Resistance to multiple hormones in patients with pseudohypoparathyroidism. Association with deficient activity of guanine nucleotide regulatory protein.

Abstract Pseudohypoparathyroidism type I is characterized by resistance (defined as a deficient urinary cAMP response) to parathyroid hormone and, in most cases, hypocalcemia and hyperphosphatemia. Many patients with pseudohypoparathyroidism type I snow a peculiar somatic phenotype termed Albright's hereditary osteodystrophy, but patients without this feature who show identical parathyroid hormone resistance have been described. Parathyroid hormone resistance in pseudohypoparathyroidism type I has been attributed to a defective parathyroid hormone receptor-adenylate cyclase complex. Recent studies have demonstrated deficient activity of the guanine nucleotide regulatory protein (G unit) of adenylate cyclase in many patients with Pseudohypoparathyroidism. Since the G unit is common to all tissues, as opposed to hormone receptors, which are tissue specific, a defective G unit should lead to resistance to multiple hormones that act by stimulating adenylate cyclase. To test this hypothesis, we studied erythrocyte G unit activity and clinical endocrine function in 29 patients with pseudohypoparathyroidism type I. Thirteen patients had deficient erythrocyte G unit activity (43 ± 9 percent of control [mean ± 1 SD]); 16 patients had normal G unit activity (92 ± 8 percent of control) (p