However, it would be inadvisable to include a genetic variant from the ABCG2 locus given that there is evidence for a role of ABCG2 in disease-related biological processes outside of hyperuricemia.12 Initially, Mendelian randomization studies used linear or logistic regression or, if individual level data were available, two-stage least squares would be used where the genetic variant is regressed against the exposure in stage 1 and fitted values from stage 1 regressed against the outcome of interest in stage 2. This evidence concerns the gene ABCG2 and hyperuricemia.