A genotype–genotype susceptibility interaction analysis was performed that included the genetic variants rs10741657 in CYP2R1, rs10877012 in CYP27B1, rs4809959 in CYP24A1, and rs731236 in VDR for the following three scenarios: to assess the susceptibility of developing hypovitaminosis D, developing RA, and greater clinical activity of the disease. Here, CYP2R1 is linked to rheumatoid arthritis.