What is the major cause of chronic traumatic encephalopathy? What are symptoms of this disorder?

Many sports, like soccer, hockey and football, involve player-on-player or player-equipment collisions in which injuries, such as concussions, are common. A concussion is a brain injury. Athletes who experience multiple concussions, that is, repeated mild traumatic brain injury, are at risk to develop a progressive form of neurodegeneration known as chronic traumatic encephalopathy (CTE).
First identified in boxers, CTE is associated with symptoms of irritability, impulsivity, aggression, depression, short-term memory loss and heightened suicidality, typically appearing 8-10 years after the disease onset. As CTE advances, dementia appears. Gait and speech abnormalities are common, and in the late stages, CTE may be mistaken for Alzheimer's disease. CTE has been identified in football, hockey, wrestling, and rugby players and may accompany exposure to blast or concussive injury associated with military service.