Pseudohypoparathyroidism refers to a heterogeneous group of disorders characterized by resistance to parathyroid hormone (PTH). Pseudohypoparathyroidism type IB is characterized clinically by isolated renal PTH resistance manifest as hypocalcemia, hyperphosphatemia, and increased serum PTH. Biochemical studies show a decreased response of urinary cAMP to exogenous PTH, but normal Gs activity in erythrocytes because the defect is restricted to renal tubule cells. In contrast to the findings in PHP IA, patients with PHP IB usually lack the physical characteristics of Albright hereditary osteodystrophy (AHO) and typically show no other endocrine abnormalities, although resistance to thyroid-stimulating hormone has been reported in PHP IB. However, patients with PHP IB may rarely show some features of AHO. [From OMIM]