Bipolar disorders etiology

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. 

Etiology and pathophysiology of bipolar disorder are shown in Table 69-2. 

Etiologic and Pathophysiologic Theories of Bipolar Disorder (Continued)... 

Bipolar disorder is characterized by episodes of mania or hypomania, which include hyperactivity, decreased need for sleep, and a euphoric or irritable mood. Additionally, persons with bipolar disorder may have episodes of depression similar to those seen in major depressive disorder. The lifetime prevalence of severe bipolar disorder is about 1% and 3-5% if milder cases are included, afflicting men and women equally. Both bipolar disorder and major depressive disorder tend to be episodic, and in the periods of time between episodes, persons may experience few or no symptoms. The etiology of bipolar disorder is predominately genetic, with a 70% concordance in monozygotic twins. The neurobiology of bipolar disorder is less well understood, and few animal models have been developed. Treatment of bipolar disorder usually involves mood stabilizer medications, including lithium, and the anticonvulsants valproate and carbamazepine. At times, antidepressant and antipsychotic medications are also used. 

There may be abnormalities in eiythrocyte membrane transport properties in patients with bipolar affective disorders, though the interpretation is confounded by the uncertainty with regard to the contribution of hypertension in patients who are coincidentally hypertensive and manic depressive. The administration of lithium also may cause adaptive change (93,117,135-137). This results in an increase in erythrocyte lithium concentrations after prolonged lithium therapy, which could be mediated either by increased flux into the cell or via reduction in efflux rate. An increased content of ankyrins, red cell membrane proteins affecting cytoskeletal structure and functions, has been found in some patients with bipolar affective disorder (138) and this raises further the role of erythrocyte membrane defects in the etiology of the disease. 

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