How researchers will look for signs of CTE in Hernandez's brain

The neurodegenerative disease can only be diagnosed after death.

Hernandez will be the latest former NFL player to be examined by the Boston University Chronic Traumatic Encephalopathy Center, which has found signs of CTE in 90 deceased players.

What is CTE?

Chronic Traumatic Encephalopathy is a neurodegenerative disease that can cause the brain to atrophy and change over time. It is believed to be caused by repeated blows to the head -- especially concussive injuries -- although researchers are also investigating if genetics could be a component in the development of CTE.

Dr. Brian Appleby, a neurologist in the Brain Health and Memory Center at the University Hospitals Cleveland Medical Center, told ABC News that there are specific types of blows to the head that predispose someone to the disease.

Appleby said these are typically "high velocity blows," including ones that are similar to those received by "wide receivers or cornerbacks who run really fast and then stop all of a sudden."

He added that these kinds of blows can also affect members of the military who are "too close to an IED explosion."

Additionally, repeated head traumas "immediately after each other" are associated with increased CTE risk, Appleby said.

How do researchers find CTE?

CTE can only be diagnosed during a posthumous examination of the brain. Tell-tale changes in the frontal lobe of the brain are one indicator of the disease, Appleby said.

"By looking at the structure of the brain, they [can] see shrinkage and atrophy at the frontal temporal lobe," Appleby said. "That can affect mood and behavior."

That's one reason why CTE "looks different than any other neurodegenerative condition," Appleby explained.

What are the symptoms of CTE?

Appleby said in some cases, the disease can result in symptoms similar to ALS or amyotrophic laterals sclerosis, which can result in a person losing control of their muscles.

Who gets CTE?

The disease used to be considered a disease that primarily affected former boxers, but it has also been found in former football players, hockey players, and military veterans. Playing these sports into adulthood isn't necessarily why people get CTE; some trauma to the brain in childhood may cause CTE to develop later on.

CTE has been diagnosed in people as young as 17.

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