Genotype data was generated using Illumina HumanHap550 BeadChip (Illumina Inc., San Diego, CA, USA). Quality control was performed including the removal of SNPs with minor allele frequencies below 1%, and those not in Hardy-Weinberg equilibrium (p < 1 × 10−5), as described previously [42 (link)]. Multi-dimensional Scaling (MDS) in PLINK [43 (link)] was used to construct three population covariates (PCs), which were used in all analyses to correct for minor differences related to ancestry.