Rare diseases often provide important insights into common disorders. Fibrodysplasia ossificans progressiva (FOP) is one of the rarest genetic conditions known. People who have this disorder essentially form two skeletons, a normal one during embryogenesis and a heterotopic one following birth. Heterotopic bone in FOP is biochemically, histologically, and biomechanically indistinguishable from normal bone. The authors' research on the genetic and molecular pathways that are ectopically activated in patients who have FOP elucidate perspectives on normal bone formation and growth, and will lead to more effective treatment of congenital and degenerative disorders of the skeleton. The working group at The University of Pennsylvania follows nearly all of the patients in the world who have FOP. Medical students in the program learn how a rare disabling skeletal disease provides a unique perspective for considering an integrated molecular and social approach to more common skeletal disorders.
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