McCune Albright Syndrome MAS OMIM

Description: Alternative titles; symbols ALBRIGHT SYNDROME POLYOSTOTIC FIBROUS DYSPLASIA; PFD; POFD this phenotype is associated with mutations in the GNAS1 gene (139320). The McCune-Albright syndrome, usually caused by mosaicism for a mutation in the GNAS1 gene, is characterized by polyostotic fibrous dysplasia, pigment patches of the skin and endocrinologic abnormalities, including precocious puberty, thyrotoxicosis, pituitary gigantism, and Cushing syndrome (219080). CLINICAL FEATURES This disorder is called McCune-Albright syndrome or simply Albright syndrome, but should not be confused with Albright hereditary osteodystrophy, or pseudohypoparathyroidism (103580). The predominant features of the syndrome occur in 3 areas: the bony skeleton, the skin, and the endocrine system. In all 3 systems, the extent of the abnormality and, in the case of the endocrine system, the nature of the abnormality, are highly variable from case to case, depending on the specific tissues involved in the mosaicism and the extent of involvement. Skeletal No bone is spared. There is a strong tendency to asymmetry. Involvement of the skull and facial bones can be striking, and in the case of these bones also, asymmetry is the rule. Pathologic fracture or bone deformity may be presenting manifestations and pseudarthrosis occurs frequently. Deafness and blindness can result from impingement of the bony process on the cranial foramina. Shepherd's crook deformity of the proximal femur is particularly characteristic of the bony involvement. (The bone lesions of neurofibromatosis are usually less extensive than are those in polyostotic fibrous dysplasia, but may be difficult to distinguish on radiologic grounds alone.) Hypophosphatemic osteomalacia ('rickets') has been observed in some cases of polyostotic fibrous dysplasia. Dent and Gertner (1976) suggested that this may represent a situation comparable to 'tumor rickets' which is associated with mesenchymal tumors and regresses when the tumor is removed. McArthur et al. (1979) described 4 patients with Albright syndrome, hypophosphatemia, and inappropriately low renal tubular reabsorption of phosphate. Three of the patients had radiologic evidence of rickets. They postulated that a substance elaborated by the dysplastic bone interfered with phosphate reabsorption in the renal tubule.