Heterogeneity of pseudohypoparathyroidism type I from the aspect of urinary excretion of calcium and serum levels of parathyroid hormone

Summary Urinary excretion of calcium (Ca) was measured in 9 patients with pseudohypoparathyroidism (PHP) type I—3 with Albright's hereditary osteodystrophy (AHO): AHO(+) and 6 without AHO: AHO(−)—and in 13 with idiopathic hypoparathyroidism (IHP), treated with active vitamin D₃ (1,25(OH)₂D₃ or 1αOHD₃) to maintain serum Ca levels at 8.4–9.5 mg/dl. Fasting urinary excretion of Ca in PHP was significantly lower than that in IHP. Moreover, fasting urinary excretion of Ca in PHP AHO(+) was lower than that in PHP AHO(−). This difference was also seen in the urine after oral loading of Ca. Urinary excretion, of sodium (Na) was not different between PHP AHP(+) and PHP AHO(−). Serum levels of immunoreactive PTH in PHP AHO(+) were higher than those in PHP AHO(−). The difference in urinary excretion of Ca between PHP AHO(+) and PHP AHO(−) may come from the difference in the circulating levels of PTH.