From my own observations these last few decades.. stuttering is carried along the mothers line... It's rare a stuttering father will pass on the possibility of the speech disorder. The environment within which a child who suddenly starts to stutter is also key to encouraging the progression. Usually they're more sensitive and hyper aware of their surroundings. So a non combative household is important to reducing the development. My cousins child came through this, I was thoroughly impressed the way they handled it.