A comparison of approaches to account for uncertainty in analysis of imputed genotypes

The availability of extensively genotyped reference samples, such as "The HapMap" and 1,000 Genomes Project reference panels, together with advances in statistical methodology, have allowed for the imputation of genotypes at single nucleotide polymorphism (SNP) markers that are untyped in a cohort or case-control study. These imputation procedures facilitate the interpretation and meta-analyses of genome-wide association studies. A natural question when implementing these procedures concerns how best to take into account uncertainty in imputed genotypes. Here we compare the performance of the following three strategies: least-squares regression on the "best-guess" imputed genotype; regression on the expected genotype score or "dosage"; and mixture regression models that more fully incorporate posterior probabilities of genotypes at untyped SNPs. Using simulation, we considered a range of sample sizes, minor allele frequencies, and imputation accuracies to compare the performance of the different methods under various genetic models. The mixture models performed the best in the setting of a large genetic effect and low imputation accuracies. However, for most realistic settings, we find that regressing the phenotype on the estimated allelic or genotypic dosage provides an attractive compromise between accuracy and computational tractability

O impacto da terapêutica de ressincronização cardíaca nas células produtoras de IL-17 circulantes em doentes com insuficiência cardíaca avançada: efeito anti-inflamatório da terapêutica de ressincronização cardíaca

Provas públicas apresentadas à Escola Superior de Saúde Dr. Lopes Dias do Instituto Politécnico de Castelo Branco para o cumprimento dos requisitos necessários à obtenção do título de Especialista.OBJETIVO: As células produtoras de IL-17 circulantes têm sido implicadas no ambiente inflamatório da insuficiência cardíaca crónica (ICC) e associadas a um mau prognóstico da doença. O objetivo deste trabalho foi avaliar o impacto da terapêutica de ressincronização cardíaca (TRC) na frequência e atividade funcional das células Th17 e Tc17, assim como a expressão de mRNA de IL-17 em doentes com ICC. MÉTODOS: Foram incluídos neste estudo 28 doentes com ICC, avaliados antes da TRC (T0) e 6 meses após (T6), e 15 controlos saudáveis. As células Th17 e Tc17 do sangue periférico foram analisadas por citometria de fluxo e a quantificação do mRNA de IL17 por PCR em tempo-real. RESULTADOS: As células Tc17 tendem a estar mais elevadas nos doentes com ICC submetidos à TRC que nos controlos (0.92% (0.24-3.32) versus 0.60% (0.09-3.68), sem atingir significado estatístico. Depois da TRC, a frequência de células Tc17 diminui significativamente, chegando a níveis semelhantes aos encontrados no grupo controlo (HG) (0.92% (0.24-3.32) ao T0 versus 0.56% (0.21-4.20) ao T6, p<0.05), devido, maioritariamente, aos doentes que responderam à TRC. Além disto, a expressão do mRNA de IL-17 foi apenas detetada num pequeno número de doentes respondedores ao T0 (27%) e apenas detetado num doente respondedor ao T6 (7%). Inversamente, nos doentes não-respondedores, a expressão de mRNA de IL-17 aumenta da avaliação inicial (17%) para T6 (42%). Relativamente às células Th17 não foram encontradas diferenças significativas entre o HG e os doentes com ICC ao T0 e ao T6. CONCLUSÃO: A resposta inflamatória mediada pelas células produtoras de IL-17 do SP parece ser suprimida pela TRC, particularmente nos doentes respondedores.ABSTRACT: PURPOSE: IL-17-producing T cells have been implicated in the inflammatory milieu of chronic heart failure (CHF), which implies a dismal prognosis in affected patients. The aim of this study was to evaluate the impact of cardiac resynchronization therapy (CRT) on the frequency and functional activity of Th17 and Tc17 cells, as well as, on IL-17 mRNA expression in patients with CHF. METHODS: 28 patients with CHF, analysed before CRT (T0) and 6 months later (T6), and 15 healthy controls (HG) were enrolled in this study. Circulating Th17 and Tc17 cells were evaluated by flow cytometry. The quantification of IL-17A mRNA expression was performed by real-time PCR. RESULTS: Circulating Tc17 cells tended to be higher in CHF patients submitted to CRT than in HG (0.92% (0.24-3.32) versus 0.60% (0.09-3.68), although not reaching statistical significance. The frequency of Tc17 cells in CHF patients significantly decreases after CRT reaching levels similar to those of HG (0.92% (0.24-3.32) at T0 versus 0.56% (0.21-4.20) at T6, p<0.05), mainly due to responders to CRT. Additionally, the expression of IL-17 mRNA was detected in a few number of responder patients at T0 (27%) and only detected in one responder at T6 (7%). Conversely, in non-responders, the proportion of patients exhibiting IL-17 mRNA expression increases from baseline (17%) to T6 (42%). No significant differences were observed in Th17 cells between HG, CHF patients in T0 and patients in T6. CONCLUSION: The inflammatory response mediated by circulating IL-17 producing cells seems to be suppressed by CRT, particularly in responders.N/

The Molecular Genetic Architecture of Self-Employment

Economic variables such as income, education, and occupation are known to affect mortality and morbidity, such as cardiovascular disease, and have also been shown to be partly heritable. However, very little is known about which genes influence economic variables, although these genes may have both a direct and an indirect effect on health. We report results from the first large-scale collaboration that studies the molecular genetic architecture of an economic variable-entrepreneurship-that was operationalized using self-employment, a widely-available proxy. Our results suggest that common SNPs when considered jointly explain about half of the narrow-sense heritability of self-employment estimated in twin data (σg2/σP2= 25%, h2= 55%). However, a meta-analysis of genome-wide association studies across sixteen studies comprising 50,627 participants did not identify genome-wide significant SNPs. 58 SNPs with p<10-5were tested in a replication sample (n = 3,271), but none replicated. Furthermore, a gene-based test shows that none of the genes that were previously suggested in the literature to influence entrepreneurship reveal significant associations. Finally, SNP-based genetic scores that use results from the meta-analysis capture less than 0.2% of the variance in self-employment in an independent sample (p≥0.039). Our results are consistent with a highly polygenic molecular genetic architecture of self-employment, with many genetic variants of small effect. Although self-employment is a multi-faceted, heavily environmentally influenced, and biologically distal trait, our results are similar to those for other genetically complex and biologically more proximate outcomes, such as height, intelligence, personality, and several diseases

Fine mapping on chromosome 13q32-34 and brain expression analysis implicates MYO16 in schizophrenia

We previously reported linkage of schizophrenia and schizoaffective disorder to 13q32–34 in the European descent Afrikaner population from South Africa. The nature of genetic variation underlying linkage peaks in psychiatric disorders remains largely unknown and both rare and common variants may be contributing. Here, we examine the contribution of common variants located under the 13q32–34 linkage region. We used densely spaced SNPs to fine map the linkage peak region using both a discovery sample of 415 families and a meta-analysis incorporating two additional replication family samples. In a second phase of the study, we use one family-based data set with 237 families and independent case–control data sets for fine mapping of the common variant association signal using HapMap SNPs. We report a significant association with a genetic variant (rs9583277) within the gene encoding for the myosin heavy-chain Myr 8 (MYO16), which has been implicated in neuronal phosphoinositide 3-kinase signaling. Follow-up analysis of HapMap variation within MYO16 in a second set of Afrikaner families and additional case–control data sets of European descent highlighted a region across introns 2–6 as the most likely region to harbor common MYO16 risk variants. Expression analysis revealed a significant increase in the level of MYO16 expression in the brains of schizophrenia patients. Our results suggest that common variation within MYO16 may contribute to the genetic liability to schizophrenia.National Institute of Mental Health (NIMH) Grant MH061399, the Lieber Center for Schizophrenia Research at Columbia University, Gray Matters Fellowship and NARSAD Young Investigator Award.http://www.nature.com/npphb201

Meta-analysis of Genome-Wide Association Studies for Extraversion: Findings from the Genetics of Personality Consortium

Extraversion is a relatively stable and heritable personality trait associated with numerous psychosocial, lifestyle and health outcomes. Despite its substantial heritability, no genetic variants have been detected in previous genome-wide association (GWA) studies, which may be due to relatively small sample sizes of those studies. Here, we report on a large meta-analysis of GWA studies for extraversion in 63,030 subjects in 29 cohorts. Extraversion item data from multiple personality inventories were harmonized across inventories and cohorts. No genome-wide significant associations were found at the single nucleotide polymorphism (SNP) level but there was one significant hit at the gene level for a long non-coding RNA site (LOC101928162). Genome-wide complex trait analysis in two large cohorts showed that the additive variance explained by common SNPs was not significantly different from zero, but polygenic risk scores, weighted using linkage information, significantly predicted extraversion scores in an independent cohort. These results show that extraversion is a highly polygenic personality trait, with an architecture possibly different from other complex human traits, including other personality traits. Future studies are required to further determine which genetic variants, by what modes of gene action, constitute the heritable nature of extraversion

A new strategy for enhancing imputation quality of rare variants from next-generation sequencing data via combining SNP and exome chip data

Background: Rare variants have gathered increasing attention as a possible alternative source of missing heritability. Since next generation sequencing technology is not yet cost-effective for large-scale genomic studies, a widely used alternative approach is imputation. However, the imputation approach may be limited by the low accuracy of the imputed rare variants. To improve imputation accuracy of rare variants, various approaches have been suggested, including increasing the sample size of the reference panel, using sequencing data from study-specific samples (i.e., specific populations), and using local reference panels by genotyping or sequencing a subset of study samples. While these approaches mainly utilize reference panels, imputation accuracy of rare variants can also be increased by using exome chips containing rare variants. The exome chip contains 250 K rare variants selected from the discovered variants of about 12,000 sequenced samples. If exome chip data are available for previously genotyped samples, the combined approach using a genotype panel of merged data, including exome chips and SNP chips, should increase the imputation accuracy of rare variants. Results: In this study, we describe a combined imputation which uses both exome chip and SNP chip data simultaneously as a genotype panel. The effectiveness and performance of the combined approach was demonstrated using a reference panel of 848 samples constructed using exome sequencing data from the T2D-GENES consortium and 5,349 sample genotype panels consisting of an exome chip and SNP chip. As a result, the combined approach increased imputation quality up to 11 %, and genomic coverage for rare variants up to 117.7 % (MAF < 1 %), compared to imputation using the SNP chip alone. Also, we investigated the systematic effect of reference panels on imputation quality using five reference panels and three genotype panels. The best performing approach was the combination of the study specific reference panel and the genotype panel of combined data. Conclusions: Our study demonstrates that combined datasets, including SNP chips and exome chips, enhances both the imputation quality and genomic coverage of rare variants

Integrating sequence and array data to create an improved 1000 Genomes Project haplotype reference panel

A major use of the 1000 Genomes Project (1000GP) data is genotype imputation in genome-wide association studies (GWAS). Here we develop a method to estimate haplotypes from low-coverage sequencing data that can take advantage of single-nucleotide polymorphism (SNP) microarray genotypes on the same samples. First the SNP array data are phased to build a backbone (or 'scaffold') of haplotypes across each chromosome. We then phase the sequence data 'onto' this haplotype scaffold. This approach can take advantage of relatedness between sequenced and non-sequenced samples to improve accuracy. We use this method to create a new 1000GP haplotype reference set for use by the human genetic community. Using a set of validation genotypes at SNP and bi-allelic indels we show that these haplotypes have lower genotype discordance and improved imputation performance into downstream GWAS samples, especially at low-frequency variants. © 2014 Macmillan Publishers Limited. All rights reserved

CFH haplotypes without the Y402H coding variant show strong association with susceptibility to age-related macular degeneration

In developed countries, age-related macular degeneration is a common cause of blindness in the elderly. A common polymorphism, encoding the sequence variation Y402H in complement factor H (CFH), has been strongly associated with disease susceptibility. Here, we examined 84 polymorphisms in and around CFH in 726 affected individuals (including 544 unrelated individuals) and 268 unrelated controls. In this sample, 20 of these polymorphisms showed stronger association with disease susceptibility than the Y402H variant. Further, no single polymorphism could account for the contribution of the CFH locus to disease susceptibility. Instead, multiple polymorphisms defined a set of four common haplotypes (of which two were associated with disease susceptibility and two seemed to be protective) and multiple rare haplotypes (associated with increased susceptibility in aggregate). Our results suggest that there are multiple disease susceptibility alleles in the region and that noncoding CFH variants play a role in disease susceptibility

Exhaustive search of the SNP-SNP interactome identifies epistatic effects on brain volume in two cohorts

The SNP-SNP interactome has rarely been explored in the context of neuroimaging genetics mainly due to the complexity of conducting ∼10 11 pairwise statistical tests. However, recent advances in machine learning, specifically the iterative sure independence screening (SIS) method, have enabled the analysis of datasets where the number of predictors is much larger than the number of observations. Using an implementation of the SIS algorithm (called EPISIS), we used exhaustive search of the genome-wide, SNP-SNP interactome to identify and prioritize SNPs for interaction analysis. We identified a significant SNP pair, rs1345203 and rs1213205, associated with temporal lobe volume. We further examined the full-brain, voxelwise effects of the interaction in the ADNI dataset and separately in an independent dataset of healthy twins (QTIM). We found that each additional loading in the epistatic effect was associated with ∼5% greater brain regional brain volume (a protective effect) in both the ADNI and QTIM samples

Genome-wide asociation analysis identifies three psoriasis susceptibility loci

We carried out a meta-analysis of two recent psoriasis genome-wide asociation studies with a combined discovery sample of 1,831 affected individuals (cases) and 2,546 controls. One hundred and two loci selected based on P value rankings were foLowed up in a thrE-stage replication study including 4,064 cases and 4,685 controls from Michigan, Toronto, Newfoundland and Germany. In the combined meta-analysis, we identified thrE new susceptibility loci, including one at NOS2 (rs4795067, combined P = 4-10-11), one at FBXL19 (rs10782001, combined P = 9-10-10) and one near PSMA6-NFKBIA (rs12586317, combined P = 2-10-8). AL thrE loci were also aSociated with psoriatic arthritis (rs4795067, combined P = 1-10-5; rs10782001, combined P = 4-10-8; and rs12586317, combined P = 6-10-5) and purely cutaneous psoriasis (rs4795067, combined P = 1-10-8; rs10782001, combined P = 2-10-6; and rs12586317, combined P = 1-10-6). We also replicated a recently identified asociation signal near RNF114 (rs495337, combined P = 2-10-7)