Doctors don't completely understand the causes of bipolar disorder. But they've gained a greater understanding in recent years of the bipolar spectrum, which includes the elated highs of mania to the lows of major depression, along with various mood states between these two extremes.
Bipolar disorder seems to often run in families and there appears to be a genetic part to this mood disorder. There is also growing evidence that environment and lifestyle issues have an effect on the disorder's severity. Stressful life events -- or alcohol or drug abuse -- can make bipolar disorder more difficult to treat.
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Experts believe bipolar disorder is partly caused by an underlying problem with specific brain circuits and the balance of brain chemicals called neurotransmitters.
Three brain chemicals -- noradrenaline (norepinephrine), serotonin, and dopamine -- are involved in both brain and bodily functions. Noradrenaline and serotonin have been consistently linked to psychiatric mood disorders such as depression and bipolar disorder. Dopamine is commonly linked with the pleasure system of the brain. Disruption to the dopamine system is connected to psychosis and schizophrenia, a severe mental disorder characterized by distortions in reality and illogical thought patterns and behaviors.
The brain chemical serotonin is connected to many body functions such as sleep, wakefulness, eating, sexual activity, impulsivity, learning, and memory. Researchers believe that abnormal functioning of brain circuits that involve serotonin as a chemical messenger contribute to mood disorders (depression and bipolar disorder).
Is Bipolar Disorder Genetic?
Many studies of bipolar patients and their relatives have shown that bipolar disorder can run in families. Perhaps the most convincing data come from twin studies. In studies of identical twins, scientists report that if one identical twin has bipolar disorder, the other twin has a greater chance of developing bipolar disorder than another sibling in the family. Researchers conclude that the lifetime chance of an identical twin (of a bipolar twin) to also develop bipolar disorder is about 40% to 70%.
In more studies at Johns Hopkins University, researchers interviewed all first-degree relatives of patients with bipolar I and bipolar II disorder and concluded that bipolar II disorder was the most common affective disorder in both family sets. The researchers found that 40% of the 47 first-degree relatives of the bipolar II patients also had bipolar II disorder; 22% of the 219 first-degree relatives of the bipolar I patients had bipolar II disorder. However, among patients with bipolar II, researchers found only one relative with bipolar I disorder. They concluded that bipolar II is the most prevalent diagnosis of relatives in both bipolar I and bipolar II families.