ABC News is reporting that scientists, who studied the brain of NFL linebacker Junior Seau, found that the popular football player suffered from a brain disease likely caused by repeated hits to the head.

Seau, who played for the San Diego Chargers from 1990 to 2002, died of a self-inflicted gunshot wound to the chest at his beachfront home in Oceanside on May 2, 2011. A toxicology report found that no alcohol, common drugs of abuse or other medications were detected in his system at the time of death.

Seau's suicide raised questions about the type of brain injuries football players sustain throughout their careers and the long-term effects. His family donated his brain to the National Institute of Health.

FOR THE FULL STORY, GO TO ABCNEWS.COM:  Junior Seau Diagnosed With Disease Caused by Hits to Head

According to an exclusive report by ABC News and ESPN, scientists revealed that Seau suffered from chronic traumatic encephalopathy, a condition that shrinks and hardens the brain tissue. The condition, researchers say, is typically caused by multiple hits to the head.

Among other symptoms, CTE patients display impulsivity, forgetfulness, depression and sometimes suicidal ideation, Dr. Russell Lonser, chairman of the Department of Neurological Surgery at Ohio State University told ABC News.

ABC News reported that more than 30 NFL players have been diagnosed with CTE. In 2012, 4,000 retired NFL players filed a class-action lawsuit against the league claiming it failed to protect them from these types of brain injuries.

Gina Seau, his ex-wife, spoke with ABC News about the former player's difficulty in sleeping and how he was withdrawn and detached from his children. She has talked before about the multiple concussions Junior Seau suffered throughout his career, a result from hits he took as a player in the NFL.

"The head-to-head contact, the collisions are just, they're out of control," Gina Seau told ABC News.

"He was a warrior and he loved the game," she added. "But ... I know that he didn't love the end of his life."

Watch the full interview with Jim Avila on Good Morning America after 10News at 7 a.m. and on World News with Diane Sawyer at 6:30 p.m.