https://www.washingtonpost.com/natio...bc3_story.html

"All people carry the APOE gene, which has many variations. A 2010 study found that athletes carrying three of the gene’s four minor variations were 10 times as likely as those who did not to have reported a concussion and more than eight times as likely to have suffered brain injury as a result."

http://www.huffingtonpost.com/ainiss...b_4394209.html

"On a positive level, the APOE gene, which has three variations -- APOE ε2, ε3, and ε4 -- helps control the distribution of fats and cholesterol in the body. But it also seems to control the way that neurons are repaired -- or aren't -- after a head injury. "If you have the wrong form," Stern explains, "it does something crazy in the brain.""

"The APOE ε4 has been specifically linked to concussions and mild traumatic brain injury and is also associated with increased risk of Alzheimer's disease. One study found that there was lower cognitive performance in older football players possessing it. But, most importantly, APOE ε4 has some strange linkage to chronic traumatic encephalopathy, or CTE. This is the degenerative brain disease that's seemingly linked to head trauma and is found in many retired football players."