PTSD can be caused by any trauma, like a car crash or abuse. PTSD is actually a fear of a traumatic memory. A person experiences flashbacks (pieces of the traumatic memory) and fears that the traumatic event will reoccur. The most effective treatment is exposure therapy - in a nutshell, you eventually write down the traumatic memory in full (not just pieces of it) and read it until it becomes boring/you understand that for example it wasn't your fault. Here is a recent meta analysis https://www.sciencedirect.com/science/article/abs/pii/S02727...