Trauma can cause stutter. If you carry genes from somebody that stutters, it can trigger them and cause you to stutter. That is what happened to me, anyways. My father stuttered when he was a kid, but recovered from it when he grew up. When I was 3 I had a traumatic experience and since then I have been a stutterer. I did not stutter before that. I started stuttering right after the event and I know it somehow altered my brain because I do not need to be anxious to stutter. In my case it is 50% mechanical and 50% emotional.