IPPSD is further subdivided, starting from the PTH receptor inactivating mutation as iPPSD1, inactivating Gsα mutations (PHP1A, PHP1C, PPHP, POH) as iPPSD2, loss of methylation of GNAS differentially methylated regions DMRs (PHP1B) as iPPSD3, PRKAR1A mutations as iPPSD4, PDE4D mutations as iPPSD5, and PDE3A mutations as iPPSD6. Here, GNAS is linked to pseudopseudohypoparathyroidism.