Rare Medical Condition Is the Secret to Contortionist’s Ability

— -- He’s been called a medical mystery, but Daniel Browning Smith just calls himself “Rubber Boy.”

“I can dislocate both arms, both legs, turn my torso 180 degrees and all kinds of crazy stuff,” Smith, 35, told ABC News’ “20/20.”

Smith holds the Guinness World Record for most flexible person and the record for fastest time passing through an unstrung tennis racket three times. He is also a stuntman, breaking his arms and legs in movies, and performs at NBA halftime shows.

The secret to his extraordinary flexibility, Smith said, is a rare medical condition called Ehlers-Danlos syndrome (EDS).

“It’s a collagen disorder, and it makes me very, very flexible,” said Smith.

The syndrome can cause extreme elasticity of the joints and skin.

“Probably one in 1,000 people have it,” Dr. Michael Holick, a physician at Boston Medical Center and professor of medicine, physiology and biophysics at Boston University School of Medicine, told “20/20.” “Most can show that they are double-jointed so that they could increase mobility of their joints.”

“My ribs actually dislocate and poke out of my chest, and I do have some muscle pain, but it’s very minor, so I’ve been very lucky,” Smith said.

But despite the negative side effects, there are also numerous upsides to having EDS, Smith said.

“I joined a circus when I was 17, and I’ve traveled the entire world,” said Smith. “It’s just been absolutely phenomenal.”