I found this a week or so ago. It's just an abstract, but it is some interesting news.

Link: http://www.pnas.org/content/early/2015/02/09/1424958112.abstract

And here's an article on it : http://isbmolecularme.com/a-breakthrough-in-understanding-the-genetic-architecture-of-bipolar-disorder/

Additionally,  here are some sources for the polymorphism question you had.

Link: http://www.futuremedicine.com/doi/abs/10.2217/14622416.9.11.1589

You may already have read these, but I hope they help!