Stephen Hawking turns 76; How has he survived ALS for more than 50 years?

Acclaimed physicist Stephen Hawking turned 76 Monday, beating the odds and outliving most people diagnosed with ALS, or Lou Gehrig's disease, by decades.

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Hawking was diagnosed with progressive and degenerative motor neurone disease in 1963 when he was 21 years old, according to Hawking.org, and given just two years to live by doctors.

He's defied those odds by more than 50 years, but it's not exactly clear why Hawking has survived almost a full lifetime, when most patients diagnosed with amyotrophic lateral sclerosis (ALS) live no more than roughly three years after diagnosis, according to the ALS Association.

It could have something to do with the age he was diagnosed. Most people develop the illness, which impairs the function of nerves and muscles, between 55 and 75, the National Institute of Neurological Disorders and Strokes (NINDS) reports. Those diagnosed with the disease at a younger age tend to live longer, according to ALS studies.

Genetics may also play a role in Hawking's lengthy survival, Live Science reported.

There is no cure for ALS, but there are several FDA-approved drugs that can extend life expectancy by about six months, according to Live Science, which doesn't explain Hawking's long survival with the disease.

While the illness may have forced Hawking into a wheelchair and left him voiceless with his only means of communication through a computer, it never slowed down his intellect  or genius and, if anything, seemed to accelerate his scientific drive and ambition. He spent 30 years as a professor at Cambridge, and, in addition to his scientific accomplishments, he's also a prolific writer and penned one of the most iconic books of the 20th century "A Brief History of Time."

Cox Media Group