Functional hypoparathyroidism can be broadly categorized as a condition in which hypocalcemia and hyperphosphatemia are the consequence of a disorder that (i) impairs development or survival of parathyroid glands, (ii) decreases secretion of biologically active PTH, or (iii) reduces target organ responsiveness to PTH (pseudohypoparathyroidism). The gene discussed is PTH; the disease is hyperphosphatemia.