GNAS and fibrous dysplasia: Now it is known that fibrous dysplasia, monostotic, polyostotic, or as part of the McCune-Albright syndrome is caused by postzygotic (somatic) mutations in the gene encoding the alpha subunit of the stimulatory G protein within the GNAS complex locus (Weinstein et al., 1991; Riminucci et al., 2006).