Junior Seau Had Brain Disease, Researchers Say

Exclusive: At family's request, scientists analyzed NFL linebacker's brain tissue after his suicide.
3:00 | 01/10/13

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Transcript for Junior Seau Had Brain Disease, Researchers Say
Return now to the alarming discovery providing some answers to the question surrounding the suicide and NFL great and father of four. Junior say out today a team of doctors confirmed that he suffered from degenerative brain disease which could be linked to the years he spent. Taking blows and giving them. On the football field tonight -- family is speaking out for the first time about this discovery in an ABC news and ESPN exclusive. Here's ABC's -- For twenty years he was a warrior on the -- Junior say after the monster in the middle -- a defensive icon whose devastating hits more than eight. Fifty tackles in his career knocked out -- But -- sudden and shocking suicide just eight months ago. The gunshot to the chest some speculating he knew his brain needed to be preserved for examination. In many agree that all those hits in the 43 year old head could've played a role in his own death. -- just test everything out. And now sales families says they did play a central role did he know that he was getting concussions. Goucher she did. And the family has results from a study on sales brain at the National Institutes of Health to back them up. ABC news and ESPN -- learned exclusively that sales brain showed signs of CTE. Chronic traumatic encephalopathy. The concussion related injury that is at the center of today's football safety controversy. Doctor Russell -- conducted the study. What was found in Junior -- spraying with cellular changes consistent with CTE. Means that he had a lot of head to head collisions over the course have. Twenty years of playing in the NFL. The actual. Settles. In his brain. -- now know. Suffered damage. Exactly at. Gina -- Al junior's former wife to whom we remain close and his four children. Decided to donate his brain to the NIH to try to understand why the man they love the new as an outgoing leader on and off the field. Changed so drastically in his final few years in ultimately ended at all detached and alone. A lot of things different -- of -- -- patterns that we saw and things that worried -- his decision making and his his ambition. Decreased. He. Would sometimes. Loses temper we -- air war over various small things -- Go off the grid for a couple weeks all symptoms experts say of CTC. Impulsivity. -- -- -- Aggressive behavior -- times depression. And sometimes suicidal. I deviation. A once deeply devoted -- highly respected family man. Sales behavior became confusing for his children. At the end it just became more in my -- that. He was disconnecting and I didn't understand but I just took a different seat in just went with then. I didn't do and it's an idea I had no idea it could be something this news. The night before. Say -- sent out this short phone text of law. Commodities that -- words alone. Means a lot. The man. -- for family that love is so important himself for him to take his own life. I can't imagine how. Severe. His English as the game that he loves so passionately. That gave his family everything may in the end have taken it all away. You see that this was the final outcome is. Really bad is it really fun. But sadly not uncommon Dave -- -- of the Chicago Bears shot himself to death to his brain diagnosed as riddled with CT. The combination of depression and lack of impulse control. Probably contributes to the suicide that we see in this group of individuals doctor Robert Cantu says junior sales death. May make a difference to football players and fans it's a tipping point of sorts and signal. That no one is immune to the chronic hard hits of the game they may law. Junior Seau played a position at high risk for head trauma middle linebacker where individuals are funneled to you to make that yet. So it's it's really no surprise to -- to Junior Seau had chronic traumatic encephalopathy that he died so violently and so young. That certainly perhaps is a bit of a shock say -- is the highest profile player to be connected to CT -- and shivers went through the league today. Marcellus Wiley it was an NFL teammate. The know that that was his -- it makes you question your mortality the times I do forget things the sleep this night she may have. You start to wonder. Are you down that path towards CTE. The NFL is facing a lawsuit brought by 4000 former players contending that the league did not do enough to protect them. And he had long term affects from its players. The NFL denies that it intentionally -- any risk from players and today had this statement in response to sales diagnosis. The finding underscores the recognized need for additional research to accelerate a Fuller understanding. Of CT. The NFL is committed to supporting a wide range of independent medical and scientific research. -- will both address CT -- and promote the long term health and safety of athletes at all levels. We have worked to -- and were doing. CTE can only be detected after death by examining the brain under a microscope. So far fifty -- in from football players have been diagnosed -- CTE. 35 of them NFL players and six of them high school athletes the sale say they just want today's players to make an informed decision. To know the risk or even the toughest in the -- Which of the NF -- do things and it doesn't take a bigger role. And making sure that people are aware of -- -- -- -- -- -- if you gonna play the sport and you have the game. Be aware and be careful and know the signs and symptoms extremely. Aware. And what could potentially happen to your life but there's a big risk has a huge risk. The -- of a thousand hits may now change the game you love in ways he never dreamed. For Nightline I'm Jim Avila in San Diego.

This transcript has been automatically generated and may not be 100% accurate.

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