CYP2R1 and type 1 diabetes mellitus: The problem of vitamin D status and T1DM risk is very complicated; it depends not only on dietary habits, supplementation intake and sunlight exposure, but also on polymorphisms in genes involved in the vitamin D metabolic pathway, including vitamin D receptor (VDR) [54,55,56,57,58,59,60,61], vitamin D binding protein (VDBP) [62,63,64,65,66,67,68], vitamin D 25-hydroxylase (CYP2R1) and 1α-hydroxylase (CYP27B1) [67,69,70,71,72].