[Genetic studies of bipolar disorder: a review]

Bipolar disorder is a severe mental illness that afflicts approximately 1% of the world's population, and is characterized by mood swings from elation to depression. Although the etiology of bipolar disorder remains unclear, heritable factors have been shown to be involved. Family, twin, and adoption studies suggest a genetic etiology. Molecular genetic studies also support a genetic component. Many chromosomal regions have been implicated by these molecular genetic studies, but no single susceptibility gene has been identified. These findings show that bipolar disorder has a complex genetic etiology in which multiple unidentified genes and environmental factors play an important role in its pathogenesis. Herein, molecular genetic studies of bipolar disorder are reviewed based on a search of Medline using the key words, bipolar, genetic, and chromosome. Studies with positive results for bipolar disorder were selected first. The findings from these molecular genetic studies are reviewed systematically, chromosome by chromosome. Causes of the differences between the reported findings and of non-replication are discussed. Finally, important factors for designing a genetic study of bipolar disorder are examined.