I went and saw a neurologist when I was 19. They needed people for some testing they were doing on stuttering. None of my immediate family up to my grandparents have ever stuttered (we don't know family history past that point). The doctors said my stutter was psychological and probably came from trauma. My speech patterns tend to fluctuate and are closely tied to my anxiety or other heightened emotions. I think there are many ways for a stutter to generate and childhood trauma can be one of the ways. (Edited for extra details.)