A detailed examination of the brain of a Penn football player who committed suicide showed he had the same disease caused by hard hits that has been associated with NFL players.

The New York Times first reported Monday that Owen Thomas was in the early stages of chronic traumatic encephalopathy, or CTE, a disease that has been linked to depression and impulse control, primarily among NFL players.

A former Penn captain, the 21-year-old Thomas was found dead in April at his off-campus apartment. He had apparently hanged himself.

The research on Thomas' brain tissue was done at Boston University, which has done much of the work on the impact of big hits on football players that has gained attention in recent years. Dr. Robert Stern, a director of the Boston University group, confirmed the findings to The Associated Press but otherwise declined comment.

Katherine Brearley, Thomas' mother, told the AP she doesn't know the extent to which brain trauma caused her son to commit suicide, and doctors cautioned against overstating the connection.

"I can only say for myself, that Owen was a very unlikely person to, in his normal state of mind, to commit suicide," she said in a telephone interview. "He didn't have a history of depression. There are no significant factors that we could see that trigger that kind of action."

Brearley said her son started playing football when he was 9 or 10 and had never been diagnosed with a concussion. He also never showed any side effects normally associated with brain trauma.

Thomas, a 6-foot-2, 240-pound defensive end, was voted one of Quakers' captains for this season.

He was a second-team All-Ivy player in 2009, starting all 10 Penn games, recording 29 tackles and finishing second in the league with six sacks.

At Penn's recent media day, the Quakers placed his No. 40 jersey in the team photo in the spot where Thomas would have been seated between captains Keiffer Garton, Bradford Blackmon and Joe D'Orazio. The Quakers took turns holding the jersey in photos that would have included Thomas — one for the captains, seniors, defensive line and Pennsylvania recruits.

Penn will honor Thomas, of Allentown, in a ceremony before its opener against Lafayette on Saturday night.

His death stunned his family.

"I thought, 'Oh my God, I didn't even know my own son.' I had no idea, I couldn't imagine," Brearley said. "I felt like a failure at not having understood my own child. But now I think to myself, if someone tells me he had a degenerative brain disease, I didn't understand that part of him."

Doctors told The Times that Thomas' CTE may have developed from subconcussive collisions, repetitive blows that cause permanent or cumulative brain injury. The newspaper reported that Thomas was the youngest and first amateur football player to be found with clear evidence of CTE.

He's the second Penn football player since 2005 to commit suicide.

"While we will never know the cause of Owen Thomas's depression and subsequent suicide, we are aware of and deeply concerned about the medical issues now being raised about football head injuries and will continue to work with the Ivy League and the medical community in addressing these issues," Penn spokeswoman Lori Doyle said Monday night. "Owen's untimely death was a terrible tragedy and we continue to grieve for his loss."

Brearley said the family didn't blame Penn or any other coaches Thomas played as a young football player.

"However, what these results point toward, the Penn coaches, and for all coaches everywhere, it looks as if it's just not about big hits that we document," she said, "the potential is there that the disease process starts with repeated small hits."

Thomas graduated from Parkland High School, where he was a three-year letter-winner and captain for two years. His older brother, Matt, was also a member of Penn's football team and graduated in 2002.

"We wish we could have Owen back. Owen was a wonderful person and a great leader," his mother said. "If his death could leave a legacy of making youth football safer for young people, it would be wonderful."