There are 3 distinct forms of FHH, namely FHH 1, 2, and 3, resulting from heterozygous loss-of-function mutations in the CaSR (located on chromosome 3q21.1, estimated prevalence 1/1000-5000), GNA11 (G-protein subunit alpha 11, located on chromosome 19p13.3—very rare), and AP2S1 (adaptor protein 2 sigma-1, located on chromosome 19q13.32-estimated prevalence 1/13 000) genes (124), respectively. Here, CASR is linked to familial hypocalciuric hypercalcemia.