Many FOP patients are children or teenagers.
Any injury to muscle or connective tissue can kick-start a flare up of the condition during which the body produces a new piece of bone around the damaged site. The bone that is formed can grow, repair itself and even harbour marrow in the same way that normal bones do. The new bone rapidly becomes permanent, and can eventually join up with the normal skeleton, leading to devastating mobility problems.
Sufferers can end up fused in a standing poisition, so rigid that they must sleep leaning in a corner. They may eventually die from starvation, when their jaw fuses shut, or suffocate as new bone crushes their lungs.
Scientists have been striving for 15 years to try to understand and cure the condition which affects one in two million people.
Horizon investigates this pioneering research, and the hope it gives to FOP patients.