An 11-year-old boy who loves playing baseball will keep playing the game for as long as he can, even though his muscles are slowly turning into bone.
Caleb Burgess, from Castle Rock, Colorado, was diagnosed last year with a rare disease called Firbrodysplasia Ossficans Progressiva (FOP), which is also called 'Stone Man Disease'.
There are only 800 documented cases worldwide, which comes to about one in every 2 million people and, on average, leaves a patient dependent on a wheelchair by the time they are 30.
Because it is so uncommon, it took several doctors and one of the world's leading experts in the matter, Dr Frederick Kaplan at the University of Pennsylvania, to pin down exactly what was wrong.
The disease slowly turns soft tissue muscles, ligaments, joints and cartilage into bone, creasing a second skeleton over the existing one.
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Caleb Burgess, from Castle Rock, Colorado, was diagnosed last year with a rare disease called Firbrodysplasia Ossficans Progressiva (FOP), which is also called 'Stone Man Disease'
So each time Caleb hurts himself while playing baseball, the injury could accelerate new bone growth in that part of his body, making it harder for him to move
Over time and as there is new bone growth, it severely limits mobility and eventually results in death. This happens when cartilage holding an individual's ribs together solidifies, making it difficult, if not impossible, to breathe.
It is caused by a genetic mutation in the ACVR1 gene, which is a part of the body's repair mechanism, according to the US National Library of Medicine. That means every time someone with the disease is injured, or even gets sick, the part of their body that would go to repair it does so with bone instead of scar tissue.
'It can happen even when someone just gets a shot at the dentist,' Dr Kaplan told Daily Mail Online.
Fibrodysplasia ossificans progressiva (FOP) is a very rare inherited disorder that causes bone to appear in tendons, ligaments and muscle.
At birth, most sufferers have shortened big toes.
Any part of the body can be affected by FOP.
It also causes swelling, limited movement and difficulty eating or speaking if the jaw is affected.
Complete immobilization can occur.
There is no cure, and treatment just focuses on relieving pain and aiding mobility.
Sufferers should avoid activities that may cause injury.
FOP eventually results in death when the cartilage holding the ribs together also solidifies, making it impossible to breathe.
Patients eventually suffocate or suffer a cardiac arrest as their bodies attempt to get enough oxygen.
Doctors aren't sure what triggers the mutated gene, but so far there is no cure or treatment.
The only thing a patient with the disease can do is avoid illness and injury, which could result in sped-up bone growth, and treat the pain.
However, Dr Kaplan said children only get one childhood, so even though they should be cognizant of their disease, they should not let it keep them from living their life.