What does your DNA really reveal about your health?

It sounded enticing: For just $99, I could spit into a tube, mail it off to a company called 23andMe, and, six to eight weeks later, receive a report explaining what my DNA reveals about my risk for 120 diseases — everything from breast cancer to gout to sudden cardiac arrest.

"Knowing how your genes may impact your health can help you plan for the future and personalize your health care with your doctor," the 23andMe website declares.