CYP2R1 and asthma: Taking the background presented into consideration, we conducted this study with the aim of evaluating the effects of SNPs in the genes involved in the vitamin D pathway (CYP27B1, CYP24A1, GC and CYP2R1) and in the gene encoding its receptor, VDR (ApaI, BsmI, FokI, TaqI and Cdx2), on the risk of developing asthma.