VDR and psoriasis: These dissimilarities between studies that research the connection between psoriasis and vitamin D at its basal circulating level and those that investigate the outcome of pharmaceutical supplementation may be explained by the natural variability in the key metabolic enzymes of vitamin D: 25-hydroxylase (CYP2R1) and 1-α-hydroxylase (CYP27B1) and vitamin D receptor (VDR) that can affect the efficacy of supplements [46], but we strongly believe that further research would be needed for other possible unknown causes.