VDR and type 1 diabetes mellitus: Type 1A diabetes mellitus has a predominantly genetic origin, there are at least 15 loci associated with T1DM, mainly polymorphic genes, such as the human leukocyte antigen (HLA) loci, interleukin 2 receptor alpha (IL2R2), insulin-variable number tandem repeat (VNTR), vitamin D receptor (VDR), cytotoxic T-lymphocyte-associated protein (CTLA)-4 genes [102, 105, 106].