In the simple polygenic score approach, we estimate wk as the single-variant coefficient derived from regressing the gene expression trait Y on variant Xk (as implemented in the eQTL analysis software Matrix eQTL46) using the reference transcriptome data. This yields an estimate, GReX^, for a GWAS study sample, of the (unobserved) genetically determined expression of each gene g: (2)GReX^g=∑kw^k,gXk
