However, from recent data, it becomes clear this original PHP classification is no longer accurate for the following four reasons: (i) broad GNAS methylation defects were also found for PHP1B patients with an AHO phenotype [7, 15–17], (ii) the degree of the methylation defect seems not to correlate with the disease severity [18], (iii) reduced Gsα activity is no longer exclusive for PHP1A with inactivating mutations but recently also was described for PHP patients with epigenetic defects [19, 20], and (iv) partial GNAS methylation defects have been described [21]. This evidence concerns the gene GNAS and pseudohypoparathyroidism type 1A.