In addition, Ap2s1+/L15 mice had significantly increased plasma PTH concentrations in association with hypophosphatemia (Table 2, Fig. 1), and this is in agreement with the findings from studies of two large FHH3 kindreds from Oklahoma (FHHOk) and Northern Ireland (FHHNI), which have demonstrated that hypercalcemic family members, compared with normocalcaemic relatives, have significantly increased serum PTH concentrations with mild hypophosphataemia (4,26). This evidence concerns the gene AP2S1 and hypophosphatemia.