In adults, inactivating mutations of CaSR gene are found in FHH, an autosomal dominant disease characterized by moderate but significant hypercalcemia, accompanied by few symptoms [11, 12], with inappropriately normal serum PTH levels, and by a low or normal urinary calcium levels [12–14] with histologically normal parathyroid glands. The gene discussed is CASR; the disease is hypercalcemia disease.