In doing studies with Amish people for over 40 years in Pennsylvania, and then analyzing the data, the authors of this paper noticed that a rare form of dwarfism caused by a homozygous recessive mutation in a gene called Sonic Hedgehog (named by nerds who work on drosophila genetics, as they discovered this gene) is NEVER comorbid with bipolar disorder. Sonic Hedgehog is a gene involved in embryogenesis! So a mutation in it can affect many pathways downstream. But since people who have this form of dwarfism NEVER have bipolar d/o, it is thought that Sonic Hedgehog may be protective against bipolar d/o. Now to find out what does the Sonic Hedgehog gene do that is protective. Might take a while… But a very interesting article. And hopefully helpful to us sooner than later.

http://www.nature.com/mp/journal/vaop/ncurrent/abs/mp2014118a.html