Search

OBJECTIVES: Susceptibility to heroin dependence is strongly influenced by genetic factors with heritability estimates as high as 0.7. A number of genes, as well as environmental factors, are likely to contribute to its etiology. Not all individuals who have ever tried heroin at some stage during their lifetime become dependent on heroin. It has been suggested that genetic factors might be more important in the transition stage to heroin dependence rather than in environmental exposures and experimenting with heroin. As the features of substance dependence and memory formation have been found to be strikingly similar, we have focused on a key enzyme involved in long-term potentiation and synaptic plasticity, namely the calcium-dependent/calmodulin-dependent protein kinase IIα (CAMKIIa). We hypothesized, that CamK2A genetic variation may play a role in the transition from occasional to regular heroin use. MATERIALS AND METHODS: Using quantitative trait association analysis, we addressed this hypothesis by correlating the self-reported time interval between occasional and regular heroin use with the frequency of 12 single nucleotide polymorphisms located within the genomic region of the CamK2A gene. A sample of 570 Caucasian patients was available for analysis. RESULTS: Single marker association analysis (rs10066581, P=0.007), as well as haplotype analysis (global P=0.005), suggested an association with the quantitative trait 'time interval from occasional to regular heroin use CONCLUSION: Our results propose that genetic variants located in the genomic region of the CamK2A gene may be involved in transition time from occasional to regular heroin use. Refereed/Peer-reviewed

The influence of genetic factors in the development of schizophrenia has been convincingly demonstrated by family, twin, and adoption studies. The statistical construct of heritability is generally used for estimating the liability due to genetic factors. Heritability estimates for schizophrenia are reported to be between 60 and 80 %. Due to the technical achievements in whole genome-wide association studies, dissection of the underlying genetic factors was intensified recently, resulting in the conclusion that schizophrenia is essentially a polygenic, complex disorder. Most likely more than 100 genes, each with small effect size, contribute to disease risk. A most recent multi-stage genome-wide association study (Ripke et al. in Nat Genet 2013) identified 22 risk loci and estimated that 8,300 independent single-nucleotide polymorphisms contributed to the risk accounting collectively for 32 % in liability. In addition to this polygenic, complex inheritance, there is also strong indication that in some patients a deletion or insertion of a larger chromosomal region [so-called copy number variation (CNV)] might play a crucial role in pathogenesis. This could be specifically important in sporadic cases with schizophrenia, since a higher frequency of de novo mutations has been associated with these CNVs. Further studies, combining much larger sample sizes as well as application of newer technology, such as deep sequencing technologies will be necessary in order to obtain a more comprehensive understanding of the genetic foundations of schizophrenia.

Background: Association of rs1344706 in the ZNF804A gene (2q32.1) with schizophrenia was first reported in a genome wide scan conducted in a sample of 479 cases and replicated in 6666 cases. Subsequently, evidence by replication was obtained in several samples with European- and Asian ancestral background. Methods: We report ascertainment, clinical characterization, quality control, and determination of ancestral background of a case control sample from Indonesia, comprising 1067 cases and 1111 ancestry matched controls. Genotyping was performed using a fluorescence-based allelic discrimination assay (TaqMan SNP genotyping assay) and a newly designed PCR-RFLP assay for confirmation of rs1344706 genotypes. Results: We confirmed association of the T-allele of rs1344706 with schizophrenia in a newly ascertained sample from Indonesia with Southeast Asian ancestral background (P = 0.019, OR = 1.155, 95%, CI 1.025-1.301). In addition, we studied several SNPs in the vicinity of rs1344706, for which nominally significant results had been reported. None of the association P values of the additional SNPs exceeded that of rs1344706. Conclusion: We provide additional evidence for association of the ZNF804A gene with schizophrenia. We conclude that rs1344706 or a yet unknown polymorphism in linkage disequilibrium is also involved in conferring susceptibility to schizophrenia in samples with different (Asian) ancestral backgrounds. Refereed/Peer-reviewed

Decades of research into the etiology of schizophrenia on a phenotypic level, i.e. studies of neuroanatomy, neuropathology, neurophysiology and other areas such as immunology have yielded only fragmentary results. A contribution of genetic factors, has been consistently shown, however, beginning with E. Kraepelin's pioneering studies at the turn of the century. Evidence has accumulated from family-, twin-, and adoption studies. Identical twins have a 48% risk of developing schizophrenia if one of them is affected. In contrast, a 17 % risk is reported for nonidentical twins. These rates are similar to other complex genetic disorders such as diabetes, hypertension and asthma. Advances in the genetic analysis of complex traits as well as progress in the Human Genome Project should provide a basis for uncovering the molecular causes of schizophrenic disorders and for investigating the neuropathology of this individually and socially devastating neuropsychiatrie disorder. There is no doubt, that discovery of the genetic variation associated with the illness would help in identifying specific targets for development of more effective, targeted treatments.

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.

PURPOSE OF REVIEW We will give an overview of more recent data concerning previously implicated candidate genes for schizophrenia. This includes functional data when available. Furthermore, studies on copy number repeats and their possible implications in schizophrenia will be described. RECENT FINDINGS Within the past year, schizophrenia genetics has focused on a more detailed investigation of previously implicated candidate genes. In addition, investigation of copy number variations has led to the identification of rare structural DNA variants that might play a major role in some cases of schizophrenia. SUMMARY There is emerging evidence that some cases of schizophrenia might be due to rare genetic structural variation, though the majority of cases should be due to a cumulative effect of common variations in multiple genes, which in combination with environmental stressors may lead to the development of schizophrenia.

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

Linkage studies in schizophrenia have identified a candidate region on chromosome 10p14-11 as reported for several independent samples. We investigated association of DNA sequence variants in a plausible candidate gene located in this region, the gene for phosphatidylinositol-4-phosphate 5-kinase IIalpha (PIP5K2A), in a sample of 65 sib-pair families for which linkage had been reported. Evidence for association was obtained for 15 polymorphisms spanning 73.6 kb in the genomic region of the gene between intron 4 and the 3' untranslated region, a region with high degree of linkage disequilibrium. Single nucleotide polymorphism (SNP) rs10828317 located in exon 7 and causing a non-synonymous amino-acid exchange (asparagine/serine) produced a P-value of 0.001 (experiment-wide significance level 0.00275) for over-transmission of the major allele coding for serine, analysed by transmission disequilibrium test using FAMHAP. Association of this SNP with schizophrenia has been also described in a sample of 273 Dutch schizophrenic patients and 580 controls (P=0.0004). PIP5K2A is involved in the biosynthesis of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2), one of the key metabolic crossroads in phosphoinositide signalling. PI(4,5)P2 plays a role in membrane transduction of neurotransmitter signals as well as in intracellular signalling, pathways that may be impaired 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.

The brain synaptic vesicular amine transporter SLCA18A2 is a key component for the uptake of monoamines like dopamine or serotonin into vesicles. We have analyzed seven DNA polymorphisms located in the genomic region of SLC18A2 for association with alcohol- and nicotine dependence, using a family-based design. Our sample comprised 131 families with alcohol-dependent offspring and 96 families with at least one nicotine-dependent offspring. For the alcohol-dependent sample, we found statistical significant association for two single markers (rs363387, P=0.03; rs363333, P=0.0066) as well as for several haplotypes (minimal P=0.0038). When the sample with alcohol dependence was stratified according to gender, we observed increased association for the male subgroup (rs363387, P=0.0011). None of the markers showed association in the sample of families with nicotine dependence. However, analysis of a combined sample of alcohol and nicotine-dependent families resulted in single markers as well as several haplotypes showing statistical significant association with substance dependence (minimal P=0.0044). We conclude that DNA polymorphisms located in SLC18A2 might contribute to the development of substance dependence.

Catechol-O-methyltransferase (COMT) has been implicated in schizophrenia by its function through its roles in monoamine neurotransmitter metabolism and its impact on prefrontal cognition, and also by its position through linkage scans and a strong cytogenetic association. Further support comes from association studies, especially family-based ones examining the COMT variant, Val 1 0 8 / 1 5 8 Met. We have studied eight markers spanning COMT and including portions of the two immediately adjacent genes, thioredoxin reductase 2 and armadillo repeat deleted in velocardiofacial syndrome (ARVCF), using association testing in 136 schizophrenia families. We found nominal evidence for association of illness to rs165849 (P=0.051) in ARVCF, and a stronger signal (global P=0.0019-0.0036) from three-marker haplotypes spanning the 3' portions of COMT and ARVCF, including Val 1 0 8 / 1 5 8 Met with Val 1 0 8 / 1 5 8 being the overtransmitted allele, consistent with previous studies. We also find Val 1 0 8 / 1 5 8 Met to be in linkage disequilibrium with the markers in ARVCF. These findings support previous association signals of schizophrenia to COMT markers, and suggest that ARVCF might contribute to this signal. ARVCF, a member of the catenin family, besides being a positional candidate, is also one due to its function, that is, its potential role in neurodevelopment, which is implicated in schizophrenia pathogenesis by several lines of evidence.

Background : Tumor necrosis factor alpha (TNFα), a cytokine involved in inflammatory processes, has been implicated in the pathophysiology of schizophrenia. The chromosomal location in the major histocompatibility complex (MHC) region on 6p21.1–21.3, a region with evidence for linkage, suggests a role in susceptibility to schizophrenia. Association of the minor (A) allele of the -G308A TNFα gene polymorphism with schizophrenia has been reported [Mol. Psychiatry 6 (2001) 79]. Methods : Association of the -G308A TNFα gene and the lymphotoxin alpha (LTα)+A252G gene polymorphisms with schizophrenia was studied in 79 sib pair families with linkage in the MHC region and in 128 trio families using the transmission disequilibrium test (TDT). Results : Weak association of the common G allele was detected for TNFα -G308A in both samples independently with borderline significance in the sib pair families (0.064) and with a nominally significant value of P =0.022 in the trio families. Combining both samples produced P =0.003, while LTα+A252G, located approximately 2–3 kb distally, revealed P =0.03 and the two locus haplotype yielded a P value of 0.001. Conclusion : Our data suggests association of the common G allele of the -G308A TNFα gene polymorphism with schizophrenia in a sample of 207 families. However, linkage disequilibrium with a different allele of the TNFα gene or another gene in the MHC region cannot be excluded.

Objective. –In a modified case–control association study we tested the assumption that two polymorphisms (A118G in exon 1 and IVS2+31 in intron 2) of the human μ-opioid receptor gene (OPRM1) confer susceptibility to opioid dependence.Methods. –In contrast to classical case–control studies both groups, opioid dependent cases and non-opioid dependent controls were recruited from individuals who have had access to drugs including opioids and who had been sentenced for violation of the “Dangerous Drugs Act” in Germany.Results. –For the two allelic variants of OPRM1 under study we did not find evidence for association with opioid dependence.Conclusions. –Despite absence of association we think that this recruitment approach introduced here, is useful since it putatively offers a more adequate matching for case–control association studies of opioid dependent individuals.

The serotonergic (5-HT) system has been implicated in the etiopathogenesis of psychoses. Since the 5-HT transporter plays an important role in regulation of 5-HT transmission, its gene can be considered as a candidate for vulnerability to psychiatric disorders. Two polymorphic sites of the 5-HT transporter gene-5-HTTLPR, a VNTR in the 5' regulatory region, and a VNTR in the second intron-were studied in a sample of 61 families with schizophrenia for transmission disequilibrium. Each family contained at least two siblings affected with schizophrenia or schizoaffective disorder (mainly schizophrenic). One hundred and thirty-nine affected offspring with parental information for genotyping, were available for analysis. No preferential transmission of either short or long alleles of the promoter polymorphism was observed. However, a transmission distortion was detected for alleles of the intronic VNTR polymorphism (chi2TDT max =14.33; P = 0.0002; corrected P value = 0.0003) resulting in more frequent than expected transmission of the 12 repeat allele. This finding adds additional evidence to the idea that the serotonergic system may be involved in development of psychoses. Molecular Psychiatry (2000) 5, 91-95.

Schizophrenia and affective disorders are relatively common neuropsychiatric diseases with a complex genetic etiology. A multigenic inheritance with variable influence of unknown environmental factors may be involved. Family studies have demonstrated the existence of both phenotypes in the same kindreds, and in certain cases, a transition from one phenotype to another occurs. In addition, intermediate phenotypes such as schizoaffective disorders are found in families with schizophrenia and affective illness. Recent genome and chromosomal scans appear to support these epidemiologic data, since susceptibility regions for both schizophrenia and affective disorders have been found to overlap, on chromosomes 10p13-p12, 13q32, 18p and 22q11-q13. These studies were performed in independently ascertained family samples with index patients afflicted either with schizophrenia or bipolar disorder. Taken together, these findings imply shared loci for schizophrenia and affective disorders among those required for the full expression of the phenotype. Identification and molecular characterization of the genetic components conferring risk to both disorders would impact positively on diagnosis, prevention, and treatment.

A sex chromosome locus for psychosis has been considered on the basis of some sex differences in genetic risk and expression of illness, and an association with X-chromosome anomalies. Previous molecular genetic studies produced weak evidence for linkage of schizophrenia to the proximal short arm of the X-chromosome, while some other regions were not ruled out. Here we report an attempt to expand the Xp findings in: (i) a multicenter collaboration focusing on 92 families with a maternal pattern of inheritance (Study I), and (ii) an independent sample of 34 families unselected for parental mode of transmission (Study II). In the multicenter study, a parametric analysis resulted in positive lod scores (highest of 1.97 for dominant and 1.19 for recessive inheritance at a theta of 0.20) for locus DXS7, with scores below 0.50 for other markers in this region (MAOB, DXS228, and ARAF1). Significant allele sharing among affected sibling pairs was present at DXS7. In the second study, positive lod scores were observed at MAOB (highest of 2.16 at a theta of 0.05 for dominant and 1.64 at a theta of 0.00 for recessive models) and ALAS2 (the highest of 1.36 at a theta of 0.05 for a recessive model), with significant allele sharing (P = 0.003 and 0.01, respectively) at these two loci. These five markers are mapped within a small region of Xp11. Thus, although substantial regions of the X-chromosome have been investigated without evidence for linkage being found, a locus predisposing to schizophrenia in the proximal short arm of the X-chromosome is not excluded.

Suggestive evidence for a potential susceptibility locus for schizophrenia at 5q31 was obtained in two family samples. Sample I consisted of 14 families with schizophrenia and revealed for the marker IL9 a lod score of 1.8 by two point lod score analysis. Sample II comprised 44 families including four from sample I and was ascertained in order to employ affected sib-pair analysis by identity by descent. A lod score of 1.8 around the marker D5S399 was obtained by multipoint analysis. The lod score remained positive, but decreased to 1.27 when the four families from sample I were excluded in order to use sample II as a statistically independent replication sample. We propose a susceptibility locus for schizophrenia with probably minor contribution in the pedigrees under investigation.

Several lines of evidence suggest an involvement of adenosine A2a receptor (A2aAR) mediated adenosinergic neuromodulation in the etiopathogenesis of schizophrenia. We therefore performed a systematic mutation scan of the complete coding region of the human A2aAR gene in a sample of 42 schizophrenic patients. We detected one rare naturally occurring receptor variant (Gly-340-Ser) and two silent mutations (405C/T and 1083C/T). To our knowledge the Gly-340-Ser substitution is the first naturally occurring molecular variant of the A2aAR identified. Determining the frequency of the three variants in 42 unrelated healthy controls, we observed a significant trend towards an overrepresentation of the 1083T variant in patients when compared to controls (p = 0.041). This trend was followed up in a large independent replication sample. However, we were not able to confirm the original trend in the second sample (p = 0.367). The Ser-340 variant was found in a single schizophrenic individual. Investigation of the patient's family revealed independent segregation between the Ser-340 variant and psychiatric illness. Our data suggest that genetically determined structural variation of the A2aAR does not play a major role in the development of schizophrenia.

OBJECTIVE: An association between the 5-HTTLPR short variant polymorphism in the promoter region of the serotonin transporter gene and risk for alcohol dependence has been reported from case-control studies that are, however, prone to chance findings related to artifacts of population structure. The authors sought additional evidence for this association from a family-based study. METHOD: Ninety-two alcohol-dependent probands and their parents were tested for nonrandom transmission of alleles from heterozygous parents to affected probands. RESULTS: Preferential transmission of the short allele was found (65 of 102 transmissions from heterozygous parents). CONCLUSIONS: The results suggest allelic association between a variant in the promoter region of the serotonin transporter gene and the risk for alcohol dependence. However, it remains to be seen whether the functional properties of this variant are directly responsible for the increased risk to alcohol dependence.

artículo (arbitrado) -- Universidad de Costa Rica. Centro de Investigación en Biología Celular y Molecular, 2008. A genome scan meta analysis (GSMA) was carried out on 32 independent genome-wide linkage scan analyses that included 3255 pedigrees with 7413 genotyped cases affected with schizophrenia (SCZ) or related disorders. The primary GSMA divided the autosomes into 120 bins, rank-ordered the bins within each study according to the most positive linkage result in each bin, summed these ranks (weighted for study size) for each bin across studies and determined the empirical probability of a given summed rank (PSR) by simulation. Suggestive evidence for linkage was observed in two single bins, on chromosomes 5q (142–168 Mb) and 2q (103–134 Mb). Genome-wide evidence for linkage was detected on chromosome 2q (119– 152 Mb) when bin boundaries were shifted to the middle of the previous bins. The primary analysis met empirical criteria for ‘aggregate’ genome-wide significance, indicating that some or all of 10 bins are likely to contain loci linked to SCZ, including regions of chromosomes 1, 2q, 3q, 4q, 5q, 8p and 10q. In a secondary analysis of 22 studies of European-ancestry samples, suggestive evidence for linkage was observed on chromosome 8p (16–33 Mb). Although the newer genome-wide association methodology has greater power to detect weak associations to single common DNA sequence variants, linkage analysis can detect diverse genetic effects that segregate in families, including multiple rare variants within one locus or several weakly associated loci in the same region. Therefore, the regions supported by this meta-analysis deserve close attention in future studies. The work reported here was supported by: Medical Research Council (UK) Grants G0400960 (CML) and G9309834 (MO); National Institute of Mental Health Grants 7R01MH062276 (to DFL [Aust/US], CL [France/La Re´union], MO [Cardiff] and DW [Bonn]), 5R01MH068922 (to PG [ENH]), 5R01MH068921 (to AEP [Johns Hopkins]), 5R01MH068881 (to BR [VCU/Ireland]), MH-41953 (to KSK [VCU/Ireland]); MH63356 and MH80299 (to WB [Palau]); MH58586 (to JMS [Aust/US]); MH 56242 (to VLM [US/Sweden]), MH61399 (EMW, MK [Kosrae, South Africa]), NIMH Grant MH062440, Canadian Institutes of Health Research Grants MOP-53216 and MOP- 12155, a National Alliance for Research on Schizophrenia and Depression Distinguished Investigator Award and Canada Research Chair in Schizophrenia Genetics (LMB, ASB [Canada]); Australian National Health and Medical Research Council Grants 910234, 941087, and 971095 (to BJM [Aust/US]), MRC project Grant G880473N, The European Science Foundation, SANE, the Iceland Department of Health, the General Hospital Reykjavik, the Joseph Levy Charitable Foundation, the Wellcome Trust Grant 055379, The Priory Hospital, the Neuroscience Research Charitable Trust, the University of Iceland and the Icelandic Science Council (HMDG [UCL]); Warner-Lambert, Parke-Davis Pharmaceuticals Company and NIMH Grant R01- MH44245 (LEL [US/International]); the Deutsche Forschungsgemeinschaft (HWM [Kiel]; MA WM, SGS, DBW [Indonesia]); the German Israeli Foundation for Scientific Research (BL; DBW); Mammalian Genotyping Service HV48141 (DBW [Indonesia]; CREST of JST (Japan Science and Technology Agency) TA [Japan]; Pfizer, Inc. and the SANE Foundation (LEL [Costa Rica]); the Israel Science Foundation, US. Israel Binational Science Foundation, the National Alliance for Research on Schizophrenia and Depression, and the Harry Stern Family Foundation (BL and YK [Israel]); the VA Merit Review Program (AF); recruitment of the NIMH Genetics Initiative sample was supported by NIMH Grants 5 UO1MH46318, UO1MH46289 and UO1MH46276; the Taiwan Schizophrenia Linkage Study was supported by NIMH Grant 1R01 MH59624-01 and Grant NHRI-90-8825PP, NHRI -EX91,92-9113PP from the National Health Research Institute, Taiwan, and support from the Genomic Medicine Research Program of Psychiatric Disorders, National Taiwan University Hospital; the VA Linkage Study was supported by funds from the Department of Veterans Affairs Cooperative Studies Program; the US/Mexico/Central America study was supported by a collaborative NIMH grant (‘Genetics of Schizophrenia in Latino Populations’) (MH60881 and MH60875) to ME [University of Texas Health Science Center at San Antonio], R Mendoza [University of California at Los Angeles-Harbor], HR [University of Costa Rica, San Jose, Costa Rica], A Ontiveros [Instituto de Informacion de Investigacion en Salud Mental, Monterrey, Mexico], HN [Medical and Family Research Group, Carracci SC, Mexico City, Mexico], and R Munoz [Family Health Centers of San Diego, CA]. UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biología Celular y Molecular (CIBCM)

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. Molecular Psychiatry (2009) 14, 786-795; doi:10.1038/mp.2009.11; published online 17 February 2009

Single nucleotide polymorphisms (SNPs) in the trace amine associated receptor trace amine associated receptor 6 gene and 3' flanking region have been shown to be associated with schizophrenia. To replicate these findings, we conducted a family-based association study with the five most significant SNPs in our sample of 79 sib-pair families (56/79 sib-pair families showed linkage to 6q23) and 125 triads. No evidence for association was obtained between these SNPs and schizophrenia in our sample, even when limited to the 56 linked families (P>0.2). We conclude that trace amine associated receptor 6 is not important for the development of schizophrenia in our family samples.

Variation in incidence of schizophrenia between populations with different ethnical background may reflect population specific differences in nature and composition of genetic and environmental factors. In order to investigate whether there are population specific susceptibility genes for schizophrenia, we collected in Indonesia families with two or more affected siblings and, as far as available, parents and unaffected siblings, suitable for genetic linkage- and association studies. After checking extensively for incompatibilities with Mendelian inheritance as well as for errors in sampling, we used 124 families from the sample of 152 originally ascertained families for linkage analysis. Genotyping was performed at the NHLBI Mammalian Genotyping Service at Marshfield Research Organisation using the Screening Set 16, which comprises 402 Short Tandem Repeat Polymorphisms (STRPs). The genotypes of 540 individuals including 267 affected with schizophrenia were used for analysis. Multipoint sib-pair linkage analysis was carried out by estimation of--allele sharing derived--maximum likelihood LOD scores (MLS) in 154 sib-pair combinations. We obtained a genome-wide significant MLS of 3.76 on chromosome 3p26.2-25.3. Genome-wide significance was estimated by performing 10,000 simulated genomescans. Additional loci were detected on 1p12, which produced suggestive evidence for linkage (MLS = 2.35), as well as on 5q14.1 (MLS = 1.56), 5q33.3 (MLS = 1.11), and 10q (MLS = 1.17), where linkage had been reported previously. In conclusion, our study detected a region with genome-wide significant linkage, which will serve as starting point for identification of schizophrenia susceptibility genes in the Indonesian population.

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. (C) 2008 Wiley-Liss, Inc.

OBJECTIVES Recent studies investigating the association of DNA variants in the metabotropic glutamate receptor gene (GRM3) with schizophrenia susceptibility revealed conflicting results. In this study, we focused on DNA sequence variants, for which association was reported and attempted to replicate association with schizophrenia or with cognitive deficits known to be present in patients with schizophrenia. METHODS A sample of 242 families with affected offspring and five single nucleotide markers located in the genomic region of GRM3 has been used to replicate association with schizophrenia. In addition, results of neuropsychological tests, trail making test B and the Stroop color-naming task were available for a subgroup of these families (N=88) and an independent sample of 148 patients with schizophrenia. Correlation of these measurements with genotypic data was performed using analysis of variance. RESULTS No statistical evidence for association with schizophrenia or correlation with cognitive deficits as measured by the trail making test B or the Stroop color-naming task and the five DNA sequence variants could be detected. A trend towards association with schizophrenia was revealed for a single marker (rs2237562, P=0.056) and for 2-marker and 3-marker haplotypes containing this variant. CONCLUSIONS Our study of DNA sequence variants in the GRM3 gene did not provide further support for genetic association with schizophrenia or for correlation with cognitive deficits.

The association of the tumor necrosis factor alpha (TNFalpha) -G308A promoter polymorphism with schizophrenia has complemented clinical findings of increased levels of the TNFalpha cytokine in schizophrenic patients, with some support for a functional consequence of the variant. Our previous studies of genetic causes in schizophrenia supported findings of linkage to the major histocompatibility complex (MHC) region where the TNFalpha gene is located as well as association with the -G308A promoter polymorphism. While the common G-allele shows association in our sample, association with the A-allele has been reported by other groups. This suggests linkage disequilibrium (LD) rather than direct involvement in the disorder. In order to define LD of DNA variants with the disorder in this area, we analyzed 36 SNPs in a 165-kb region around this polymorphism. We detected nominally significant associations (P < 0.05) of three markers (including the -G308A promoter polymorphism) and multiple haplotypes with schizophrenia in our sample of 204 families (79 sib-pairs and 125 trios). The association is largely restricted to a 30 kb high LD region/block and should assist in the identification of a schizophrenia susceptibility gene within the block or elsewhere in the MHC.

Evidence from epidemiological studies and segregation analysis suggests oligo- or polygenic inheritance in schizophrenia. Since model independent methods are thought to be most appropriate for linkage analysis in complex disorders, we performed a genome-wide autosomal screen in 71 families from Germany and Israel containing 86 independent affected sib-pairs with parental genotype information for statistical analysis strictly identity by descent. We genotyped 305 individuals with 463 markers at an average distance of approximately 10 cM genome-wide, and 1–2 cM in candidate regions (5q, 6p, q, 8p, 10p, 18p, 22q). The highest multipoint LOD scores (ASPEX) were obtained on 6p (D6S260, LOD = 2.0; D6S274, LOD = 2.2, MHC region, LOD = 2.15) and on 10p (D10S1714, LOD = 2.1), followed by 5q (D5S2066, LOD = 1.36), 6q (D6S271, LOD = 1.12; D6S1613, LOD = 1.11), 1q (D1S2675, LOD = 1.04), and 18p (broad disease model: D18S1116, LOD = 1.0). One hundred and thirty-three additional family members were available for some of the families (extended families) and were genotyped for these regions. GENEHUNTER produced a maximum NPL of 3.3 (P = 0.001) for the MHC region and NPL of 3.13 (P = 0.0015) for the region on 10p. There is support for these regions by independent groups. In genome-wide TDT analysis (sTDT, implemented in ASPEX), no marker passed the significance level of 0.0001 given by multiple testing, but nominal significance values for D10S211 (P = 0.03) and for GOLF (P = 0.0032) support further the linkage results on 10p and 18p. Our survey of 22 chromosomes identified candidate regions which should be useful to screen for schizophrenia susceptibility genes.

Schizophrenia is a genetically influenced disease with a broad and heterogeneous phenotype transmitted in families. Of particular interest is the familial-genetic relationship between schizophrenia and affective disorders. Taking advantage of refined epidemiological methods, the dichotomy between both groups of disorders is not less consistently found than expected. Recently, linkage studies identified multiple candidate regions for susceptibility genes for each of both disorders. Several of these candidate regions for schizophrenia are overlapping with candidate regions for bipolar disorder. Thus, the hypothesis of an etiological dichotomy of schizophrenia and affective disorders faces a new challenge.

A possible association between the small conductance calcium-regulated potassium channel gene, hSKCa3, and schizophrenia has recently been described by Chandy et al1 using a case-control design with patients with schizophrenia (n = 141) and matched controls (n = 158). The gene may be considered as an excellent candidate gene for psychiatric disorders, since it plays a role in modulating neuronal firing patterns by regulating the slow component of afterhyperpolarisation. In addition, the gene contains a highly polymorphic trinucleotide sequence (CAG) within exon 1, which encodes a polyglutamine stretch. The possible contribution of unstable trinucleotide repeats to the development of psychiatric disorders has previously been discussed.2–4 Chandy et al1 reported an over-representation of alleles with higher repeat number in schizophrenics as compared to controls (P = 0.0035). In an attempt to replicate these findings, we have performed a family-based study with 193 offspring/parent combinations using a sample of 49 multiplex families (two or more affected siblings with parents) and a second sample of 83 simplex families (one affected offspring with parents). No evidence for the association of longer repeats with schizophrenia was obtained when each sample was tested separately or when both samples were combined and tested for transmission disequilibrium.

Schizophrenia is assumed to be a complex multifactorial disorder with several environmental and genetic factors contributing to its development. The disorder is unique in terms of the expression of symptoms, which are related to the exclusive ability of humans to think and communicate these thoughts to the members of their species. Therefore, no potent animal-, or cell models are available in order to validate existing hypotheses. In contrast to other disorders with similar complex etiology, but availability of model organisms, i.e. diabetes type II, age-related macular degeneration or Alzheimer’s disease, pathogenesis of schizophrenia is still unknown, despite a considerable amount of research. In this issue, Tandon et al highlight and summarize the main achievements and possible conclusions of the research efforts in the past decades. The review indicates that research targeting the etiology of schizophrenia is clearly innovative and unique, and the techniques used in order to achieve the aim of dissecting the causes of schizophrenia undoubtedly appropriate. However, the field is suffering from confounding issues related to phenotype definition as well as such related to verification or falsification of findings which are either overseen or simply ignored. Without solving these

We previously reported genome-wide significant linkage to chromosome 3p in a sib-pair family sample from Indonesia. A promising candidate gene within the linked region is the metabotropic glutamate receptor subtype 7 (GRM7), involved in glutamatergic neurotransmission. We genotyped 18 single nucleotide polymorphisms in GRM7 in the sample of 124 Indonesian sib-pair families that had provided the signifi- cant linkage finding. Transmission disequilibrium analysis revealed nominally significant transmission distortion of rs17031835 in intron 1 of GRM7 (p=0.004, before correction for multiple testing), along with haplotypes containing rs17031835. No other single marker was found to be significantly associated with schizophrenia in our sample. The results from our study provide support for the idea that glutamatergic neurotransmission and specifically the GRM7 gene might be relevant to the development of schizo- phrenia. Further studies supporting this finding are warranted.

Linkage disequilibrium and haplotype structure of five GABA A receptor subunit genes investigated for association with schizophrenia