Editor's Note: Dr. Sanjay Gupta gets a candid look at the mental deterioration of a former NFL player and the toll that chronic traumatic encephalopathy can take on a family on "Sanjay Gupta, M.D." at 7:30 a.m. ET Saturday and Sunday.
(CNN) -- Former NFL lineman Shane Dronett's transformation from an affable prankster, quick to flash a wry smile, to a person who was often frightened -- and frightening -- was subtle at first.
It began in 2006, with a bad dream.
"He woke up in the middle of the night and started screaming and told everyone to run out of the house," said Chris Dronett, Shane Dronett's wife. "He thought that someone was blowing up our house. It was very frightening."
Chris tried to dismiss the incident as isolated, except that two weeks later, there was another outburst, then another, until they were an almost-nightly occurrence. And as Shane's fear and paranoia began overwhelming him, so did episodes of confusion and rage that sometimes turned violent.
Only three years after retiring from the NFL in 2006, Shane was suffering. The tragic culmination of his pain came when he committed suicide in 2009 at 38.
Scientists at the Boston University School of Medicine's Center for the Study of Traumatic Encephalopathy tested Shane's brain tissue and confirmed that before he died he was suffering with a brain disease -- chronic traumatic encephalopathy -- that seems to afflict football players.
"There is evidence of CTE in his brain making him yet another former NFL player who had definite CTE," said Chris Nowinski, co-director of the traumatic encephalopathy center. Nowinski said the center has found evidence of CTE in the brains of 13 of 14 former NFL players, including Dronett.
Usually found in much older dementia patients, CTE is an accumulation of an abnormal protein in the brain called tau, which is associated with repeated head traumas -- concussions or subconcussive hits -- that are not allowed to heal. CTE can also diminish brain tissue and is associated with memory loss, depression, impulsive behavior and rage.X