AHO in combination with PTH resistance and a diminished in vitro measured activity of Gsα protein characterizes pseudohypoparathyroidism type Ia (PHPIa, MIM: 103,580), the most common subtype of the rare group of disorders summarized under the term pseudohypoparathyroidism (PHP). Here, GNAS is linked to pseudohypoparathyroidism type 1A.