PTH and hypoparathyroidism: Pseudohypoparathyroidism type 1B (PHP1B; also termed inactivating PTH/PTHrP signaling disorder, iPPSD; ref. 1) is a disorder of hormone resistance in which the inability of parathyroid hormone (PTH) to activate endocrine signaling processes in target cells leads to a state of functional hypoparathyroidism (2–4).