A 4-year-old boy in Watertown, N.Y., is growing an extra skeleton due to a rare genetic condition, the Watertown Daily Times reported Thursday.

Shane Terry has fibrodysplasia ossificans progressiva, or FOP, which causes bone to form in muscles, tendons, ligaments and other connective tissue.

In time, bridges of extra bone will develop across his joints, eventually restricting movement and forming a second skeleton and will cause for his body will lock up.

Like most little boys, Shane likes to run around and play rough, but a fall could trigger a flare-up, creating a hard lump at the site of injury. When the lump fades, the tissue will change into bone.

“When he was first diagnosed, I wanted to keep him in a bubble,” Kimberly A. Hayes, Shane’s mother, told the newspaper. “Through an FOP group online, I learned that I need to let him be as much of a kid as I can. I have to look at every situation to see which would be safest for Shane.”

Shane’s condition is so rare that he is just one of 600 confirmed cases across the globe, according to the International Fibrodysplasia Ossificans Progressiva Association.

Shane, whose twin sibling was stillborn at 20 weeks, has two deformed vertebrae in his neck, crooked pinky fingers and malformed big toes.

Shane's mother could opt to have surgery to remove his extra bones, but that will most likely worsen his condition, according to the IFOPA Web site.

At this point, there is no cure and he could be wheelchair-bound by the time he is 30. Doctors said the average life expectancy for some with FOP is 41.

Click here for photos of Shane and to read more on this story from the Watertown Daily Times.