PTH and pseudohypoparathyroidism type 1A: 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).