FHH is an autosomal-dominant genetic disease with high penetrance, caused by an inactivating mutation in the gene encoding the calcium sensing receptor, CaSR. The loss-of-function leads to decreased sensitivity of the CaSR to ionized calcium (Ca++), shifting the set-point for Ca++-regulated parathyroid hormone (PTH) release to the right [1]. The gene discussed is CASR; the disease is familial hypocalciuric hypercalcemia.