Histological analysis of parathyroid gland size from wild-type and mutant uc482 mice revealed that parathyroid gland areas in all genotypes were significantly larger, in keeping with diet-induced secondary hyperparathyroidism, in mice on the low diet compared to the control diet (uc482+/Y = 7697 ± 1596 μm2/g vs 3545 ± 824 μm2/g, P = 0.002; uc482−/Y = 7887 ± 1016 μm2/g vs 3797 ± 802 μm2/g, P < 0.001; uc482+/+ = 7525 ± 1780 μm2/g vs 4220 ± 1348 μm2/g, P = 0.013; and uc482+/− = 7693 ± 276 μm2/g vs 5123 ± 782 μm2/g, P = 0.004, n = 4) (Fig. 4G, H). Here, HAPSTR2-OT1 is linked to secondary hyperparathyroidism.