GNAS and pseudohypoparathyroidism: Pseudohypoparathyroidism (PHP) and related disorders, collectively known as inactivating parathyroid hormone (PTH)-related peptide (PTH/PTHrP) signaling disorders (iPPSD), are rare conditions caused by genetic or epigenetic defects at the GNAS complex locus on chromosome 20q13.3, which impair the function of the stimulatory G protein (Gsα) or lead to abnormal Gsα expression and other splice variants [1].