Depression isn't the only psychological illness to encompass people from all walks of life. Almost 4 percent of U.S. adults suffer from bipolar disorder. Also called manic-depressive disorder and manic depression, a person with this condition swings between bouts of clinical depression and mania (a state of elevated irritability and energy that is essentially the opposite of depression). While most people who experience mania are also clinically depressed, the majority of people with depression do not also have episodes of mania [source: Levinson].
Bipolar disorder, like MDD, appears to be largely a result of genetics. Specifically, a number of adoption studies have shown that biological relatives of bipolar patients are substantially more likely to have the disorder than are adoptive relatives. While a major life change may trigger a manic or depressive episode in someone with the condition, biology appears to be the root cause of bipolar disorder. However, there is no evidence suggesting that an adopted person with bipolar disorder has the illness due to the mere fact that he or she is adopted [source: National Library of Medicine, Taylor].
Adoption may not increase a person's risk of psychological disorders, but it can lead to behavioral problems. Attention Deficit Hyperactivity Disorder (ADHD) -- distinguished from general misbehavior as a pattern of hostile, aggressive or disruptive behavior lasting six months or more -- affects somewhere between 5 and 9 percent of American children. With symptoms varying from inattentiveness to hyperactivity and impulsive actions, the causes of ADHD are difficult to pinpoint. There is a strong suggestion that the disorder can be inherited: 40 percent of children with ADHD will have a parent with ADHD [source: Adesman]. Nevertheless, a 2008 study published in the Archives of Pediatric and Adolescent Medicine indicates that although most adopted children are psychologically healthy, they are subject to "slightly increased risk" of ADHD; 15 percent of the adopted children studied suffered from ADHD, roughly twice the rate of the nonadopted subjects [source: Trudeau].
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