Forty patients with
hypocalcemia and/or Albright's hereditary osteodystrophy were studied. Based on the estimation of serum
calcium and
parathyroid hormone (PTH) levels as well as the urinary cAMP 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 three 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
calcium concentration in some patients with PHP, the increased PTH levels were, however, normalized during iv
calcium infusions. In two 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
calcium 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.