Characteristic clinical features of fibrodysplasia ossificans progressiva (FOP). (Left) Extra-skeletal bone formation in a three-dimensional reconstructed computed tomography scan of a 12-year-old child. (Right) Radiograph of the feet of a 3-year-old child showing the symmetrical great toe malformations.

Image Credit: Eileen Shore, PhD and Frederick Kaplan, MD, University of Pennsylvania School of Medicine; Nature Genetics, 23 April 2006, DOI: 10.1038/ng1783