Clinical and genetic correlates of severity in schizophrenia in India: an ordinal logistic regression approach.

Genetic association studies of schizophrenia typically utilize diagnostic status as the trait of interest. Among Indian schizophrenia (SZ) participants, we evaluated genetic associations (selected single nucleotide polymorphisms (SNPs) associated with SZ) with selected indices of severity and symptom pattern. Ordinal logistic regression enabled us to analyze variables with multiple categories as outcome variables, while incorporating key demographic variables; this form of analysis may be useful in future genetic association studies. No significant associations were detected following corrections for multiple comparisons.

Novel, replicated associations between dopamine D3 receptor gene polymorphisms and schizophrenia in two independent samples.

BACKGROUND: Meta-analyses have suggested an association between schizophrenia (SZ) and a coding polymorphism (rs6280/Ser9Gly) at the dopamine D3 receptor gene (DRD3), but results have been inconsistent. Because most studies have evaluated only rs6280, the inconsistencies might reflect associations with other variants. METHODS: We analyzed polymorphisms spanning 109kb in two independent samples (United States: 13 single nucleotide polymorphisms (SNPs), 331 cases, 151 trios, 274 control subjects; India: 11 SNPs, 141 trios). RESULTS: In the U.S. samples, significant associations were detected with eight SNPs, including rs6280 (p = .001, odds ratio: 1.5). Consistent associations in the case-control and family-based analyses were detected with a common haplotype spanning intron 1 to the 3' region of the gene (rs324029-rs7625282-rs324030-rs2134655-rs10934254; case-control, p = .002; transmission disequilibrium test [TDT], p = .0009; global p-values = .002 and .007, respectively). In the Indian sample, one SNP was associated (rs10934254, p = .03). Moreover, over-transmission of the same common haplotype as the U.S. sample was observed in this cohort (TDT, p = .005; global test, p = .009). Ser9Gly (rs6280) was associated with SZ against this haplotype background but not other haplotypes. CONCLUSIONS: These data suggest previous inconsistencies might have resulted from associations with other DRD3 variants. A liability locus might be in linkage disequilibrium (LD) with or carried against, an associated haplotype 3' to rs6280. Comprehensive SNP evaluation in larger samples is needed.

Differing correlates for suicide attempts among patients with schizophrenia or schizoaffective disorder in India and USA.

BACKGROUND: Suicide is one of the most common causes of death among persons with schizophrenia. Differing risk factors have been identified in published studies. The differences may have arisen because a uniform set of variables was not analyzed. Alternatively, the nature and effect of risk factors may vary in different settings. To test these possibilities, we investigated the same set of variables in two independent cross-national samples ascertained using identical protocols. METHODS: Patients with schizophrenia or schizoaffective disorder (DSM IV criteria) were recruited in India (n=460) and the USA (n=424). RESULTS: Consistent with earlier publications, a diagnosis of schizoaffective disorder, history of depression, pattern of symptoms and educational status were significantly associated with suicide attempts in the US sample. None of these variables were significantly associated in the Indian sample. CONCLUSIONS: The impact of known risk factors for suicide attempts among patients with schizophrenia differs across ethnic groups.

Evaluation of a susceptibility gene for schizophrenia: genotype based meta-analysis of RGS4 polymorphisms from thirteen independent samples.

BACKGROUND: Associations between schizophrenia (SCZ) and polymorphisms at the regulator of G-protein signaling 4 (RGS4) gene have been reported (single nucleotide polymorphisms [SNPs] 1, 4, 7, and 18). Yet, similar to other SCZ candidate genes, studies have been inconsistent with respect to the associated alleles. METHODS: In an effort to resolve the role for RGS4 in SCZ susceptibility, we undertook a genotype-based meta-analysis using both published and unpublished family-based and case-control samples (total n = 13,807). RESULTS: The family-based dataset consisted of 10 samples (2160 families). Significant associations with individual SNPs/haplotypes were not observed. In contrast, global analysis revealed significant transmission distortion (p = .0009). Specifically, analyses suggested overtransmission of two common haplotypes that account for the vast majority of all haplotypes. Separate analyses of 3486 cases and 3755 control samples (eight samples) detected a significant association with SNP 4 (p = .01). Individual haplotype analyses were not significant, but evaluation of test statistics from individual samples suggested significant associations. CONCLUSIONS: Our collaborative meta-analysis represents one of the largest SCZ association studies to date. No individual risk factor arose from our analyses, but interpretation of these results is not straightforward. Our analyses suggest risk due to at least two common haplotypes in the presence of heterogeneity. Similar analysis for other putative susceptibility genes is warranted.

Genetic susceptibility to tardive dyskinesia among schizophrenia subjects: IV. Role of dopaminergic pathway gene polymorphisms.

OBJECTIVE: Tardive dyskinesia (TD) is an antipsychotic induced side effect observed in 20-30% of schizophrenia subjects on long-term typical antipsychotic treatment. We tested the possible association of 24 polymorphisms from six dopaminergic genes: namely, dopamine receptors D1, D2, D3, D4; the dopamine transporter (DAT); and the catalyzing enzyme catechol-O-methyltransferase (COMT), with TD. METHODS: Multiple SNP/VNTR markers from candidate genes were analyzed using suitable approaches and allelic, genotypic and haplotypic associations were tested. RESULTS: 120 bp duplication marker, 1.2 kb upstream from initiation codon of DRD4 gene showed a significant genotypic association [chi2 = 9.29, P = 0.009; OR (95% CI) = 0.52 (0.31-0.86) for genotype 120 dup/120 dup]. In the COMT gene, a significant allelic [chi2 = 13.87, P = 0.0002] as well as genotypic association [chi2 = 16.08, P = 0.0003; OR (95% CI) = 0.24 (0.11-0.55) for genotype GG] was observed with the 408 C>G (exon 4) single nucleotide polymorphism and a significant genotypic association [chi2 = 6.32, P = 0.04; OR (95% CI) = 0.50 (0.33-0.92) for genotype GG] was observed with 472 G > A (exon 4, Val 158 Met) SNP. 120 bp dup-T-repeat 3 in DRD4 and G-C-A-insC in COMT genes were observed to be TD associated haplotypes. CONCLUSIONS: Our study presents a detailed analysis of the possible role of dopaminergic genes in the genesis of TD. DRD4 and COMT genes were observed to be the most important candidates in North Indian schizophrenia subjects. These suggestive associations need to be investigated in replicate studies.

Association and linkage analyses of RGS4 polymorphisms in schizophrenia.

Gene expression analyses of postmortem cerebral cortex suggest that transcription of the regulator of G-protein signaling 4 (RGS4) is decreased in a diagnosis-specific manner in subjects with schizophrenia. To evaluate the possible role of RGS4 in the pathogenesis of schizophrenia, we conducted genetic association and linkage studies using samples ascertained independently in Pittsburgh and New Delhi and by the NIMH Collaborative Genetics Initiative. Using the transmission disequilibrium test, significant transmission distortion was observed in the Pittsburgh and NIMH samples. Among single-nucleotide polymorphisms (SNPs) spanning approximately 300 kb, significant associations involved four SNPs localized to a 10 kb region at RGS4, but the associated haplotypes differed. A trend for transmission distortion was also present in the Indian sample for haplotypes incorporating the same SNPs. Consistent with the linkage/association observed from the family-based tests, samples with affected siblings (NIMH, India) showed higher levels of allele sharing, identical by descent, at RGS4. When the US patients were contrasted to two population-based control samples, however, no significant differences were observed. To check the specificity of the transmission bias, we therefore examined US families with bipolar I disorder (BD1) probands. This sample also showed a trend for transmission distortion, and differed significantly from the population-based controls for the four-SNP haplotypes tested in the other samples. The transmission distortion is unlikely to be due to chance, but its mechanism and specificity require further study. Our results illustrate the potential power of combining gene expression profiling and genomic analyses to identify susceptibility genes for genetically complex disorders.

Molecular genetics of schizophrenia: past, present and future.

Schizophrenia is a severe neuropsychiatric disorder with a polygenic mode of inheritance which is also governed by non-genetic factors. Candidate genes identified on the basis of biochemical and pharmacological evidence are being tested for linkage and association studies. Neurotransmitters, especially dopamine and serotonin have been widely implicated in its etiology. Genome scan of all human chromosomes with closely spaced polymorphic markers is being used for linkage studies. The completion and availability of the first draft of Human Genome Sequence has provided a treasure-trove that can be utilized to gain insight into the so far inaccessible regions of the human genome. Significant technological advances for identification of single nucleo-tide polymorphisms (SNPs) and use of microarrays have further strengthened research methodologies for genetic analysis of complex traits. In this review, we summarize the evolution of schizophrenia genetics from the past to the present, current trends and future direction of research.

Candidate gene polymorphisms among North Indians and their association with schizophrenia in a case-control study.

Knowledge of candidate gene polymorphisms in a population is useful for a variety of gene-disease association studies, particularly for some complex traits. A number of candidate genes, a majority of them from the monoaminergic pathway in the brain, have been very popular in association studies with schizophrenia, a neuropsychiatric disorder. In this study diallelic/multiallelic polymorphisms in some dopaminergic, serotonergic and membrane-phospholipid-related genes have been evaluated in a control population recruited from North India. Association, if any, of these allelic variants with schizophrenia has been tested using a case-control approach. The case data have been taken from our published family-based association studies in schizophrenia. Of the eight genes tested in this study, association with schizophrenia was observed for only two gene polymorphisms, one in the promoter region of the serotonin 2A receptor gene and the other in the tryptophan hydroxylase gene. One new allele for the dopamine transporter gene (with eight repeats, 570-bp size), not reported in any population so far, has been identified in one individual in our sample. The data generated in this study, besides providing a normative background for various disease association studies, are a significant contribution to the population-specific genome database, a currently growing requirement.