A 10-episode miniseries entitled “American Sports Story: Aaron Hernandez” debuts on Sept. 17 on FX. It explores the rise and fall of NFL player Aaron Hernandez — the New England Patriots tight end who was convicted of murder in 2015 and died by suicide in his prison cell two years later.

Hernandez was diagnosed with chronic traumatic encephalopathy, also known as CTE, after his death. The disease can cause impulsive and aggressive behavior, emotional instability and suicidal thoughts, . A researcher who studied Hernandez's brain that he had the most severe case of the brain disorder that she'd seen in a person his age, raising questions about the root of his violence.

Hernandez was 27 when he died. Researchers have not made a direct link between Hernandez’s disease and his behavior. Here what to know about CTE and Hernandez's brain.

CTE is an incurable degenerative brain disorder that causes the death of nerve cells in the brain due to repeated head injuries, according to Mayo Clinic. It doesn't appear right away and gets worse over time, . The condition can lead to behavioral changes, cognitive impairment and progress to other brain disorders, such as dementia.

CTE usually starts in the front of the brain, where most head trauma occurs, and then spreads over time to other regions, Dr. Jesse Mez, co-director of clinical research at Boston University’s Chronic Traumatic Encephalopathy Center, tells . The effects of CTE may take years to show, as the disease tends to .