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.
In other words, in the interpretation of activist courts. "Equal protection under the law" in my world has never meant, and still means nothing more than that, not "equality of results in every human situation". Sorry, I know of that clause, I never agreed with that interpretation remotely, so if that's the best we've got, then IMO, even if you only considered Constitutional reasons, Paul voted correctly.
Anti-discrimination laws in general is one of the most anti-free-market concepts in existence. All choice is based on discrimination. The concept of some outside party trying to discern what is "good" and "bad" discrimination has never been anything more than absurd.
If we hadn't already gotten to the point where hiring anyone was such a legal landmine of lawsuits waiting to happen every time an employer breathed wrong that it's not even worth it anymore unless you have a legal team the size of Xerxes's army, this will handily take care of that.