Familial hypocalciuric hypercalcemia type I (FHH1, OMIM: #145980) is a genetic disorder characterized by hypercalcemia, hypocalciuria, normal to mildly elevated PTH levels, and in some patients mildly reduced bone mineral density and hypermagnesemia [14]. The gene discussed is PTH; the disease is familial hypocalciuric hypercalcemia 1.