The EXT PGS scores were calculated using PRS-CS (Ge, Chen, Ni, Feng, & Smoller, 2019). PRS-CS uses a Bayesian regression and continuous shrinkage method to correct for the non-independence among nearby SNPs. Per recommendations of the PRS-CS developers, SNPs in the EXT PGS were limited to those from HapMap3 that overlapped between the original GWAS summary statistics and the LD reference panel (1000 Genomes Phase III reference panel). For participants of EA, we used estimates from Karlsson Linnér et al. (2021) to compute the EXT PGS scores. For individuals of AA, the EXT PGS was constructed using the weights from the results of the GWAS based on EA samples, noting that summary statistics from an ancestry matched GWAS are not currently available. EXT PGS scores were standardized (z-scored) to improve the interpretability of results.
