The first methods for testing for genetic overlap were family studies [3, 4, 5, 6, 7]. In order to estimate genetic overlaps among many pairs of phenotypes, family designs require measuring multiple traits on the same individuals. Consequently, it is challenging to scale family designs to a large number of traits, especially traits that difficult or costly to measure (e.g., low-prevalence diseases). More recently, genome-wide association studies (GWAS) have allowed us to obtain effect-size estimates for specific genetic variants, so it is possible to test for shared genetics by looking for correlations in effect-sizes across traits, which does not require measuring multiple traits per individual.
