Multicenter linkage study of schizophrenia candidate regions on chromosomes 5q, 6q, 10p, and 13q: schizophrenia linkage collaborative group III

Genetic variation and susceptibility to schizophrenia: Work in progress

After finishing my pharmacy studies, I became interested in undertaking a PhD in the genetics of psychiatric disorders, specifically, the genetics of schizophrenia. At this time in 1990, only limited information about the human genome was available. Still, the research soon picked up some speed with introduction of the polymerase chain reaction (PCR) into research laboratories and the growing knowledge about the structure of the human genome. In my research, I aim to identify altered genes that increase the susceptibility to schizophrenia. The idea was that identifying these genes allows an understanding of the underlying biochemistry, therefore facilitating the development of targeted pharmacotherapies. While we have come closer to achieving this aim, the complexity of the identified genetic architecture and the phenotypes implies that there is still much research to be completed before we can achieve this aim.

Thyroid hormones regulate reelin expression in neuropsychiatric disorders

The incidence and prevalence of hypothyroidism in pregnancy have increased over the past two decades, leading to the occurrence of neuropsychiatric disorders. However, the underlying mechanisms of thyroid hormone (TH)-regulated gene expression and neuropsychiatric development during the postnatal period remain unknown. Recent achievements have shown that reelin, a large extracellular glycoprotein, plays a crucial role in neuronal migration and localization during the development of neocortex and cerebellar cortex, thereby participating in the development of neuropsychiatric diseases. Reelin-induced neuronal migration requires triiodothyronine (T3) from the deiodination of thyroxine (T4) by fetal brain deiodinases. Previous studies have reported decreased reelin levels and abnormal gene expression, which are the same as the pathological alternations in reelin-induced neuropsychiatric disorders including schizophrenia and autism. Low T3 in the fetal brain due to hypothyroxinemia during pregnancy may be detrimental to neuronal migration, leading to neuropsychiatric disorders. In this review, we focus on the reelin expression between hypothyroidism and neuropsychiatric disorders.

Genetic polymorphisms of PIP5K2A and course of schizophrenia

Background

Schizophrenia is a severe highly heritable mental disorder. The clinical heterogeneity of schizophrenia is expressed in the difference in the leading symptoms and course of the disease. Identifying the genetic variants that affect clinical heterogeneity may ultimately reveal the genetic basis of the features of schizophrenia and suggest novel treatment targets. PIP5K2A (Phosphatidylinositol-4-Phosphate 5-Kinase Type II Alpha) has been investigated as a potential susceptibility gene for schizophrenia.

Methods

In this work, we studied the possible association between eleven polymorphic variants of PIP5K2A and the clinical features of schizophrenia in a population of 384 white Siberian patients with schizophrenia. Genotyping was carried out on QuantStudio 5 Real-Time PCR System with a TaqMan Validate SNP Genotyping Assay (Applied Biosystems, USA).

Results

PIP5K2A rs8341 (χ² = 6.559, p = 0.038) and rs946961 (χ² = 5.976, p = 0.049) showed significant association with course of schizophrenia (continuous or episodic). The rs8341*CT (OR = 1.63, 95% CI: 1.04–2.54) and rs946961*CC (OR = 5.17, 95% CI: 1.20–22.21) genotypes were associated with a continuous type of course, while the rs8341*TT genotype (OR = 0.53, 95% CI: 0.29–0.97) was associated with an episodic type of course of schizophrenia. Therefore rs8341*TT genotype presumably has protective effect against the more severe continuous course of schizophrenia compared to the episodic one.

Conclusions

Our experimental data confirm that PIP5K2A is a genetic factor influencing the type of course of schizophrenia in Siberian population. Disturbances in the phosphatidylinositol pathways may be a possible reason for the transition to a more severe continuous course of schizophrenia.

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.

Association of HLA-A, -B, -C, -DRB1 and -DQB1 alleles at amino acid level in individuals with schizophrenia: A study from South India

BACKGROUND

Schizophrenia, a chronic severe psychiatric illness of unknown aetiology, has been shown to be associated with HLA alleles but at varied degree in different population. The present study has focussed on analysing the frequency of HLA class I and class II alleles in persons with schizophrenia from South India.

METHODS

Ninety seven individuals with schizophrenia and 103 age- and gender-matched controls were typed for HLA- A, B, C, DRB1 and DQB1 loci by next-generation sequencing in Illumina MiniSeq using MIA FORA NGS FLEX HLA typing kit.

RESULTS

The results showed that HLA-A*01:01:01, B*37:01:01 and C*01:02:01 were positively associated with schizophrenia while HLA-B*35:03:01 and DRB1*04:03:01 were negatively associated. Gender-specific associations revealed that DRB1*10:01:01 and DQB1*05:01:01 were positively associated while DQB1*03:02:01 was negatively associated with female subjects with schizophrenia. A*24:02:01~B*37:01:01~C*06:02:01~DRB1*10:01:01~DQB1*05:01:01 is the predominant haplotype in schizophrenia population when compared to healthy controls. Amino acid association in susceptible and protective alleles has shown that the presence of peptide in the peptide-binding groves of mature HLA-A protein (K, M, V, R and V at 44th, 67th, 150th, 156th and 158th position), HLA-B protein (D and S at 77th and 99th position) and HLA-C protein (M at 99th position) confer susceptibility to the disease, only in the absence of E (Glutamic acid) at 74th position in mature HLA-DRB1 protein. Interaction of amino acids in protective alleles namely B*35:01:01 and DRB1*04:03:01 has revealed that aspartic acid at 114th (D) position in mature HLA-B protein and glutamic acid (E) at 74th position of mature HLA-DRB1 protein have a combined effect in protecting against the disease.

CONCLUSION

The study has revealed the HLA association with schizophrenia in south Indian population. The amino acid interaction with the disease needs to be confirmed in a larger population.

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

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

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

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

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

Plasma and cerebrospinal fluid G72 protein levels in schizophrenia and major depressive disorder

G72 is a modulator of D-amino acid oxidase, the enzyme that degrades D-serine, an amino acid that plays a critical role in glutamate neurotransmission, and has been implicated in psychiatric disorders. The aim of this study was to examine whether plasma or cerebrospinal fluid (CSF) G72 protein levels were altered in either schizophrenia or major depressive disorder (MDD) and whether any correlation between G72 levels and disease severity existed. Initially, 27 schizophrenic patients, 26 MDD patients, and 27 healthy controls matched for age, sex, and ethnicity were enrolled. Compared to those of controls, plasma or CSF G72 levels were not significantly different in patients with schizophrenia or MDD. Although we found a significant positive correlation between plasma G72 levels and a positive symptoms score on the positive and negative syndrome scale (PANSS), this was not replicated in the second study (40 schizophrenic patients). CSF G72 levels showed no significant correlation with PANSS scores. In MDD, neither plasma nor CSF G72 levels correlated significantly with depression severity. Since severity of our patients were relatively mild, further investigations in a large number of subjects including drug-free patients, younger patients, and more severely affected patients are warranted.

Emerging Synaptic Molecules as Candidates in the Etiology of Neurological Disorders

Synapses are complex structures that allow communication between neurons in the central nervous system. Studies conducted in vertebrate and invertebrate models have contributed to the knowledge of the function of synaptic proteins. The functional synapse requires numerous protein complexes with specialized functions that are regulated in space and time to allow synaptic plasticity. However, their interplay during neuronal development, learning, and memory is poorly understood. Accumulating evidence links synapse proteins to neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. In this review, we describe the way in which several proteins that participate in cell adhesion, scaffolding, exocytosis, and neurotransmitter reception from presynaptic and postsynaptic compartments, mainly from excitatory synapses, have been associated with several synaptopathies, and we relate their functions to the disease phenotype.

Genetic Consideration of Schizotypal Traits: A Review

Schizotypal traits are of interest and importance in their own right and also have theoretical and clinical associations with schizophrenia. These traits comprise attenuated psychotic symptoms, social withdrawal, reduced cognitive capacity, and affective dysregulation. The link between schizotypal traits and psychotic disorders has long since been debated. The status of knowledge at this point is such schizotypal traits are a risk for psychotic disorders, but in and of themselves only confer liability, with other risk factors needing to be present before a transition to psychosis occurs. Investigation of schizotypal traits also has the possibility to inform clinical and research pursuits concerning those who do not make a transition to psychotic disorders. A growing body of literature has investigated the genetic underpinnings of schizotypal traits. Here, we review association, family studies and describe genetic disorders where the expression of schizotypal traits has been investigated. We conducted a thorough review of the existing literature, with multiple search engines, references, and linked articles being searched for relevance to the current review. All articles and book chapters in English were sourced and reviewed for inclusion. Family studies demonstrate that schizotypal traits are elevated with increasing genetic proximity to schizophrenia and some chromosomal regions have been associated with schizotypy. Genes associated with schizophrenia have provided the initial start point for the investigation of candidate genes for schizotypal traits; neurobiological pathways of significance have guided selection of genes of interest. Given the chromosomal regions associated with schizophrenia, some genetic disorders have also considered the expression of schizotypal traits. Genetic disorders considered all comprise a profile of cognitive deficits and over representation of psychotic disorders compared to the general population. We conclude that genetic variations associated with schizotypal traits require further investigation, perhaps with targeted phenotypes narrowed to assist in refining the clinical end point of significance.

Association of HOMER1 rs2290639 with suicide attempts in Hong Kong Chinese and the potentially functional role of this polymorphism

OBJECTIVE

Animal evidence and genetic studies suggest that HOMER1 (homer homolog 1) is involved in the etiology of suicidal behavior and major depression disorder (MDD). However, most of genetic studies were performed in Caucasians and the potentially functional role of associated polymorphisms in HOMER1 was seldom reported. The purpose of this study was to investigate the association of a HOMER1 polymorphism rs2290639 with suicide attempts (SA) and MDD in Hong Kong Chinese, and then briefly elucidate the potentially functional role of the associated polymorphism.

METHODS

NEO personality inventory, impulsiveness and depression rating scales were completed by the subjects. The association studies of HOMER1 rs2290639 with SA or MDD were performed by case-control association studies. The bioinformatics analyses were adapted to predict potential transcription factors binding sites for the associated polymorphism.

RESULTS

The association studies and meta-analysis suggested that the HOMER1 rs2290639 was significantly associated with susceptibility to SA but seemed not to be associated with MDD in Hong Kong Chinese. This polymorphism might affect the transcription of the HOMER1 gene through interacting with a reliable transcription factor as found by three of four bioinformatics tools. In addition, close correlations between impulsiveness and NEO personality five factors were found in SA and MDD patients, which provide a possible way to assess the impulsiveness of patients through subjects' personality profiles for Hong Kong Chinese.

CONCLUSIONS

The HOMER1 rs2290639 polymorphism was significantly associated with susceptibility to SA in Hong Kong Chinese affected by psychiatric disorders, which might be explained by the potentially functional role of this polymorphism.

Analysis of Shared Haplotypes amongst Palauans Maps Loci for Psychotic Disorders to 4q28 and 5q23-q31

To localize genetic variation affecting risk for psychotic disorders in the population of Palau, we genotyped DNA samples from 203 Palauan individuals diagnosed with psychotic disorders, broadly defined, and 125 control subjects using a genome-wide single nucleotide polymorphism array. Palau has unique features advantageous for this study: due to its population history, Palauans are substantially interrelated; affected individuals often, but not always, cluster in families; and we have essentially complete ascertainment of affected individuals. To localize risk variants to genomic regions, we evaluated long-shared haplotypes, ≥10 Mb, identifying clusters of affected individuals who share such haplotypes. This extensive sharing, typically identical by descent, was significantly greater in cases than population controls, even after controlling for relatedness. Several regions of the genome exhibited substantial excess of shared haplotypes for affected individuals, including 3p21, 3p12, 4q28, and 5q23-q31. Two of these regions, 4q28 and 5q23-q31, showed significant linkage by traditional LOD score analysis and could harbor variants of more sizeable risk for psychosis or a multiplicity of risk variants. The pattern of haplotype sharing in 4q28 highlights <i>PCDH10</i>, encoding a cadherin-related neuronal receptor, as possibly involved in risk.

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

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

A joint history of the nature of genetic variation and the nature of schizophrenia

This essay traces the history of concepts of genetic variation and schizophrenia from Darwin and Mendel to the present. For Darwin, the important form of genetic variation for evolution is continuous in nature and small in effect. Biometricians led by Pearson agreed and developed statistical genetic approaches utilizing trait correlations in relatives. Mendel studied discontinuous traits and subsequent Mendelians, led by Bateson, assumed that important genetic variation was large in effect producing discontinuous phenotypes. Although biometricians studied 'insanity', schizophrenia genetics under Kraepelin and Rüdin utilized Mendelian approaches congruent with their anatomical-clinical disease model of dementia praecox. Fisher showed, assuming many genes of small effect, Mendelian and Biometrical models were consilient. Echoing prior conflicts, psychiatric genetics since then has utilized both biometrical models, largely in twins, and Mendelian models, based on advancing molecular techniques. In 1968, Gottesman proposed a polygenic model for schizophrenia based on a threshold version of Fisher's theory. Since then, rigorous studies of the schizophrenia spectrum suggest that genetic risk for schizophrenia is more likely continuous than categorical. The last 5 years has seen increasingly convincing evidence from genome-wide association study (GWAS) and sequencing that genetic risk for schizophrenia is largely polygenic, and congruent with Fisher's and Gottesman's models. The gap between biometrical and molecular Mendelian models for schizophrenia has largely closed. The efforts to ground a categorical biomedical model of schizophrenia in Mendelian genetics have failed. The genetic risk for schizophrenia is widely distributed in human populations so that we all carry some degree of risk.

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

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

Expression of the G72/G30 gene in transgenic mice induces behavioral changes

The G72/G30 gene complex is a candidate gene for schizophrenia and bipolar disorder. However, G72 and G30 mRNAs are expressed at very low levels in human brain, with only rare splicing forms observed. We report here G72/G30 expression profiles and behavioral changes in a G72/G30 transgenic mouse model. A human BAC clone containing the G72/G30 genomic region was used to establish the transgenic mouse model, on which gene expression studies, western blot and behavioral tests were performed. Relative to their minimal expression in humans, G72 and G30 mRNAs were highly expressed in the transgenic mice, and had a more complex splicing pattern. The highest G72 transcript levels were found in testis, followed by cerebral cortex, with very low or undetectable levels in other tissues. No LG72 (the long putative isoform of G72) protein was detected in the transgenic mice. Whole-genome expression profiling identified 361 genes differentially expressed in transgenic mice compared with wild-type, including genes previously implicated in neurological and psychological disorders. Relative to wild-type mice, the transgenic mice exhibited fewer stereotypic movements in the open field test, higher baseline startle responses in the course of the prepulse inhibition test, and lower hedonic responses in the sucrose preference test. The transcriptome profile changes and multiple mouse behavioral effects suggest that the G72 gene may play a role in modulating behaviors relevant to psychiatric disorders.

The DAO gene is associated with schizophrenia and interacts with other genes in the Taiwan Han Chinese population

BACKGROUND

Schizophrenia is a highly heritable disease with a polygenic mode of inheritance. Many studies have contributed to our understanding of the genetic underpinnings of schizophrenia, but little is known about how interactions among genes affect the risk of schizophrenia. This study aimed to assess the associations and interactions among genes that confer vulnerability to schizophrenia and to examine the moderating effect of neuropsychological impairment.

METHODS

We analyzed 99 SNPs from 10 candidate genes in 1,512 subject samples. The permutation-based single-locus, multi-locus association tests, and a gene-based multifactorial dimension reduction procedure were used to examine genetic associations and interactions to schizophrenia.

RESULTS

We found that no single SNP was significantly associated with schizophrenia. However, a risk haplotype, namely A-T-C of the SNP triplet rsDAO7-rsDAO8-rsDAO13 of the DAO gene, was strongly associated with schizophrenia. Interaction analyses identified multiple between-gene and within-gene interactions. Between-gene interactions including DAO*DISC1 , DAO*NRG1 and DAO*RASD2 and a within-gene interaction for CACNG2 were found among schizophrenia subjects with severe sustained attention deficits, suggesting a modifying effect of impaired neuropsychological functioning. Other interactions such as the within-gene interaction of DAO and the between-gene interaction of DAO and PTK2B were consistently identified regardless of stratification by neuropsychological dysfunction. Importantly, except for the within-gene interaction of CACNG2, all of the identified risk haplotypes and interactions involved SNPs from DAO.

CONCLUSIONS

These results suggest that DAO, which is involved in the N-methyl-d-aspartate receptor regulation, signaling and glutamate metabolism, is the master gene of the genetic associations and interactions underlying schizophrenia. Besides, the interaction between DAO and RASD2 has provided an insight in integrating the glutamate and dopamine hypotheses of schizophrenia.

Linkage replication for chromosomal region 13q32 in schizophrenia: evidence from a Brazilian pilot study on early onset schizophrenia families

We report analyses of a Brazilian study of early onset schizophrenia (BEOS) families. We genotyped 22 members of 4 families on a linkage SNP array and report here non-parametric linkage analyses using MERLIN® software. We found suggestive evidence for linkage on two chromosomal regions, 13q32 and 11p15.4. A LOD score of 2.71 was observed at 13q32 with a one LOD interval extending from 60.63–92.35 cM. From simulations, this LOD score gave a genome-wide empirical corrected p = 0.33, after accounting for all markers tested. Similarly 11p15.4 showed the same maximum LOD of 2.71 and a narrower one LOD interval of 4–14 cM. Of these, 13q32 has been reported to be linked to schizophrenia by multiple different studies. Thus, our study provides additional supporting evidence for an aetiological role of variants at 13q32 in schizophrenia.

Incorporation of molecular data and redefinition of phenotype: new approaches to genetic epidemiology of bipolar manic depressive illness and schizophrenia

Considerable advances have been made in identifying specific genetic components of bipolar manic depressive illness (BP) and schizophrenia (SZ), despite their complex inheritance. Meta-analysis of all published whole-genome linkage scans reveals overall support for illness genes in several chromosomal regions. In two of these regions, on the lonq arm of chromosome 13 and on the long arm of chromosome 22, the combined studies of BP and SZ are consistent with a common susceptibility locus for the two disorders. This lends some plausibility to the hypothesis of some shared genetic predispositions for BP and SZ. Other linkages are supported by multiple studies of specific chromosomal regions, most notably two regions on chromosome 6 in SZ. The velocardiofacial syndrome is associated with deletions very close to the linkage region on chromosome 22, and with psychiatric manifestations of both BP and SZ. Endophenotypes of SZ, previously demonstrated to be heritable, have been found to have chromosomal linkage in at least one study. These include eye-tracking abnormalities linked to the short arm of chromosome 6, and abnormality of the P50 cortical evoked potential linked to chromosome 15. Variants in specific genes have been associated with susceptibility to illness, and other genes have been associated with susceptibility to side effects of pharmacological treatment. These genetic findings may eventually be part of an integrated genetic, environmental, and interactive-factor epidemiology of the major mental illnesses.

Genome-wide association study of multiplex schizophrenia pedigrees

OBJECTIVE

The authors used a genome-wide association study (GWAS) of multiply affected families to investigate the association of schizophrenia to common single-nucleotide polymorphisms (SNPs) and rare copy number variants (CNVs).

METHOD

The family sample included 2,461 individuals from 631 pedigrees (581 in the primary European-ancestry analyses). Association was tested for single SNPs and genetic pathways. Polygenic scores based on family study results were used to predict case-control status in the Schizophrenia Psychiatric GWAS Consortium (PGC) data set, and consistency of direction of effect with the family study was determined for top SNPs in the PGC GWAS analysis. Within-family segregation was examined for schizophrenia-associated rare CNVs.

RESULTS

No genome-wide significant associations were observed for single SNPs or for pathways. PGC case and control subjects had significantly different genome-wide polygenic scores (computed by weighting their genotypes by log-odds ratios from the family study) (best p=10(-17), explaining 0.4% of the variance). Family study and PGC analyses had consistent directions for 37 of the 58 independent best PGC SNPs (p=0.024). The overall frequency of CNVs in regions with reported associations with schizophrenia (chromosomes 1q21.1, 15q13.3, 16p11.2, and 22q11.2 and the neurexin-1 gene [NRXN1]) was similar to previous case-control studies. NRXN1 deletions and 16p11.2 duplications (both of which were transmitted from parents) and 22q11.2 deletions (de novo in four cases) did not segregate with schizophrenia in families.

CONCLUSIONS

Many common SNPs are likely to contribute to schizophrenia risk, with substantial overlap in genetic risk factors between multiply affected families and cases in large case-control studies. Our findings are consistent with a role for specific CNVs in disease pathogenesis, but the partial segregation of some CNVs with schizophrenia suggests that researchers should exercise caution in using them for predictive genetic testing until their effects in diverse populations have been fully studied.

An ICA with reference approach in identification of genetic variation and associated brain networks

To address the statistical challenges associated with genome-wide association studies, we present an independent component analysis (ICA) with reference approach to target a specific genetic variation and associated brain networks. First, a small set of single nucleotide polymorphisms (SNPs) are empirically chosen to reflect a feature of interest and these SNPs are used as a reference when applying ICA to a full genomic SNP array. After extracting the genetic component maximally representing the characteristics of the reference, we test its association with brain networks in functional magnetic resonance imaging (fMRI) data. The method was evaluated on both real and simulated datasets. Simulation demonstrates that ICA with reference can extract a specific genetic factor, even when the variance accounted for by such a factor is so small that a regular ICA fails. Our real data application from 48 schizophrenia patients (SZs) and 40 healthy controls (HCs) include 300K SNPs and fMRI images in an auditory oddball task. Using SNPs with allelic frequency difference in two groups as a reference, we extracted a genetic component that maximally differentiates patients from controls (p < 4 × 10⁻¹⁷), and discovered a brain functional network that was significantly associated with this genetic component (p < 1 × 10⁻⁴). The regions in the functional network mainly locate in the thalamus, anterior and posterior cingulate gyri. The contributing SNPs in the genetic factor mainly fall into two clusters centered at chromosome 7q21 and chromosome 5q35. The findings from the schizophrenia application are in concordance with previous knowledge about brain regions and gene function. All together, the results suggest that the ICA with reference can be particularly useful to explore the whole genome to find a specific factor of interest and further study its effect on brain.

Association of estrogen receptor genes and schizophrenia: a preliminary study

Gender differences in various clinical features of schizophrenia have been noted and estrogen has been regarded to play important roles. A few previous studies on the association between estrogen receptor (ER) genotypes and schizophrenia focused mainly on ER α gene but failed to report consistent results. The present study was designed to analyze the differences in the frequencies of both ERα and ERβ gene polymorphisms in subjects with schizophrenia compared to healthy controls among Korean population. Moreover, we investigate the association between different genotypes of ER genes and various clinical variables of schizophrenia. We observed that PvuII and XbaI polymorphisms of ERα gene showed significant differences between patients with schizophrenia and control groups (p=0.006). Among clinical variables, only the age of onset was related to RsaI genotype of ERβ gene (p=0.039). In conclusion, the present study suggests that ERα gene polymorphisms may be associated with the pathogenesis of schizophrenia and RsaI AA genotype of ERβ might have protective effect on age at onset of schizophrenia in Korean patients with schizophrenia.

DAOA variants and schizophrenia: influence on diagnosis and treatment outcomes

OBJECTIVE

The present study explored whether d-amino acid oxidase activator (DAOA) variants were associated with schizophrenia and whether they could predict the clinical outcomes of patients treated with various antipsychotics.

METHODS

Two hundred and twenty-one (221) patients with schizophrenia and 170 psychiatrically healthy controls were genotyped for seven DAOA single-nucleotide polymorphisms (SNPs) (rs3916966, rs3916967, rs2391191, rs3916968, rs7139958, rs9558571 and rs778293). We also administered baseline and final clinical measures, including the Positive and Negative Symptoms Scale (PANSS), to patients with schizophrenia.

RESULTS

None of the SNPs under investigation was associated with the development of schizophrenia. However, the rs7139958 AA and rs9558571 TT as well as the rs7139958 A and rs9558571 T genotypes were associated with higher scores on the PANSS positive subscale among patients with schizophrenia, possibly reflecting their greater susceptibility to the development of more severe positive symptoms. No other allele, genotype, or haplotype under investigation was significantly associated with any of the clinical parameters, including clinical improvement, in patients with schizophrenia.

CONCLUSION

Our results suggested that rs7139958 and rs9558571 SNPs may be associated with more severe baseline positive symptoms in patients with schizophrenia. However, further research is needed to draw more definitive conclusions given the limitations of our study.

The genetic architecture of schizophrenia: new mutations and emerging paradigms

Although a genetic component of schizophrenia has been acknowledged for a long time, the underlying architecture of the genetic risk remains a contentious issue. Early linkage and candidate association studies led to largely inconclusive results. More recently, the availability of powerful technologies, samples of sufficient sizes, and genome-wide panels of genetic markers facilitated systematic and agnostic scans throughout the genome for either common or rare disease risk variants of small or large effect size, respectively. Although the former had limited success, the role of rare genetic events, such as copy-number variants (CNVs) or rare point mutations, has become increasingly important in gene discovery for schizophrenia. Importantly, recent research building upon earlier findings of de novo recurrent CNVs at the 22q11.2 locus, has highlighted a de novo mutational paradigm as a major component of the genetic architecture of schizophrenia. Recent progress is bringing us closer to earlier intervention and new therapeutic targets.

Homer-1 polymorphisms are associated with psychopathology and response to treatment in schizophrenic patients

The HOMER 1 protein plays a crucial role in mediating glutamatergic neurotransmission. It has previously shown to be a candidate gene for etiology and pathophysiology of different psychiatric diseases such as schizophrenia. To identify genes involved in response to antipsychotics, subgroups of animals were treated with haloperidol (1 mg/kg, n = 11) or saline (n = 12) for one week. By analyzing microarray data, we replicated the observed increase of Homer 1 gene expression. Furthermore, we genotyped 267 schizophrenic patients, who were treated monotherapeutically with different antipsychotics within randomized-controlled trials. Psychopathology was measured weekly using the PANSS for a minimum of four and a maximum of twelve weeks. Correlations between PANSS subscale scores at baseline and PANSS improvement scores after four weeks of treatment and genotypes were calculated by using a linear model for all investigated SNP's. We found an association between two HOMER 1 polymorphisms (rs2290639 and rs4704560) and different PANSS subscales at baseline. Furthermore all seven investigated polymorphisms were found to be associated with therapy response in terms of a significant correlation with different PANSS improvement subscores after four weeks of antipsychotic treatment. Most significant associations have been shown between the rs2290639 HOMER 1 polymorphism and PANSS subscales both at baseline conditions and after four weeks of antipsychotic treatment. This is the first study which shows an association between HOMER 1 polymorphisms and psychopathology data at baseline and therapy response in a clinical sample of schizophrenic patients. Thus, these data might further help in detecting differential therapy response in individuals with schizophrenia.

Is the EFNB2 locus associated with schizophrenia? Single nucleotide polymorphisms and haplotypes analysis

Recently, evidence of linkage of schizophrenia to chromosome 13q22-q34 has been demonstrated in multiple studies. Based on structure and function, EFNB2 may be considered as a compelling candidate gene for schizophrenia on chromosome 13q33. We genotyped three single-nucleotide polymorphisms (SNPs: rs9520087, rs11069646, and rs8000078) in this region in 846 Han Chinese subjects (477 cases and 369 controls). Significant association between an allele of marker rs9520087 and schizophrenia was found. Furthermore, since no LD was observed in the three SNPs linkage disequilibrium estimation, all three SNPs were used in multiple SNPs haplotype analysis, and a strongly significant difference was found for the common haplotype TTC. Overall our findings indicate that EFNB2 gene may be a candidate susceptibility gene for schizophrenia in the Han Chinese population, and also provide further support for the potential importance of the NMDA receptor pathway in the etiology of schizophrenia.

Functional evolution of the trace amine associated receptors in mammals and the loss of TAAR1 in dogs

Background

The trace amine associated receptor family is a diverse array of GPCRs that arose before the first vertebrates walked on land. Trace amine associated receptor 1 (TAAR1) is a wide spectrum aminergic receptor that acts as a modulator in brain monoaminergic systems. Other trace amine associated receptors appear to relate to environmental perception and show a birth-and-death pattern in mammals similar to olfactory receptors.

Results

Across mammals, avians, and amphibians, the TAAR1 gene is intact and appears to be under strong purifying selection based on rates of amino acid fixation compared to neutral mutations. We have found that in dogs it has become a pseudogene. Our analyses using a comparative genetics approach revealed that the pseudogenization event predated the emergence of the Canini tribe rather than being coincident with canine domestication. By assessing the effects of the TAAR1 agonist β-phenylethylamine on [³H]dopamine uptake in canine striatal synaptosomes and comparing the degree and pattern of uptake inhibition to that seen in other mammals, including TAAR1 knockout mice, wild type mice and rhesus monkey, we found that the TAAR1 pseudogenization event resulted in an uncompensated loss of function.

Conclusion

The gene family has seen expansions among certain mammals, notably rodents, and reductions in others, including primates. By placing the trace amine associated receptors in an evolutionary context we can better understand their function and their potential associations with behavior and neurological disease.

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

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

Association analysis of the PIP4K2A gene on chromosome 10p12 and schizophrenia in the Irish study of high density schizophrenia families (ISHDSF) and the Irish case-control study of schizophrenia (ICCSS)

Molecular studies support pharmacological evidence that phosphoinositide signaling is perturbed in schizophrenia and bipolar disorder. The phosphatidylinositol-4-phosphate-5-kinase type-II alpha (PIP4K2A) gene is located on chromosome 10p12. This region has been implicated in both diseases by linkage, and PIP4K2A directly by association. Given linkage evidence in the Irish Study of High Density Schizophrenia Families (ISHDSF) to a region including 10p12, we performed an association study between genetic variants at PIP4K2A and disease. No association was detected through single-marker or haplotype analysis of the whole sample. However, stratification into families positive and negative for the ISHDSF schizophrenia high-risk haplotype (HRH) in the DTNBP1 gene and re-analysis for linkage showed reduced amplitude of the 10p12 linkage peak in the DTNBP1 HRH positive families. Association analysis of the stratified sample showed a trend toward association of PIP4K2A SNPs rs1417374 and rs1409395 with schizophrenia in the DTNBP1 HRH positive families. Despite this apparent paradox, our data may therefore suggest involvement of PIP4K2A in schizophrenia in those families for whom genetic variation in DTNBP1 appears also to be a risk factor. This trend appears to arise from under-transmission of common alleles to female cases. Follow-up association analysis in a large Irish schizophrenia case-control sample (ICCSS) showed significant association with disease of a haplotype comprising these same SNPs rs1417374-rs1409395, again more so in affected females, and in cases with negative family history of the disease. This study supports a minor role for PIP4K2A in schizophrenia etiology in the Irish population.

Two complex genotypes relevant to the kynurenine pathway and melanotropin function show association with schizophrenia and bipolar disorder

Prior studies of mRNA expression, protein expression, and pathway metabolite levels have implicated dysregulation of the kynurenine pathway in the etiology of schizophrenia and bipolar disorder. Here we investigate whether genes involved in kynurenine pathway regulation might interact with genes that respond to kynurenine metabolites, to enhance risk for these psychiatric phenotypes. Candidate genes were selected from prior studies of genetic association, gene expression profiling and animal models. A single nucleotide polymorphism (SNP) in each of six genes, TDO2, HM74, HM74A, MCHR1, MCHR2 and MC5R, was tested for association with phenotype (475 Caucasians, 88 African Americans with schizophrenia; 97 Caucasians, 3 African Americans with bipolar disorder; 191 Caucasian, 49 African American controls). An A allele in HM74 was significantly associated with schizophrenia and with schizophrenia plus bipolar disorder combined, odds ratios (OR) of 1.48, p=0.011 and 1.50, p=0.007, respectively. Augmentation of disease risk was found for the complex genotype HM74[A,any]+MCHR1[T,any]+MCHR2[C,any] which conferred an OR maximal for the combined diagnostic category of schizophrenia plus bipolar disorder (1.70, p=0.003), carried by 30% of the cases. TDO2[CC]+MC5R[G, any]+MCHR2[GC] conferred an OR maximal for schizophrenia alone (4.84, p=0.005), carried by 8% of schizophrenia cases. The combined risk posed by these related, complex genotypes is greater than any identified single locus and may derive from co-regulation of the kynurenine pathway by interacting genes, a lack of adequate melanotropin-controlled sequestration of the kynurenine-derived pigments, or the production of melanotropin receptor ligands through kynurenine metabolism.

Genomewide linkage scan of schizophrenia in a large multicenter pedigree sample using single nucleotide polymorphisms

A genomewide linkage scan was carried out in eight clinical samples of informative schizophrenia families. After all quality control checks, the analysis of 707 European-ancestry families included 1615 affected and 1602 unaffected genotyped individuals, and the analysis of all 807 families included 1900 affected and 1839 unaffected individuals. Multipoint linkage analysis with correction for marker-marker linkage disequilibrium was carried out with 5861 single nucleotide polymorphisms (SNPs; Illumina version 4.0 linkage map). Suggestive evidence for linkage (European families) was observed on chromosomes 8p21, 8q24.1, 9q34 and 12q24.1 in nonparametric and/or parametric analyses. In a logistic regression allele-sharing analysis of linkage allowing for intersite heterogeneity, genomewide significant evidence for linkage was observed on chromosome 10p12. Significant heterogeneity was also observed on chromosome 22q11.1. Evidence for linkage across family sets and analyses was most consistent on chromosome 8p21, with a one-LOD support interval that does not include the candidate gene NRG1, suggesting that one or more other susceptibility loci might exist in the region. In this era of genomewide association and deep resequencing studies, consensus linkage regions deserve continued attention, given that linkage signals can be produced by many types of genomic variation, including any combination of multiple common or rare SNPs or copy number variants in a region.

Influence of TAAR6 polymorphisms on response to aripiprazole

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Evidence for the association of the DAOA (G72) gene with schizophrenia and bipolar disorder but not for the association of the DAO gene with schizophrenia

Background

Previous linkage and association studies have implicated the D-amino acid oxidase activator gene (DAOA)/G30 locus or neighbouring region of chromosome 13q33.2 in the genetic susceptibility to both schizophrenia and bipolar disorder. Four single nucleotide polymorphisms (SNPs) within the D-amino acid oxidase (DAO) gene located at 12q24.11 have also been found to show allelic association with schizophrenia.

Methods

We used the case control method to test for genetic association with variants at these loci in a sample of 431 patients with schizophrenia, 303 patients with bipolar disorder and 442 ancestrally matched supernormal controls all selected from the UK population.

Results

Ten SNPs spanning the DAOA locus were genotyped in these samples. In addition three SNPs were genotyped at the DAO locus in the schizophrenia sample. Allelic association was detected between the marker rs3918342 (M23), 3' to the DAOA gene and both schizophrenia (χ² = 5.824 p = 0.016) and bipolar disorder (χ² = 4.293 p = 0.038). A trend towards association with schizophrenia was observed for two other DAOA markers rs3916967 (M14, χ² = 3.675 p = 0.055) and rs1421292 (M24; χ² = 3.499 p = 0.062). A test of association between a three marker haplotype comprising of the SNPs rs778293 (M22), rs3918342 (M23) and rs1421292 (M24) and schizophrenia gave a global empirical significance of p = 0.015. No evidence was found to confirm the association of genetic markers at the DAO gene with schizophrenia.

Conclusion

Our results provide some support for a role for DAOA in susceptibility to schizophrenia and bipolar disorder.

CNR1 gene is associated with high neuroticism and low agreeableness and interacts with recent negative life events to predict current depressive symptoms

Cannabinoid receptor 1 (CB1) gene (CNR1) knockout mice are prone to develop anhedonic and helpless behavior after chronic mild stress. In humans, the CB1 antagonist rimonabant increases the risk of depressed mood disorders and anxiety. These studies suggest the hypothesis that genetic variation in CB1 receptor function influences the risk of depression in humans in response to stressful life events. In a population sample (n=1269), we obtained questionnaire measures of personality (Big Five Inventory), depression and anxiety (Brief Symptom Inventory), and life events. The CNR1 gene was covered by 10 SNPs located throughout the gene to determine haplotypic association. Variations in the CNR1 gene were significantly associated with a high neuroticism and low agreeableness phenotype (explained variance 1.5 and 2.5%, respectively). Epistasis analysis of the SNPs showed that the previously reported functional 5' end of the CNR1 gene significantly interacts with the 3' end in these phenotypes. Furthermore, current depression scores significantly associated with CNR1 haplotypes but this effect diminished after covariation for recent life events, suggesting a gene x environment interaction. Indeed, rs7766029 showed highly significant interaction between recent negative life events and depression scores. The results represent the first evidence in humans that the CNR1 gene is a risk factor for depression--and probably also for co-morbid psychiatric conditions such as substance use disorders--through a high neuroticism and low agreeableness phenotype. This study also suggests that the CNR1 gene influences vulnerability to recent psychosocial adversity to produce current symptoms of depression.

Trace amine-associated receptor 1 as a monoaminergic modulator in brain

Brain monoaminergic systems play critical roles in mood, cognition, emotion, reward, learning and attention, and aberrance in brain monoaminergic activity is associated with a variety of neuropsychiatric disorders/diseases. The present commentary focuses on trace amine-associated receptor 1 (TAAR1) and its potential regulatory roles in brain monoaminergic systems. TAAR1 was discovered in 2001 and has been established to be a G-protein-coupled receptor signaling through the cAMP pathway. This receptor is activated by a broad spectrum of agonists, although there are notable species differences in ligand efficacy and potency. TAAR1 is expressed and widely distributed in brain monoaminergic systems and co-localized with the dopamine transporter in a subset of dopaminergic neurons in rhesus monkey and mouse brain substantia nigra. TAAR1 activation by the common biogenic amines, the trace amine beta-phenylethylamine and methamphetamine alters the monoamine transporter function in both mouse and rhesus monkey brain synaptosomes, suggesting a modulatory role for this receptor in the presynaptic regulation of monoaminergic activity. However, little is known about other functional roles of TAAR1 in the brain. With a purpose to promote further studies on this receptor, we herein discuss the recent findings that provide insights into the functional significance and biological relevance of this receptor as a modulator in brain monoaminergic systems.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Association of PIP5K2A with schizophrenia: a study in an indonesian family sample

PIP5K2A variants have been shown to be associated with schizophrenia in Caucasian populations. This study tested 12 PIP5K2A SNPs for association with schizophrenia in a sample of 152 sib-pair families of Indonesian descent. All SNPs had previously been tested for association with schizophrenia in a German family sample by Schwab et al. [2006; Mol Psychiatry] and seven SNPs were nominally associated with schizophrenia in this previous study. The purpose of the study was to examine whether previously implicated PIP5K2A variants influence susceptibility to schizophrenia in populations of non-European descent. No single markers showed nominal association with schizophrenia in this Indonesian family sample, however multi-marker haplotypes including a previously associated exonic SNP marker revealed nominally significant association (P = 0.03). Power to detect association was greater than 80% for all previously implicated variants except for rs11013052, where power was greatly reduced due to the low minor allele frequency of this marker in the Indonesian sample. An explorative study combining the results of this study with those of our previous study indicated that rs11013052 was significantly associated with schizophrenia in the combined sample (P = 0.002). The results of this study suggest that any contribution of previously implicated DNA variants within the PIP5K2A gene to schizophrenia susceptibility in the Indonesian population is only minor.

FBXL21 association with schizophrenia in Irish family and case-control samples

FBXL21 gene encodes an F-box containing protein functioning in the SCF ubiquitin ligase complex. The role of the F-box protein is to recruit proteins designated for degradation to the ligase complex so they would be ubiquitinated. Using both family and case-control samples, we found consistent associations in and around FBXL21 gene. In the family sample (Irish study of high density schizophrenia families, ISHDSF, 1,350 subjects from 273 families), a minimal PDT P-value of 0.0011 was observed at rs31555. In the case-control sample (Irish case-control study of schizophrenia, ICCSS, 814 cases and 625 controls), significant associations were observed at two markers (rs1859427 P = 0.0197, and rs6861170 P = 0.0197). In haplotype analyses, haplotype 1-1 (C-T) of rs1859427-rs6861170 was overtransmitted in the ISHDSF (P = 0.0437) and was overrepresented in the ICCSS (P = 0.0177). For both samples, the associated alleles and haplotypes were identical. These data suggested that FBXL21 may be associated with schizophrenia in the Irish samples.

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

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

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

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