Veterans now face two daunting questions arising from a third study linking concussions with degenerative brain diseases, which can cause cognitive, behavioral and mood impairment – and ultimately death.

The newest study, another collaboration between Boston University and the Boston VA Healthcare System, found evidence of chronic traumatic encephalopathy (CTE) in 68 brains that had been donated to them posthumously. They included 64 athletes, including 18 who were also military vets, plus three additional vets without a sports background and one individual who was neither – he had a history of injurious head-banging behavior.

Among the athletes, 34 were professional football players. However, nine of the athletes had played only college football. And six had played only high school football.

But all showed the classic signs of CTE: tangled knots of a protein known as tau in the brain cells. These tau lesions can damage brain cells and ultimately lead to their death, according to Dr. Ann McKee, lead author of the study.

The study also added another new element. It concluded the CTE is a progressive disorder, and it divided CTE into four stages, each with its own distinctive symptoms. Headaches and deteriorating attention and concentration were common in stage one. In stage two, symptoms expanded to include depression, explosive outbursts, and short-term memory impairment.  By stage three, victims were having trouble thinking and were having difficulty with executive functions like planning, organization, multitasking and judgment. Dementia , including memory loss and cognitive impairments  severe enough to impact daily living, were characteristic of stage four.

It’s alarming to think that high school and college football players could be doing such damage to their brains that they would die early of degenerative brain diseases, but the study provided several examples: Eric Pelly, a former high school football and rugby player who died at the age of 18 from complications resulting from concussions and who was diagnosed with stage 1`CTE, and Ron Perryman, a former Boston College linebacker who died from respiratory failure associated with Amyotrophic  Lateral Sclerosis (ALS) at the age of 42 and was diagnosed with both CTE and motor neuron disease (MND).

So there are two daunting questions that vets, athletes and anyone suffering from brain injuries need to ask.

First, how and why does an earlier injury lead to a possible degenerative brain disorder years later?

And second, what can we do to prevent it?

We’ll consider those questions in the next two parts of this series of columns.