Pseudohypoparathyroidism and Idiopathic Hypoparathyroidism: Relationship between Serum Calcium and Parathyroid Hormone Levels and Urinary Cyclic Adenosine-3′,5′- Monophosphate Response to Parathyroid Extract*

Abstract

Forty patients with hypocalcemia and/or Albright''s hereditary osteodystrophy were studied. Based on the estimation of serum Ca and parathyroid hormone (PTH) levels as well as the urinary c[cyclic]AMP response to infusions with parathyroid extract, it was possible to classify all of the patients studied as cases with idiopathic hypoparathyroidism (n = 6, low PTH, normal cAMP response), pseudohypoparathyroidism (PHP) type I (n = 18, high PTH, low cAMP response) and type II (n = 2, high PTH, normal cAMP response), as well as pseudopseudohypoparathyroidism (n = 14, normal PTH, normal cAMP response). In 3 cases studied at the age of 12, 17 and 23 yr, the signs of Albright''s hereditary osteodystrophy were not observed. PTH levels were unusually high for a given serum Ca concentration in some patients with PHP, the increased PTH levels were, however, normalized during i.v. Ca infusions. In 2 young children with PHP, a gradual increase of serum PTH levels occurred despite persistent normocalcemia over a period of 3 yr. This suggests that factors other than hypocalcemia or frequent small unobservable falls of the serum Ca concentration, such as a deficient formation of 1,25-dihydroxyvitamin D3, secretion of an abnormal PTH, or an abnormal metabolism of the hormone, may contribute to the secondary hyperparathyroidism in PHP.