chromosome 1q contains a few loci for which modest evidence of linkage with schizophrenia has been reported in several independent studies. However, markers showing the peak linkage signal are dispersed over a large chromosomal region. In addition, inconsistent findings have been generated from different populations or different subgroups of the same populations. The purpose of the current study is to determine whether those loci are linked to schizophrenia in the Korean population. We investigated 46 Korean multiplex schizophrenia families, initially using 11 microsatellite markers spanning around 91 cM region of 1p22 approximately 42. In a non-parametric linkage analysis, D1S249 located on 1q32.1 showed statistical evidence suggestive of linkage. At the second stage analysis for narrowing down the region, four additional nearby markers were genotyped. In the single point analysis, we found another suggestive linkage signal at D1S2891. The highest NPL score of 2.67 (P = 0.0039) was obtained in the multi-point analysis. This study provides supportive evidence for linkage of chromosome 1q32 with schizophrenia.

Fine mapping by genetic association implicates the chromosome 1q23.3 gene UHMK1, encoding a serine/threonine protein kinase, as a novel schizophrenia susceptibility gene

BACKGROUND

Linkage studies by us and others have confirmed that chromosome 1q23.3 is a susceptibility locus for schizophrenia. Based on this information, several research groups have published evidence that markers within both the RGS4 and CAPON genes, which are 700 kb apart, independently showed allelic association with schizophrenia. Tests of allelic association with both of these genes in our case control sample were negative. Therefore, we carried out further fine mapping between the RGS4 and CAPON genes.

METHODS

Twenty-nine SNP and microsatellite markers in the 1q23.3 region were genotyped in the United Kingdom based sample of 450 cases and 450 supernormal control subjects.

RESULTS

We detected positive allelic association after the eighth marker was genotyped and found that three microsatellite markers (p = .011, p = .014, p = .049) and two SNPs (p = .004, p = .043) localized in the 700 kb region between the RGS4 and CAPON genes, within the UHMK1 gene, were associated with schizophrenia. Tests of significance for marker rs10494370 remained significant following Bonferroni correction (alpha = .006) for multiple tests. Tests of haplotypic association were also significant for UHMK1 (p = .009) using empirical permutation tests, which make it unnecessary to further correct for both multiple alleles and multiple markers.

CONCLUSIONS

These results provide preliminary evidence that the UHMK1 gene increases susceptibility to schizophrenia. Further confirmation in adequately powered samples is needed. UHMK1 is a serine threonine kinase nuclear protein and is highly expressed in regions of the brain implicated in schizophrenia.

A genetic association study of chromosome 11q22-24 in two different samples implicates the FXYD6 gene, encoding phosphohippolin, in susceptibility to schizophrenia

Previous linkage analyses of families with multiple cases of schizophrenia by us and others have confirmed the involvement of the chromosome 11q22-24 region in the etiology of schizophrenia, with LOD scores of 3.4 and 3.1. We now report fine mapping of a susceptibility gene in the 11q22-24 region, determined on the basis of a University College London (UCL) sample of 496 cases and 488 supernormal controls. Confirmation was then performed by the study of an Aberdeen sample consisting of 858 cases and 591 controls (for a total of 2,433 individuals: 1,354 with schizophrenia and 1,079 controls). Seven microsatellite or single-nucleotide polymorphism (SNP) markers localized within or near the FXYD6 gene showed empirically significant allelic associations with schizophrenia in the UCL sample (for D11S1998, P=.021; for rs3168238, P=.009; for TTTC20.2, P=.048; for rs1815774, P=.049; for rs4938445, P=.010; for rs4938446, P=.025; for rs497768, P=.023). Several haplotypes were also found to be associated with schizophrenia; for example, haplotype Hap-F21 comprising markers rs10790212-rs4938445-rs497768 was found to be associated with schizophrenia, by a global permutation test (P=.002). Positive markers in the UCL sample were then genotyped in the Aberdeen sample. Two of these SNPs were found to be associated with schizophrenia in the Scottish sample (for rs4938445, P=.044; for rs497768, P=.037). The Hap-F21 haplotype also showed significant association with schizophrenia in the Aberdeen sample, with the same alleles being associated (P=.013). The FXYD6 gene encodes a protein called "phosphohippolin" that is highly expressed in regions of the brain thought to be involved in schizophrenia. The protein functions by modulating the kinetic properties of Na,K-ATPase to the specific physiological requirements of the tissue. Etiological base-pair changes in FXYD6 or in associated promoter/control regions are likely to cause abnormal function or expression of phosphohippolin and to increase genetic susceptibility to schizophrenia.

Towards understanding the schizophrenia code: an expanded convergent functional genomics approach

Identifying genes for schizophrenia through classical genetic approaches has proven arduous. Here, we present a comprehensive convergent analysis that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a psychomimetic agent - phencyclidine (PCP), and an anti-psychotic - clozapine), with human genetic linkage data and human postmortem brain data, as a Bayesian strategy of cross validating findings. Topping the list of candidate genes, we have three genes involved in GABA neurotransmission (GABRA1, GABBR1, and GAD2), one gene involved in glutamate neurotransmission (GRIA2), one gene involved in neuropeptide signaling (TAC1), two genes involved in synaptic function (SYN2 and KCNJ4), six genes involved in myelin/glial function (CNP, MAL, MBP, PLP1, MOBP and GFAP), and one gene involved in lipid metabolism (LPL). These data suggest that schizophrenia is primarily a disorder of brain functional and structural connectivity, with GABA neurotransmission playing a prominent role. These findings may explain the EEG gamma band abnormalities detected in schizophrenia. The analysis also revealed other high probability candidates genes (neurotransmitter signaling, other structural proteins, ion channels, signal transduction, regulatory enzymes, neuronal migration/neurite outgrowth, clock genes, transcription factors, RNA regulatory genes), pathways and mechanisms of likely importance in pathophysiology. Some of the pathways identified suggest possible avenues for augmentation pharmacotherapy of schizophrenia with other existing agents, such as benzodiazepines, anticonvulsants and lipid modulating agents. Other pathways are new potential targets for drug development. Lastly, a comparison with our earlier work on bipolar disorder illuminates the significant molecular overlap between schizophrenia and bipolar disorder.

Association between the 5q31.1 gene neurogenin1 and schizophrenia

Multiple lines of evidence suggest that schizophrenia results from aberrant neurodevelopment. The neurogenin1 gene (neurog1) consists of a single 1,666 bp exon that encodes a basic helix-loop-helix (bHLH) transcription factor that causes neuronal differentiation and induces cortical and glutamatergic differentiation programs. Because of its function and its location in 5q31.1, which has been linked to schizophrenia in multiple samples, we tested it for association with the disorder. We sequenced neurog1 in 25 affected subjects from the Irish Study of High-Density Schizophrenia Families. We observed a 5'-UTR SNP at position -60, already present in databases as rs8192558, and tested it along with rs2344485, rs8192559, and rs2344484. Narrow, intermediate, and broad diagnostic definitions were used. The major alleles of rs8192558 and rs2344484 were over-transmitted to affected subjects using both Pedigree Disequilibrium Test (PDT) (0.01 < or = P < or = 0.06) and FBAT (0.02 < or = P < or = 0.07). A haplotype consisting of the major alleles of all four SNPs was significantly over-transmitted in FBAT to the broad definition (P = 0.049), with trend significance to the narrow and intermediate definitions, and with trend significance in PDT. In confirmatory tests using 657 cases and 411 controls, this haplotype was slightly but not significantly over-represented in cases (81% vs. 77%, P = 0.21). These results, along with a priori evidence for the involvement of neurog1 in neurodevelopment, suggest that variants in neurog1 might have a small effect on susceptibility to schizophrenia. This gene should be tested in additional and larger samples.

GABRB2 association with schizophrenia: commonalities and differences between ethnic groups and clinical subtypes

BACKGROUND

Single nucleotide polymorphisms (SNPs) and haplotypes in intron 8 of type A gamma-aminobutyric acid (GABA(A)) receptor beta2 subunit gene (GABRB2) were initially found to be associated with schizophrenia in Chinese. This finding was subjected to cross-validation in this study with Japanese (JP) and German Caucasian (GE) subjects.

METHODS

Single nucleotide polymorphisms discovery and genotyping were carried out through resequencing of a 1839 base pair (bp) region in GABRB2. Tagging SNPs (tSNPs) were selected based on linkage disequilibrium (LD), combinations of which were analyzed with Bonferroni correction and permutation for disease association. Random resampling was applied to generate size- and gender-balanced cases and control subjects.

RESULTS

Out of the 17 SNPs (9.2/kilobase [kb]) revealed, 6 were population-specific. Population variations in LD were observable, and at least two low LD points were identified in both populations. Although disease association at single SNP level was only shown in GE, strong association was demonstrated in both JP (p = .0002 - .0191) and GE (p = .0033 - .0410) subjects, centering on haplotypes containing rs1816072 and rs1816071. Among different clinical subtypes, the most significant association was exhibited by systematic schizophrenia.

CONCLUSIONS

Cross-population validation of GABRB2 association with schizophrenia has been obtained with JP and GE subjects, with the genotype-disease correlations being strongest in systematic schizophrenia, the most severe subtype of the disease.

Are some genetic risk factors common to schizophrenia, bipolar disorder and depression? evidence fromDISC1, GRIK4 andNRG1

Depression is common in patients with schizophrenia and it is well established from family studies that rates of depression are increased among relatives of probands with schizophrenia, making it likely that the phenotypes described under the categories of affective and non-affective psychoses share some genetic risk factors. Family linkage studies have identified several chromosomal regions likely to contain risk genes for schizophrenia and bipolar disorder, suggesting common susceptibility loci. Candidate gene association studies have provided further evidence to suggest that some genes including two of the most studied candidates, Disrupted in Schizophrenia 1 (DISC1) and Neuregulin 1 (NRG1) may be involved in both types of psychosis. We have recently identified another strong candidate for a role in both schizophrenia and affective disorders, GRIK4 a glutamate receptor mapped to chromosome 11q23 [Glutamate Receptor, Ionotropic, Kainate, type 4]. This gene is disrupted by a translocation breakpoint in a patient with schizophrenia, and case control studies show significant association of GRIK4 with both schizophrenia and bipolar disorder. Identifying genes implicated in the psychoses may eventually provide the basis for classification based on biology rather than symptoms, and suggest novel treatment strategies for these complex brain disorders.

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.

The ups and downs of Wnt signaling in prevalent neurological disorders

In order to function properly, the brain must be wired correctly during critical periods in early development. Mistakes in this process are hypothesized to occur in disorders like autism and schizophrenia. Later in life, signaling pathways are essential in maintaining proper communication between neuronal and non-neuronal cells, and disrupting this balance may result in disorders like Alzheimer's disease. The Wnt/beta-catenin pathway has a well-established role in cancer. Here, we review recent evidence showing the involvement of Wnt/beta-catenin signaling in neurodevelopment as well as in neurodegenerative diseases. We suggest that the onset/development of such pathological conditions may involve the additive effect of genetic variation within Wnt signaling components and of molecules that modulate the activity of this signaling cascade.

FZD3 is not a risk gene for schizophrenia: a case-control study in a Caucasian sample

BACKGROUND

Polymorphisms in the human frizzeled-3 (FZD3) gene have been associated with schizophrenia in an Asian population sample. However, this finding could not be confirmed in subsequent studies investigating other populations. Here we attempted to replicate this finding in a sample of 192 German chronically ill schizophrenic subjects.

METHODS

Three single nucleotide polymorphisms in the FZD3 gene have been genotyped by primer extension and MALDI-TOF measurement. Subsequently, associations for single markers as well as haplotypes were tested.

RESULTS

In German patients, neither single markers nor haplotypes in FZD3 were associated with schizophrenia. Further exploratory analyses using a different diagnostic approach did also not yield significant results.

CONCLUSIONS

FZD3 is unlikely to play a role in the genetic predisposition towards schizophrenia in the Caucasian population.

Chasing genes for mood disorders and schizophrenia in genetically isolated populations

Major affective disorders and schizophrenia are among the most common brain diseases worldwide and their predisposition is influenced by a complex interaction of genetic and environmental factors. So far, traditional linkage mapping studies for these complex disorders have not achieved the same success as the positional cloning of genes for Mendelian diseases. The struggle to identify susceptibility genes for complex disorders has stimulated the development of alternative approaches, including studies in genetically isolated populations. Since isolated populations are likely to have both a reduced number of genetic vulnerability factors and environmental background and are therefore considered to be more homogeneous compared to outbred populations, the use of isolated populations in genetic studies is expected to improve the chance of finding susceptibility loci and genes. Here we review the role of isolated populations, based on linkage and association studies, in the identification of susceptibility genes for bipolar disorder and schizophrenia.

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

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

Know thy neighbor: a survey of diseases and complex syndromes that map to chromosomal regions encoding TRP channels

On the basis of their ever-expanding roles, not only in sensory signaling but also in a plethora of other, often Ca(2+)-mediated actions in cell and whole body homeostasis, it is suggested that mutations in TRP channel genes not only cause disease states but also contribute in more subtle ways to simple and complex diseases. A survey is therefore presented of diseases and syndromes that map to one or multiple chromosomal loci containing TRP channel genes. A visual map of the chromosomal locations of TRP channel genes in man and mouse is also presented.

Decreased levels of apolipoprotein A-I in plasma of schizophrenic patients

This study aims to identify the effects of antipsychotics on plasma proteins, and on the proteins associated with schizophrenia. We applied proteomics technology to screen protein aberrations in Sprague-Dawley rats treated with antipsychotics and schizophrenic patients undergoing medication. ApoA-I was found significantly increased in the chlorpromazine-treated rats and decreased in the patients with treatment-resistant schizophrenia, which suggest that decreased levels of apoA-I might be associated with the pathology of schizophrenia and that chlorpromazine increases apoA-I levels as part of its therapeutic action.

Association study of IL10, IL1beta, and IL1RN and schizophrenia using tag SNPs from a comprehensive database: suggestive association with rs16944 at IL1beta

Genetic association studies of several candidate cytokine genes have been motivated by evidence of immune dysfunction among patients with schizophrenia. Intriguing but inconsistent associations have been reported with polymorphisms of three positional candidate genes, namely IL1beta, IL1RN, and IL10. We used comprehensive sequencing data from the Seattle SNPs database to select tag SNPs that represent all common polymorphisms in the Caucasian population at these loci. Associations with 28 tag SNPs were evaluated in 478 cases and 501 unscreened control individuals, while accounting for population sub-structure using the genomic control method. The samples were also stratified by gender, diagnostic category, and exposure to infectious agents. Significant association was not detected after correcting for multiple comparisons. However, meta-analysis of our data combined with previously published association studies of rs16944 (IL1beta -511) suggests that the C allele confers modest risk for schizophrenia among individuals reporting Caucasian ancestry, but not Asians (Caucasians, n=819 cases, 1292 controls; p=0.0013, OR=1.24, 95% CI 1.09, 1.41).

Variations in the vesicular monoamine transporter 1 gene (VMAT1/SLC18A1) are associated with bipolar i disorder

The vesicular monoamine transporter 1 gene (VMAT1/SLC18A1) maps to the shared bipolar disorder (BPD)/schizophrenia (SZ) susceptibility locus on chromosome 8p21. Vesicular monoamine transporters are involved in transport of monoamine neurotransmitters which have been postulated to play a relevant role in the etiology of BPD and/or SZ. Variations in the VMAT1 gene might affect transporter function and/or expression and might be involved in the etiology of BPD and/or SZ. Genotypes of 585 patients with BPD type I and 563 control subjects were obtained for three missense single nucleotide polymorphisms (SNPs) (Thr4Pro, Thr98Ser, Thr136Ile) and four non-coding SNPs (rs988713, rs2279709, rs3735835, rs1497020). All cases and controls were of European descent. Allele frequencies differed significantly for the potential functional polymorphism Thr136Ser between BPD patients and controls (p=0.003; df=1; OR=1.34; 95% CI: 1.11-1.62). Polymorphisms in the promoter region (rs988713: p=0.005, df=1; OR=1.31; 95% CI: 1.09-1.59) and intron 8 (rs2279709: p=0.039, df=1; OR=0.84; 95% CI: 0.71-0.99) were also associated with disease. Expression analysis confirmed that VMAT1 is expressed in human brain at the mRNA and protein level. Results suggest that variations in the VMAT1 gene may confer susceptibility to BPD in patients of European descent. Additional studies are necessary to confirm this effect and to elucidate the role of VMAT1 in central nervous system physiology.

Association study of the vesicular monoamine transporter 1 (VMAT1) gene with schizophrenia in a Japanese population

Background

Vesicular monoamine transporters (VMATs) mediate accumulation of monoamines such as serotonin, dopamine, adrenaline, and noradrenaline from the cytoplasm into storage organelles. The VMAT1 (alternatively solute carrier family 18: SLC18A1) regulates such biogenic amines in neuroendocrine systems. The VMAT1 gene maps to chromosome 8p21.3, a locus with strong evidence of linkage with schizophrenia. A recent study reported that a non-synonymous single nucleotide polymorphism (SNP) of the gene (Pro4Thr) was associated with schizophrenia.

Methods

We attempted to replicate this finding in a Japanese sample of 354 schizophrenics and 365 controls. In addition, we examined 3 other non-synonymous SNPs (Thr98Ser, Thr136Ile, and Val392Leu). Genotyping was performed by the TaqMan allelic discrimination assay.

Results

There was no significant difference in genotype or allele distribution of the three SNPs of Pro4Thr, Thr136Ile, or Val392Leu between patients and controls. There was, however, a significant difference in genotype and allele distributions for the Thr98Ser polymorphism between the two groups (P = 0.01 for genotype and allele). When sexes were examined separately, significant differences were observed in females (P = 0.006 for genotype, P = 0.003 for allele), but not in males. The Thr98 allele was more common in female patients than in female controls (odds ratio 1.69, 95% CI 1.19–2.40, P = 0.003). Haplotype-based analyses also provided evidence for a significant association in females.

Conclusion

We failed to replicate the previously reported association of Pro4Thr of the VMAT1 gene with schizophrenia. However, we obtained evidence for a possible role of the Thr98Ser in giving susceptibility to schizophrenia in women.