This syndrome, independently described by McCune [105] and Albright et al. [106], is characterized by a triad of sexual precocity, fibrous dysplasia of bone, and hyperpigmented skin lesions termed café-au-lait spots. Patients with the McCune-Albright syndrome (MAS) are mosaic for constitutively activating Gsα mutations that occur during early embryonic development [107-109]. This is consistent with the observation that MAS occurs sporadically and is never transmitted to the next generation. All identified mutations are at residue Arg201 (Cys or His), suggesting that changes in residue Gln227 may result in higher constitutive activity and are, therefore, less viable. Because of the mosaicism, patients with MAS show significant variation in their clinical presentation. In general, the abnormalities involve bone, skin, and endocrine organs. Fibrous dysplastic bone lesions are usually found in multiple bones. It is important to note that some patients with the constitutively activating Gsα mutations present with fibrous dysplasia alone, affecting either a single bone or multiple bones. In patients with isolated fibrous dysplasia, histological changes appear to be indistinguishable form those seen in the context of MAS [110, 111]. As
