FHH is a genetically heterogeneous disorder, which is characterized by mild to moderate elevations in serum calcium concentrations, low urinary calcium excretion, and normal to elevated circulating parathyroid hormone (PTH), and the three recognized types, FHH1, FHH2, and FHH3, are due to loss-of-function mutations of the CaSR, Gα11, and AP2σ, respectively (Hannan et al., 2016, Nesbit et al., 2013a, Nesbit et al., 2013b). Here, PTH is linked to familial hypocalciuric hypercalcemia.