GNAS and pseudopseudohypoparathyroidism: Many years later, genetic and/or epigenetic alterations at the guanine nucleotide-binding protein, alpha-stimulating (Gsα) locus (GNAS) were identified as the cause of this condition in about 70% of patients with a clinical diagnosis of PHP/PPHP [4], or iPPSD2 (inactivating PTH/PTHrP signalling disorder) and iPPSD3 according to the new proposed classification [5].