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Schizotypal personality traits may increase proneness to psychosis and likely index familial vulnerability to schizophrenia (SZ), implying shared genetic determinants with SZ. Here, we sought to investigate the contribution of common genetic risk variation for SZ on self-reported schizotypy in 2 ethnically homogeneous cohorts of healthy young males during compulsory military service, enrolled in the Athens Study of Proneness and Incidence of Schizophrenia (ASPIS, N = 875) and the Learning on Genetics of Schizophrenia Spectrum study (LOGOS, N = 690). A follow-up psychometric assessment was performed in a sub-sample of the ASPIS (N = 121), 18 months later at military service completion. Polygenic risk scores (PRS) for SZ were derived based on genome-wide association meta-analysis results from the Psychiatric Genomics Consortium. In the ASPIS, higher PRSSZ significantly associated with lower levels of positive (ie, perceptual distortions), disorganization and paranoid facets of schizotypy, whereas no association with negative (ie, interpersonal) facets was noted. Importantly, longitudinal data analysis in the ASPIS subsample revealed that PRSSZ was inversely associated with positive schizotypy at military induction (stressed condition) but not at follow-up (nonstressed condition), providing evidence for environmental rather than SZ-implicated genetic influences. Moreover, consistent with prior reports, PRSSZ was positively correlated with trait anxiety in the LOGOS and additionally the recruits with higher PRSSZ and trait anxiety exhibited attenuated paranoid ideation. Together, these findings do not support an etiological link between increased polygenic liability for SZ and schizotypy, suggesting that psychosocial stress or trait anxiety may impact schizotypal phenotypic expressions among healthy young adults not genetically predisposed to SZ.

Neurocognitive abilities constitute complex traits with considerable heritability. Impaired neurocognition is typically observed in schizophrenia (SZ), whereas convergent evidence has shown shared genetic determinants between neurocognition and SZ. Here, we report a genome-wide association study (GWAS) on neuropsychological and oculomotor traits, linked to SZ, in a general population sample of healthy young males (n = 1079). Follow-up genotyping was performed in an identically phenotyped internal sample (n = 738) and an independent cohort of young males with comparable neuropsychological measures (n = 825). Heritability estimates were determined based on genome-wide single-nucleotide polymorphisms (SNPs) and potential regulatory effects on gene expression were assessed in human brain. Correlations with general cognitive ability and SZ risk polygenic scores were tested utilizing meta-analysis GWAS results by the Cognitive Genomics Consortium (COGENT) and the Psychiatric Genomics Consortium (PGC-SZ). The GWAS results implicated biologically relevant genetic loci encoding protein targets involved in synaptic neurotransmission, although no robust individual replication was detected and thus additional validation is required. Secondary permutation-based analysis revealed an excess of strongly associated loci among GWAS top-ranked signals for verbal working memory (WM) and antisaccade intra-subject reaction time variability (empirical P < 0.001), suggesting multiple true-positive single-SNP associations. Substantial heritability was observed for WM performance. Further, sustained attention/vigilance and WM were suggestively correlated with both COGENT and PGC-SZ derived polygenic scores. Overall, these results imply that common genetic variation explains some of the variability in neurocognitive functioning among young adults, particularly WM, and provide supportive evidence that increased SZ genetic risk predicts neurocognitive fluctuations in the general population., (© 2015 The Authors American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc.)

Aim: We investigated the catechol-O-methyltrasferase (COMT) gene, which is a strong functional and positional candidate gene for schizophrenia and therapeutic response to antipsychotic medication., Materials & Methods: Single-locus as well as detailed haplotype-based association analysis of the COMT gene with schizophrenia and antipsychotic treatment response was carried out using seven COMT polymorphisms in 398 schizophrenia patients and 241 healthy individuals from a homogeneous south Indian population. Further responsiveness to risperidone treatment was assessed in 117 schizophrenia patients using Clinical Global Impressions (CGI). A total of 69 patients with a CGI score of 2 or less met the criteria of good responders and 48 were patients who continued to have a score of 3 and above and were classified as poor responders to risperidone treatment., Results: The association of SNP rs4680 with schizophrenia did not remain significant after adjusting for multiple testing. Haplotype analysis showed highly significant association of seven COMT marker haplotypes with schizophrenia (CLUMP T4 p-value = 0.0001). Our results also demonstrated initial significant allelic associations of two SNPs with drug response (rs4633: chi(2) = 4.36, p-value = 0.036, OR: 1.80, 95% CI: 1.03-3.15; and rs4680: chi(2) = 4.02, p-value = 0.044, OR: 1.76, 95% CI: 1.01-3.06) before multiple correction. We employed two-marker sliding window analysis for haplotype association and observed a significant association of markers located between intron 1 and intron 2 (rs737865, rs6269: CLUMP T4 p-value = 0.021); and in exon 4 (rs4818, rs4680: CLUMP T4 p-value = 0.028) with drug response., Conclusion: The present study thus indicates that the interacting effects within the COMT gene polymorphisms may influence the disease status and response to risperidone in schizophrenia patients. However, the study needs to be replicated in a larger sample set for confirmation, followed by functional studies.

Aim: We investigated 16 polymorphisms from three genes, dopamine receptor D2 (DRD2), catechol-O-methyl transferase (COMT) and brain derived neurotrophic factor (BDNF), which are involved in the dopaminergic pathways, and have been reported to be associated with susceptibility to schizophrenia and response to antipsychotic therapy., Materials & Methods: Single-locus association analyses of these polymorphisms were carried out in 254 patients with schizophrenia and 225 controls, all of southern Indian origin. Additionally, multifactor-dimensionality reduction analysis was performed in 422 samples (243 cases and 179 controls) to examine the gene-gene interactions and to identify combinations of multilocus genotypes associated with either high or low risk for the disease., Results: Our results demonstrated initial significant associations of two SNPs for DRD2 (rs11608185, genotype: chi(2) = 6.29, p-value = 0.043; rs6275, genotype: chi(2) = 8.91, p-value = 0.011), and one SNP in the COMT gene (rs4680, genotype: chi(2) = 6.67, p-value = 0.035 and allele: chi(2) = 4.75, p-value = 0.029; odds ratio: 1.33, 95% confidence interval: 1.02-1.73), but not after correction for multiple comparisons indicating a weak association of individual markers of DRD2 and COMT with schizophrenia. Multifactor-dimensionality reduction analysis suggested a two locus model (rs6275/DRD2 and rs4680/COMT) as the best model for gene-gene interaction with 90% cross-validation consistency and 42.42% prediction error in predicting disease risk among schizophrenia patients., Conclusion: The present study thus emphasizes the need for multigene interaction studies in complex disorders such as schizophrenia and to understand response to drug treatment, which could lead to a targeted and more effective treatment.

Schizophrenia is a complex multifactorial disorder for which the pathobiology still remains elusive. Dysfunction of the dopamine D2 receptor signaling has been associated with the illness, but numerous studies provide confounding results. This study investigates the association of synonymous polymorphisms (His313 and Pro319) in the dopamine D2 receptor gene with schizophrenia using a case-control approach, with 101 cases and 145 controls. Our results demonstrated that genotype distribution for the His313 polymorphism was significantly different between schizophrenia patients and control subjects (p=0.0012), while the Pro319 polymorphism did not show any association with the disease. The results suggest that the synonymous SNP His313 in DRD2 may be associated with the illness. However, there is a need for further replication studies with larger sample sets.