GNAS and progressive osseous heteroplasia: However, we note that POH is classified among the pseudohypoparathyroidism (PHP) disorders, caused by deficiencies in Gnas/Gsα and/or downstream signaling effectors, some of which are accompanied by resistance to PTH and/or other hormones and by altered serum biochemistries (Linglart et al., 2018; Mantovani and Elli, 2018).