Mental disorders are dysfunctions of mental ability that cause their
sufferers problems that range from undue stress to an
inability to function. Some mental disorders, such as mental retardation and Alzheimer disease, may be the result of organic brain damage. Others, such as schizophrenia, severe depression, and bipolar disorder may involve a genetic defect in at least some cases. Mental disorders can also result from environmental factors, such as the
traumatic events that in some individuals can trigger the onset of post-traumatic stress disorder. The mental disorders that are recognized by the American Psychiatric Association are described in the Diagnostic and Statistical Manual of Mental Disorders (DSM).
The study of mental disorders is called psychopathology. A number of treatment options exist for
sufferers, including psychoanalysis and various forms of psychotherapy. Behavior modification seeks to alleviate disorders by changing habitual behaviors, while drug therapy attempts to change a patient's perceptions through an alteration of body chemistry directly or indirectly involving the brain. In extreme manifestations of some forms of mental disorder, institutionalization may be required.