The iPPSD2 subtype includes disorders (PHP1A, PPHP, AHO and POH) deriving from inactivating GNAS genetic alterations, both point mutations in Gsα-coding exons 1–13 and structural rearrangements (deletions, duplications or inversions affecting part or the whole gene) [10, 56]. The gene discussed is GNAS; the disease is progressive osseous heteroplasia.