VDR and alopecia: This heterodimer binds to the vitamin D response element (VDRE) on genomic DNA to regulate the expression of various genes involved in bone formation, hair follicle formation, cell differentiation, immune response, etc. When a mutation occurs in the gene encoding VDR, the aforementioned VDR-dependent vitamin D actions do not occur, causing symptoms such as bow legs/knock knees due to osteodystrophy, and alopecia due to hair follicle dysplasia; this condition is called vitamin D-dependent type II rickets (VDDRII)1–4.