Former pro football player Kevin Turner, shown here during a 1998 NFL game, has been diagnosed with chronic traumatic encephalopathy, known as CTE, a neurodegenerative disease associated with repeated head trauma.
Scientists believe repeated head trauma can cause CTE, a progressive degenerative disease of the brain. Symptoms include depression, aggression and disorientation, but scientists can definitively diagnose it only after death. Here are a few of the former athletes who have been diagnosed with CTE.
BMX star Dave Mirra, who was found dead of a self-inflicted gunshot on February 4, was found to have chronic traumatic encephalopathy.
Former Minnesota Vikings linebacker Fred McNeill died in November at 63 due to complications from ALS. However, an autopsy confirmed that he suffered from CTE. What makes McNeill's case even more remarkable, though, is that he was potentially the first to be diagnosed while alive. Doctors used an experimental new technology to examine his brain.
NFL MVP and Oakland Raiders quarterback Ken Stabler, who died in July, suffered from chronic traumatic encephalopathy, researchers at Boston University said.
Kansas City Chiefs linebacker Jovan Belcher shot and killed his girlfriend before killing himself two years ago. Pathology reports show he probably had CTE.
Hall of Famer Mike Webster was the first former NFL player to be diagnosed with CTE. After his retirement, Webster suffered from amnesia, dementia, depression, and bone and muscle pain.
Evidence of CTE was found in the brain of football player Lew Carpenter after his death in 2010 at the age of 78.
Pro Football Hall of Famer Louis Creekmur, who played for the Detroit Lions from 1950 to 1959, suffered decades of cognitive decline before his death.
Linebacker John Grimsley of the Houston Oilers died of an accidental gunshot wound to the chest. Analysis of his brain tissue confirmed damage to the neurofibrillary tangles that had begun to affect his behavior and memory.
Offensive lineman Terry Long of the Pittsburgh Steelers committed suicide by drinking antifreeze. Although the antifreeze caused swelling of the brain, football-related brain injuries were a contributing factor to his death.
Pro Football Hall of Famer John Mackey suffered from dementia for years before dying at the age of 69.
Ollie Matson, who played 14 NFL seasons starting in the 1950s, suffered from dementia until his death in 2011.
Andre Waters spent most of his 12 seasons with the Philadelphia Eagles before his suicide at age 44.
Wrestler Chris Benoit was found dead at his suburban Atlanta home along with his wife, Nancy, and son in an apparent murder-suicide. Testing found that the damage to his brain was similar to that of an elderly Alzheimer's patient.
Reggie Fleming, who played for six NHL teams, mainly in the 1960s, was the first hockey player to be diagnosed with CTE.
Hockey player Bob Probert was found to have CTE after suffering from heart failure at the age of 45.