Oh sweet summer child. The astute business person will construct a score that happens to correlate with these known genetic defects and then sell it to insurance anyway with the plausible cover correlated source.
That really isn't how most health insurance works in the US now. As far as I know, there really is no such think as refusing health insurance to an eligible person. Now other types of insurance like life, home, auto, those are a different story. But regular health insurance just has to accept your application.