Shared and specific susceptibility loci for schizophrenia and bipolar disorder: a dense genome scan in Eastern Quebec families

-G308A tumor necrosis factor alpha functional polymorphism and schizophrenia risk: meta-analysis plus association study

Research on -G308A functional polymorphism in the tumor necrosis factor alpha (TNFalpha) gene as a susceptibility factor for schizophrenia has provided contrasting results in different populations. Therefore we conducted a meta-analysis of the published case-control association studies and a replication study in a large sample. Meta-analyses (total sample: 2512 cases versus 3223 controls) showed that the AA genotype was weakly associated with schizophrenia susceptibility in Caucasoids (Odd Ratio OR=1.65, 95% CI=1.00-2.71 Z=1.98 p=0.05). The replication case-control association study (323 DSM-IV-TR schizophrenia patients and 346 controls) showed that the A allele conferred an increased susceptibility for schizophrenia only in males (OR=1.73, 95% CI=1.07-2.79, p=0.025), and the association became more specific when only patients of the paranoid subtype were compared to the controls (relative risk ratio=3.09, 95% CI=1.28-7.47, p=0.012). The presence of the A allele was also associated with a later age at onset of schizophrenia in the whole sample (F(1,291)=7.094, p=0.008). Our results confirm that TNFalpha A allele could have an effect on vulnerability to schizophrenia but further studies revaluating the role of gender and diagnostic subtypes are necessary to confirm these findings.

Additional support for linkage of schizophrenia and bipolar disorder to chromosome 3q29

After publishing a genome scan and follow-up fine mapping, suggesting schizophrenia and bipolar disorder linkage to chromosome 3q29, we now genotyped 11 additional SNPs (single nucleotide polymorphisms), in order to narrow down a potential candidate region. Linkage was performed using the GENEHUNTER program version 2.1r3. A NPL score Z(all) of 3.891 (p=0.000156) was observed with SNP rs225. In short, we found significant linkage scores most telomeric on chromosome 3q29, spanning 3.46 Mbp (7 SNPs).

Preliminary evidence for linkage to chromosome 1q31-32, 10q23.3, and 16p13.3 in a South African cohort with bipolar disorder

Although the genetic variants predisposing to the development of bipolar disorder (BPD) have yet to be conclusively identified, replicated reports of linkage to particular chromosomal regions have been encouraging. Here we carried out a non-parametric linkage analysis of nine of these candidate loci in a unique South African sample of 47 BPD pedigrees (N = 350). Three polymorphic markers per region of interest (3 x 9) were typed in a Caucasian cohort of Afrikaner and British origin. Statistically significant evidence for linkage was obtained at 1q31-32, 10q23.3, and 16p13.3 with maximum NPL scores of 2.52, 2.01, and 1.84, respectively. Our results add to the growing evidence that these chromosomal regions harbor genetic variants that play a role in the development of bipolar spectrum illness. Negative results were obtained for the remaining six candidate loci, possibly due to limited statistical power.

Will neuroimaging ever be used to diagnose pediatric bipolar disorder?

There is a great need for discovery of biological markers that could be used diagnostically for pediatric onset disorders, particularly those with potentially confusing phenomenology such as pediatric-onset bipolar disorder (BD). Obtaining these markers would help overcome current subjective diagnostic techniques of relying on parent and child interview and symptomatic history. Brain imaging may be the most logical choice for a diagnostic tool, and certain neurobiological abnormalities have already been found in pediatric BD. However, much work remains to be done before neuroimaging can be used reliably to diagnose this disorder, and because of the nature of BD and the limitations of imaging technology and technique, neuroimaging will likely at most be only a diagnostic aide in the near future. In this paper we discuss the characteristics of pediatric BD that complicate the use of biological markers as diagnostic tools, how neuroimaging techniques have been used to study pediatric BD so far, and the limitations and potential of such techniques for future diagnostic use.

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

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

Molecular genetics of bipolar disorder and depression

In this review, all papers relevant to the molecular genetics of bipolar disorder published from 2004 to the present (mid 2006) are reviewed, and major results on depression are summarized. Several candidate genes for schizophrenia may also be associated with bipolar disorder: G72, DISC1, NRG1, RGS4, NCAM1, DAO, GRM3, GRM4, GRIN2B, MLC1, SYNGR1, and SLC12A6. Of these, association with G72 may be most robust. However, G72 haplotypes and polymorphisms associated with bipolar disorder are not consistent with each other. The positional candidate approach showed an association between bipolar disorder and TRPM2 (21q22.3), GPR50 (Xq28), Citron (12q24), CHMP1.5 (18p11.2), GCHI (14q22-24), MLC1 (22q13), GABRA5 (15q11-q13), BCR (22q11), CUX2, FLJ32356 (12q23-q24), and NAPG (18p11). Studies that focused on mood disorder comorbid with somatic symptoms, suggested roles for the mitochondrial DNA (mtDNA) 3644 mutation and the POLG mutation. From gene expression analysis, PDLIM5, somatostatin, and the mtDNA 3243 mutation were found to be related to bipolar disorder. Whereas most previous positive findings were not supported by subsequent studies, DRD1 and IMPA2 have been implicated in follow-up studies. Several candidate genes in the circadian rhythm pathway, BmaL1, TIMELESS, and PERIOD3, are reported to be associated with bipolar disorder. Linkage studies show many new linkage loci. In depression, the previously reported positive finding of a gene-environmental interaction between HTTLPR (insertion/deletion polymorphism in the promoter of a serotonin transporter) and stress was not replicated. Although the role of the TPH2 mutation in depression had drawn attention previously, this has not been replicated either. Pharmacogenetic studies show a relationship between antidepressant response and HTR2A or FKBP5. New technologies for comprehensive genomic analysis have already been applied. HTTLPR and BDNF promoter polymorphisms are now found to be more complex than previously thought, and previous papers on these polymorphisms should be treated with caution. Finally, this report addresses some possible causes for the lack of replication in this field.

Chasing genes for mood disorders and schizophrenia in genetically isolated populations

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

Susceptibility genes for schizophrenia: Characterisation of mutant mouse models at the level of phenotypic behaviour

A wealth of evidence indicates that schizophrenia is heritable. However, the genetic mechanisms involved are poorly understood. Furthermore, it may be that genes conferring susceptibility interact with one another and with non-genetic factors to modulate risk status and/or the expression of symptoms. Genome-wide scanning and the mapping of several regions linked with risk for schizophrenia have led to the identification of several putative susceptibility genes including neuregulin-1 (NRG1), dysbindin (DTNBP1), regulator of G-protein signalling 4 (RGS4), catechol-o-methyltransferase (COMT), proline dehydrogenase (PRODH) and disrupted-in-schizophrenia 1 (DISC1). Genetic animal models involving targeted mutation via gene knockout or transgenesis have the potential to inform on the role of a given susceptibility gene on the development and behaviour of the whole organism and on whether disruption of gene function is associated with schizophrenia-related structural and functional deficits. This review focuses on data regarding the behavioural phenotype of mice mutant for schizophrenia susceptibility genes identified by positional candidate analysis and the study of chromosomal abnormalities. We also consider methodological issues that are likely to influence phenotypic effects, as well as the limitations associated with existing molecular techniques.

Genome-wide scan supports the existence of a susceptibility locus for schizophrenia and bipolar disorder on chromosome 15q26

Schizophrenia (SZ) and bipolar disorder (BPD) are two severe psychiatric diseases with a strong genetic component. In agreement with the 'continuum theory', which suggests an overlap between these disorders, the existence of genes that affect simultaneously susceptibility to SZ and BPD has been hypothesized. In this study we performed a 7.5 cM genome scan in a sample of 16 families affected by SZ and BPD, all originating from the same northeast Italian population. Using both parametric and non-parametric analyses we identified linkage peaks on four regions (1p, 1q, 4p and 15q), which were then subjected to a follow-up study with an increased marker density. The strongest linkage was obtained on chromosome 15q26 with a non-parametric linkage of 3.05 for marker D15S1014 (nominal P=0.00197). Interestingly, evidence for linkage with the same marker has been reported previously by an independent study performed on SZ and BPD families from Quebec. In this region, the putative susceptibility gene ST8SIA2 (also known as SIAT8B) was recently associated with SZ in a Japanese sample. However, our allele frequency analyses of the two single-nucleotide polymorphisms (SNPs) with putative functional outcome (rs3759916 and rs3759914) suggest that these polymorphisms are unlikely to be directly involved in SZ in our population. In conclusion, our results support the presence of a gene in 15q26 that influences the susceptibility to both SZ and BPD.

Candidate genes, pathways and mechanisms for alcoholism: an expanded convergent functional genomics approach

We describe a comprehensive translational approach for identifying candidate genes for alcoholism. The approach relies on the cross-matching of animal model brain gene expression data with human genetic linkage data, as well as human tissue data and biological roles data, an approach termed convergent functional genomics. An analysis of three animal model paradigms, based on inbred alcohol-preferring (iP) and alcohol-non-preferring (iNP) rats, and their response to treatments with alcohol, was used. A comprehensive analysis of microarray gene expression data from five key brain regions (frontal cortex, amygdala, caudate-putamen, nucleus accumbens and hippocampus) was carried out. The Bayesian-like integration of multiple independent lines of evidence, each by itself lacking sufficient discriminatory power, led to the identification of high probability candidate genes, pathways and mechanisms for alcoholism. These data reveal that alcohol has pleiotropic effects on multiple systems, which may explain the diverse neuropsychiatric and medical pathology in alcoholism. Some of the pathways identified suggest avenues for pharmacotherapy of alcoholism with existing agents, such as angiotensin-converting enzyme (ACE) inhibitors. Experiments we carried out in alcohol-preferring rats with an ACE inhibitor show a marked modulation of alcohol intake. Other pathways are new potential targets for drug development. The emergent overall picture is that physical and physiological robustness may permit alcohol-preferring individuals to withstand the aversive effects of alcohol. In conjunction with a higher reactivity to its rewarding effects, they may able to ingest enough of this nonspecific drug for a strong hedonic and addictive effect to occur.

Lack of genetic association between the phospholipase A2 gene and bipolar mood disorder in a European multicentre case-control study

The possible association between phospholipase A2 gene and bipolar mood disorder was examined in 557 bipolar patients and 725 controls (all personally interviewed), recruited from seven countries (Belgium, Bulgaria, Croatia, Germany, Greece, Italy, and UK). The frequencies of the eight alleles that were identified did not differ between patients and control individuals in the whole population, while the power to detect an association based on our sample was relatively high. Some differences were noted among the various ethnic groups, but no significant trends existed, suggesting that population stratification by country may not be responsible for a type II error. On the basis of these results, mutations of the phospholipase A2 gene, at least in the region close to the polymorphism examined between exons 1 and 2, are not involved in the pathogenesis of bipolar mood disorder.

Genetic linkage study for bipolar disorders on chromosomes 17 and 18 in families with a high expression of mental illness from the Balearic Islands

Genetically, bipolar disorder is a complex genetic illness, in which both genes and environmental factors play an important role in pathogenesis. Linkage studies have reported suggestive evidence for genomic regions, especially on chromosome 18, but in most cases they have been inconclusive. A total of 12 pedigrees, from the islands of Majorca and Minorca (Balearic Archipelago), with a high expression of mental illness, have been studied. A scan of 29 polymorphic short tandem repeat markers was performed, spanning chromosomes 17 and 18 for bipolar and other affective disorder susceptibility loci. Narrow (only bipolar I disorder) and broad (bipolar plus other affective disorders) diagnosis criteria were employed. The loci D18S63, D18S452, D18S53, D18S61, D18S1161 and D17S831 showed LOD score values of less than -2. Thus, the positive linkage found by other authors on the regions 18p11.2 and 18p11.3 has not been reproduced in the families studied. The data obtained in chromosome 17 suggested two possible regions that could contain a bipolar disorder susceptibility gene: 17q11 (D17S1857, D17S798) and especially 17q24-qter (D17S949, D17S928). The maximum significant linkage was to D17S949 (17q24), following a recessive mode of inheritance. We have also found a positive LOD score value for D18S478 marker located in the region 18q12.

Toward constructing an endophenotype strategy for bipolar disorders

Research aimed at elucidating the underlying neurobiology and genetics of bipolar disorder, and factors associated with treatment response, have been limited by a heterogeneous clinical phenotype and lack of knowledge about its underlying diathesis. We used a survey of clinical, epidemiological, neurobiological, and genetic studies to select and evaluate candidate endophenotypes for bipolar disorder. Numerous findings regarding brain function, brain structure, and response to pharmacological challenge in bipolar patients and their relatives deserve further investigation. Candidate brain function endophenotypes include attention deficits, deficits in verbal learning and memory, cognitive deficits after tryptophan depletion, circadian rhythm instability, and dysmodulation of motivation and reward. We selected reduced anterior cingulate volume and early-onset white matter abnormalities as candidate brain structure endophenotypes. Symptom provocation endophenotypes might be based on bipolar patients' sensitivity to sleep deprivation, psychostimulants, and cholinergic drugs. Phenotypic heterogeneity is a major impediment to the elucidation of the neurobiology and genetics of bipolar disorder. We present a strategy constructed to improve the phenotypic definition of bipolar disorder by elucidating candidate endophenotypes. Studies to evaluate candidate endophenotypes with respect to specificity, heritability, temporal stability, and prevalence in unaffected relatives are encouraged.

Critical appraisal of DNA microarrays in psychiatric genomics

Transcriptome profiling using DNA microarrays are data-driven approaches with the potential to uncover unanticipated relationships between gene expression alterations and psychiatric disorders. Studies to date have yielded both convergent and divergent findings. Differences may be explained, at least in part, by the use of a variety of microarray platforms and analytical approaches. Consistent findings across studies suggest, however, that important relationships may exist between altered gene expression and genetic susceptibility to psychiatric disorders. For example, GAD67, RGS4, DTNBP1, NRG1, and GABRAB2 show expression alterations in the postmortem brain of subjects with schizophrenia, and these genes have been also implicated as putative, heritable schizophrenia susceptibility genes. Thus, we propose that for some genes, altered expression in the postmortem human brain may have a dual origin: polymorphisms in the candidate genes themselves or upstream genetic-environmental factors that converge to alter their expression level. We hypothesize that certain gene products, which function as "molecular hubs," commonly show altered expression in psychiatric disorders and confer genetic susceptibility for one or more diseases. Microarray gene expression studies are ideally suited to reveal these putative disease-associated molecular hubs and to identify promising candidates for genetic association studies.

Thyroid hormones and retinoids: a possible link between genes and environment in schizophrenia

Phenotypic discordance for schizophrenia in monozygotic twins clearly indicates involvement of environmental factors as key determinants in disease development. Positive findings from genome scans, linkage and association studies apply in only a minority of those affected, while post-mortem brain investigations reveal altered expression of genes and proteins involved in numerous neurodevelopmental, metabolic and neurotransmitter pathways. Such altered expressions could result, on the one hand, from mutations in coding regions or polymorphisms in the promoter and regulatory regions in genes within those areas identified by gene searches or, on the other hand, from inadequate amounts of modulators, transporters and synthesizers of transcription factors necessary for regulation of the putative genes. Hormones and vitamins are such modulators. They could serve as bridges between genes and environment in schizophrenia. Multiple evidence supports the suggestion of retinoids and thyroid hormones as plausible actors in these roles. Both are not only essential for normal development of the central nervous system but also regulate the expression of many neurotransmitters, their synthesizing enzymes and receptors, and other genes in broader signaling transduction cascades affecting pathways that are altered in response to treatment. Functional and positional candidate genes include retinoic acid and thyroid hormone receptors, retinaldehyde dehydrogenases and deiodinases, which synthesize the powerful morphogens, retinoic acid and triiodothyronine, and the enzymes involved in their inactivation. This review highlights selective evidence supporting the retinoid and thyroid hormone hypotheses of schizophrenia.

Association between polymorphisms in the promoter region of the sialyltransferase 8B (SIAT8B) gene and schizophrenia

BACKGROUND

Sialyltransferase 8B (SIAT8B) and 8D (SIAT8D) are two polysialyltransferases that catalyze the transfer of polysialic acid (PSA) to the neural cell adhesion molecule 1 (NCAM1). PSA modification of NCAM1 plays an important role in neurodevelopment of the brain and disruption of this process is postulated as an etiologic factor in psychiatric disorders. Altered levels of the PSA-NCAM1 in the brain of schizophrenics have been reported, suggesting a role for this molecule in the disorder.

METHODS

We performed an association study of single nucleotide polymorphisms (SNPs) within SIAT8B and SIAT8D, using 188 schizophrenics and 156 age and gender matched controls. All genotypes were determined by polymerase chain reaction (PCR) amplification and direct sequencing.

RESULTS

Two polymorphisms, -1126T > C and -851T > C, located in the promoter region of SIAT8B showed nominally significant association with schizophrenia (allelic associations, p = .014 and p = .007, respectively), and haplotypes constructed from three additional SNPs located in the same linkage disequilibrium block were associated with schizophrenia. Furthermore an in vitro promoter assay revealed that a reporter construct containing a risk haplotype for SIAT8B had significantly higher transcriptional activity compared with one containing a protective haplotype (p = .021). In contrast, no significant association was observed between any variations in SIAT8D and schizophrenia.

CONCLUSIONS

The present study suggests that functional promoter SNPs of SIAT8B could confer a risk for schizophrenia in the Japanese population.

Schizophrenia and bipolar disorder: differences and overlaps

PURPOSE OF REVIEW

Following the recent progress mainly in the fields of genetics and neurobiology, the validity of the diagnostic distinction between schizophrenia and bipolar disorder is increasingly challenged.

RECENT FINDINGS

Evidence for basic neurobiological processes common for both disorders is expanding with regard to (a) susceptibility genes, (b) neurodevelopment (for example myelination), and (c) brain functions (for example sensory gating, visuospatial achievement). Recent epidemiological studies also stress communalities.

SUMMARY

The diagnostic split between schizophrenia and bipolar disorder is unable to define distinct etiological and/or pathophysiological entities.

Genome-wide linkage scan in a large bipolar disorder sample from the National Institute of Mental Health genetics initiative suggests putative loci for bipolar disorder, psychosis, suicide, and panic disorder

We conducted a 9-cM genome scan in a large bipolar pedigree sample from the National Institute of Mental Health genetics initiative (1060 individuals from 154 multiplex families). We performed parametric and nonparametric analyses using both standard diagnostic models and comorbid conditions thought to identify phenotypic subtypes: psychosis, suicidal behavior, and panic disorder. Our strongest linkage signals (genome-wide significance) were observed on chromosomes 10q25, 10p12, 16q24, 16p13, and 16p12 using standard diagnostic models, and on 6q25 (suicidal behavior), 7q21 (panic disorder) and 16p12 (psychosis) using phenotypic subtypes. Several other regions were suggestive of linkage, including 1p13 (psychosis), 1p21 (psychosis), 1q44, 2q24 (suicidal behavior), 2p25 (psychosis), 4p16 (psychosis, suicidal behavior), 5p15, 6p25 (psychosis), 8p22 (psychosis), 8q24, 10q21, 10q25 (suicidal behavior), 10p11 (psychosis), 13q32 and 19p13 (psychosis). Over half the implicated regions were identified using phenotypic subtypes. Several regions - 1p, 1q, 6q, 8p, 13q and 16p - have been previously reported to be linked to bipolar disorder. Our results suggest that dissection of the disease phenotype can enrich the harvest of linkage signals and expedite the search for susceptibility genes. This is the first large-scale linkage scan of bipolar disorder to analyze simultaneously bipolar disorder, psychosis, suicidal behavior, and panic disorder.

Carving chaos: genetics and the classification of mood and psychotic syndromes

Though Kraepelin's century-old division of major mental illness into mood disorder and schizophrenia remains in place, debate abounds over the most appropriate classification. Although these arguments previously rested solely on clinical grounds, they now are rooted in genetics and neurobiology. This article reviews evidence from the fields of genetic epidemiology, linkage, association, cytogenetics, and gene expression. Taken together, these data suggest some overlap in the genes that predispose to bipolar disorder and schizophrenia. One gene, DAOA (D-amino acid oxidase activator, also known as G72), has been repeatedly implicated as an overlap gene, while DISC1 and others may constitute additional shared susceptibility genes. Further, some evidence implicates syndromes of co-occurring mood and psychotic symptoms in association with the putative risk alleles in overlap genes. From a nosologic perspective, the existence of overlap genes, coupled with the genotype-phenotype correlations discovered to date, supports the reality of the much debated schizoaffective disorder. Potential non-overlap syndromes--such as nonpsychotic bipolar disorder or cyclothymic temperament, on the one hand, and negative symptoms or the deficit syndrome, on the other--could turn out to have their own unique genetic determinants. If genotypes are to be the anchor points of a clinically useful system of classification, they must ultimately be shown to inform prognosis, treatment, and prevention. No gene variants have yet met these tests in bipolar disorder or schizophrenia.

A neuronal nitric oxide synthase (NOS-I) haplotype associated with schizophrenia modifies prefrontal cortex function

Nitric oxide (NO) is a gaseous neurotransmitter thought to play important roles in several behavioral domains. On a neurobiological level, NO acts as the second messenger of the N-methyl-D-aspartate receptor and interacts with both the dopaminergic as well as the serotonergic system. Thus, NO is a promising candidate molecule in the pathogenesis of endogenous psychoses and a potential target in their treatment. Furthermore, the chromosomal locus of the gene for the NO-producing enzyme NOS-I, 12q24.2, represents a major linkage hot spot for schizophrenic and bipolar disorder. To investigate whether the gene encoding NOS-I (NOS1) conveys to the genetic risk for those diseases, five NOS1 polymorphisms as well as a NOS1 mini-haplotype, consisting of two functional polymorphisms located in the transcriptional control region of NOS1, were examined in 195 chronic schizophrenic, 72 bipolar-I patients and 286 controls. Single-marker association analysis showed that the exon 1c promoter polymorphism was linked to schizophrenia (SCZ), whereas synonymous coding region polymorphisms were not associated with disease. Long promoter alleles of the repeat polymorphism were associated with less severe psychopathology. Analysis of the mini-haplotype also revealed a significant association with SCZ. Mutational screening did not detect novel exonic polymorphisms in patients, suggesting that regulatory rather than coding variants convey the genetic risk on psychosis. Finally, promoter polymorphisms impacted on prefrontal functioning as assessed by neuropsychological testing and electrophysiological parameters elicited by a Go-Nogo paradigm in 48 patients (continuous performance test). Collectively these findings suggest that regulatory polymorphisms of NOS1 contribute to the genetic risk for SCZ, and modulate prefrontal brain functioning.

A two-stage linkage analysis of Chinese schizophrenia pedigrees in 10 target chromosomes

We performed a two-stage linkage scan involving 25 Chinese schizophrenia families, focusing on 10 target chromosomes which have already been the subject of considerable research. We initially genotyped 237 individuals with 186 markers, five candidate regions were then chosen for fine mapping and 49 additional markers were genotyped. In region 1q21-23, a maximum multipoint HLOD (HLOD=2.38) was observed between D1S484 and D1S2705, under the dominant model. In region 5q35, dominant HOLD of 2.36, 2.04, and 2.31 were found at marker D5S2030, D5S408, and D5S2006, respectively. Consistent multipoint results also supported linkage to this region under the same dominant model, with a highest HOLD of 2.47. Furthermore, single-point HLODs (HLOD=1.95 at D22S274, and HLOD=1.91 at D22S1157) were found in region 22q13, under the dominant model. Evidence from these three regions satisfied the criteria for suggestive linkage and should help in identifying schizophrenia susceptibility genes.

Shared Susceptibility Region On Chromosome 15 Between Autism And Catatonia

We have compiled significant linkage results from 20 genome scans for the autism syndrome disorder (ASD) and 2 for catatonia in schizophrenia (SZ). Localization of the markers has been updated across the studies using the same cytological (Genetic Location Database), physical (National Center for Biological Information), and genetic (Marshfield) maps. Eight autosomal chromosomes (1, 2, 3, 7, 9, 13, 15, and 17) showed significant linkages with ASD, and one with catatonia (15). Chromosome 15 was further characterized for SZ genome scans (N = 4) since catatonia was observed in SZ patients, for candidate genes for ASD and catatonia, and for the numerous chromosomal rearrangement and abnormalities associated to ASD. From these results, we observed that four potential susceptibility regions for ASD could be observed on chromosome 15 at 15q11-q13, 15q14-q21, 15q22-q23, and 15q26, respectively. All the four regions were shared between ASD and SZ, with 15q15-q21 being also shared with catatonia. Strong candidate genes, such as gamma-aminobutyric acid receptor B3, A5, and G3, have shown associations with ASD at 15q11-q13 susceptibility region where the majority of the chromosomal rearrangements are also found. On the other hand, negative association results were observed at 15q14-q21 susceptibility region for catatonia with the genes encoding the zinc transporter SLC30A4, the cholinergic receptor nicotinic alpha polypeptide 7, and the delta-like 4 Drosophila. Further, fine mapping and candidate gene analyses are needed to highlight potential common genes between ASD and catatonia for this chromosome.

Genetic Linkage and Association Analysis for Loneliness in Dutch Twin and Sibling Pairs Points to a Region on Chromosome 12q23–24

We obtained evidence from a large study in Dutch twins (N=8,387) and siblings (N=2,295) that variation in loneliness has a genetic component. The heritability estimate for loneliness, which was assessed as an ordinal trait, was 40% and did not differ between males and females. There were 682 sibling pairs with genotypic (around 400 microsatellite markers) data. We combined phenotypic and genotypic data to carry out a genome scan to localize QTLs for loneliness. One region on chromosome 12q23.3-24.3, showed near suggestive linkage. Genetic association tests within this region revealed significant association (p-value 0.009) with one of the alleles of marker D12S79 and with one of the alleles of neighbouring marker D12S395 (p-value 0.043). We review evidence for linkage in this region for psychiatric disorders and discuss our findings within this context.

Genetic investigation of chromosome 5q GABAA receptor subunit genes in schizophrenia

We previously performed a genome-wide linkage scan in Portuguese schizophrenia families that identified a risk locus on chromosome 5q31-q35. This finding was supported by meta-analysis of 20 other schizophrenia genome-wide scans that identified 5q23.2-q34 as the second most compelling susceptibility locus in the genome. In the present report, we took a two-stage candidate gene association approach to investigate a group of gamma-aminobutyric acid (GABA) A receptor subunit genes (GABRA1, GABRA6, GABRB2, GABRG2, and GABRP) within our linkage peak. These genes are plausible candidates based on prior evidence for GABA system involvement in schizophrenia. In the first stage, associations were detected in a Portuguese patient sample with single nucleotide polymorphisms (SNPs) and haplotypes in GABRA1 (P=0.00062-0.048), GABRP (P=0.0024-0.042), and GABRA6 (P=0.0065-0.0088). The GABRA1 and GABRP findings were replicated in the second stage in an independent German family-based sample (P=0.0015-0.043). Supportive evidence for association was also obtained for a previously reported GABRB2 risk haplotype. Exploratory analyses of the effects of associated GABRA1 haplotypes on transcript levels found altered expression of GABRA6 and coexpressed genes of GABRA1 and GABRB2. Comparison of transcript levels in schizophrenia patients and unaffected siblings found lower patient expression of GABRA6 and coexpressed genes of GABRA1. Interestingly, the GABRA1 coexpressed genes include synaptic and vesicle-associated genes previously found altered in schizophrenia prefrontal cortex. Taken together, these results support the involvement of the chromosome 5q GABAA receptor gene cluster in schizophrenia, and suggest that schizophrenia-associated haplotypes may alter expression of GABA-related genes.

Bipolar I disorder and schizophrenia: a 440-single-nucleotide polymorphism screen of 64 candidate genes among Ashkenazi Jewish case-parent trios

Bipolar, schizophrenia, and schizoaffective disorders are common, highly heritable psychiatric disorders, for which familial coaggregation, as well as epidemiological and genetic evidence, suggests overlapping etiologies. No definitive susceptibility genes have yet been identified for any of these disorders. Genetic heterogeneity, combined with phenotypic imprecision and poor marker coverage, has contributed to the difficulty in defining risk variants. We focused on families of Ashkenazi Jewish descent, to reduce genetic heterogeneity, and, as a precursor to genomewide association studies, we undertook a single-nucleotide polymorphism (SNP) genotyping screen of 64 candidate genes (440 SNPs) chosen on the basis of previous linkage or of association and/or biological relevance. We genotyped an average of 6.9 SNPs per gene, with an average density of 1 SNP per 11.9 kb in 323 bipolar I disorder and 274 schizophrenia or schizoaffective Ashkenazi case-parent trios. Using single-SNP and haplotype-based transmission/disequilibrium tests, we ranked genes on the basis of strength of association (P<.01). Six genes (DAO, GRM3, GRM4, GRIN2B, IL2RB, and TUBA8) met this criterion for bipolar I disorder; only DAO has been previously associated with bipolar disorder. Six genes (RGS4, SCA1, GRM4, DPYSL2, NOS1, and GRID1) met this criterion for schizophrenia or schizoaffective disorder; five replicate previous associations, and one, GRID1, shows a novel association with schizophrenia. In addition, six genes (DPYSL2, DTNBP1, G30/G72, GRID1, GRM4, and NOS1) showed overlapping suggestive evidence of association in both disorders. These results may help to prioritize candidate genes for future study from among the many suspected/proposed for schizophrenia and bipolar disorders. They provide further support for shared genetic susceptibility between these two disorders that involve glutamate-signaling pathways.

Theories of schizophrenia: a genetic-inflammatory-vascular synthesis

BACKGROUND

Schizophrenia, a relatively common psychiatric syndrome, affects virtually all brain functions yet has eluded explanation for more than 100 years. Whether by developmental and/or degenerative processes, abnormalities of neurons and their synaptic connections have been the recent focus of attention. However, our inability to fathom the pathophysiology of schizophrenia forces us to challenge our theoretical models and beliefs. A search for a more satisfying model to explain aspects of schizophrenia uncovers clues pointing to genetically mediated CNS microvascular inflammatory disease.

DISCUSSION

A vascular component to a theory of schizophrenia posits that the physiologic abnormalities leading to illness involve disruption of the exquisitely precise regulation of the delivery of energy and oxygen required for normal brain function. The theory further proposes that abnormalities of CNS metabolism arise because genetically modulated inflammatory reactions damage the microvascular system of the brain in reaction to environmental agents, including infections, hypoxia, and physical trauma. Damage may accumulate with repeated exposure to triggering agents resulting in exacerbation and deterioration, or healing with their removal. There are clear examples of genetic polymorphisms in inflammatory regulators leading to exaggerated inflammatory responses. There is also ample evidence that inflammatory vascular disease of the brain can lead to psychosis, often waxing and waning, and exhibiting a fluctuating course, as seen in schizophrenia. Disturbances of CNS blood flow have repeatedly been observed in people with schizophrenia using old and new technologies. To account for the myriad of behavioral and other curious findings in schizophrenia such as minor physical anomalies, or reported decreased rates of rheumatoid arthritis and highly visible nail fold capillaries, we would have to evoke a process that is systemic such as the vascular and immune/inflammatory systems.

SUMMARY

A vascular-inflammatory theory of schizophrenia brings together environmental and genetic factors in a way that can explain the diversity of symptoms and outcomes observed. If these ideas are confirmed, they would lead in new directions for treatments or preventions by avoiding inducers of inflammation or by way of inflammatory modulating agents, thus preventing exaggerated inflammation and consequent triggering of a psychotic episode in genetically predisposed persons.