The family of Aaron Hernandez, former New England Patriots tight end, donated his brain to science and just recently they found that the ex-football player suffered from chronic traumatic encephalopathy (CTE). 
Hernandez was serving a life sentence for homicide and committed suicide in his cell earlier this year. Right before his arrest, Hernandez acted very paranoid, used PCP (Phencyclidine), and carried a gun with him at all times.
Dr. Ann McKee, the director of the school’s CTE center said that the 27-year-old’s brain was “clearly at the severe end of the spectrum” for his age group. She diagnosed Hernandez with Stage 3 CTE (out of 4), which surprisingly had never been seen before in brains younger than 46-years-old. He had the most severe case of CTE ever discovered in someone in his age group. This degenerative brain disease is associated with repeated head trauma, which often occurs in football and other physical sports.
Most of the damage occurred in Hernandez’s frontal lobes, a region of the brain associated with decision-making, judgment, and cognition. Symptoms include control problems, aggression, depression, and paranoia. 
“We can’t take the pathology and explain the behavior,” McKee said, according to commentary relayed by The Washington Post. “But we can say collectively, in our collective experience, that individuals with CTE, and CTE of this severity, have difficulty with impulse control, decision-making, inhibition of impulses for aggression, emotional volatility, rage behaviors. We know that collectively.”
A Boston University study of 202 brains of deceased American football players earlier this year found CTE in 87 percent of them, with the number climbing to 99 percent among NFL players.
“It is no longer debatable whether or not there is a problem in football; there is a problem,” McKee said in a statement at the time. ”[It] is time to come together to find solutions.”