GNAS (Guanine Nucleotide Binding Protein, Alpha, Stimulating Activity Polypeptide, G-S-alpha) is a component of the heterotrimeric G protein complex that has been shown to be mutated in less than 1% of myelodysplastic syndrome. Mutations of Arg201 of GNAS are typically activating mutations which have been described in various types of solid tumors and McCune Albright syndrome.