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(NEWSER)– An ALS patient's life expectancy averages just two to five years after diagnosis, and only about 5% make it past 20 years, the ALS Association notes.

But Stephen Hawking, the 73-year-old theoretical physicist and subject of The Theory of Everything, an Academy Award-winning biopic, has beaten the odds and lived with his motor neuron disease for 52 years—and no one's sure why, though some experts suggest factors that may have increased his life span in today's Washington Post. Scientists also don't know for certain what causes ALS (aka Lou Gehrig's disease) in general and are studying genetic and environmental links, the CDC notes.

But although the underlying reasons for Hawking's long-term survival are unclear, researchers' thoughts on it aren't. "He is exceptional," neurology professor Nigel Leigh told the British Medical Journal in 2002. "I am not aware of anyone else who has survived with [ALS] as long."

Photo: Getty Images

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