Bipolar disorder (BD) is a paradigmatic complex phenotype with many genetic and non-genetic determinants. BD is characterized by episodes of mania and depression (1). Onset is usually in late adolescence, although BD typically recurs and relapses throughout life. BD affects approximately 1% of the world’s population, and carries a lifetime risk for completed suicide as high as 17%. Family, twin, and adoption studies all support a substantial genetic component in BD (2-4). The sibling recurrence risk is between 7 and 10, and heritability is estimated to be about 80%. While this is consistent with a strong genetic component, the identification of specific genetic variations that influence BD susceptibility has been difficult.
