The laws vary from state to state. The Federal government has proposed laws, but today nothing is definite. Currently there are no laws that specifically address the issue of an insurance company denying you a policy based on the genetic test results.
Your doctor recommends a genetic test to help determine your susceptibility to particular diseases. The problem is when the test becomes a matter of record in your patient file. Don’t be so quick to think that an insurance company will not get access to your file and base their decision on your health insurance on what they find.