punctuation

Mary, your commas are fine except for the one after disorder. You should use parentheses (round brackets) around DSM-IV and remove the extra closed bracket after disorder. Additionally, you should give the full name of the publication in italics and use lower case for diseases. When quoting sources, it is important to do so accurately – in this case, there is a phrase missing that changes the meaning slightly.

" . . . the development of characteristic symptoms following exposure to an extreme traumatic stressor involving direct personal experience of an event that involves actual or threatened death or serious injury, or other threat to one's physical integrity . . ."

The Diagnostic Statistical Manual of Mental Disorders-IV (DSM-IV) describes the essential features of post-traumatic stress disorder as "the development of characteristic symptoms following exposure to an extreme traumatic stressor involving direct personal experience of an event that involves actual or threatened death or serious injury, or other threat to one's physical integrity."

The Chicago Manual of Style (16th Ed.)

"8.143 DISEASES, PROCEDURES, AND SUCH

Names of diseases, syndromes, diagnostic procedures, anatomical parts, and the like are lowercased, except for proper names forming part of the term. Acronyms and initialisms are capitalized."