Demaryius Thomas was suffering from stage 2 chronic traumatic encephalopathy (CTE) when he died last year, according to his parents.
In a statement via the Concussion Legacy Foundation, Katina Stuckey Smith and Bobby Thomas said their son's diagnosis came after an examination of his brain following his death in December.
“Once I became aware of CTE and began to familiarize myself with the symptoms, I noticed that Demaryius was isolating himself and I saw other changes in him,” Thomas’ mother, Katina Smith, said in the CLF news release . “He was just so young, and it was horrible to see him struggle. His father and I hope all families learn the risks of playing football. We don’t want other parents to have to lose their children like we did.”
Thomas' parents previously told ABC News their 33-year-old son died of cardiac arrest caused by a seizure disorder.
In the years before his death, "Thomas developed depression, anxiety, panic attacks, and trouble with his memory," the new release added.
Thomas' parents released the findings of their son's brain study through the Concussion Legacy Foundation (CLF). He is one of more than 300 former NFL players who have been diagnosed with CTE by Dr. Ann McKee, a professor of neurology and pathology at Boston University's CTE Center and the BU CTE Center research team.
As noted in the press release, there has been speculation Thomas' death may be related to an epileptic seizure given that late-stage CTE can be associated with epilepsy. However, researchers believe "it is far more likely that he developed post-traumatic epilepsy after a motor vehicle accident and fall he experienced several years before his death."
Thomas, a wide receiver, was the 22nd overall pick out of Georgia Tech in the 2010 NFL Draft. He went on to become a Super Bowl champion with the Denver Broncos in 2015 and a five-time Pro Bowler.
He played with the Broncos, Texans, Patriots, and Jets during his nine seasons in the NFL and was lauded as one of the best wide receivers in the league.