Ex-NFL Player, 25, With CTE Highlights How Dangerous Disease Can Develop Early

— -- The confirmation that a former NFL player had signs of CTE (chronic traumatic encephalopathy) at age 25 has highlighted how the debilitating illness can strike even those in the first few years of their careers.

The degenerative disease involves a buildup of the abnormal protein called tao, which is also found in Alzheimer's patients and is associated with a breakdown of brain tissue. It's believed to be caused by repetitive trauma to the brain, according to the CTE Center at Boston University, and symptoms include memory loss, confusion, impulse control problems, aggression, depression anxiety and progressive dementia.

The family of Adrian Robinson Jr. confirmed through their attorney that the former football player had CTE at the time of his death, when he committed suicide by hanging.

Robinson tested positive during a posthumous CTE test at the brain bank in Boston University, his family attorney confirmed to ABC News. CTE can only be diagnosed posthumously after researchers examine brain tissue for specific proteins and lesions.

Robinson died after a two-year career in the NFL. Ben Andreozzi, the attorney for Robinson’s family, told ABC News that the lineman had at least two reported concussions during his NFL career.

Andreozzi said that after he experienced multiple concussions, Robinson’s family started to notice behavioral changes in the man, who played for the Redskins and Steelers.

“After he took his life, [his family] started reflecting and realized he had become a bit more aggressive, angry and developed a little bit of a darker side,” Andreozzi said. “Prior to the concussions, by all accounts, he was a wonderful person to be around.”

Experts say Robinson's case highlights how much more study is needed to understand who is affected by the disease and at what age.

Dr. Allen Sills, a neurosurgeon at Vanderbilt University Medical Center in Nashville, Tennessee, explained that experts are still unable to diagnose CTE while a patient is alive, making study incredibly difficult.

"We are still learning exactly what CTE is and how to diagnose it," Sills explained. "To date we are not able to diagnose it to prior to death. We really don’t have a good understanding of who may develop it."

Additionally, Sills pointed out that signs of CTE often include behavioral changes but that it's nearly impossible to directly link those changes to a CTE diagnosis.

"It’s difficult to correlate changes seen in the brain during autopsy to behavior during life," he explained.

David Hovda, professor of neurosurgery and director of UCLA's Brain Injury Research Center, said while being 25 with CTE is "unusual," it was not unheard of and that even a teenager has been found to have the disease.

Hovda said one problem is that experts still aren't sure why some people react differently to concussions and who is at greater risk for destructive symptoms.

"There are players and athletes that are more susceptible … to having long-term problems following a single concussion," he explained.