Former NFL player Kevin Turner had the most advanced stage of chronic traumatic encephalopathy (CTE) when he died, Boston University brain researchers announced Thursday.

Dr. Ann McKee said at a Thursday news conference that an autopsy showed Turner had died of the brain trauma-related condition, rather than amyotrophic lateral sclerosis (ALS), otherwise known as Lou Gehrig’s disease. Turner had been diagnosed with ALS, a motor neuron disease that presents itself similarly to CTE.

“This is not ALS; this is CTE,’’ McKee said. “The severity of Mr. Turner’s CTE was extraordinary and unprecedented for an athlete who died in his 40s.”

Turner died in March at age 46. He had spoken of his certainty that his declining physical state leading to his death was due to his football career. Doctors said they believed he had such advanced CTE because he endured decades of head traumas while playing football.

“We believed the extreme severity of Kevin Turner’s disease is related to his 25-season career and the fact that he began playing tackle football at age 5, while his brain was still rapidly developing and more vulnerable,” said B.U. professor Robert Cantu.

NFL officials had denied any links between CTE and football, but league executive Jeff Miller admitted to the link in March. McKee’s research originally established a link between CTE and ALS in 2010.

Get The Brief. Sign up to receive the top stories you need to know right now. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Julia Zorthian at julia.zorthian@time.com.