Isn't passed every time doesn't mean that there aren't correlations. I don't think they've isolated how it's passed, but I was pretty sure they know it is passed. It's not that most people do pass it on. We just have higher risks.

Heck, I'd worry more about passing on my families heart & cancer problems than my MS, and so far I've had neither cancer nor heart problems. We all pass some of the good and some of the bad. It's a crap shoot on what's sent.