I haven't done a whole heck of a lot of research, but if there is a genetic component, I wish breeders would DO SOMETHING about it!!!!!!
My little boy Charm had coliced 13 times by the time he was 3 years old! 7 of them required hospital visits. For a $500 horse, I sure have put thousands into him!!! But I'm not sure if perhaps the climate just didn't settle with him... we were in dry, sandy, dusty CA, with bad quality hay. Now, we have moved to CO and switched him to bagged hay, and so far (knocking on would) he hasn't had one problem. I own his mother as well, and she has "stomach o' steel" as we call it... this girl is the only one that never had problems with bad hay, and is pretty much a garbage disposal for anything she can get into her mouth. So if it's genetic, it either came from his father, or things like this skip a generation.
Perhaps it's just environmental though? Even if mine weren't all colicing, they were having other issues from the climate, frequent dehydration, sand intake, going off feed, etc. Not that you can blame anyone in those types of situations, but maybe it's just that whatever caused the first one to colic had the same effect on the other one. On the other hand, if it wasn't doing anything to your other horses, maybe their genetics caused it to only effect the two of them? Interesting....