This idea is a bit of a leap but the article below indicates that there are genes that govern how stress can effect us.  If there is a gene that may explain why some people suffer post-traumatic stress disorder, maybe there is a gene that explains why some people get mm. David

"A stress-related gene may help explain why some people suffer post-traumatic stress disorder, a study in JAMA said."

http://online.wsj.com/art...

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