PTH-dependent hypercalcemia is usually caused by parathyroid tumors, which may give rise to primary hyperparathyroidism (PHPT) or tertiary hyperparathyroidism, which usually arises in association with chronic renal failure and in the treatment of hypophosphatemic rickets.
We also performed an oral phosphate loading test and compared serum phosphate, intact PTH, and intact fibroblast growth factor 23 (iFGF23) in this patient versus patients with other forms of hypophosphatemic rickets, the results of which further revealed that the mechanism of hypophosphatemia in HHRH is independent of FGF23.
New tools (molecular probes and antibodies) have allowed dissection out of some of the molecular and cellular mechanisms underlying the adaptation of phosphate transport to dietary content, the phosphaturic effect of parathyroid hormone or glucocorticoids and the renal phosphate leak in hypophosphataemic rickets.
Nevertheless, these results suggest that absolute PTH resistance is not a feature of X-linked hypophosphatemic ricket, although subtle forms of resistance at the level of the 25-hydroxyvitamin D 1 alpha-hydroxylase enzyme are not excluded by these data.