Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant disorder, familial hypocalciuric hypercalcemia type 1 (FHH1) is the most prevalent form of FHH and is caused by an inactivating mutation in the CASR gene, resulting in a loss of function of the calcium-sensing receptor (CaSR). The gene discussed is CASR; the disease is familial hypocalciuric hypercalcemia 1.