While there are studies suggesting it is very genetic, I (genetics undergrad degree/med school + currently doing another graduate degree in genetics) think it’s more that child raising patterns and family stress levels are often inter generational, so it’s not that there is a stuttering gene passed down, but rather the environment conditions that cultivate stuttering are passed down. I started stuttering at age 6, when my sister was born and my already very emotionally unavailable parents became even more unavailable to me. I stuttered very consistently until my early teens, when I did the McGuire program at 13 and it basically “cured” me (I rarely stutter as an adult, only when I’m out of breath or extremely anxious). Childhood speech therapy was useless for me, I needed costal breathing therapy to teach me how to breathe properly so I could project words and not be blocked. I had an uncle that grew out of it and one of my sister’s did as well. But I wouldn’t have grown out of it without costal breathing therapy + joining drama and debating clubs as exposure therapy in my teen years. I now engage in high speaking careers (worked in politics before med school and also have a startup) without fear but you wouldn’t have believed that if you saw me at age 12.