Beyond the hideous and nightmarish extensions of where this kind of logic could lead us that I'm sure others will point out, I'll only ask exactly the question Paul would ask (and probably did), since he will likely wind up being a centerpiece of the discussion:
Where is this power granted to the federal government in the Constitution?
Try the equal protection clause, as currently interpreted by SCOTUS. According to SCOTUS, it also gave congress the power to pass the civil rights act of 1964, and since that forbids the discrimination of people based on race, it is not a stretch to say that congress has the power to forbid discrimination based on other genetically-determined factors unless there is a compelling business reason (like hiring a person with a disability in a position whose responsibilities they cannot fulfill because of that disability). The chance that the person is genetically prone to a problem later on that could cost the company more in health insurance doesn’t sound like a compelling enough business reason to me.