Mental Disorder, Depression

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Depression, a mental disorder in which sadness, dejection, and anger last for a prolonged period of time, affects an estimated 350 million people around the world (WHO, 2012). In the United States, clinical depression, the leading mental illness, is diagnosed in one out of every ten adults and continues to be a growing health concern, especially among teenagers (Hettema, 2010). Though frequently perceived as acquired through environmental stress, the onset of depression, suggested by recent studies, is often facilitated by genetic factors. The genetic basis of depression was first assessed in the early 1990s. In one study, researchers surveyed incidences of depression among identical and fraternal twins, respectively sharing 100% and 50% of genetic make-up, hypothesizing that the former would display higher resemblance for the condition of depression if the disorder is hereditary. Indeed, collected data showed that both identical twins had experienced depression in 67% of observed cases, while the same condition occurred among 19% of fraternal twins (Hettema, 2010). The conclusion follows that genes are indeed part of the cause as the heritability of depression was projected to be 37-50%. Soon after, a systematic meta-analysis of surveys found individuals biologically related to depression patients to be three times as likely to develop the condition as those without a family history of the disorder (Sullivan, 2000). In the past decade, molecular studies mapping the loci of
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