A medical expert believes that famous theoretical physicist Stephen Hawking may have been misdiagnosed and could have been suffering from polio for much of his life.

Christopher B. Cooper, Professor Emeritus of Medicine and Physiology at the University of California, Los Angeles, recently claimed in a letter to the Financial Times that it is possible that Hawking contracted polio in his youth.

The suggestion flies in the face of the common understanding that Hawking suffered from amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease, which he was first diagnosed with in 1963 at the age of 21.

According to Cooper, the likelihood of Hawking being diagnosed with ALS was “low,” especially given the fact the scientist survived with the disease for 55 years before passing away on March 14 at the age of 76.

Cooper claimed that survival period doesn’t “match our understanding of ALS.” According to the ALS Association, the average person is expected to survive between two and five years from the time of diagnosis.

“Usually, it is relentlessly progressive and the median survival from the time of diagnosis is around three years with fewer than 20 percent of ALS patients surviving longer than 10 years,” Cooper wrote.

The medical expert also said that it was unlikely that Hawking would have been diagnosed with ALS at such a young age. “Typically, its [ALS’s] onset is in the later years of life,” the professor wrote.

Instead, Cooper theorized that the impairments to Hawking’s neurological system and motor skills were caused by poliomyelitis, more commonly known as polio. The disease was common in the first half of the 20th century, but rates of infection dropped to almost zero when the polio vaccine was introduced in 1955.

Cooper’s timeline doesn’t exactly add up, seeing as Hawking was diagnosed in 1963, but he suggests it is possible Hawking contracted the disease after the vaccine was introduced. “Perhaps Hawking was unlucky to contract poliomyelitis or a similar viral infection a few years later in 1963,” he wrote.