Explainer-What is CTE and its connection to the NFL and other contact sports?

NEW YORK :A gunman who opened fire in a Midtown Manhattan office building on Monday believed he suffered a brain injury that he blamed on the National Football League, New York's mayor said, thrusting the issue of chronic traumatic encephalopathy back into headlines this week.

According to police, Shane Tamura, a 27-year-old former high school football player with a history of mental illness, killed four people with an assault rifle in a Park Avenue office tower that houses NFL headquarters before shooting himself in the chest.

The following is a breakdown of what CTE is and its relationship to contact sports.

WHAT IS CTE?

CTE is a degenerative disease caused by repeated impacts to the head, including both concussive and asymptomatic non-concussive hits. Doctors are only able to make a confirmed diagnosis after death, though common symptoms including aggression and dementia may surface while a patient is living.

WHAT IS THE RELATIONSHIP BETWEEN THE NFL AND CTE?

Research has found a connection between CTE and athletes who have competed in tackle football at both the professional and amateur levels.

The NFL has acknowledged a link between football-related concussions and CTE. In 2015, the league agreed to a roughly $1-billion settlement for concussion-related lawsuits with thousands of retired players after the deaths of some high-profile players.

Boston University's CTE Center diagnosed 345 former NFL players with CTE out of 376 studied, as of 2023.

"If they've been exposed to football for a long time, that increases their risk," Dr. Ann McKee, director of the CTE Center, told Reuters. 

DID TAMURA PLAY IN THE NFL?

Tamura did not compete in the NFL, the highest level of professional American football, but played at a Los Angeles