A study conducted by the National Institutes of Health has determined that NFL linebacker Junior Seau suffered from a degenerative brain disease called chronic traumatic encephalopathy, or CTE. The diagnosis brings closure, but also mixed feelings to his family.

Junior Seau was a professional football player, beloved both on and off the field. During his 20-year career, he played for the San Diego Chargers, leading the team to its only Super Bowl appearance. He also played for the Miami Dolphins and finished his career with the New England Patriots. He retired in 2009. Last year, Seau committed suicide, dying from a single self-inflicted gunshot wound to the head.

Immediately afterwards, Seau's family was inundated from calls from researchers who asked if they could study the athlete's brain. They settled on the National Institutes of Health.

The National Institutes of Health conducted a study on his brain that was "blinded" in order to determine that researchers would come to an independent conclusion, according to ESPN. Three neuropathologists outside the NIH were given three brains. One belonged to Seau, one belonged to a person who had suffered from Alzheimer's disease and one belonged to a person who had suffered from no neurological disorder. Each pathologist, and two government researchers, concluded that Seau had CTE.

The NIH explains that "the neuropathologists found abnormal, small clusters called neurofibrillary tangles of a protein known as tau within multiple regions of Mr. Seau's brain," in a statement. "Tau is a normal brain protein that folds into tangled masses in the brain cells of patients with Alzheimer's disease and a number of other progressive neurological disorders. The regional brain distribution of the tau tangles observed in this case is unique to CTE and distinguishes it from other brain disorders."

The study of CTE and football is still just beginning. While boxers were long determined to have a connection with the disease, which has been linked to repetitive hits to the head, the link between CTE and football was only formally established in 2005.

However, Seau is not the first professional football player who has committed suicide and has received a diagnosis of CTE. Dave Duerson and Ray Easterling have also suffered the same fate, the Associated Press reports. Mary Ann Easterling, Ray Easterling's widow, is one of nearly 4,000 plaintiffs named in at least 175 lawsuits against the NFL who argue that the league has withheld all of the harmful effects that concussions can have.

The NFL has donated $30 million to the National Institutes of Health.

According to Boston University's Center for the Study of Traumatic Encephalopathy, CTE is characterized by symptoms like aggression, confusion, dementia, depression, impaired judgment, impulse control problems and memory loss.

The family says that the diagnosis helped explain Seau's personality changes over the past few years.

Jake Seau, a high school junior who quit football to focus on lacrosse, said, "He lived for those games, Sunday and Monday nights, you know? And to find out that that's possibly what could've killed him or caused his death is really hard."