Targeted ablation of the fgf-23 gene in mice disrupts calcium, phosphorus and 1,25 (OH)2D homeostasis [34], [48], giving rise to hypercalcemia, hyperphosphatemia and increased serum 1,25(OH)2D concentrations, the latter due to significantly increased renal expression of CYP27B1 mRNA and protein. The gene discussed is CYP27B1; the disease is Hypercalcemia.