What are the Genetic Factors of Bipolar Disorder?
Important evidence supporting a genetic cause of bipolar disorder has been found in epidemiologic research (twin and family studies) and gene identification efforts. Twin studies have found that among identical twins, if one twin has bipolar I disorder, there is a 33% to 90% chance that the other twin will also have the disorder. In contrast, among nonidentical twins, if one twin has the illness, there is only a 5% to 25% chance the other twin will be affected.
Family studies have found that first-degree relatives of bipolar I disorder probands (the original family members studied) are more likely to have bipolar I disorder than first-degree relatives of control subjects. Moreover, bipolar disorder tends to be more prevalent among relatives of people with unipolar depression than among relatives of those without mood disorders.
Although researchers have not yet found a specific gene for bipolar disorder, associations between mood disorders (particularly bipolar I) and genetic markers have been reported for chromosomes 5, 11, and X.
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