"If one of your parents has Huntington's disease, there's a 50% chance that you will inherit the altered gene and will eventually develop Huntington's too." Have they never heard of genetic diagnostics? For example with a combination of preimplantation generic testing and in-vitro fertilization you can prevent passing on known genetic mutations to the next generation.
While technically possible, that option isn’t really available to most people. Tho I suppose 17 hour brain surgery with gene therapy is also not available to most people, so fair enough. Anyway, they’re just describing the heritability of the disease there.
(And of course this research is still worth doing to help the population who already have the illness)