Table 1.

Possible Origins of an Association between a Biological Abnormality and Posttraumatic Stress Disorder

1.	The abnormality was preexisting and increased the risk of the individual's being exposed to a traumatic event.
2.	The abnormality was preexisting and increased the individual's vulnerability to develop PTSD upon the traumatic exposure.
3.	The traumatic exposure caused the abnormality, and the abnormality caused the PTSD.
4.	The traumatic exposure caused the PTSD, and the PTSD caused the abnormality.
5.	The traumatic event independently caused both the abnormality and the PTSD.
6.	The traumatic exposure caused PTSD, the PTSD caused a sequel or complication, and the sequel or complication caused the abnormality.