I came to comment something similar! I took a stuttering course in college and we also learned it was about 70% genetic and 30% environment. I’m a speech therapist and family history of stuttering is important when we consider treatment for a young child. If other family members have stuttered than it’s more likely that their stutter will persist/not spontaneously go away. Also, more men stutter than women, however when girls stutter at a young age their stutter is more likely to persist into adulthood than boys. There’s still a ton of research that needs to be done regarding stuttering though, a lot we don’t know.