Heterozygous germline inactivating GNAS mutations on the maternally transmitted allele lead to type Ia or type Ic pseudohypoparathyroidism (PHP‐1a, PHP‐1c), which is associated with hormonal resistance to parathyroid hormone (PTH), thyroid‐stimulating hormone (TSH), gonadotropins (LH, FSH), growth hormone‐releasing hormone (GHRH), calcitonin, and some neurotransmitters of the central nervous system. The gene discussed is PTH; the disease is pseudohypoparathyroidism type 1C.