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Negligible impact on missing heritability of autoimmune-locus rare coding-region variants

ABSTRACT: Genome wide association studies (GWAS) have identified common variants of modest effect size at hundreds of loci for common autoimmune diseases - however a substantial fraction of heritability remains unexplained, and to which rare variants may contribute. To discover rare variants and test them for association with a phenotype, the majority of studies re-sequence a small initial sample size and then genotype the discovered variants in a larger sample set. This approach will fail to analyse a large fraction of the rare variants present in the entire sample set. Here we perform simultaneous amplicon sequencing-based variant discovery and genotyping for coding exons of 25 GWAS risk genes in 41,911 white-European origin UK subjects comprising 24,892 subjects with six autoimmune disease phenotypes and 17,019 controls, and show that rare coding-region variants at known loci play a negligible role in common autoimmune disease susceptibility. These results do not support the rare variant - synthetic genome-wide association hypothesis. Many known autoimmune disease risk loci contain multiple independent common and low frequency variant association signals, and so genes in these loci are a priori stronger candidates to harbor rare coding-region variants than other genes. Our data suggest that the missing heritability for common autoimmune diseases may not lie in the rare coding-region variant portion of the allelic spectrum, but perhaps as others have proposed in very many common variant signals of weak effect.

PROVIDER: EGAS00001000476 | EGA |

REPOSITORIES: EGA

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Project description:Background: The identification of causal variants responsible for disease associations from genome-wide association studies (GWAS) facilitates functional understanding of the disease mechanisms implicated by GWAS. One of the earliest GWAS associations to COPD spans an intragenic region within FAM13A, but the causal variants at this loci have not yet been identified. Massively parallel reporter assays (MPRA) can be used to prioritize functional regulatory variants in a high-throughput manner. Methods: We used an integrated approach using fine-mapping in over 10,000 subjects from COPD GWAS studies, two MPRA experiments, traditional reporter assays, chromatin conformation capture, and CRISPR-based gene editing to characterize COPD-associated regulatory variants in FAM13A in human bronchial epithelial cell lines. Results: Conditional genetic association and fine mapping analyses identified two independent COPD association signals in FAM13A. MPRA identified 45 common functional regulatory variants, and six COPD-associated putative functional variants were prioritized for further functional investigation. Three variants demonstrated significant activity in traditional reporter assays, and one variant, rs2013701, was selected for further testing in the endogenous genomic context based on a direction of effect consistent with postulated mechanisms of FAM13A-mediated COPD susceptibility. CRISPR-based genome editing for this variant confirmed allele-specific effects on FAM13A expression and altered rates of cellular proliferation, providing multiple levels of functional characterization for this COPD-associated variant. Conclusions: Comprehensive screening for regulatory variants near FAM13A identified the presence of extensive functional regulatory variation within a 250kb window of FAM13A in HBECs. Focused functional evaluation of the COPD-associated functional variants in LD with the two independent association signals in this region prioritized the common variant rs2013701, for which multiple parallel lines of functional evidence confirm allelic effects on FAM13A regulation.

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Negligible impact on missing heritability of autoimmune-locus rare coding-region variants

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