ADA already 'prevents' job based discrimination based on DNA.* https://www.ada.gov/
An employer buying DNA on potential job candidates is opening themselves up to a world of litigation for little real gain. Similarly, health insurance may no longer discriminate based on prior health conditions due to the dreaded 'Obama Care'.
We can debate if that's enough, or if these things should be rolled back. However, at a practical level it's currently a non issue.
PS: While most of this is not a significant disability. If people treat DNA condition X as an issue then it fall under "or a person who is perceived by others as having such an impairment. "