The Q-Q plot (Supplementary Fig. 1a) from the discovery GWAS exhibits substantial inflation (λGC = 1.41). According to the estimated intercept from a linkage disequilibrium (LD) Score regression11, only a small share of this inflation (~5%) in test statistics is due to confounding biases such as cryptic relatedness and population stratification. To account for these biases, we inflated GWAS standard errors by the square root of the LD Score regression intercept12.
