  The DSM treats mental disorders as syndromes along the lines of the minimal medical model. Individuals who share a DSM diagnosis have a subset of symptoms in common, often drawn from a larger list so that although some people may have all their symptoms in common, there may be no overlap at all in other cases. These collections of symptoms are also supposed to unfold over time in more or less the same way, once we make due allowances for some individual variation. They are also expected to respond to treatment in the same way. The previous version of the DSM assumed that each diagnosis represented malfunction in some mental, physical or behavioural trait or capacity (DSM-IV-TR, xxi). However, the diagnoses were listed without worrying about what that underlying malfunction might be, and in most cases there was (and remains) no agreement about what causes what. DSM-5 defines mental disorders (p. 20) as syndromes comprising clinically significant disturbances of cognition, emotion or behaviour that reflect underlying dysfunctions. These are normally associated with distress or social disability, but cannot be diagnosed if the behaviour is culturally normal or merely socially deviant, unless it reflects a dysfunction. 