Accordingly, PHP1a, PHP1c, pseudopseudohypoparathyroidism, and progressive osseous heteroplasia are classified as iPPSD2 due to loss of function mutation in GSα, and PHP1b is named iPPSD3 and occurs due to methylation changes at the GNAS differentially methylated region (Thiele et al., 2016). Here, GNAS is linked to pseudopseudohypoparathyroidism.