KIR2DS4 and psoriasis: To determine whether copy number of KIR2DL1, KIR2DL2, KIR2DS1, KIR2DS4, KIR3DL1, or KIR3DS1 were associated with psoriasis independent of HLA ligands, we imputed the copy number (0, 1, or 2 copies) of these genes in the PAGE+ cohort of 7198 cases and 4714 controls and performed association testing using a general (0 vs 1 vs 2 copies) logistic regression model adjusted for the top 10 principal components (PCs) of ancestry.