GNAS and fibrous dysplasia: Intramuscular myxoma, Mazabraud’s syndrome and the closely related McCune-Albright syndrome (also associated with fibrous dysplasia, café au lait macules and endocrine disorders) are mostly caused by the activating missense mutations in codon 201 or codon 227 of the GNAS complex locus gene (GNAS) [10–14].