Posttraumatic stress disorder holds an unusual position among the entries of the manual. What makes it unusual?

1. Diagnosis requires that the person was exposed to, witnessed, or experienced the details of a traumatic event. 2. That event must involve actual or threatened death, serious injury or sexual violence. 3. Because this criterion names extreme trauma as the cause, posttraumatic stress disorder is the only listed disorder in which a cause is explicitly specified. 4. Risk factors are listed at length for it, including trauma severity and lack of social support, so the first option fails. 5. Distress and impairment still matter, and comorbidity is common, so neither of the remaining options describes it. _Source: OpenStax Psychology (1st ed., CC BY 4.0), Ch 15 "Psychological Disorders", section 15.6 Posttraumatic Stress Disorder_