On a warm September night in Boston, Dr. Ann McKee leaned over the brain slice placed before her. The slice displayed the gaping holes in brain structure characteristic of the degenerative brain disease known as chronic traumatic encephalopathy, or CTE.

The brain being examined was that of Aaron Hernandez, an ex-NFL star who was convicted of murder in 2015 and sentenced to life without the possibility of parole. In April, two years after his conviction, Hernandez killed himself in prison. He was 28.

Dr. McKee’s research team at Boston University determined that Hernandez had developed stage III CTE prior to his death. CTE has been found in a wide array of football players ranging from the high school to professional level, and Hernandez is not the only ex-NFL player to commit suicide after the development of this degenerative brain disease.

One of the largest challenges associated with CTE is that it can only be diagnosed in the deceased. As Whitman College Professor of Biology Thomas Knight explained, “CTE is only detected in the brain post-mortem. So far there are no clinical diagnostic tools to detect CTE in living subjects.”

In 2013, Hernandez was arrested for the murder of Odin Lloyd, who was dating the sister of Hernandez’s fiancée. Hernandez had been a star tight end for the New England Patriots and the former University of Florida All-American was one of the rising stars in the NFL prior to his arrest and subsequent conviction.

According to the researchers at Boston University, “CTE is associated with aggressiveness, explosiveness, impulsivity, depression, memory loss and other cognitive changes.”

Following the stage III CTE diagnosis, Hernandez’s fiancée Shayanna Jenkins-Hernandez and daughter Avielle Hernandez sued the NFL. The suit accuses the NFL of knowingly withholding medical information from Hernandez and explaining that, “Aaron was exposed to repeated traumatic head impacts between 2010 and 2013, greatly increasing the risk he would develop a degenerative neurological disorder, such as CTE.”

According to Hernandez’s former agent and lawyer, Javier Baez, the Boston University researchers stated this was “the most severe case they had ever seen in someone of Aaron’s age.”

Although Hernandez may represent a case study that demonstrates the many severe symptoms associated with CTE, he is far from the only player to have developed the disorder following a career in the NFL.

In July, a study in the medical journal JAMA revealed that CTE was detected in 110 of the 111 brains of ex-NFL players studied. Even more strikingly, this same study discovered CTE in 48 of the 53 college players and 3 of the 14 high school players examined.

This study determined 4 different stages of CTE and acknowledged that repeated hits to the head can lead to the accumulation of a protein called Tau in certain regions of the brain.

In response to the study, the NFL released a statement, noting “there are still many unanswered questions relating to the cause, incidence and prevalence of long-term effects of head trauma such as CTE.” The NFL promised to donate $100 million dollars in support of independent medical research in the field of neuroscience.

Whitman College does not have a football program, but repeated hits to the head can occur in many sports ranging from soccer to basketball.

Although these studies may not have a major impact on the NFL—a powerful corporation with extensive lobbying power—they may have a widespread impact on if parents decide to allow their children to play football growing up. Hopefully these scientific discoveries will lead to a safer sports landscape for all.