AP2S1 and Hypercalcemia: Our results revealed that Ap2s1+/L15 mice, which harbored a germline heterozygous Ap2s1 p.Arg15Leu mutation, had a similar plasma biochemical phenotype to that reported for FHH3 patients, who have heterozygous loss-of-function AP2S1 missense Arg15 mutations (p.Arg15Cys, p.Arg15His or p.Arg15Leu), and with those having the AP2σ2 p.Arg15Leu mutation being affected with the severest hypercalcaemia (3,7).