Bipolar Disorder and Genetics
What is bipolar disorder, and how is it recognized?Bipolar disorder is a mood disorder characterized by episodes of manic mood and behavior. These manic episodes often precede or follow episodes of depressed mood, which is why the disease is also referred to as manic depressive illness.
The American Psychiatric Association has established criteria for recognizing the manic phase of bipolar disorder such as:
The person's mood may seem too happy, high, excited, irritable, or angry for most of the time, day and night, over several days.
During this period of time, at least three of the following symptoms are present (four, if the primary mood is irritability):º Inflated self-esteem or grandiosity
º Decreased need for sleep
º Racing thoughts
º Increased physical, mental, sexual activity
º Reckless behavior such as spending sprees, promiscuity, foolish business investments, erratic driving.
The mood disturbance is severe enough to damage one's job, affect relationships, or require hospitalization.
During this period of disturbed mood, the person may hear voices, have visions, or have beliefs or behavior that seem strange or unusual.
Is bipolar disorder a genetic condition?
Bipolar disorder runs in families.
The children of parents with manic depression are at increased risk for developing the disease themselves, even if they are adopted and raised by parents who do not have this condition. This clearly points to the involvement of genetic influences.
Twin studies provide additional support for the importance of genetic factors. The identical twin of someone who suffers from manic depression is at a much greater risk for the illness than a fraternal twin. Because identical twins share all their genes and fraternal twins share only half their genes, this difference in risk highlights the role of heredity as a cause of the disorder.
Do other factors play a role in determining who develops the disorder?
Environmental factors are also believed to play a role in determining who is susceptible to the disease. Such factors may include certain viral infections, toxic agents, and emotional stress.
What is currently known about the specific genes involved?
Because bipolar disorder, or manic depression, is common in the general population, it is believed that several -- possibly many -- genes are involved in the illness. (About 1% of the population suffer from bipolar disorder, and an additional 10% to 15% have related conditions such as hypomania and depression.)
In recent years, linkage between the illness and genetic markers has been reported by several investigators, but the genes themselves have yet to be isolated.
The Columbia Bipolar Genetic Study has reported a possible marker for the disease gene on chromosome 21. This finding has been reproduced by other investigators.
Other groups have reported possible markers on other chromosomes, including chromosomes 4, 13, 18, and the X-chromosome.
The disease may not be caused by the same gene or genes in all individuals.
Some genes may be involved because they interact with other genes.