Extreme sports suicides... or result of a lifetime accumulation of concussions CTS?

Jeff Phillips out of the blue dead at 30.  http://gwarizm.com/2011/04/27/the-jeff-phillips-tragedy/
Dave Mirra at age 40  http://justacarguy.blogspot.com/2016/02/dave-mirra-has-left-us-he-needed-out.html