Any endocrine system disorder in which the cause of the disease is inactivation of the GNAS gene. Phenotypes include pseudohypoparathyroidism Ia, Ib, and Ic (PHP-Ia, -Ib, -Ic), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). The disease is disorder of GNAS inactivation (MONDO_0800466, a Monarch Disease Ontology term).