GNAS and pseudohypoparathyroidism type 1A: When GNAS mutations are inherited maternally, AHO is associated with the development of pseudohypoparathyroidism type 1a (PHP1a), i.e. PTH-resistance leading to hypocalcemia and hyperphosphatemia, resistance to several other peptide hormones that mediate their actions through G protein-coupled receptors, as well as obesity and various degrees of cognitive impairment.