Mirra killed himself in February after a concussion-filled sports career
                                
                                
                                    (Newser) -
                                    Dave Mirra, the legendary BMX star who  killed himself  in February, had chronic traumatic encephalopathy—a disease more commonly seen in football players and boxers,  ESPN  reports. He's believed to be the first action sports athlete to be diagnosed with it. "The key is brain injury," says...