GNAS and progressive osseous heteroplasia: Based on the 1980 classification of the cAMP response to PTH and Gsα functional activity, PHP was divided into PHP1A, pseudo-PHP (PPHP), and its variant progressive osseous heteroplasia (POH), PHP1B, PHP1C, and PHP-2 according to the presence or absence of AHO, together with an in vivo response to exogenous PTH and the measurement of Gsα protein activity in peripheral erythrocyte membranes in vitro (3, 4).