FHH comprises three genetically distinct conditions, designated as FHH types 1–3 (Table 1), which are due to loss-of-function mutations affecting the CaSR, Gα11 and AP2σ proteins, respectively (Pollak et al. 1993, Nesbit et al. 2013a,b). Here, CASR is linked to familial hypocalciuric hypercalcemia.