Fibrous dysplasia of bone and McCune-Albright syndrome.

Fibrous dysplasia of bone is a genetic, non-inheritable disease, characterized by bone pain, bone deformities and fracture, involving one or several bones. It is caused by mis-sense mutations occurring post-zygotically in the gene coding for the alpha-subunit of the stimulatory G-protein, Gs, in the guanine nucleotide binding, alpha stimulating (GNAS) complex locus in chromosome 20q13. This mutation results in osteoblastic differentiation defects, and bone resorption is often increased. The bone lesions may be associated with endocrine dysfunctions and café-au-lait spots; this is known as McCune-Albright syndrome. Patients with polyostotic fibrous dysplasia often have renal phosphate wasting. The disease, however, has a wide clinical spectrum, so many patients are asymptomatic. Diagnosis relies on radiographs and pathology. Bisphosphonates have been used in the treatment of fibrous dysplasia to relieve bone pain and improve lytic lesions, but they are still under clinical evaluation. Calcium, vitamin D and phosphorus supplements may be useful in some patients. Surgery is also helpful to prevent and treat fracture and deformities.