Im the only one who stutter in my entire family tree and I have a severe one but I don't disagree that some of the cases are definitely genetic. Have you heard about that one guy who used to stutter severely and a doctor cured his stutter through hypnosis and he even reveled the reason behind his stuttering, it was a trauma caused by his father. His family used to raise chickens and when his father left home the kid went to the farm and grabbed a bunch of chicks and threw them into the river to see if they can swim like ducks but they all drowned and when his father came back home he found out about what he did and he punshed him and traumatized him and after that the kid started to stutter and kept stuttering until like 50 or something like that. Childhood trauma can causes stuttering for some people