What happens with HD is that it is an autosomal recessive (if, in fact, it is a genetic disease). That means that you have to have an HD gene from your mom and dad both. If you only get one gene from one parent you won't have HD but you will be passing it on to 1/2 your descendants.
Again, they won't show symptoms of the disease unless your mate also passed along an HD gene.
And so on down the line.
Two ways to stop this gene ~ the ethical way which is don't have kids! The unethical way which is to go to an in vitro operator who will test fertilized eggs and toss any with the HD gene.
When the genetic discovery was made many people had already married (or engaged in other pair bonding arrangements) and they had kids so they stopped having kids.
A high school pal's father, a retired navy master chief, had HD and I watched him slowly become a wheelchair bound vegetable in the space of three or four years.
I had met him when he was leaving the service, still healthy, but showing some of the first signs. It was pitiful and it broke his family's hearts to see him bleed away. Bill, my age, was convinced that he was a carrier and swore he would never pass it on.