I don't know if anyone has read this or mentioned it here before. It is called "The PTSD Breakthrough: Compass RESET Program" by Dr. Frank Lawlis.
It takes a different approach based on new studies and was first published in 2010, so is pretty new.
It discussed physical causes of PTSD that can make a person more susceptible to witnessing or experiencing actual traumas. Some of these physical causes are:
Brain injury to the soft tissues caused by concussion. This can be a serious concussion or a simple concussion you might get by falling on your head, car accidents, maybe even getting punched hard as a kid.
there is also a kind of brain damage caused by extremely loud sounds, which can be explosions you might hear in war, or even loud sounds that can cause damage, or maybe setting off fireworks too close to you. makes me wonder about all that loud rock music listened to as a teenager at max volume!
There is also brain toxicity. This can be caused by drugs and alcohol, but these aren't the main culprits since you are aware of them and can stop them at will. It's the hidden toxins we are exposed to in the environment or diet that go unnoticed. Things like lead, mercury, chemicals, pesticides, PCBs.
If you have had any of these in your life,they can make you more prone to PTSD if you experience traumatic events. If you have a number of these or a combination of these from all categories, you are definitely susceptible to PTSD.
The book also talks about how medication is not the simple answer because often PTSD gets misdiagnosed as depression or something else, and some meds can only add to the problem,including meds that warn may increase the chance of suicide!
I just had a chance to read this and it was the first I heard of this new approach to PTSD.