"Even seemingly minor things like preschool immunizations, injections for dental work, [or] minor bumps and bruises from falling off a bicycle, can cause these children to lock up their jaw, lock up their joints that never move again," Kaplan said.
Tiffany is now 17 years old and requires an oxygen machine because the extra bone constricting her rib cage doesn't allow her to fully expand her lungs. She knows the next flare-up could rob her of even more mobility.
"A flare-up can happen overnight while you're sleeping. Like, you'll be walking around one day, and you'll go to bed and the next day you won't be able to move. That's how fast it works," Tiffany said.
Tiffany is eager to explain what her life is like to give others a better understanding of what she goes through.
"I would say, let me tie your arms to your sides where you can't move them and then put a neck brace and a back brace where you won't be able to move and then stay in a wheelchair all the time, and then tell me how you feel," Tiffany said.
Today, for the first time, there may be hope for Tiffany, Hayden and other children with FOP. For 15 years, Kaplan has been searching for the gene that causes FOP. Earlier this year, he found it.
The devastation wrought by FOP is caused by the alteration of a single letter of the 6 billion that make up our genetic code.
"It was overwhelming. Finally, we knew the cause of this horrible, catastrophic, disastrous transformation of connective tissue into bone," Kaplan said.
The discovery of this "master switch" will eventually help people with other bone diseases, such osteoporosis, and people who need hip replacements, for which the body needs to make new bone.
Discovering the gene is only half the battle. Now Kaplan is trying to find a cure for FOP. "My lifelong goal since I've started working on FOP is not just to modify the symptoms but to change the course of the disease. And eventually stop it," Kaplan said.
For Tiffany, a cure would mean not losing any more movement. For the Pheifs, it would mean Hayden could have the kind of future his parents originally never thought possible.