CYP2R1 and vitamin D deficiency: Furthermore, Ahn et al. (Ahn et al. 2010) observed heterogeneity between different cohorts in the GWAS and the association of 25(OH)D concentration with CYP2R1. A missense mutation in CYP2R1 in exon 2 (L99P) is known to lead to vitamin D deficiency (Cheng et al. 2004).