Since the first description in 1942, several PHP subtypes (PHP type 1A/PHP1A – MIM#103580, pseudopseudohypoparathyroidism/PPHP – MIM#612463, PHP type 1B/PHP1B-MIM#603233, PHP type 1C/PHP1C – MIM#612462, PHP type 2/PHP2 – MIM#203330 and progressive osseous heteroplasia POH – MIM#166350) have been defined by the presence/absence of specific clinical/biochemical features and by the presence/absence of underlying genetic, further divided into maternal or paternal, or epigenetic molecular GNAS defects (2–4). The gene discussed is GNAS; the disease is progressive osseous heteroplasia.