Genome-wide association studies (GWAS) are a well-established and effective method of identifying genetic loci associated with common diseases or traits (1). GWAS involve the analysis of at least hundreds of thousands of variants across the genome in large cohorts of individuals, often split into cases and controls, to identify variants associated with the trait of interest. The majority of variants identified by GWAS are assumed not to be causal but to tag a region of linkage disequilibrium containing one or more functional variants. GWAS have identified reproducible genomic loci associated with many common human diseases, including cardiovascular disease (2), inflammatory bowel disease (3), type 2 diabetes (4) and breast cancer (5).
