Causes of Bipolar Disorder

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Bipolar disorder has a number of contributing factors, including genetic, biochemical, psychodynamic, and environmental elements.

Genetics

• Bipolar disorder, especially BP-I, has a major genetic component. The evidence indicating a genetic role in bipolar disorder takes several forms.
1. First-degree relatives of people with BP-I are approximately 7 times more likely to develop BP-I than the general population. Remarkably, offspring of a parent with bipolar disorder have a 50% chance of having another major psychiatric disorder.
2. Twin studies demonstrate a 33-90% chance for BP-I in identical twins.
3. Adoption studies prove that a common environment is not the only factor that makes bipolar disorder occur in families. Children whose biologic parents have either BP-I disorder or a major depressive disorder remain at increased risk of developing an affective disorder, even if they are reared in a home with adopted parents who are not affected.
4. Numerous genetic studies of BPI disorder suggest multiple different genetic loci, but, as yet, no genes have been definitively identified. This is, in part, because many genes contribute small effects to the disorder in different individuals and, partly, because no objective means of identifying a particular genetic subtype is available. However, studies are ongoing, and technological and statistical advances may lead to a breakthrough in the next decade.

Biochemical Causes

• Multiple biochemical pathways likely contribute to bipolar disorder, which is why detecting one particular abnormality is difficult.
• A number of neurotransmitters have been linked to this disorder, largely based on patients' responses to psychoactive agents. For instance, the blood pressure drug reserpine was noted incidentally to cause depression. This led to the catecholamine hypothesis, which holds that an increase in epinephrine and norepinephrine causes mania and a decrease in epinephrine and norepinephrine causes depression.
• Drugs like cocaine, which also act on this neurotransmitter system, exacerbate mania. Other agents that exacerbate mania include L-dopa, which implicates dopamine and serotonin-reuptake inhibitors, which, in turn, implicate serotonin.
• Hormonal imbalances may contribute to the clinical picture of bipolar disorder.

Psychodynamic

Many practitioners see the dynamics of bipolar disorder as being linked through one common pathway. They see the depression as the manifestation of the losses, ie, the loss of self-esteem and the sense of worthlessness. Therefore, that mania serves as a defense against the feelings of depression. (Melanie Klein was one of the major proponents of this formulation.)

Psychodynamic

In some instances, the cycle either may be directly linked to external stresses or the external pressures may serve to exacerbate some underlying genetic or biochemical predisposition.

Pregnancy is a particular stress for women with a history of manic depression and increases the possibility of postpartum psychosis (Chaudron, 2003).

Risk Factors For Bipolar Disorder

Genetic or hereditary factors contribute to the risk of bipolar disorder. Studies have demonstrated that the prevalence of bipolar disorder is higher among the parents of bipolar patients. Eighty to ninety percent of individuals with bipolar disorder have a relative with either depression or bipolar disorder. However, hereditary factors are not the only cause of bipolar disorder.

Studies of identical twins suggest that both genes and other factors play a role in the cause of bipolar disorder. Identical twins share all the same genes. If bipolar disorder were caused entirely by genes, then the identical twin of a patient with the illness would always develop the illness, which is not the case. However, if one twin has bipolar disorder, the other twin is more likely to develop the illness. There is a slightly greater risk of developing the disease among siblings as well.

Personality. Although persons with any personality type can develop clinical depression, it is more common in persons with temperaments inclined to dysthymia and cyclothymia. Unipolar depression is more likely to develop in persons who are introverted and have anxious tendencies. Such persons often lack the requisite social skills to adjust to significant life pressures and have difficulty recovering from a depressive episode. Persons with bipolar disorders tend to be extroverted and achievement-oriented; they often use activity to combat depression.

Seasons. A higher incidence of bipolar disorder occurs in people who were born in the winter and in those who had experienced complications around the time of birth. The time of the year appears to play a role in increasing the risk for episodes. Mania is more likely to occur in the summer and depressive episodes from October through May (which is different from seasonal affective disorder, a depressive disorder that only occurs in darker months).

Socioeconomic Status. Bipolar disorder is more prevalent among people in a higher socioeconomic status. The rate of the disorder is estimated to be 10 to 20 times higher among people in the creative arts than in the general population.

Loss of a Parent.  Childhood loss of a parent does not increase a person's risk of developing a mood disorder. However, if such a person develops a mood disorder, depression tends to develop at a younger age and follow a chronically intermittent course, leading to marked personality disturbance and suicide attempts.

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Reviewed: 03/2006