An examination of the brain of former Chargers linebacker Junior Seau showed evidence of a degenerative disorder seen before in people who have suffered repetitive head injuries, the National Institute of Neurological Disorders and Stroke announced Thursday.
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 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. Seau's family donated his brain to the National Institutes of Health, which includes the NINDS.
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 (CTE), a condition that shrinks and hardens the brain tissue. The condition, researchers said, is typically caused by multiple hits to the head.
According to an NINDS statement, Seau's brain looked normal upon initial viewing, but neuropathologists using microscopes discovered that a normal brain protein called Tau had folded into tangled masses, like it does in brain cells of patients with Alzheimer's disease and other progressive neurological disorders.
The statement said that the way the Tau tangles were distributed in the brain led to the CTE diagnosis. CTE has been found previously in autopsies of people who have suffered repetitive head injuries, including athletes who played contact sports, people who suffered multiple concussions and military veterans exposed to blast injuries.
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Gina Seau, his ex-wife, spoke with ABC News about the former player's difficulty in sleeping and how he was withdrawn and detached from his children.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."
The NINDS statement said research into CTE is still in an early stage, and physicians cannot make a diagnosis in a living person. NINDS also expressed gratitude to the Seau family for the research opportunity.
The Chargers deferred comment and referred to a statement from the NFL, which said the findings showed a need for further understanding of CTE.
"The NFL, both directly and in partnership with the NIH, Centers for Disease Control and other leading organizations, is committed to supporting a wide range of independent medical and scientific research that will both address CTE and promote the long-term health and safety of athletes at all levels," the NFL statement says.
"The NFL clubs have already committed a $30 million research grant to the NIH, and we look forward to making decisions soon with the NFL Players Association on the investment of $100 million for medical research that is committed in the Collective Bargaining Agreement. We have work to do, and we're doing it."
Watch Jim Avila's interview with the Seau family on World News with Diane Sawyer at 6:30 p.m. on ABC 10.