As expected under polygenicity11, we observe inflation of the median test statistic (λGC = 1.206). The estimated intercept from LD Score regression (1.012) suggests that nearly all of the inflation is due to polygenic signal rather than bias. We also performed family-based analyses that similarly suggest minimal confounding due to population stratification (Online Methods). Using a clumping procedure (Supplementary Note), we identified three approximately independent SNPs reaching genome-wide significance (“lead SNPs”). These three lead SNPs are indicated in the Manhattan plot (Figure 1a) and listed in Table 1. The SNPs have estimated effects in the range 0.015 to 0.018 standard deviations (SDs) per allele (each R2 ≈ 0.01%).
