Scientists are learning about the possible causes of bipolar disorder. Most scientists now agree that there is no single cause for bipolar disorder; rather, many factors act together to produce the illness.
Because bipolar disorder tends to run in families, researchers have been seeking specific genes that may increase a person's chance of developing the illness. But genes are not the whole story. Studies of identical twins, who share all the same genes, indicate that both genes and other factors play a role in bipolar disorder. If bipolar disorder was caused entirely by genetics, then the identical twin of someone with the illness would always develop the illness, and research has shown that this is not the case. But if one twin has bipolar disorder, the other twin is more likely to develop the illness than is another sibling.
In addition, findings suggest that bipolar disorder, like other mental illnesses, does not occur because of a single gene. It is likely that many genes act together, in combination with other factors such as the person's environment. Finding these genes, each of which contributes only a small amount toward the vulnerability to bipolar disorder, has been extremely difficult. But scientists expect that the advanced research tools now being used will lead to these discoveries and to new and better treatments for bipolar disorder.
