PTH and familial hypocalciuric hypercalcemia: Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant disorder of extracellular calcium (Ca2+o) homeostasis characterized by lifelong elevations in serum calcium concentrations in association with normal or mildly elevated serum parathyroid hormone (PTH) concentrations and normal or low fractional excretion of calcium (1–4).