Former NFL player who killed 6 people had stage 2 CTE

At least five dead after shooting in South Carolina 0:48

(CNN) -

A former NFL player who shot and killed six people before committing suicide in South Carolina this year had "unusually severe" stage 2 chronic traumatic encephalopathy (CTE).

It is a brain disease related to head injury, said a Boston University neuropathologist.

During a press conference Tuesday, Dr. Ann McKee said 32-year-old Phillip Adams had an extraordinary amount of CTE pathology in both frontal lobes of the brain.

The disease is characterized by an unusual accumulation of a protein called tau.

The severity of the disease is classified into four stages based on the amount and location of tau accumulation in the brain.

Stage 4 is the most serious.

McKee stated that Adams' pathology was similar to that of former NFL player Aaron Hernandez, who committed suicide while in prison for murder.

McKee had tested Hernandez's brain for the disease.

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Phillip Adams

"However, Adams's CTE pathology was different from other young NFL players with a CTE diagnosis. It was different in that it was unusually severe in both frontal lobes," he said.

In its predominantly frontal lobe, Adams's CTE pathology was similar to that of Hernández, 27.

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The disease can only be diagnosed after death.

What is the Adams CTE?

According to McKee's analysis published in 2017, Hernandez was found to have stage 3 CTE, which is commonly associated with memory and cognitive loss, as well as behavioral changes and impaired judgment.

Hernandez was found to have early degeneration of brain cells and large tears in a central brain membrane.

McKee said Tuesday that Adams' CTE pathology may have contributed to his behavior.

"When you have frontal lobe disease, you can have angry behaviors, violent tendencies, depression, impulsivity, all kinds of things. And that's, I think, what we saw in Phillip Adams," McKee told CNN's "New Day." this Wednesday.

Adams, 32, shot two technicians working on fixing the air conditioning outside the home of a prominent doctor in Rock Hill on April 7, authorities said.

He then broke into the home of Dr. Robert Lesslie, where Lesslie, his wife and two grandchildren, ages 5 and 9, were killed, authorities said.

One of the air conditioning technicians died at the scene and the other died days later.

At the time, authorities said they did not know Adams' motive.

York County Medical Examiner Sabrina Gast said April 9 that her office contacted Boston University to study Adams's brain to see if he had CTE.

In a statement, the Adams family said they are not surprised by the results.

Rather, they were shocked at how bad his condition was.

"As we process these results, we are deeply saddened by the events that occurred on April 7 and we continue to pray for the families of the victims. We are pleased to have a better understanding of the mental confusion that Phillip was facing during the last moments of his life." says the statement.

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How can CTE disease develop?

In football, CTE can occur not only from forceful blows that result in concussions, but from the constant rattling of the brain within the skull that occurs during tackles and other plays.

These repeated blows are known as subconcussive blows and can result in the accumulation of tau in the brain.

CTE develops when protein begins to clump around small blood vessels and in other parts of the brain.

From there, the protein spreads and destroys other parts of the brain.

There is no cure.

Boston University says neurodegenerative disease can lead to "memory loss, confusion, impaired judgment, impulse control problems, aggression, depression, suicidal tendencies, Parkinson's, and eventually progressive dementia."

Many colleges are trying to find ways to diagnose CTE in life, McKee said Wednesday.

"We are getting very close with brain scans, looking for the tau protein with imaging. We are getting very close with what we call fluid biomarkers, blood tests, as well as cerebrospinal fluid tests, but we haven't done it yet," McKee said. .

Soccer and degenerative brain diseases 4:46

Adams statistics

Adams played defensive back from 2010 to 2015 for teams such as the San Francisco 49ers, Seattle Seahawks, Oakland Raiders, New York Jets and Atlanta Falcons.

In 2012, he suffered two concussions in a three-game span with the Raiders, his former agent told CNN in April.

He had five interceptions and 121 tackles in 78 games, according to NFL.com.

He also returned 37 punts while with the Raiders and 49ers.

Adams played at South Carolina State University in Orangeburg prior to his NFL days.

He was a Rock Hill native and attended Rock Hill High School, according to the school's athletic media guide.

- CNN's Nadia Kounang and Steve Almasy contributed to this report.