Is it, after weighing up the options, to have a termination? No.
Is it immoral to bring them into the world? Is is fuck.
No more immoral then having a kid if you're poor, living in somewhere associated with low life expectancy (Gaza, Scotland), or if your family has a history of heart disease, diabetes or mental health issues.
Some people would argue that it is immoral to have a child if you do not have the resources to take care of it. As for life expectancy that's an entirely environmental factor. You can alter life expectancy through individual behaviour or by changing environment.
Having a child with a history of inherited diseases is another issue, yes. However what's worse, having a child when there's a chance of heart disease or diabetes (neither of which are, on their own, entirely debilitating) or having a child when there's a 100% chance of being severely mentally and physically disabled?