What would happen if some soft tissue cells in your body randomly got the message to transform into stiff bone cells? Patients born with a disease called fibrodysplasia ossificans progressiva (FOP) are locked into this fate, often becoming severely disabled before adulthood.

The disease first manifests itself at birth, when a baby appears normal but has bent big toes. By early childhood, however, some of the body’s connective tissues—including muscles, ligaments and tendons—have begun ossifying into skeletal bone, locking the joints and distorting posture and movement. Some bone formation appears to be spontaneous, while some can be brought on by trauma from surgery or even a mild impact.

via How Can a Genetic Mutation Cause Muscle to Turn into Bone?: Scientific American.