X-Men, step aside: Check out real-life mutants with these 5 amazing superpowers

As you watch the X-Men punch and kick on movie screens across the country, another kind of mutant might be sitting right next to you, munching popcorn. The medical literature is peppered with tales of these nonfiction mutants: People whose genetic mutations give them unbreakable bones or incredible flexibility or eye-popping strength.

Here, five superpowers that would have even a comic book hero green with envy.

1. Endurance

Throughout his career, Finnish skier Eero Mäntyranta was suspected of blood doping because his red blood cell count was 20 percent higher than that of other athletes. But scientists later discovered that a mutated gene gave Mäntyranta and 50 members of his family high sensitivity to the hormone erythropoietin, or EPO.

Normally, EPO steps up red blood cell production during exertion, bringing in more oxygen to keep the muscles going. For Mäntyranta, this process was accelerated, so his body overproduced hemoglobin. With deeply reddened skin and a higher-than-normal blood-oxygen capacity, Mäntyranta won seven Olympic medals (three gold) in the 1960s.

2. Flexibility

Daniel Browning “Rubberboy” Smith can pass his body through a tennis racket and turn his torso 180 degrees, and he can also do this.

Garry “Stretch” Turner can cover his mouth with his neck skin, among other feats.

They have Ehlers-Danlos Syndrome, an inherited condition that alters the structure of collagen in their bodies, giving them great elasticity in their connective tissues in their skin, joints, and muscles. Browning discovered his abilities at age 4, when he jumped off a bunk bed and landed in a split. He now holds the Guinness World Record for Most Flexible Man.

3. Strength

Liam Hoekstra of Michigan has myostatin-related muscle hypertrophy. The condition comes from a mutation in the gene that instructs the body to produce myostatin, which limits muscle growth. With abnormally low levels of the protein, the body produces muscle unchecked. Babies with this condition have well-developed musculature at birth, and are far stronger than their peers as they get older.

Geneticists in Boston have also studied a German boy with the condition, and there may be others.

4. Wakefulness

Most of us can’t function without seven to nine hours of sleep a night. But a rare few, like Abby Ross, can live and function on six hours or less of sleep per night. Researchers discovered a mother and daughter with the same ability in 2009. These “short sleepers” have a mutation on DEC2, the circadian rhythm regulator gene.

The mutation has been dubbed “the Thatcher gene,” after former British prime minister Margaret Thatcher. She reportedly ran the United Kingdom on four hours of sleep per night. Those with this mutation not only sleep less, but also seem to have a built-in immunity to the effects of sleep deprivation.

5. Durability

Low-density lipoprotein receptor-related protein 5, LRP5, is the gene that determine’s your body’s bone density. One or two tweaks to it, though, and you’re born with nearly indestructible bones.

One such person was discovered after he emerged unharmed from a car accident. Scientists hope to further study of the phenomenon to develop treatments for conditions such as brittle-bone disease and osteoporosis.