My dad stutters and so does his mom. Also my dad's other two brothers stutter and so do their sons. My dad's mom (who stutters) also had kids with another man but their kids do not stutter. My dad's dad does not stutter. If you're interested in the future information about this topic, this video talks about the genetic component of stuttering and also about people who don't have a family history of it and why potentially they stutter. https://youtu.be/y3iSzlUms3s?feature=shared Skip to 18:34 for the genetic part being discussed. The whole video is interesting and you may learn a lot about the condition. So check it out if you have time.