on clinical disease prediction, and remarking on the problem of ‘missing heritability’ of risk for common diseases unaccounted for by common variants [1], the arena of pharmacogenetics was often singled out as an exception [2]. GWAS of drug response traits are quite exceptional in having provided a number of clinically significant genetic predictors of drug outcomes, with estimated effect sizes sometimes orders of magnitude greater than those seen for any human disease [3,4]. Despite this, GWAS of drug response traits currently represent only a small fraction of the total number of GWAS performed to date [101].