While low calcium levels and increased PTH stimulate the production of 1,25(OH)D, elevated levels of 1,25(OH)D suppresses PTH secretion and promotes the conversion of vitamin D into its inactive form, 24,25-hydroxylated vitamin D (24,25(OH)D) [25], thus providing a protective mechanism against hypercalcemia. The gene discussed is PTH; the disease is hypercalcemia disease.