text: (CNN) -- His was a suicide with a macabre twist. In February, former Chicago Bears safety David Duerson shot himself in the chest, but not before leaving behind a note requesting his brain be studied for evidence of a disease striking football players. 
  
  The plaintive note read, "Please, see that my brain is given to the NFL's brain bank." 
  
  Today, scientists announced that Duerson's brain tissue showed "moderately advanced" evidence of chronic traumatic encephalopathy, a dementia-like brain disease afflicting athletes exposed to repeated brain trauma. 
  
  "Dave Duerson had classic pathology of CTE and no evidence of any other disease," said Dr. Ann McKee, a neuropathologist with the Bedford VA Medical Center, and co-director of the Boston University School of Medicine Center for the Study of Traumatic Encephalopathy. "He had severe involvement of areas that control judgment, inhibition, impulse control, mood and memory." 
  
  CTE has been found in the brains of 14 of 15 former NFL players thus far studied at the center. Their cases share a common thread -- repeated concussions, sub-concussive blows to the head, or both. The picture beginning to emerge from these cases is that trauma could be causing brain damage. 
  
  A brain with CTE is riddled with dense clumps of a protein called tau. Under a microscope, tau appears as brown tangles that look similar to dementia. Except the cases of CTE have shown this progressive, dementia-like array in players well in advance of a typical dementia diagnosis, which typically occurs in the 70s or 80s. 
  
  Mike Webster, an offensive lineman with the Pittsburgh Steelers whose CTE was also diagnosed posthumously, was 50 when he died. John Grimsley, a nine-year NFL veteran who played most of his career with the Houston Oilers, was 45, and Duerson was 50. Scientists at Boston University have found evidence of CTE in the brain of an athlete as young as 18. 