Identification of a novel neuregulin 1 at-risk haplotype in Han schizophrenia Chinese patients, but no association with the Icelandic/Scottish risk haplotype

Genetics of schizophrenia (Review)

A comprehensive review of the body of genetic studies on schizophrenia seems even more daunting than the battle a psychiatrist wages daily in the office with her archenemy of a thousand faces. The following article reunites some genetic, epigenetic and environmental factors of schizophrenia from revered and vast studies in a chronological and progressive fashion. Twin studies set the basics of heritability and a particular study by Davis and Phelps considers the widely ignored influence of prenatal environment in the development of schizophrenia. Mostly ignited by linkage studies, candidate gene studies explore further by fine-mapping the hypothesized variants [mostly in the forms single nucleotide polymorphisms (SNPs) and less but with greater impact copy number variations (CNVs)] associated with the disease. Genome-wide association studies (GWAS) increase considerably the sample sizes and thus the validity of the results, while the next-generation sequencing (NGS) attain the highest yet unreplicated level of validity results.

GABAergic Abnormalities Associated with Sensorimotor Cortico-striatal Community Structural Deficits in ErbB4 Knockout Mice and First-Episode Treatment-Naïve Patients with Schizophrenia

The current study was designed to explore how disruption of specific molecular circuits in the cerebral cortex may cause sensorimotor cortico-striatal community structure deficits in both a mouse model and patients with schizophrenia. We used prepulse inhibition (PPI) and brain structural and diffusion MRI scans in 23 mice with conditional ErbB4 knockout in parvalbumin interneurons and 27 matched controls. Quantitative real-time PCR was used to assess the differential levels of GABA-related transcripts in brain regions. Concurrently, we measured structural and diffusion MRI and the cumulative contribution of risk alleles in the GABA pathway genes in first-episode treatment-naïve schizophrenic patients (n = 117) and in age- and sex-matched healthy controls (n = 86). We present the first evidence of gray and white matter impairment of right sensorimotor cortico-striatal networks and reproduced the sensorimotor gating deficit in a mouse model of schizophrenia. Significant correlations between gray matter volumes (GMVs) in the somatosensory cortex and PPI as well as glutamate decarboxylase 1 mRNA expression were found in controls but not in knockout mice. Furthermore, these findings were confirmed in a human sample in which we found significantly decreased gray and white matter in sensorimotor cortico-striatal networks in schizophrenic patients. The psychiatric risk alleles of the GABA pathway also displayed a significant negative correlation with the GMVs of the somatosensory cortex in patients. Our study identified that ErbB4 ablation in parvalbumin interneurons induced GABAergic dysregulation, providing valuable mechanistic insights into the sensorimotor cortico-striatal community structure deficits associated with schizophrenia.

Sex Differences in Psychiatric Disease: A Focus on the Glutamate System

Alterations in glutamate, the primary excitatory neurotransmitter in the brain, are implicated in several psychiatric diseases. Many of these psychiatric diseases display epidemiological sex differences, with either males or females exhibiting different symptoms or disease prevalence. However, little work has considered the interaction of disrupted glutamatergic transmission and sex on disease states. This review describes the clinical and preclinical evidence for these sex differences with a focus on two conditions that are more prevalent in women: Alzheimer's disease and major depressive disorder, and three conditions that are more prevalent in men: schizophrenia, autism spectrum disorder, and attention deficit hyperactivity disorder. These studies reveal sex differences at multiple levels in the glutamate system including metabolic markers, receptor levels, genetic interactions, and therapeutic responses to glutamatergic drugs. Our survey of the current literature revealed a considerable need for more evaluations of sex differences in future studies examining the role of the glutamate system in psychiatric disease. Gaining a more thorough understanding of how sex differences in the glutamate system contribute to psychiatric disease could provide novel avenues for the development of sex-specific pharmacotherapies.

BACE1-Dependent Neuregulin-1 Signaling: An Implication for Schizophrenia

Schizophrenia is a chronic psychiatric disorder with a lifetime prevalence of about 1% in the general population. Recent studies have shown that Neuregulin-1 (Nrg1) is a candidate gene for schizophrenia. At least 15 alternative splicing of NRG1 isoforms all contain an extracellular epidermal growth factor (EGF)-like domain, which is sufficient for Nrg1 biological activity including the formation of myelin sheaths and the regulation of synaptic plasticity. It is known that Nrg1 can be cleaved by β-secretase (BACE1) and the resulting N-terminal fragment (Nrg1-ntf) binds to receptor tyrosine kinase ErbB4, which activates Nrg1/ErbB4 signaling. While changes in Nrg1 expression levels in schizophrenia still remain controversial, understanding the BACE1-cleaved Nrg1-ntf and Nrg1/ErbB4 signaling in schizophrenia neuropathogenesis is essential and important. In this review paper, we included three major parts: (1) Nrg1 structure and cleavage pattern by BACE1; (2) BACE1-dependent Nrg1 cleavage associated with schizophrenia in human studies; and (3) Animal studies of Nrg1 and BACE1 mutations with behavioral observations. Our review will provide a better understanding of Nrg1 in schizophrenia and a potential strategy for using BACE1 cleavage of Nrg1 as a unique biomarker for diagnosis, as well as a new therapeutic target, of schizophrenia.

Efficacy, acceptability and tolerability of 8 atypical antipsychotics in Chinese patients with acute schizophrenia: A network meta-analysis

OBJECTIVE

We aimed to create hierarchies of the efficacy, acceptability and tolerability of eight atypical antipsychotics in the treatment of Chinese patients with acute schizophrenia.

METHOD

We systematically searched for RCT articles published between January 1st 2005 and December 31st 2014 in electronic databases (Medline, Pubmed, Embase, the Cochrane Library and ClinicalTrial.gov for studies in English and the China National Knowledge Infrastructure, Wan Fang, and VIP Information/Chinese Scientific Journals Database for studies in Chinese). The primary outcome was efficacy, as measured by the change of PANSS total score. Pairwise comparisons were performed using random-effects model by the Dersimonian-Laird method and network meta-analyses were performed in a Bayesian set.

RESULTS

Sixty high-quality RCTs with 6418 participants were included. A pattern of superiority from olanzapine, paliperidone and amisulpride was seen in the primary outcome. Only paliperidone was found better than aripiprazole (odds ratio, 0.49 [95% credible intervals, 0.25 to 0.99]), ziprasidone (0.42 [0.21 to 0.85]) and quetiapine (0.36 [0.13 to 0.93]) in terms of all-cause discontinuation. The best and worst drugs in terms of weight gain, EPS and somnolence were aripiprazole and olanzapine, clozapine and amisulpride, aripiprazole and clozapine, respectively. The rank of efficacy did not change substantially in sensitivity analyses or in meta-regressions.

CONCLUSION

Our findings provided the hierarchies of eight antipsychotics in efficacy, acceptability and tolerability. These findings are expected to help Chinese clinicians to select the appropriate antipsychotic drug for their patients.

Meta-analysis reveals associations between genetic variation in the 5' and 3' regions of Neuregulin-1 and schizophrenia

Genetic, post-mortem and neuroimaging studies repeatedly implicate neuregulin-1 (NRG1) as a critical component in the pathophysiology of schizophrenia. Although a number of risk haplotypes along with several genetic polymorphisms in the 5' and 3' regions of NRG1 have been linked with schizophrenia, results have been mixed. To reconcile these conflicting findings, we conducted a meta-analysis examining 22 polymorphisms and two haplotypes in NRG1 among 16 720 cases, 20 449 controls and 2157 family trios. We found significant associations for three polymorphisms (rs62510682, rs35753505 and 478B14-848) at the 5'-end and two (rs2954041 and rs10503929) near the 3'-end of NRG1. Population stratification effects were found for the rs35753505 and 478B14-848(4) polymorphisms. There was evidence of heterogeneity for all significant markers and the findings were robust to publication bias. No significant haplotype associations were found. Our results suggest genetic variation at the 5' and 3' ends of NRG1 are associated with schizophrenia and provide renewed justification for further investigation of NRG1's role in the pathophysiology of schizophrenia.

Genetic association between NRG1 and schizophrenia, major depressive disorder, bipolar disorder in Han Chinese population

Schizophrenia, major depressive disorder, and bipolar disorder are three major psychiatric disorders affecting around 0.66%, 3.3%, and 1.5% of the Han Chinese population respectively. Several genetic linkage analyses and genome wide association studies identified NRG1 as a susceptibility gene of schizophrenia, which was validated by its role in neurodevelopment, glutamate, and other neurotransmitter receptor expression regulation. To further investigate whether NRG1 is a shared risk gene for major depressive disorder, bipolar disorder as well as schizophrenia, we performed an association study among 1,248 schizophrenia cases, 1,056 major depression cases, 1,344 bipolar disorder cases, and 1,248 controls. Totally 15 tag SNPs were genotyped and analyzed, and no population stratification was found in our sample set. Among the sites, rs4236710 (corrected Pgenotye  = 0.015) and rs4512342 (Pallele  = 0.03, Pgenotye  = 0.045 after correction) were associated with schizophrenia, and rs2919375 (corrected Pgenotye  = 0.004) was associated with major depressive disorder. The haplotype rs4512342-rs6982890 showed association with schizophrenia (P = 0.03 for haplotype "TC" after correction), and haplotype rs4531002-rs11989919 proved to be a shared risk factor for both major depressive disorder ("CC": corrected P = 0.009) and bipolar disorder ("CT": corrected P = 0.003). Our results confirmed that NRG1 was a shared common susceptibility gene for major mental disorders in Han Chinese population.

Neurological dysfunctions associated with altered BACE1-dependent Neuregulin-1 signaling

Inhibition of BACE1 is being pursued as a therapeutic target to treat patients suffering from Alzheimer's disease because BACE1 is the sole β-secretase that generates β-amyloid peptide. Knowledge regarding other cellular functions of BACE1 is therefore critical for the safe use of BACE1 inhibitors in human patients. Neuregulin-1 (Nrg1) is a BACE1 substrate and BACE1 cleavage of Nrg1 is critical for signaling functions in myelination, remyelination, synaptic plasticity, normal psychiatric behaviors, and maintenance of muscle spindles. This review summarizes the most recent discoveries associated with BACE1-dependent Nrg1 signaling in these areas. This body of knowledge will help to provide guidance for preventing unwanted Nrg1-based side effects following BACE1 inhibition in humans. To initiate its signaling cascade, membrane anchored Neuregulin (Nrg), mainly type I and III β1 Nrg1 isoforms and Nrg3, requires ectodomain shedding. BACE1 is one of such indispensable sheddases to release the functional Nrg signaling fragment. The dependence of Nrg on the cleavage by BACE1 is best manifested by disrupting the critical role of Nrg in the control of axonal myelination, schizophrenic behaviors as well as the formation and maintenance of muscle spindles.

Paliperidone extended-release tablets in Chinese patients with schizophrenia: meta-analysis of randomized controlled trials

BACKGROUND

Previous meta-analyses have compared paliperidone extended-release (ER) tablets with other antipsychotics, but none have involved Chinese patients or studies from People's Republic of China. Further, the results of these meta-analyses may not be applicable to Chinese patients. In the present study, we evaluated the efficacy, safety, and acceptability of paliperidone ER compared with other second-generation antipsychotics (SGAs) for Chinese patients with schizophrenia.

METHODS

Randomized controlled studies of paliperidone ER and other SGAs as oral monotherapy in the acute phase treatment of schizophrenia were retrieved from Medline, Embase, and the Cochrane Library (CENTRAL), as well as from Chinese databases including the China National Knowledge Infrastructure, Wanfang, and VIP Information/Chinese Scientific Journals Database. We pooled data on response rates, chance of withdrawal due to adverse events, probability of adverse events, and odds of withdrawal for any reason.

RESULTS

Fifty randomized controlled trials were identified. The response rate for paliperidone ER was significantly higher than that of other pooled SGAs (risk ratio [RR] 0.83, 95% confidence interval [CI] 0.72-0.96) and ziprasidone (RR 0.57, 95% CI 0.39-0.82). Paliperidone ER significantly reduced the chance of withdrawal due to adverse events and the chance of any adverse events compared with other pooled SGAs (RR 0.32, 95% CI 0.17-0.58 and RR 0.88, 95% CI 0.79-0.97) and risperidone (RR 0.31, 95% CI 0.14-0.67 and RR 0.70, 95% CI 0.57-0.86). The incidence of extrapyramidal symptoms on paliperidone ER was comparable with other pooled SGAs (RR 0.94, 95% CI 0.66-1.35) and significantly lower than that of risperidone (RR 0.56, 0.41-0.77) but higher than that of olanzapine (RR 1.88, 95% CI 1.05-3.36). Paliperidone ER was superior to other pooled SGAs (RR 0.32, 95% CI 0.21-0.49 and RR 0.50, 95% CI 0.35-0.72) and olanzapine (RR 0.23, 95% CI 0.15-0.33 and RR 0.33, 95% CI 0.23-0.47) as far as weight gain and somnolence were concerned. Further, prolactin-related adverse events caused by paliperidone ER were comparable with other pooled SGAs (RR 1.30, 95% CI 0.73-2.33), but outnumbered those caused by olanzapine (RR 7.53, 95% CI 2.05-27.71).

CONCLUSION

Paliperidone ER is efficacious, safe, and well accepted when compared with other pooled SGAs for the treatment of Chinese patients with schizophrenia.

Association of the 3' region of the neuregulin 1 gene with bipolar I disorder in the Chinese Han population

BACKGROUND

Based on the function of neuregulin 1 (NRG1) in neurodevelopment, susceptibility to bipolar disorder presumably involves this gene. The 3' region of NRG1 contains the majority of the coding exons, and transcripts from this region encode 8 of the 9 known NRG1 isoforms; therefore, this region is likely to be predominant versus the 5' region in terms of their relative contributions to NRG1 function. We investigated the association between the 3' region of the NRG1 gene and bipolar I disorder (BPI) in the Chinese Han population and performed further analyses depending on the presence or absence of psychotic features.

METHODS

A total of 385 BPI patients and 475 healthy controls were recruited for this study. Thirty tag single nucleotide polymorphisms (SNPs) across the 3' region of the NRG1 gene were genotyped for allelic and haplotypic associations with BPI and subgroups with psychotic features (BPI-P) or without psychotic features (BPI-NP).

RESULTS

Individual marker analysis showed that 2 SNPs (rs12547858 and rs6468121) in this region were significantly associated with BPI. Moreover, subgroup analyses showed significant but marginal associations of rs6468121 with BPI-P and rs3757933 with BPI-NP. Haplotype analyses showed that 6 haplotypes were associated with BPI only.

LIMITATIONS

The sample size was relatively small. The investigated tag SNPs only represented 83% of the information on the targeted region. There might be a retrospective bias in the subgroup analyses.

CONCLUSION

The results suggest that the 3' region of the NRG1 gene plays a role in BPI susceptibility in the Chinese Han population. In addition, the preliminary results show that BPI with psychotic features and BPI without psychotic features may constitute different sub-phenotypes; however, this finding should be confirmed in a larger population sample.

Schizophrenia-risk variant rs6994992 in the neuregulin-1 gene on brain developmental trajectories in typically developing children

The neuregulin-1 (NRG1) gene is one of the best-validated risk genes for schizophrenia, and psychotic and bipolar disorders. The rs6994992 variant in the NRG1 promoter (SNP8NRG243177) is associated with altered frontal and temporal brain macrostructures and/or altered white matter density and integrity in schizophrenic adults, as well as healthy adults and neonates. However, the ages when these changes begin and whether neuroimaging phenotypes are associated with cognitive performance are not fully understood. Therefore, we investigated the association of the rs6994992 variant on developmental trajectories of brain macro- and microstructures, and their relationship with cognitive performance. A total of 972 healthy children aged 3-20 years had the genotype available for the NRG1-rs6994992 variant, and were evaluated with magnetic resonance imaging (MRI) and neuropsychological tests. Age-by-NRG1-rs6994992 interactions and genotype effects were assessed using a general additive model regression methodology, covaried for scanner type, socioeconomic status, sex and genetic ancestry factors. Compared with the C-carriers, children with the TT-risk-alleles had subtle microscopic and macroscopic changes in brain development that emerge or reverse during adolescence, a period when many psychiatric disorders are manifested. TT-children at late adolescence showed a lower age-dependent forniceal volume and lower fractional anisotropy; however, both measures were associated with better episodic memory performance. To our knowledge, we provide the first multimodal imaging evidence that genetic variation in NRG1 is associated with age-related changes on brain development during typical childhood and adolescence, and delineated the altered patterns of development in multiple brain regions in children with the T-risk allele(s).

Neuregulin-1 (NRG-1) and its susceptibility to schizophrenia: a case-control study and meta-analysis

Neuregulin-1 is widely investigated due to its hypothesised association with schizophrenia. Single-nucleotide polymorphisms rs764059, rs2954041 and rs3924999 were investigated (417 patients with schizophrenia and 429 controls). We failed to demonstrate a significant association between rs2954041 and rs3924999 with schizophrenia in the three ethnic groups studied (Malay, Chinese, and Indian), while rs764059 was found to be monomorphic.

Personalized medicine in psychiatry: problems and promises

The central theme of personalized medicine is the premise that an individual's unique physiologic characteristics play a significant role in both disease vulnerability and in response to specific therapies. The major goals of personalized medicine are therefore to predict an individual's susceptibility to developing an illness, achieve accurate diagnosis, and optimize the most efficient and favorable response to treatment. The goal of achieving personalized medicine in psychiatry is a laudable one, because its attainment should be associated with a marked reduction in morbidity and mortality. In this review, we summarize an illustrative selection of studies that are laying the foundation towards personalizing medicine in major depressive disorder, bipolar disorder, and schizophrenia. In addition, we present emerging applications that are likely to advance personalized medicine in psychiatry, with an emphasis on novel biomarkers and neuroimaging.

Association between a Missense Polymorphism (rs3924999, Arg253Gln) of Neuregulin 1 and Schizophrenia in Korean Population

Neuregulin 1 (NRG1) is associated with the pathogenesis of schizophrenia through controlling activation and signaling of neurotransmitter receptors. Influence to schizophrenia development by the NRG1 gene may differ in individuals, and genetic polymorphism is one of the factors affecting their differences. Association between three single nucleotide polymorphisms (SNPs) (rs7014762, -1174 A/T; rs11998176, -788 A/T; rs3924999, Arg253Gln) of NRG1 and the development of schizophrenia was analyzed in 221 schizophrneia and 359 control subjects. Polymerase chain reaction and direct sequencing were performed to obtain genotype data of NRG1 SNPs of the subjects. In analysis of genetic data, multiple logistic regression models (codominant1, codominant2, dominant, recessive, and log-additive model) were applied. SNPStats and SPSS 18.0 were used to calculate odds ratio (OR), 95% confidence interval (CI), and p-value of each model. The genotype distributions of rs3924999 were associated with schizophrenia development (OR=0.67, 95% CI=0.47-0.95, p=0.022 in the dominant model and OR=0.69, 95% CI=0.51-0.93, p=0.013 in the log-addtive model) and allelic distributions also showed significant association (OR=0.70, 95% CI=0.52-0.93, p=0.014). The results suggest that rs3924999 of the NRG1 gene may be associated with schizophrenia susceptibility.

Is neuregulin 1 involved in determining cerebral volumes in schizophrenia? Preliminary results showing a decrease in superior temporal gyrus volume

BACKGROUND/AIMS

Reduced left superior temporal gyrus (STG) volume is one of the most replicated imaging findings in schizophrenia. However, it remains unclear whether genes play any role in our understanding of such structural alteration. It has been proposed that Neuregulin 1 (NRG1) might be a promising gene involved in schizophrenia, because of its role in neurodevelopment and neuroplasticity. In this study, the association between NRG1 and STG anatomy in patients with schizophrenia was explored for the first time.

METHODS

We investigated a 1-year treated prevalence cohort of patients with schizophrenia in contact with the South Verona Community-Based Mental Health Service. A blood sample was collected for DNA extraction and brain structure was assessed with an MRI scan. A total of 27 subjects with schizophrenia underwent both assessments and were included in the study.

RESULTS

We investigated the association between the polymorphism SNP8NRG222662 (rs4623364) of NRG1 and volume of the STG. We found that patients homozygous for the C allele had reduced left STG gray and white matter volumes in comparison to those homozygous for the G allele (p < 0.01 and p < 0.001, respectively).

CONCLUSIONS

This exploratory study suggests that NRG1 may be involved in determining STG size in schizophrenia, and may play a role in the neurogenetic basis of the language disturbances seen in this disorder. However, due to our small sample size, the results should be regarded as preliminary and replicated in a larger sample.

Genetic associations between neuregulin-1 SNPs and neurocognitive function in multigenerational, multiplex schizophrenia families

OBJECTIVES

Recent work shows promising associations between schizophrenia and polymorphisms in neuregulin-1 (NRG1) and a large literature also finds strong familial relationships between schizophrenia and cognitive deficits. Given the role of NRG1 in glutamate regulation and glutamate's effect on cognition, we hypothesized that cognitive deficits may be related to variation within NRG1, providing a possible mechanism to increase risk for schizophrenia.

METHODS

This study examined the associations between NRG1, cognition, and schizophrenia using a multigenerational multiplex family sample (total N=419, 40 families), including 58 affected participants (schizophrenia or schizoaffective disorder-depressed type) and their 361 unaffected relatives. Participants were genotyped for 40 NRG1 single nucleotide polymorphisms (SNPs), chosen largely based on previous associations with schizophrenia. All participants completed structured diagnostic interviews and a computerized neurocognitive battery assessing eight cognitive domains. Variance component quantitative trait analyses tested for associations between individual NRG1 SNPs and cognitive performance in the total sample, a subsample of healthy participants with no Diagnostic and Statistical Manual of Mental Disorders diagnosis, and using general intelligence as a covariate.

RESULTS

Effect sizes (within-family β coefficients) ranged from 0.08 to 0.73, and 61 of these associations were nominally significant (P≤0.05), with 12 associations at P≤0.01, although none achieved the modified Bonferroni significance threshold of P<0.0003. Attention was the most frequently nominally associated domain and rs10503929, a nonsynonymous SNP, was the most frequently nominally associated SNP.

CONCLUSION

Although not significant experiment-wise, these findings suggest that further study of the associations between variation in NRG1 and cognition may be productive.

Concise review: the promise of human induced pluripotent stem cell-based studies of schizophrenia

Schizophrenia (SCZD) is a heritable developmental disorder. Although the molecular mechanism of disease remains unclear, insights into the disorder have been made through a vast array of experimental techniques. Together, magnetic resonance brain imaging, pharmacological, and post-mortem pathological studies have observed decreased brain volume, aberrant neurotransmitter signaling, reduced dendritic arborization, and impaired myelination in SCZD. Genome-wide association studies (GWAS) have identified common single nucleotide polymorphisms as well as rare copy number variants that contribute to SCZD, while mouse models of candidate SCZD genes show behavioral abnormalities and anatomical perturbations consistent with human disease. The advent of human induced pluripotent stem cells (hiPSCs) makes it possible to study SCZD using live human neurons with a genetic predisposition toward SCZD, even without knowledge of the genes interacting to produce the disease state. SCZD hiPSC neurons show cellular defects comparable to those identified in post-mortem human and mouse studies, and gene expression changes are consistent with predictions made by GWAS. SCZD hiPSC neurons represent a new tool to look beyond phenotype and begin to dissect the molecular mechanisms of SCZD.

Neuregulin-1 genotype is associated with structural differences in the normal human brain

The human neuregulin-1 (NRG-1) gene is highly expressed in the brain, is implicated in numerous functions associated with neuronal development, and is a leading candidate gene for schizophrenia. The T allele of SNP8NRG243177, part of a risk haplotype for schizophrenia, has been previously associated with decreases in white matter in the right anterior internal capsule and the left anterior thalamic radiation. To our knowledge no studies have described the effects of SNP8NRG243177 on grey matter volume at a voxelwise level. We assessed associations between this SNP and brain structure in 79 general population volunteers from the Northern Finland 1966 Birth Cohort (NFBC 1966). We show, for the first time, that genetic variation in SNP8NRG243177 is associated with variation in frontal brain structure in both grey and white matter. T allele carriers showed decreased grey matter volume in several frontal gyri, including inferior, middle and superior frontal gyri and the anterior cingulate gyrus, as well as decreased white matter volume in the regions of the genu and body of the corpus callosum, anterior and superior corona radiata, anterior limb of the internal capsule and external capsule regions traversed by major white matter tracts of the anterior thalamic radiation, and the inferior fronto-occipital fasciculus. These results suggest that this genetic variant may mediate risk for schizophrenia, in part, through its effect on brain structure in these regions.

Specific regulation of NRG1 isoform expression by neuronal activity

Neuregulin 1 (NRG1) is a trophic factor that has been implicated in neural development, neurotransmission, and synaptic plasticity. NRG1 has multiple isoforms that are generated by usage of different promoters and alternative splicing of a single gene. However, little is known about NRG1 isoform composition profile, whether it changes during development, or the underlying mechanisms. We found that each of the six types of NRG1 has a distinct expression pattern in the brain at different ages, resulting in a change in NRG1 isoform composition. In both human and rat, the most dominant are types III and II, followed by either type I or type V, while types IV and VI are the least abundant. The expression of NRG1 isoforms is higher in rat brains at ages of E13 and P5 (in particular type V), suggesting roles in early neural development and in the neonatal critical period. At the cellular level, the majority of NRG1 isoforms (types I, II, and III) are expressed in excitatory neurons, although they are also present in GABAergic neurons and astrocytes. Finally, the expression of each NRG1 isoform is distinctly regulated by neuronal activity, which causes significant increase in type I and IV NRG1 levels. Neuronal activity regulation of type IV expression requires a CRE cis-element in the 5' untranslated region (UTR) that binds to CREB. These results indicate that expression of NRG1 isoforms is regulated by distinct mechanisms, which may contribute to versatile functions of NRG1 and pathologic mechanisms of brain disorders such as schizophrenia.

Lack of association to a NRG1 missense polymorphism in schizophrenia or bipolar disorder in a Costa Rican population

A missense polymorphism in the NRG1 gene, Val>Leu in exon 11, was reported to increase the risk of schizophrenia in selected families from the Central Valley region of Costa Rica (CVCR). The present study investigated the relationship between three NRG1 genetic variants, rs6994992, rs3924999, and Val>Leu missense polymorphism in exon 11, in cases and selected controls from an isolated population from the CVCR. Isolated populations can have less genetic heterogeneity and increase power to detect risk variants in candidate genes. Subjects with bipolar disorder (BD, n=358), schizophrenia (SZ, n=273), or unrelated controls (CO, n=479) were genotyped for three NRG1 variants. The NRG1 promoter polymorphism (rs6994992) was related to altered expression of NRG1 Type IV in other studies. The expression of NRG1 type IV in the dorsolateral prefrontal cortex (DLPFC) and the effect of the rs6994992 genotype on expression were explored in a postmortem cohort of BD, SZ, major depressive disorder (MDD) cases, and controls. The missense polymorphism Val>Leu in exon 11 was not significantly associated with schizophrenia as previously reported in a family sample from this population, the minor allele frequency is 4%, thus our sample size is not large enough to detect an association. We observed however an association of rs6994992 with NRG1 type IV expression in DLPFC and a significantly decreased expression in MDD compared to controls. The present results while negative do not rule out a genetic association of these SNPs with BD and SZ in CVCR, perhaps due to small risk effects that we were unable to detect and potential intergenic epistasis. The previous genetic relationship between expression of a putative brain-specific isoform of NRG1 type IV and SNP variation was replicated in postmortem samples in our preliminary study.

Increased expression of receptor phosphotyrosine phosphatase-β/ζ is associated with molecular, cellular, behavioral and cognitive schizophrenia phenotypes

Schizophrenia is a serious and chronic mental disorder, in which both genetic and environmental factors have a role in the development of the disease. Neuregulin-1 (NRG1) is one of the most established genetic risk factors for schizophrenia, and disruption of NRG1 signaling has been reported in this disorder. We reported previously that NRG1/ErbB4 signaling is inhibited by receptor phosphotyrosine phosphatase-β/ζ (RPTP β/ζ) and that the gene encoding RPTPβ/ζ (PTPRZ1) is genetically associated with schizophrenia. In this study, we examined the expression of RPTPβ/ζ in the brains of patients with schizophrenia and observed increased expression of this gene. We developed mice overexpressing RPTPβ/ζ (PTPRZ1-transgenic mice), which showed reduced NRG1 signaling, and molecular and cellular changes implicated in the pathogenesis of schizophrenia, including altered glutamatergic, GABAergic and dopaminergic activity, as well as delayed oligodendrocyte development. Behavioral analyses also demonstrated schizophrenia-like changes in the PTPRZ1-transgenic mice, including reduced sensory motor gating, hyperactivity and working memory deficits. Our results indicate that enhanced RPTPβ/ζ signaling can contribute to schizophrenia phenotypes, and support both construct and face validity for PTPRZ1-transgenic mice as a model for multiple schizophrenia phenotypes. Furthermore, our results implicate RPTPβ/ζ as a therapeutic target in schizophrenia.

Biological validation of increased schizophrenia risk with NRG1, ERBB4, and AKT1 epistasis via functional neuroimaging in healthy controls

CONTEXT

NRG1 is a schizophrenia candidate gene and plays an important role in brain development and neural function. Schizophrenia is a complex disorder, with etiology likely due to epistasis.

OBJECTIVE

To examine epistasis between NRG1 and selected N-methyl-d-aspartate-glutamate pathway partners implicated in its effects, including ERBB4, AKT1, DLG4, NOS1, and NOS1AP.

DESIGN

Schizophrenia case-control sample analyzed using machine learning algorithms and logistic regression with follow-up using neuroimaging on an independent sample of healthy controls.

PARTICIPANTS

A referred sample of schizophrenic patients (n = 296) meeting DSM-IV criteria for schizophrenia spectrum disorder and a volunteer sample of controls for case-control comparison (n = 365) and a separate volunteer sample of controls for neuroimaging (n = 172).

MAIN OUTCOME MEASURES

Epistatic association between single-nucleotide polymorphisms (SNPs) and case-control status; epistatic association between SNPs and the blood oxygen level-dependent physiological response during working memory measured by functional magnetic resonance imaging.

RESULTS

We observed interaction between NRG1 5' and 3' SNPs rs4560751 and rs3802160 (likelihood ratio test P = .00020) and schizophrenia, which was validated using functional magnetic resonance imaging of working memory in healthy controls; carriers of risk-associated genotypes showed inefficient processing in the dorsolateral prefrontal cortex (P = .015, familywise error corrected). We observed epistasis between NRG1 (rs10503929; Thr286/289/294Met) and its receptor ERBB4 (rs1026882; likelihood ratio test P = .035); a 3-way interaction with these 2 SNPs and AKT1 (rs2494734) was also observed (odds ratio, 27.13; 95% confidence interval, 3.30-223.03; likelihood ratio test P = .042). These same 2- and 3-way interactions were further biologically validated via functional magnetic resonance imaging: healthy individuals carrying risk genotypes for NRG1 and ERBB4, or these 2 together with AKT1, were disproportionately less efficient in dorsolateral prefrontal cortex processing. Lower-level interactions were not observed between NRG1 /ERBB4 and AKT1 in association or neuroimaging, consistent with biological evidence that NRG1 × ERBB4 interaction modulates downstream AKT1 signaling.

CONCLUSION

Our data suggest complex epistatic effects implicating an NRG1 molecular pathway in cognitive brain function and the pathogenesis of schizophrenia.

The neuregulin signaling pathway and schizophrenia: from genes to synapses and neural circuits

Numerous genetic linkage and association studies implicate members of the Neuregulin-ErbB receptor (NRG-ErbB) signaling pathway as schizophrenia "at risk" genes. An emphasis of this review is to propose plausible neurobiological mechanisms, regulated by the Neuregulin-ErbB signaling network, that may be altered in schizophrenia and contribute to its etiology. To this end, the distinct neurotransmitter pathways, neuronal subtypes and neural network systems altered in schizophrenia are initially discussed. Next, the review focuses on the possible significance of genetic studies associating NRG1 and ErbB4 with schizophrenia, in light of the functional role of this signaling pathway in regulating glutamatergic, GABAergic and dopaminergic neurotransmission, as well as modulating synaptic plasticity and gamma oscillations. The importance of restricted ErbB4 receptor expression in GABAergic interneurons is emphasized, particularly their expression at glutamatergic synapses of parvalbumin-positive fast-spiking interneurons where modulation of inhibitory drive could account for the dramatic effects of NRG-ErbB signaling on gamma oscillations and pyramidal neuron output. A case is made for reasons that the NRG-ErbB signaling pathway constitutes a "biologically plausible" system for understanding the pathogenic mechanisms that may underlie the complex array of positive, negative and cognitive deficits associated with schizophrenia during development.

Cytokine hypothesis of schizophrenia pathogenesis: evidence from human studies and animal models

The pathogenesis of schizophrenia has yet to be fully characterized. Gene-environment interactions have been found to play a crucial role in the vulnerability to this disease. Among various environmental factors, inflammatory immune processes have been most clearly implicated in the etiology and pathology of schizophrenia. Cytokines, regulators of immune/inflammatory reactions and brain development, emerge as part of a common pathway of genetic and environmental components of schizophrenia. Maternal infection, obstetric complications, neonatal hypoxia and brain injury all recruit cytokines to mediate inflammatory processes. Abnormal expression levels of specific cytokines such as epidermal growth factor, interleukins (IL) and neuregulin-1 are found both in the brain and peripheral blood of patients with schizophrenia. Accordingly, cytokines have been proposed to transmit peripheral immune/inflammatory signals to immature brain tissue through the developing blood-brain barrier, perturbing structural and phenotypic development of the brain. This cytokine hypothesis of schizophrenia is also supported by modeling experiments in animals. Animals treated with specific cytokines of epidermal growth factor, IL-1, IL-6, and neuregulin-1 as embryos or neonates exhibit schizophrenia-like behavioral abnormalities after puberty, some of which are ameliorated by treatment with antipsychotics. In this review, we discuss the neurobiological mechanisms underlying schizophrenia and novel antipsychotic candidates based on the cytokine hypothesis.

Association analysis of Neuregulin 1 candidate regions in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe heritable psychiatric disorders involving a complex genetic aetiology. Neuregulin 1 (NRG1) is a leading candidate gene for SCZ, and has recently been implicated in BPD. We previously reported association of two NRG1 haplotypes with SCZ and BPD in a Scottish case-control sample. One haplotype is located at the 5' end of the gene (region A), and the other is located at the 3' end (region B). Here, association to haplotypes within regions A and B was assessed in patients with SCZ and BPD in a second Scottish case-control sample and in the two Scottish samples combined. Association to region B was also assessed in patients with SCZ and BPD in a German case-control sample, and in all three samples combined. No evidence was found for association in the new samples when analysed individually; however, in the joint analysis of the two Scottish samples, a region B haplotype comprising two SNPs (rs6988339 and rs3757930) was associated with SCZ and the combined case group (SCZ: p=0.0037, OR=1.3, 95% CI: 1.1-1.6; BPD+SCZ: p=0.0080, OR=1.2, 95% CI: 1.1-1.5), with these associations withstanding multiple testing correction at the single-test level (SCZ: p(st)=0.022; BPD+SCZ: p(st)=0.044). This study supports the involvement of NRG1 variants in the less well studied 3' region in conferring susceptibility to SCZ and BPD in the Scottish population.

Research review: Cholinergic mechanisms, early brain development, and risk for schizophrenia

The onset of diagnostic symptomology for neuropsychiatric diseases is often the end result of a decades-long process of aberrant brain development. Identification of novel treatment strategies aimed at normalizing early brain development and preventing mental illness should be a major therapeutic goal. However, there are few models for how this goal might be achieved. This review uses the development of a psychophysiological correlate of attentional deficits in schizophrenia to propose a developmental model with translational primary prevention implications. Review of genetic and neurobiological studies suggests that an early interaction between alpha7 nicotinic receptor density and choline availability may contribute to the development of schizophrenia-associated attentional deficits. Therapeutic implications, including perinatal dietary choline supplementation, are discussed.

Nature and nurture in neuropsychiatric genetics: where do we stand?

Both genetic and nongenetic risk factors, as well as interactions and correlations between them, are thought to contribute to the etiology of psychiatric and behavioral phenotypes. Genetic epidemiology consistently supports the involvement of genes in liability. Molecular genetic studies have been less successful in identifying liability genes, but recent progress suggests that a number of specific genes contributing to risk have been identified. Collectively, the results are complex and inconsistent, with a single common DNA variant in any gene influencing risk across human populations. Few specific genetic variants influencing risk have been unambiguously identified. Contemporary approaches, however, hold great promise to further elucidate liability genes and variants, as well as their potential inter-relationships with each other and with the environment. We will review the fields of genetic epidemiology and molecular genetics, providing examples from the literature to illustrate the key concepts emerging from this work.

Positron emission tomography in schizophrenia: a new perspective

PET is an important functional imaging technique that can be used to investigate neurotransmitter receptors and transporters directly by mapping human brain function. PET is increasingly being used greatly to advance our understanding of the neurobiology and pathophysiology of schizophrenia.

METHODS

This review focuses on the use of PET tracers and kinetic modeling in identifying regional brain abnormalities and regions associated with cognitive functioning in schizophrenia. A variety of PET tracers have been used to identify brain abnormalities, including (11)C, (15)O-water, (18)F-fallypride, and L-3,4-dihydroxy-6-(18)F-fluorophenylalanine ((18)F-FDOPA).

RESULTS

Some studies have used compartmental modeling to determine tracer binding kinetics. The most consistent findings show a difference in the dopamine content in the prefrontal cortex, anterior cingulate gyrus, and hippocampus between healthy controls and patients with schizophrenia. Studies also show a higher density of D(2) receptors in the striatum and neural brain dysconnectivity.

CONCLUSION

Future investigations integrating clinical, imaging, genetic, and cognitive aspects are warranted to gain a better understanding of the pathophysiology of this disorder.

A novel method for haplotype clustering and visualization

In population genetics, it is common to represent the haplotype diversity at a genomic region between multiple populations using well-constructed visual representations. This typically requires the chromosomes from these populations to be grouped according to some definition of haplotypic similarity. Here, we introduce a novel algorithm for clustering haplotypes with the specific aim of addressing haplotype diversity within or between populations. The algorithm allows for missing data in the haplotypes and appropriately downweighs single nucleotide polymorphisms with higher extent of missingness. By identifying the canonical haplotypes in a genomic region, defined as the haplotype forms, which most chromosomes are similar to, the algorithm maps each chromosome to either a unique canonical haplotype or as a mosaic of the identified canonical haplotypes. This mapping can subsequently be utilized for producing graphical visualizations of the haplotype clustering for understanding the extent of haplotype diversity in the region. The clustering application has been implemented in R for distribution as haplosim, and we also provide a visualization script hapvisual for graphical display of the clustering results. The outcome of such analysis can be informative in understanding the extent of haplotype diversity between populations, in addressing the reproducibility of established association signals across multiple populations, and also in the investigation of positive selection in the human genome.

Gene expression of neuregulin-1 isoforms in different brain regions of elderly schizophrenia patients

One important risk gene in schizophrenia is neuregulin-1 (NRG1), which is expressed in different isoforms in the brain. To determine if alterations of NRG1 are present in schizophrenia, we measured gene expression of NRG1 and its main isoforms as well as the impact of genetic variation of NRG1 in an exploratory study examining three brain regions instead of only one as published so far. In all, we examined post-mortem samples from 11 schizophrenia patients and eight normal subjects. We investigated gene expression of total NRG1 and isoforms I, II and III by real-time PCR in the prefrontal cortex (Brodmann areas 9 and 10) and right hippocampal tissue. For the genetic study, we genotyped the NRG1 polymorphism SNP8NRG221533, which is within the core haplotype of the original publication. Compared to controls, gene expression of the NRG1 isoform I was decreased and isoform II increased in the prefrontal cortex (BA10) of schizophrenia patients. There were no statistically significant differences between individuals carrying at least one C allele of SNP8NRG221533 compared to individuals homozygous for the T allele. The decreased expression of NRG1 isoform I and overexpression of isoform II may be related to deficits in receptor function as well as abnormal migration and myelination. However, our study sample was small and results of this exploratory study should be verified in a larger sample.

Neuregulin-1 genotypes and eye movements in schizophrenia

Neuregulin-1 (NRG-1) is a putative susceptibility gene for schizophrenia but the neurocognitive processes that may involve NRG-1 in schizophrenia are unknown. Deficits in antisaccade (AS) and smooth pursuit eye movements (SPEM) are promising endophenotypes, which may be associated with brain dysfunctions underlying the pathophysiology of schizophrenia. The aim of this study was to investigate the associations of NRG-1 genotypes with AS and SPEM in schizophrenia patients and healthy controls. Patients (N = 113) and controls (N = 106) were genotyped for two NRG-1 single nucleotide polymorphisms (SNPs); SNP8NRG222662, a surrogate marker for the originally described Icelandic NRG-1 risk haplotype, and SNP8NRG243177, which has recently been associated with individual differences in brain function. Subjects underwent infrared oculographic assessment of AS and SPEM. The study replicates previous findings of impaired AS and SPEM performance in schizophrenia patients (all P < 0.005; all d = 0.5-1.5). SNP8NRG243177 risk allele carriers had marginally increased variability of AS spatial error (P = 0.050, d = 0.3), but there were no significant genotype effects on other eye movement variables and no significant diagnosis-by-genotype interactions. Generally, risk allele carriers (G allele for SNP8NRG222662 and T allele for SNP8NRG243177) had numerically worse performance than non-carriers on most AS and SPEM variables. The results do not suggest that NRG-1 genotype significantly affects AS and SPEM task performance. However, the power of the sample to identify small effects is limited and the possibility of a type II error must be kept in mind. Larger samples may be needed to reliably investigate such gene effects on oculomotor endophenotypes.

Identification of neuroglycan C and interacting partners as potential susceptibility genes for schizophrenia in a Southern Chinese population

Chromosome 3p was reported by previous studies as one of the regions showing strong evidence of linkage with schizophrenia. We performed a fine-mapping association study of a 6-Mb high-LD and gene-rich region on 3p in a Southern Chinese sample of 489 schizophrenia patients and 519 controls to search for susceptibility genes. In the initial screen, 4 SNPs out of the 144 tag SNPs genotyped were nominally significant (P < 0.05). One of the most significant SNPs (rs3732530, P = 0.0048) was a non-synonymous SNP in the neuroglycan C (NGC, also known as CSPG5) gene, which belongs to the neuregulin family. The gene prioritization program Endeavor ranked NGC 8th out of the 129 genes in the 6-Mb region and the highest among the genes within the same LD block. Further genotyping of NGC revealed 3 more SNPs to be nominally associated with schizophrenia. Three other genes (NRG1, ErbB3, ErbB4) involved in the neuregulin pathways were subsequently genotyped. Interaction analysis by multifactor dimensionality reduction (MDR) revealed a significant two-SNP interaction between NGC and NRG1 (P = 0.015) and three-SNP interactions between NRG1 and ErbB4 (P = 0.009). The gene NGC is exclusively expressed in the brain. It is implicated in neurodevelopment in rats and was previously shown to promote neurite outgrowth. Methamphetamine, a drug that may induce psychotic symptoms, was reported to alter the expression of NGC. Taken together, these results suggest that NGC may be a novel candidate gene, and neuregulin signaling pathways may play an important role in schizophrenia.

NRG1 gene in recurrent major depression: no association in a large-scale case-control association study

The Neuregulin 1 (NRG1) gene was initially implicated in schizophrenia (SZ) and has recently been associated with bipolar disorder (BPD) in two studies. An association with major depressive disorder (MDD) has not yet been investigated but is warranted in view of the genetic overlap between MDD and BPD. We have performed a large-scale case-control study investigating the association between NRG1 polymorphisms and MDD, genotyping a selection of 14 single nucleotide polymorphisms (SNPs) spanning the NRG1 gene in a sample of 1,398 patients of White European ancestry with a diagnosis of MDD and 1,304 ethnically matched controls from three clinical sites in the UK. We found no single marker or haplotype associations that withstood correction for multiple testing. Our findings do not provide evidence that NRG1 plays a role in MDD or that this gene explains part of the genetic overlap with BPD.

In vivo evidence of differential impact of typical and atypical antipsychotics on intracortical myelin in adults with schizophrenia

CONTEXT

Imaging and post-mortem studies provide converging evidence that patients with schizophrenia have a dysregulated developmental trajectory of frontal lobe myelination. The hypothesis that typical and atypical medications may differentially impact brain myelination in adults with schizophrenia was previously assessed with inversion recovery (IR) images. Increased white matter (WM) volume suggestive of increased myelination was detected in the patient group treated with an atypical antipsychotic compared to a typical one.

OBJECTIVE

In a follow-up reanalysis of MRI images from the original study, we used a novel method to assess whether the difference in WM volumes could be caused by a differential effect of medications on the intracortical myelination process.

DESIGN, SETTING, AND PARTICIPANTS

Two different male cohorts of healthy controls ranging in age from 18-35 years were compared to cohorts of subjects with schizophrenia who were treated with either oral risperidone (Ris) or fluphenazine decanoate (Fd).

MAIN OUTCOME MEASURE

A novel MRI method that combines the distinct tissue contrasts provided by IR and proton density (PD) images was used to estimate intracortical myelin (ICM) volume.

RESULTS

When compared with their pooled healthy control comparison group, the two groups of schizophrenic patients differed in the frontal lobe ICM measure with the Ris group having significantly higher volume.

CONCLUSIONS

The data suggest that in adults with schizophrenia antipsychotic treatment choice may be specifically and differentially impacting later-myelinating intracortical circuitry. In vivo MRI can be used to dissect subtle differences in brain tissue characteristics and thus help clarify the effect of pharmacologic treatments on developmental and pathologic processes.

Analysis of a promoter polymorphism in the SMDF neuregulin 1 isoform in Schizophrenia

BACKGROUND/AIMS

Neuregulin 1 (NRG1) is a positional candidate gene in schizophrenia (SZ). Two major susceptibility loci in the NRG1 gene approximately one million nucleotides apart have been identified in genetic studies. Several candidate functional allelic variants have been described that might be involved in disease susceptibility. However, the findings are still preliminary. We recently mapped active promoters and other regulatory domains in several SZ and bipolar disorder (BD) candidate genes using ChIP-chip (chromatin immunoprecipitation hybridized to microarrays). One was the promoter for the NRG1 isoform, SMDF, which maps to the 3' end of the gene complex. Analysis of the SNP database revealed several polymorphisms within the approximate borders of the region immunoprecipitated in our ChIP-chip experiments, one of which is rs7825588.

METHODS

This SNP was analyzed in patients with SZ and BD and its effect on promoter function was assessed by electromobility gel shift assays and luciferase reporter constructs.

RESULTS

A significant increase in homozygosity for the minor allele was found in patients with SZ (genotype distribution chi(2) = 7.32, p = 0.03) but not in BD (genotype distribution chi(2) = 0.52, p = 0.77). Molecular studies demonstrated modest, but statistically significant allele-specific differences in protein binding and promoter function.

CONCLUSION

The findings suggest that homozygosity for rs725588 could be a risk genotype for SZ.

Family-based association study of Neuregulin 1 with psychotic bipolar disorder

The Neuregulin 1 gene (NRG1) has been associated with schizophrenia, and, to a lesser extent, with bipolar disorder (BP). We investigated the association of NRG1 with BP in a large family sample, and then performed analyses according to the presence of psychotic features or mood-incongruent psychotic features. We genotyped 116 tagSNPs and four Icelandic "core" SNPs in 1,199 subjects from 314 nuclear families. Of 515 BP offspring, 341 had psychotic features, and 103 had mood-incongruent psychotic features. In single-marker and sliding window haplotype analyses using FBAT, there was little association using the standard BP or mood-incongruent psychotic BP phenotypes, but stronger signals were seen in the psychotic BP phenotype. The most significant associations with psychotic BP were in haplotypes within the 5' "core" region. The strongest global P-value was across three SNPs: NRG241930-NRG243177-rs7819063 (P = 0.0016), with an undertransmitted haplotype showing an individual P = 0.0007. The most significant individual haplotype was an undertransmitted two-allele subset of the above (NRG243177-rs7819063, P = 0.0004). Additional associations with psychotic BP were found across six SNPs in a 270 kb central region of the gene. The most 3' of these, rs7005606 (P = 0.0029), is located approximately 4 kb from the type I NRG1 isoform promoter. In sum, our study suggests that NRG1 may be specifically associated with the psychotic subset of BP; however, our results should be interpreted cautiously since they do not meet correction for multiple testing and await independent replication.

Genome-wide comparisons of variation in linkage disequilibrium

Current genome-wide surveys of common diseases and complex traits fundamentally aim to detect indirect associations where the single nucleotide polymorphisms (SNPs) carrying the association signals are not biologically active but are in linkage disequilibrium (LD) with some unknown functional polymorphisms. Reproducing any novel discoveries from these genome-wide scans in independent studies is now a prerequisite for the putative findings to be accepted. Significant differences in patterns of LD between populations can affect the portability of phenotypic associations when the replication effort or meta-analyses are attempted in populations that are distinct from the original population in which the genome-wide study is performed. Here, we introduce a novel method for genome-wide analyses of LD variations between populations that allow the identification of candidate regions with different patterns of LD. The evidence of LD variation provided by the introduced method correlated with the degree of differences in the frequencies of the most common haplotype across the populations. Identified regions also resulted in greater variation in the success of replication attempts compared with random regions in the genome. A separate permutation strategy introduced for assessing LD variation in the absence of genome-wide data also correctly identified the expected variation in LD patterns in two well-established regions undergoing strong population-specific evolutionary pressure. Importantly, this method addresses whether a failure to reproduce a disease association in a disparate population is due to underlying differences in LD structure with an unknown functional polymorphism, which is vital in the current climate of replicating and fine-mapping established findings from genome-wide association studies.

A two-method meta-analysis of Neuregulin 1(NRG1) association and heterogeneity in schizophrenia

NRG1 is one of the most researched genes associated with schizophrenia. Although three meta-analyses in this area have been published, the results have been inconclusive and even conflicting. Family based studies can be problematical due to the difficulty of synthesizing them with case-control studies. Heterogeneity is another persistently difficult problem which tends to be side-stepped in genetic studies. To deal with these points, we performed a meta-analysis of 26 published case-control and family-based association studies up to September 2008 covering 8049 cases, 8869 controls and 1515 families. The matrix of coancestry coefficient was also calculated using population genetics. Across these studies, the conclusions are as follows: Firstly, only SNP8NRG221132, 420M9-1395(0) and 478B14-848(0) showed significant association in the relatively small sample size. Secondly, we applied both Kazeem's and Lohmueller's methods for synthesizing family and case control studies and there was no statistically significant difference between the results from the two methods, suggesting that either method can be used. In addition, the association analysis of case-control studies was statistically consistent with that of family studies. Finally, the matrix of coancestry coefficient suggested obvious population stratification. The study reveals that one SNP of the NRG1 gene does not contribute significantly to schizophrenia and that population stratification is evident. In future genetic association analysis on complex psychic diseases, haplotype blocks and population structure should be given greater consideration.

Interspecies comparisons of functional genetic variations and their implications in neuropsychiatry

Animal studies are important for the identification and functional characterization of the biological substrates underlying complex psychiatric disorders. However, novel insights into the relationship between the genome and behavior are needed for the development of fully valid translational models. Based on the notion that in different species, the same genes may independently give rise to alleles with similar functional and phenotypic effects, either under similar selection or through similar genomic mechanisms, we propose the use of genetic validity as a tool for identifying analogous pathology between animals and human neuropsychiatric disorders. Furthermore, the identification of copy number variants which disrupt entire genes, reinforces the notion that transgenic animals, such as knockouts or knock-ins, may provide unexpectedly valid disease models for psychiatric traits. To illustrate interspecies comparison of genetic variations in relation to neurobehavioral traits, examples are provided for the BDNF, COMT, and DISC1 genes in mouse and man. We propose that alignment of individual genetic variations with endophenotypes obtained from mice and across categories of neuropsychiatric disorders will provide an important step in translational research.

Linkage analysis of schizophrenia in African-American families

While many studies have sought a window into the genetics of schizophrenia, few have focused on African-American families. An exception is the Project among African-Americans to Explore Risks for Schizophrenia (PAARTNERS), which seeks to identify novel and known risk variation for schizophrenia by genetic analyses of African-American families. We report a linkage study of diagnostic status in 217 African-American families using the Illumina Linkage Panel. Due to assumed incomplete and time-dependent penetrance, we performed linkage analysis using two different treatments of diagnosis: (1) treating both affected and unaffected individuals as informative for linkage (using the program SIBPAL) and (2) treating only affected individuals as informative (using the program MERLIN). We also explore three definitions of affected status: narrowly defined schizophrenia; one broadened to include schizoaffective disorder; and another including all diagnoses indicating psychosis. Several regions show a decrease in the evidence for linkage as the definition broadens 8q22.1 (rs911, 99.26 cM; SIBPAL p-value [p] goes from 0.006 to 0.02), 16q24.3 (rs1006547, 130.48 cM; p from 0.00095 to 0.0085), and 20q13.2 (rs1022689, 81.73 cM; p from 0.00015 to 0.032). One region shows a substantial increase in evidence for linkage, 11p15.2 (rs722317, 24.27 cM; p from 0.0022 to 0.0000003); MERLIN results support the significance of the SIBPAL results (p=0.00001). Our linkage results overlap two broad, previously-reported linkage regions: 8p23.3-p12 found in studies sampling largely families of European ancestry; and 11p11.2-q22.3 reported by a study of African-American families. These results should prove quite useful for uncovering loci affecting risk for schizophrenia.

Neuregulin 1 ICE-single nucleotide polymorphism in first episode schizophrenia correlates with cerebral activation in fronto-temporal areas

The Neuregulin (NRG1) gene has been associated with schizophrenia, but its functional implications are largely unknown. Our aim was to assess differential brain activation between patients carrying an at-risk allele on the Neuregulin 1 gene and patients without this genetic risk. Neural signal changes between 14 first episode schizophrenia patients with the at risk allele (SNP8NRG221533) from the Icelandic core haplotype and 14 without were measured with fMRI during a working memory task. Patients without the at risk allele showed greater activations (P < 0.05; corrected) in the left hippocampus, precuneus and cerebellum, as well as the right anterior cingulate. Brain regions previously associated with the pathology of Schizophrenia are differentially affected in those with a genetic at risk status in the NRG1 gene. Heterogeneity of structural and functional measures within patients characterized by clinical phenotypes may be in part due to this genetic variation.

Neuregulin 1 and age of onset in the major psychoses

Genetic vulnerability to psychiatric illness extends across major psychiatric illness. Neuregulin 1 (NRG1) is a large gene on chromosome 8p, that has been identified as a susceptibility factor in bipolar disorder and schizophrenia. In particular, a core at risk haplotype has received considerable attention for a putative role in the pathophysiology of the major psychoses (schizophrenia and bipolar disorder). This core haplotype can be represented by three markers 478B14-848, 420M9-1395, and SNP8NRG221533. We genotyped 312 families with bipolar probands, and 120 families with schizophrenia probands. Association of the core haplotype was tested for with age-at-onset and with three phenotypes: major psychosis, schizophrenia, and bipolar disorder. Neither age of onset (P = 0.893) nor the major psychosis phenotype (P = 0.374) was associated with the core haplotype in the overall sample. Ours was the first study to investigate the NRG1 core haplotype with age of onset of major psychoses, and despite our preliminary negative findings, this area deserves further investigation.

Role of glutamate in schizophrenia: integrating excitatory avenues of research

Schizophrenia is a debilitating lifelong disorder affecting up to 1% of the population worldwide, producing significant financial and emotional hardship for patients and their families. As yet, the causes of schizophrenia and the mechanism of action of antipsychotic drugs are unknown, and many patients do not respond well to currently available medications. Attempts to find risk factors for the disorder using epidemiological methods have shown that schizophrenia is highly heritable, and path analyses predict that the disorder is caused by several genes in combination with nongenetic factors. Therefore, intensive research efforts have been made to identify genes creating vulnerability to schizophrenia and also genes predicting response to treatment. Interactions of the glutamatergic system with dopaminergic and serotonergic circuitry are crucial for normal brain function, and their disruption may be a mechanism by which the pathophysiology of schizophrenia is manifest. Genes within the glutamatergic system are therefore strong candidates for investigation, and these include the glutamate receptor genes in addition to genes encoding neuregulin, dysbindin, D-amino acid oxidase and G72/G30. These genetic studies could eventually reveal new targets for antipsychotic drug treatment, which currently focuses on inhibition of the dopaminergic system. However, a recent breakthrough indicates clinical efficacy of a drug stimulating the metabotropic glutamate receptor II, LY2140023, which has improved efficacy for negative and cognitive symptoms of schizophrenia. Studies of larger patient samples are required to consolidate these data. Further investigation of glutamatergic targets is likely to reinvigorate antipsychotic drug development.

Impact of neuregulin-1 on the pathophysiology of schizophrenia in human post-mortem studies

To a large extend schizophrenia has been shown to be heritable, with neuregulin-1 (NRG1) one of the candidate genes considered to play a role in the pathophysiology of the disorder. While several polymorphisms within this gene have been reported to be associated with schizophrenia, the impact of NRG1 risk genotypes on disturbed brain function and symptoms of the disease is unknown and might be elucidated using post-mortem studies. Neuregulins are signalling proteins and the NRG1 family encodes at least 15 different splice variants, classified into four isoforms. They play an important role in cell differentiation, migration, myelination and proliferation of oligodendrocytes and neurons. Dysfunction in these processes may be related to neurodevelopmental disturbances in schizophrenia. NRG1 isoforms are differentially expressed in relevant brain regions of schizophrenia patients such as the prefrontal cortex and hippocampus and may contribute to pathophysiological processes. Different NRG1 genotypes have been shown to influence gene expression of isoforms and the risk-associated variants are in primarily non-coding and promoter regions, probably operating by altering gene expression or splicing. In addition, NRG1 regulates the expression of the nicotinic acetylcholine receptor, and expression of the gamma-aminobutyric acid (GABA(A)) and N-methyl-D: -aspartate receptor in the brain. However, the contribution of NRG1 risk genotypes to expression of isoforms and cognitive or psychotic symptoms in patients remain to be investigated in prospective post-mortem studies. In animal models of ischemia/hypoxia, NRG1 has been shown to act as a therapeutic, neuroprotective agent and should be investigated in more detail in transgenic animal models.