One day after former 49ers wide receiver Dwight Clark announced he has amyotrophic lateral sclerosis (ALS) — and suspects football as the cause — several medical experts acknowledged potential connections between the neuromuscular disease and head trauma associated with the sport.

Nearly all of the doctors interviewed Monday by The Chronicle called the link controversial, partly because it went undetected for so long. But one neurologist insisted ALS has become more recognized in the past five years as “part of the picture” surrounding chronic traumatic encephalopathy (CTE), a degenerative brain disease found in dozens of former NFL players.

Dr. Sam Gandy, director of the Center for Cognitive Health and the NFL Neurological Care Program at Mount Sinai Hospital in New York, said cases of ALS patients with a history of head trauma “began to sort of pile up” in recent years.

“It’s not nearly the most common picture,” Gandy said, “but when it happens in athletes or veterans and former soldiers, it’s almost certainly due to the trauma.”

Another neurologist, Dr. Dale Lange of the Hospital for Special Surgery in New York, disputed any definitive cause-and-effect but added that “repeated head trauma absolutely puts you at increased risk of neurogenerative disease, including dementia and ALS.”

This is not the first time the risks of a sport have been tied to ALS, commonly known as Lou Gehrig’s disease. A study released in 2005 found that Italian professional soccer players got the disease at a rate nearly six times greater than the general population.

The study did not identify a specific cause, but it raised the question of whether players repeatedly heading the ball might make them more susceptible.

Even so, Dr. Santosh Kesari, chairman of Neurosciences and Neurotherapeutics at the Pacific Neuroscience Institute in Santa Monica, remained cautious about drawing a straight line between the head trauma of football and ALS.

“There is some data that moderate to severe brain injury can put you at risk for ALS, but it’s really not clear whether this is just chance,” Kesari said. “There’s just no conclusive data.”

CTE has attracted more attention in recent years, but Clark became the latest in a string of former NFL players to receive an ALS diagnosis.

Steve Gleason, a former New Orleans safety, has waged a high-profile fight with ALS since he announced he had the disease in 2011. Kevin Turner, a former Alabama fullback who spent eight years in the NFL, died last March after being treated for ALS. Turner donated his brain for research and was posthumously discovered also to have CTE.

Other former NFL players who have been afflicted with ALS include former Raiders running back Steve Smith, 52, who was diagnosed in 2002; ex-linebacker O.J. Brigance, 47; and former safety Orlando Thomas, who died at 42 in 2014.

Asked about the Clark news, Gandy said, “The NFL history, with any sort of brain degeneration, raises the question of whether it’s associated with repetitive trauma. We may be seeing it more now because players are so much larger and the force (of collisions) is so much greater. Three-hundred-pound guys weren’t very common in the ’60s.”

That’s true, but three 49ers players from the 1960s — Bob Waters, Gary Lewis and Matt Hazeltine — died of ALS. This cluster of cases naturally sparked widespread concern, but no conclusive cause was found.

Theories ranged from pain-killing medicine the players had taken to the fertilizer used on the 49ers’ practice fields at the time. Research has since established a connection between certain pesticides and Parkinson’s disease, Gandy said, but not to ALS.

About 6,000 people in the U.S. are diagnosed with ALS every year, according to the ALS Association. Many of those cases involve a genetic form of the disease and are unrelated to trauma.

As for Clark and other former NFL players, Dr. Viet Nguyen, assistant professor of neurology at the Stanford School of Medicine, suspects the link between football and ALS because red flags are “pointing in the same direction.”

Nguyen also expects ongoing research to yield more understanding in the years ahead.

“If I were a member of the public and a fan of football, it’s moving slowly because these are your favorite players and you want the answers right now,” Nguyen said. “In science, you have to remember correlation is not causation. Really, you want to know why there’s a link and what can you do to prevent that link.”

Family: Gale Sayers has dementia

KANSAS CITY, Mo. — Relatives of Pro Football Hall of Famer Gale Sayers say the former Chicago Bears running back has been diagnosed with dementia.

His wife, Ardythe Sayers, told the Kansas City Star that her 73-year-old husband was diagnosed four years ago and she blames Sayers’ football career. He played for the Bears for seven seasons, starting in 1965 after setting records at the University of Kansas.

“Like the doctor at the Mayo Clinic said, ‘Yes, a part of this has to be on football,’” Ardie Sayers said at their home in Wakarusa, Ind. “It wasn’t so much getting hit in the head. It’s just the shaking of the brain when they took him down with the force they play the game in.”

Ardie Sayers and the rest of the family had made no secret of his condition, but hadn’t shared it publicly.

Sayers is regarded as one of the greatest players in NFL history. The “Kansas Comet” played his entire career with the Bears, piling up 4,956 yards rushing in his 68-game career and was voted to four Pro Bowls. Sayers scored 22 touchdowns and 132 points in his first season, both then-rookie records.

Associated Press