Jon Hamilton reports on NPR about three research studies showing that schizophrenia, while having a definite genetic component may need a viral kicker to turn on the appropiate genes in utero. An old Danish twin study that I read about 25 years ago, and can't cite, shows a link between birth trauma, in genetically susceptible people, and schizophrenia. I guess you have to have the genes, then have something else needs to happen.

Here's the link: