Has there ever been any proof that Alis Parkinson's was caused by boxing?

Didn’t Rahman who had 10-15 fights get it around the same time?

 

He's a year younger but I don't remember him looking as bad at the same age as Muhammad. That could be because he wasn't in the public eye as much.

 

"Rahman, who began boxing alongside his older brother at age 10, stopped fighting in the late '60s. “I think my father's Parkinson's came out earlier because of boxing,” she said. “Whereas his brother, Parkinson's just came out in his 70s, late 60s. My father got it practically in his 30s…"