Former New England Patriots tight end Aaron Hernandez had the most severe case of chronic traumatic encephalopathy ever discovered in someone his age, researchers at the Boston University School of Medicine disclosed at a conference Thursday.
Dr. Ann McKee, the director of the school's CTE center, said the 27-year-old's brain was "clearly at the severe end of the spectrum" for his age group, diagnosing Hernandez with Stage 3 CTE (out of 4), which hasn't been seen before in brains younger than 46 years old.
Hernandez died of an apparent suicide earlier this year while serving a life sentence for homicide. In the troubled years before his arrest, Hernandez reportedly became extremely paranoid, began regularly using PCP, and carried a gun with him at all times.
CTE is a degenerative brain disease associated with repeated head trauma, and is commonly diagnosed in players of high-impact sports like football and boxing.
The damage in particular affected Hernandez's frontal lobes, McKee said, a region of the brain associated with decision-making, judgment and cognition.
Symptoms of CTE include impulse control problems, aggression, depression and paranoia, according to the Concussion Legacy Foundation.
McKee cautioned attendees that a CTE diagnosis alone is insufficient in explaining all of Hernandez's behavior, but it does offer a significant clue.
"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."