McCune-Albright syndrome (MAS; OMIM # 174800) is a rare, sporadic disease caused by a post-zygotic, somatic, activating mutation in the guanine-nucleotide binding protein α-subunit (GNAS1) gene, encoding for the sub-unit α of the regulatory G-protein (Gsα). The gene discussed is GNAS; the disease is McCune-Albright syndrome.