CYP2R1 and allergic rhinitis: Therefore, PER patients of <16 years old and PER females may be susceptible to the genetic effect caused by VDR and CYP2R1. Interestingly, Mai et al [6] recently reported that vitamin D appears to play different roles in the development of allergic rhinitis among men and women in Norway and that lower serum 25(OH)D levels were associated with an increased risk of allergic rhinitis among men but a reduced risk of allergic rhinitis among women.