MaidofStars - genes aren't my strong area, but I believe that's something different.
I.e. My condition is an Autosomal dominant genetic condition. My children would only need my faulty gene and they will have the condition. There is a 50-80% chance of it being faulty. Huntingdon's is another example of this.
Then there are conditions where the child needs a faulty gene from both parents, which is an Autosomal recessive condition. I.e. Cystic Fibrosis and Sickle Cell.
But there also conditions that fall under genetic conditions - heart disease, Autism, Spina Bifida, MND, etc. When you have this condition and have a child their chances rise slightly, but it's not a direct heritable condition in the same way as my condition. There will be other factors including both patents, environmental, their general health, and it can come from other sources - not from parents/family members.
That's my understanding, anyway.