I can tell you my grandpa stutters, and my dad, and a couple of my uncles and cousins and so do I. Fun part is I have the worst stutter of everyone on my dad's side, all like 60 people? They all have have very light repetitions and occasional ~1 second blocks. I have blocks so long you could measure them with a calenders, and repetitions so bad you'd think I'm s malfunctioning CD player.  Although I used to not have a stutter at all. But one day was I was I believe 6, my neighbor Rottweiler scared me so bad that I couldn't talk at all for about 2 months. I tell went to speech therapy for the next 11 years and it st least helped me be able to say my name.  Still takes me about 15 seconds to say my name and about 2 minutes to make an order at in and out but oh well. And if you're curious I hate dogs and own a cat. A now 13 year old, half Maine coon calico