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As defined by experts, a mental disorder is "a clinically significant behavioral or psychological syndrome or psychological pattern that occurs in an individual and that is associated with present disability or with a significantly increased risk of suffering, death, pain, disability, or an important loss of freedom."〔American Psychiatric Association (APA). (2000). Diagnostic and Statistical Manual of Mental Disorders-Rext Revised. Washington, DC: Author〕 The causes of mental disorders are generally complex and vary depending on the particular disorder and the individual. Although the causes of some mental disorders are unknown, it has been found that different biological, psychological, and environmental factors can all contribute to the development or progression of mental disorders. Most mental disorders are a result of a combination of several different factors rather than just a single factor. ==Research results== Risk factors for mental illness include genetic inheritance, such as parents having depression, repeating generational patterns,〔(BMC Psychiatry | Full text | A three generation study of the mental health relationships between grandparents, parents and children )〕〔(Parents with Mental Illness: They Cycle of Intergenerational Mental Illness | Melanie Boursnell - Academia.edu )〕 and dispositions like personality. Correlations of mental disorders with drug use include cannabis, alcohol〔(JAMA Network | JAMA Psychiatry | Tests of Causal Links Between Alcohol Abuse or Dependence and Major Depression )〕 and caffeine. Particular mental illnesses have particular risk factors, for instance including unequal parental treatment, adverse life events and drug use in depression,〔(Cannabis and mental health )〕 migration and discrimination, childhood trauma, bereavement or separation in families, and cannabis use in schizophrenia and psychosis,〔 and parenting factors, child abuse, family history (e.g. of anxiety), and temperament and attitudes (e.g. pessimism) in anxiety. Many psychiatric disorders include problems with impulse and other emotional control. In February 2013 a study found common genetic links between five major psychiatric disorders: autism, ADHD, bipolar disorder, major depressive disorder, and schizophrenia. Abnormal functioning of neurotransmitter systems has been implicated in several mental disorders, including serotonin, norepinephrine, dopamine and glutamate systems. Differences have also been found in the size or activity of certain brain regions in some cases. Psychological mechanisms have also been implicated, such as cognitive (e.g. reasoning) biases, emotional influences, personality dynamics, temperament and coping style. Studies have indicated that variation in genes can play an important role in the development of mental disorders, although the reliable identification of connections between specific genes and specific categories of disorder has proven more difficult. Environmental events surrounding pregnancy and birth have also been implicated. Traumatic brain injury may increase the risk of developing certain mental disorders. There have been some tentative inconsistent links found to certain viral infections, to substance misuse, and to general physical health. Social influences have been found to be important, including abuse, neglect, bullying, social stress, traumatic events and other negative or overwhelming life experiences. The specific risks and pathways to particular disorders are less clear, however. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Causes of mental disorders」の詳細全文を読む スポンサード リンク
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