Aaron Hernandez had the most severe CTE case ever seen: Scientists reveal his brain tissue showed extreme damage to memory and impulse control

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Diagnosed: Aaron Hernandez killed himself at the age of 27 in April while serving life in prison for murder. The scientists who analyzed his brain have now confirmed it was the worst case of CTE they have ever seen

The neuroscientist who analyzed Aaron Hernandez's brain has confirmed that he suffered the worst case ever seen in someone so young, with severe damage to regions that affect memory, impulse control and behavior.

The 27-year-old former New England Patriots player killed himself in April while serving life in prison for murder.

In September, Dr Ann McKee of the CTE Center at Boston University posthumously diagnosed Hernandez with chronic traumatic encephalopathy, a football-linked disease that causes dementia and aggression.

On Thursday, Dr McKee formally presented her findings and confirmed that she had never encountered such extreme degradation in a young brain, pointing out areas of severe tissue damage and microbleeds likely caused by blows to the head.

They also found a variant of the APOE gene, which has been linked to increased risk of Alzheimer's, but the scientists emphasized that no gene could inflict the same damage as years of heavy impact from tackling.  

Dr McKee says she could not say for certain that Hernandez's criminal and suicidal acts were a result of his severe case of CTE, nor whether other 27-year-old players could plausibly have the same pathology. But she says Hernandez suffered substantial damage to several important regions, including the frontal lobe.

His attorneys have sued the NFL and football helmet maker Riddell, accusing them of failing to warn Hernandez about the dangers of football.

'In any individual, we can't take the pathology and explain the behavior,' Dr Ann McKee said, speaking at the landmark event at Boston's annual CTE conference.

'But we can say collectively, in our collective experience, that individuals with CTE and CTE of this severity have difficulty with impulse control, decision making, inhibition or impulses or aggression, often emotional volatility and rage behavior.' 

Worst case of CTE: These scans show how Aaron Hernandez's brain was so severely damaged compared to a healthy 27-year-old brain. He was diagnosed with stage three out of four, with four being the most severe. His scans reveal significant damage (circled) to regions that control memory, impulse control and behavior

Ann McKee, director of the BU CTE Center and chief of neuropathology for the VA Boston Healthcare System, and Victor Alvarez MD, neuropathologist at VA Boston Healthcare System, conduct the post-mortem study of the brain of former NFL player Aaron Hernandez

Hernandez (pictured in November 2011 during his first season) was regarded as one of the NFL's top tight ends. He landed a $40 million contract with the New England Patriots in 2012

Dr McKee told the conference that the only other brains they have studied with this level of damage were at least 20 years older than Hernandez. 

'In this age group, he's clearly at the severe end of the spectrum,' McKee said. 

'There is a concern that we're seeing accelerated disease in young athletes. Whether or not that's because they're playing more aggressively or if they're starting at younger ages, we don't know. But we are seeing ravages of this disease, in this specific example, of a young person.' 

Hernandez was diagnosed with stage three out of four, with four being the most severe.

His brain scans reveal huge clumps of tau protein in Hernandez's frontal lobes, and in the nerve cells around small blood vessels, a unique feature of CTE.

These proteins, also seen in dementia, disrupts the normal functioning of the brain, triggering aggressiveness, explosiveness, impulsivity, depression, memory loss and other cognitive changes.

Boston's ongoing investigation into football-linked brain injury is studying hundreds of former players' brains, including Aaron Hernandez, Junior Seau, Dave Duerson, and Andre Waters - all of whom committed suicide and had CTE.

Seau and Duerson both shot themselves in the chest with the expressed intention of donating their brains to scientists to examine them for disease. 

As expected, tests subsequently showed that both men and Waters, who were all over the age of 40, had CTE. Hernandez, however, was in his mid-20s - with a far more severe pathology.  

Pieces of Aaron Hernandez's brain in the Boston University lab

A close-up look at Hernandez's brain and the severe damage to it

This is Hernandez's brain scan: It shows the classic features of CTE. There is severe deposition of tau protein in the frontal lobes of the brain (top row). The bottom row shows microscopic deposition of tau protein in nerve cells around small blood vessels, a unique feature of CTE

Dr McKee cautioned that she has not received many brains of players so young who played to such a high level as Aaron Hernandez, who started playing before the age of eight and was regarded as one of the NFL's top tight ends.

The tests showed Hernandez had early brain atrophy and large perforations in the septum pellucidum, a central membrane which is essential to control behavior.

Hernandez's brain scans revealed he had a variant of the APOE gene, which has been linked to neurodegenerative diseases like Alzheimer's, a similar disease to CTE. However, CTE uniquely affects certain nerve cells which Alzheimer's appears not to. 

Chronic traumatic encephalopathy (CTE) is a degenerative brain disease that is caused by repeated hits to the head. 

Over time, these hard impacts result in confusion, depression, dementia, explosiveness, aggression, and suicidal thoughts.

Researchers are still unclear on how CTE affects behavior, but a growing swell of studies is offering some answers.

• CTE sufferers have clumps of tau protein built up in the frontal lobe, which controls emotional expression and judgment (similar to dementia)
• This interrupts normal functioning and blood flow in the brain, disrupting and killing nerve cells
• By stage 3 - i.e. Hernandez's stage - the tau deposits expand from the frontal lobe (at the top) to the temporal lobe (on the sides). This affects the amygdala and the hippocampus, which controls emotion and memory

The disgraced star had a $41 million NFL contract when he was arrested at his home in June 2013 and charged with the murder of a semi-pro football player Odin Lloyd.

Lloyd was the boyfriend of Hernandez's fiancee's sister. He was found dead in an industrial park on June 17, 2013, riddled with bullets. Surveillance footage showed Hernandez at the scene an hour before, then arriving at home minutes after gunshots were fired. 

In April 2015, Hernandez was convicted of first-degree murder, and sentenced to life in prison.

While in prison, Hernandez was charged with another killing - a double murder committed by a drive-by shooting. But in April this year, he was acquitted of both charges. 

The next day, he took his own life. 

His family has since filed a lawsuit against the NFL and the Patriots on behalf of Hernandez's four-year-old daughter Avielle, claiming the club and the league knew about the connections between football and CTE long before Hernandez was drafted.

From golden boy to convict: The tragic story of Aaron Hernandez 

Aaron Hernandez was born into a sports dynasty, and he was a star.

Growing up in Bristol, Connecticut, he excelled in football, basketball, and sprint running.

But his idyllic childhood took a turn at the age of 16 in 2006 when his father, a coach who was his inspiration and best friend, died during a routine hernia surgery.

Hernandez left high school in January 2007 to join the University of Florida Gators.

Within months, he was involved in a fight, sucker-punching a restaurant manager. The police report said he ruptured the man's eardrum.

He was also suspended for marijuana.

And in his sophomore year, he was named in a police report about a club shooting, naming him as one of a few Gator players which triggered the argument.

But despite his run-ins with the law, he was incredibly skilled.

Hernandez smiles from the sidelines in the fourth quarter during a game against the Houston Texans in December 10, 2012, shortly after landing his $40 million contract

It meant he was able to skip his senior year to go pro in 2010.

He was expected to be the first pick. Ultimately, he was left until the fourth pick, selected by the Patriots. It has since emerged that Hernandez had written a personal letter to the team asking them to draft him - a factor which was likely significant.

And they weren't disappointed. In 2012, he landed a $40 million contract for his third season.

But he didn't see that season through.

In June 2013, Hernandez was arrested and charged with the murder of Odin Lloyd, the boyfriend of his fiancee's sister.

Lloyd was a semi-pro football player. He was found dead in a park on June 17, 2013, with bullet wounds.

Indicted: Hernandez is escorted into the courtroom of the Attleboro District Court for his hearing on August 22, 2013 in North Attleboro, Massachusetts

On June 28, Hernandez was detained, with an arrest warrant that said he was seen with Lloyd at 2.30am on the day of his murder. Gunshots were heard at around 3.25am, and at 3.29am, surveillance footage showed Hernandez arriving home in his car, which was five minutes from the crime scene.

In April 2015, Hernandez was convicted of first-degree murder, and sentenced to life in prison.

While in prison, Hernandez was charged with another killing - a double murder committed by a drive-by shooting. But in April this year, he was acquitted of both charges. 

The next day, he took his own life, and penned three suicide notes, including one to his fiancee Shayanna Jenkins.

They were discovered in the cell were Aaron Hernandez hanged himself, leading investigators to officially declare his death a suicide.

The notes were discovered next to a Bible opened to John 3:16, the same verse that Hernandez had written across his forehead in marker.

That verse reads: 'For God so loved the world that he gave his one and only son, that whoever believes in him shall not perish but have eternal life.'