BMX legend Dave Mirra suffered from chronic traumatic encephalopathy (CTE) when he died.
A University of Toronto neuropathologist confirmed the diagnosis and had several other neuropathologists back up her findings.
Mirra was 41 when he died from a self-inflicted gunshot wound in February.
Mirra's brain displayed the same tau protein deposits that have been seen in football players who have been diagnosed with CTE, the Toronto neuropathologist, Dr. Lili-Naz Hazrati, told ESPN The Magazine.
"I couldn't tell the difference," she said. "The trauma itself defines the disease, not how you got the trauma.