I honestly don't know much about the causes of the disease but I don't think taking blows to the head is an initial cause. Maybe it increases the of severity if it's already there.

It is such a shame though, I have often wondered what Ali would be like on TV these days as a proud old man still cracking jokes and all on talk shows and stuff. He was just so quick witted and funny, I often watch the Parkinson interviews because he was so damn entertaining to listen to.