GNAS and pseudohypoparathyroidism type 1A: Patients carrying GNAS loss-of-function mutations on maternally inherited alleles have pseudohypoparathyroidism type Ia (PHP-Ia, MIM 103580) that is characterized by AHO and resistance to multiple stimulatory G protein-coupled hormones (e.g. Parathormone (PTH) and others) [5]–[10], while patients with paternally inherited GNAS mutations are reported as having only AHO features or pseudopseudohypoparathyroidism (PPHP) (Table 1) [2], [4], [11], [12].