Biological Theories of Manic-Depression Essay

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Biological Theories of Manic-Depression

Like every mental illness, there is no definitive evidence concerning the etiology of manic-depression, also known as bipolar disorder. The disorder is characterized by alternating periods of depression and mania and occurs in 1% of the population. The depressive episodes can range in severity from dysthymia to major depressive episodes. The major depressive episodes are classified as periods of at least two weeks in length during which sadness, lethargy, insomnia or excessive sleep, increase or decrease in appetite, hopelessness, and suicidal ideation or suicide attempts are present. Dysthymia is the milder form of depression, during which suicidal ideation and attempts are not present. Manic
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Many scientists have isolated single genes to which they believe manic-depression can be attributed; however, very few agree on which gene it is. Egeland (1987) announced that she and her colleagues had found a gene that provided a strong diathesis toward manic-depression on chromosome 11. Two different groups of researchers (Detera-Wadleigh et al., 1987 and Hodgkinson et al., 1987) found no connection between the same gene and manic-depression, which led to the theory that more than one gene may be responsible for the disorder. At the same time, Baron et al. (1987) announced they had found a genetic link between manic-depression and a different gene. Both Baron and Egeland later stated that their findings may be inconclusive ((1)). In 1993, Bredbecka et al. announced that the gene for manic-depression is on the X-chromosome; the next year Berrettini et al. (1994) reported to have found the gene that contributes to the disorder on chromosome 18 and Straub et al. (1994) reported it to be on chromosome 21. McMahon et al. (1995) found evidence to suggest that manic-depression was more likely to be inherited from mothers than from fathers, proposing that the gene for the disorder would be different in women and men. At the same time, Stine (1995) published a paper supporting the theory that the gene for manic-depression is on chromosome 18. Gershon’s research found that cases of manic-depression in which there