I agree with RxQueen. I think people are born with BP and that the MI "reveals itself" once something triggers it.

In the same vein, I believe that people who carry genes for BP may never experience BP because nothing triggers the disorder. However, that logic implies those with BP genes can pass down those genes and that's why some people appear to have no family history of BP.

Of course, BP is a genetic mutation. The disorder had to have started *somewhere*. So I do think that sometimes people who don't have a family history may have the genetic mutation occur during pregnancy.