Former Patriots fullback Kevin Turner lived the last six years of his life believing he was dying from amyotrophic lateral sclerosis, or ALS, commonly known as Lou Gehrig’s disease.

In fact, Turner, who died in March at age 46, spent his excruciating final years stricken with a severe case of football-related chronic traumatic encephalopathy, or CTE, which caused a motor neuron disease similar to ALS, researchers at Boston University announced Thursday.

A top researcher also disclosed that as many as 17 other athletes who were believed to have died of ALS instead were primarily victims of CTE, the degenerative brain disease found in athletes with a history of repetitive brain injuries.

“This is not ALS; this is CTE,’’ Dr. Ann McKee, the director of BU’s CTE Center, said at a news conference attended by Turner’s parents and the families of other National Football League players who were diagnosed with CTE.

“This is the best circumstantial evidence we will ever get that this ALS-type of motor neuron disease is caused by CTE,’’ McKee said, as Turner’s mother, Myra, fought back tears.

McKee said former Boston College linebacker Ron Perryman, who died in 2011 at age 42, also was misdiagnosed with ALS before a postmortem autopsy of his brain indicated he had developed the ALS-type motor neuron disease caused by CTE.

Turner’s father, Raymond, cited the findings as evidence that the NFL needs to do more to protect its players from potentially fatal brain damage.

“It’s a big money thing, I realize that, but they can make it safer,’’ Raymond Turner said.

The BU CTE Center has diagnosed the disease in 91 deceased football players (CTE can only be diagnosed through postmortem brain autopsies) and dozens of athletes who played other contact sports, as well as military veterans.

McKee, a neuropathologist who is a leading CTE researcher, said autopsies on the brains of 17 athletes initially thought to have died of ALS found that they were actually were primarily victims of CTE. She said those athletes included soccer and football players who began developing ALS-like symptoms in their 20s.

In Turner’s case, she said, the severity of his disease was “extraordinary and unprecedented for an athlete who died in his 40s.’’

While the discovery helps establish that athletes diagnosed with ALS might be suffering from CTE, the findings are unlikely to immediately change how patients are treated because no treatment has been developed for CTE.

Researchers called for greater funding so they can focus on finding ways to diagnose the disease in the living and explore possible treatments.

Studies have shown that the risk of athletes developing CTE is increased the more they play contact sports and are exposed to head blows. The damage is particularly acute in children.

The NFL, which did not respond to a request to comment, has instituted a number of measures in recent years aimed at promoting safety, including a $100 million commitment to improving helmet technology and advancing medical research. The league also has launched a flag football initiative for younger players.

Some of those measures took effect after Turner became a lead plaintiff in the landmark lawsuit that led the NFL to reach a $1 billion settlement with former players who hadpossible brain damage. Turner’s heirs, including his three children, are eligible to receive as much as $5 million under the settlement.

McKee first reported a link between repetitive head trauma and a new form of motor neuron disease similar to ALS in 2010. Two years later, a research team affiliated with the National Centers for Disease Control found that NFL players with at least five years of experience in the league were four times more likely to die of ALS than the general population.

Turner began playing tackle football in his native Alabama at age 5. He retired at age 30 after playing four years for the University of Alabama (1988-1991), three years for the Patriots (1992-1994), and five years for the Philadelphia Eagles (1995-1999).

As a fullback, Turner typically blocked for other players and was known for leading his blocks with his head — a practice that is now discouraged. A third-round draft choice by the Patriots, he played in every regular-season game of his New England career and scored seven touchdowns.

However, Turner suffered numerous head injuries along the way and became so dazed, he told McKee, that he sometimes forgot what city he was playing in when his teams were on the road.

Turner’s CTE and ALS-like symptoms began to emerge more rapidly soon after he completed his NFL career. As his health deteriorated, he created a charitable foundation to raise awareness about motor neuron diseases related to brain injuries in athletes. And he pledged his brain to the BU CTE Center for research.

Tamara Alan, executive director of the Kevin Turner Foundation, heralded McKee’s findings as a breakthrough made possible by Turner’s commitment to eradicating brain damage in sports.

“Kevin always used to say it’s not enough to make a difference; you need to be the difference,’’ Alan said, her voice cracking with emotion. “I think today Kevin is the difference.’’

Turner’s oldest son, Nolan, also began playing tackle football when he was 5. As Turner’s medical woes worsened, he persuaded Nolan to forgo tackle football until he reached high school.

But football runs deep in the Turner family, and Nolan is now a freshman safety on the Clemson football team. His grandfather, Raymond, stood before a group of reporters Thursday and said softly, “That kind of worries me a little bit.’’

Bob Hohler can be reached at robert.hohler@globe.com.