NEW YORK (AP) — The family of former Bears safety Dave Duerson has agreed to donate his brain for research into chronic traumatic encephalopathy, a condition linked to athletes who have sustained repeated concussions.

Chris Nowinski at the Center for the Study of Traumatic Encephalopathy at Boston University School of Medicine told The Associated Press he was contacted by a representative of the NFL Players Association on Friday, then worked with a representative of Duerson’s family.

“I can confirm that Mr. Duerson’s family has agreed to donate his brain to the CSTE at BU School of Medicine,” Nowinski said in an e-mail.

Duerson died Thursday in Sunny Isles Beach, Fla. The Miami-Dade medical examiner ruled the death a suicide, Miami-Dade police spokesman Roy Rutland said Sunday. He confirmed that a gun was used but did not specify where Duerson shot himself.

It’s unclear why Duerson killed himself, although his company had been forced into receivership several years ago and he had lost his home to foreclosure, former Bears coach Mike Ditka told the AP in a phone interview Sunday.

“I knew he had some problems, I knew he lost the business, I knew all that,” said Ditka, whose Gridiron Greats Assistance Fund works to help provide for retired players, which includes funding research into health-related issues such as brain injuries.

“It’s just a tragedy,” Ditka said. “It really is.”

A native of Muncie, Ind., Duerson was a third-round draft pick by the Bears in 1983 out of Notre Dame and played 11 seasons in the NFL. He won Super Bowls with the 1985 Bears and 1990 Giants and played in four Pro Bowls.

Ditka said he isn’t sure whether Duerson was having any issues connected with his playing career, but he acknowledged that it has become common among former players.

“A lot of these guys have gone through a lot of suffering,” Ditka said. “You played the game, you had a concussion, and you went back in. That’s how it was. If they showed you three fingers, and you saw two, it was good enough. You played the game.”

Chronic traumatic encephalopathy is associated with cognitive and behavioral problems later in life and eventually causes dementia. Also known as punch drunk syndrome, it has been most common in boxers. In recent years, CTE has been shown to exist in other athletes, including professional and college football players and a pro hockey player.

CSTE is a collaboration between BU Medical School and the Sports Legacy Institute that’s addressing what it calls the “concussion crisis” in sports. The group has been at the forefront of research into head trauma in sports and received a $1 million gift from the NFL, which it has pushed for better treatment of concussions.

Nowinski, a former pro wrestling star and football player at Harvard, is the president at the Sports Legacy Institute.

NFL Commissioner Roger Goodell said as he arrived for labor negotiations Sunday that he didn’t know details about Duerson’s case.

“He’s a good man,” Goodell said. “It’s sad.”

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Associated Press writers Rasha Madkour in Miami and Caryn Rousseau in Chicago contributed to this report.

Copyright 2011 The Associated Press.