I agee with Meg, life is too short to focus on negative and the what ifs. My husband has ALS and we made a decision to not ruin today with worry about tomorrow. I admit we each have our moments, but for the most part we have done that since his diagnosis. Along with anti-depressants we are getting through this.
You could find yourself in a fit of worry, depression, and feelig hopeless if you found out. And, as we all pray a cure my be found and your worse fears may never be realized. Therefore, worry for nothing!
You could test positive, but this disease is crazy and you may never come through with any issues at all. So, I would vote....don't do it!