Genetics of stuttering on my paternal side is weird. My grandfather was a stutterer and he had five boys, 1 of them (my uncle) used to stutter. My dad does not stutter at all, but I do (I'm an only child). The uncle who used to stutter has 2 sons, only 1 stutters. So altogether, among my uncle's sons, 2 out of 4 (including me) male offspring have a stutter.