Renal-resistant hormonoplethoric hypoparathyroidism with evidence for a defective response to cAMP

A 15.5-yr-old black male is reported with hypocalcemia, hyperphosphatemia, and severe osteitis fibrosa cystica. While hypocalcemic and hyperphosphatemic, the circulating parathyroid hormone (PTH) level and urinary cAMP excretion were increased. An infusion of exogenous PTH produced a normal maximal excretion of urinary cAMP but failed to increase phosphate excretion. Correction of the hypocalcemia by administration of 200,000 U vitamin D daily lowered the endogenous PTH level and basal excretion of cAMP to normal; at that time, infusion of PTH produced both a normal rise in urinary cAMP and a normal phosphaturic response. This pattern of response suggests pseudohypoparathyroidism with a calcium-sensitive defect in renal phosphate transport distal to the PTH receptor adenyl cyclase mechanism, producing hyperphosphatemia, hypocalcemia, and secondary hyperparathyroidism. The osteitis fibrosa cystica was presumably due to the increased PTH, suggesting that resistance to PTH was present in kidney but not bone.