Genetic and Functional Studies of Non-Coding Variants in Human Disease
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CitationAlston, Jessica Shea. 2012. Genetic and Functional Studies of Non-Coding Variants in Human Disease. Doctoral dissertation, Harvard University.
AbstractGenome-wide association studies (GWAS) of common diseases have identified hundreds of genomic regions harboring disease-associated variants. Translating these findings into an improved understanding of human disease requires identifying the causal variants(s) and gene(s) in the implicated regions which, to date, has only been accomplished for a small number of associations. Several factors complicate the identification of mutations playing a causal role in disease. First, GWAS arrays survey only a subset of known variation. The true causal mutation may not have been directly assayed in the GWAS and may be an unknown, novel variant. Moreover, the regions identified by GWAS may contain several genes and many tightly linked variants with equivalent association signals, making it difficult to decipher causal variants from association data alone. Finally, in many cases the variants with strongest association signals map to non-coding regions that we do not yet know how to interpret and where it remains challenging to predict a variants likely phenotypic impact. Here, we present a framework for the genetic and functional study of intergenic regions identified through GWAS and describe application of this framework to chromosome 9p21: a non-coding region with associations to type 2 diabetes (T2D), myocardial infarction (MI), aneurysm, glaucoma, and multiple cancers. First, we compare methods for genetic fine-mapping of GWAS associations, including methods for creating a more comprehensive catalog of variants in implicated regions and methods for capturing these variants in case- control cohorts. Next, we describe an approach for using massively parallel reporter assays (MPRA) to systematically identify regulatory elements and variants across disease-associated regions. On chromosome 9p21, we fine-map the T2D and MI associations and identify, for each disease, a collection of common variants with equivalent association signals. Using MPRA, we identify hundreds of regulatory elements on chromosome 9p21 and multiple variants (including MI- and T2D-associated variants) with evidence for allelic effects on regulatory activity that can serve as a foundation for further study. More generally, the methods presented here have broad potential application to the many intergenic regions identified through GWAS and can help to uncover the mechanisms by which variants in these regions influence human disease.
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