Causes of Bipolar Disorder

Bipolar Disorder: What Causes Bipolar Disorder?

Doctors don't completely understand the causes of bipolar disorder. But they've gained a greater understanding in the past 10 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.

Experts do believe that bipolar disorder often runs in families, and there is a genetic component 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.

What causes bipolar disorder?

Experts believe bipolar disorder is partly caused by an underlying problem with 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. Another brain chemical, 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 serotonin levels contribute to mood disorders (depression and bipolar).

Is there a genetic link to bipolar disorder?

A multitude of controlled studies of bipolar patients and their relatives have shown that bipolar disorder does run in families. Perhaps the most convincing data comes from twin studies. In the studies of identical twins with the same genes, 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. Using statistical data, 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 further studies at Johns Hopkins, 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 onlyone 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.

Studies at Stanford that explored the genetic connection of bipolar disorder found that children with one biological parent with bipolar I or bipolar II disorder have an increased likelihood for getting bipolar disorder. In this study, researchers reported that 51% of the bipolar offspring had a psychiatric disorder, most commonly major depression, dysthymia (mild depression), bipolar disorder, or attention-deficit/hyperactivity disorder (AD/HD). Interestingly, the bipolar parents in the study who had a childhood history of AD/HD were more likely to have children with bipolar disorder -- but not AD/HD.

In other findings, researchers report that first-degree relatives of a person diagnosed with bipolar I or II disorder are at an increased risk for major depression when compared to first-degree relatives of those with no history of bipolar disorder. Scientific findings also show that the lifetime risk of affective disorders in relatives with family members who have bipolar disorder increases, depending on the number of diagnosed relatives.