Thus, the aim of the present study was to find the dose of 25OHD3 effective enough to restore Ca2+ and PTH levels in a CYP27B1 knockout (CYP27B1-/-) mouse model with CKD, therefore independently of conversion into 1,25(OH)2D3, and to test the same dose in CYP27B1+/+ mice to evaluate its safety and efficacy in decreasing PTH. This evidence concerns the gene PTH and chronic kidney disease.