BF you do a lot of research. I commend you for that. The genetics cause for PTSD is unconvincing to me. When it comes to PTSD, it seems the medical community is all over the place.
My response to that article would be
-Variations in serotonin production have little to do with developing PTSD. PTSD is psychological. It's like saying some people are more prone to lacerations of their skin because their blood doesn't clot as well after getting cut.
-If 2 people are involved in a traumatic event and only 1 shows PTSD symptoms, it is a mistake to think the other was not affected.