Bipolar disorders environmental factors

The precise etiology of bipolar disorder is unknown. Thought to be genetically based, bipolar disorder is influenced by a variety of factors that may enhance gene expression. These include trauma, environmental factors, anatomic abnormalities, exposure to chemicals or drugs, and others.3-5 Neurochemical abnormalities in bipolar disorder may be caused by these factors, as discussed further in the pathophysiology section. 

These data show that for three psychotic disorders (schizophrenia, bipolar disorder and unipolar depression) the genetic contribution is over 50% but for reactive depression (in response to a traumatic life event ) and tuberculosis, an infectious disease caused by a species of Mycobacterium, environmental factors account for over 90% of the variance. 

Major depressive and bipolar disorders arise from the interactions between the susceptibility genes and environmental factors 888... 

Both genetic and nongenetic factors play roles in the transmission of mood disorders. The familial nature of mood disorders is well established. Studies over the past 20 years have consistently documented higher rates of mood disorder in the relatives of individuals with major depression and bipolar disorder than in relatives of healthy controls [6,7], The familial aggregation of mood disorders is the outcome of both genetic and environmental factors. 

Nevertheless, this is an area of intensive research, with the potential for improved diagnosis and heatment. The best estimates are that several genes are involved (5-15). The environmental influence in bipolar disorder is less than that for major depressive disorder. Some risk factors have been identified, including negative stressful life events. 

Twin studies reviewed by Tsuang and Faraone (1990), demonstrate a concordance rate for monozygotic pairs of 58 to 74 percent and for same-sex dizygotic pairs of 17 to 29 percent. From these studies, the importance of shared environmental factors in bipolar disorder was also elucidated. 

Bipolar disorder is likely caused by genetic factors, environmental triggers, and the dysregulation of neurotransmitters, neurohormones, and secondary messenger systems in the brain. 

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