An enduring memory of my niece’s third birthday party is the fortune telling session that took place under the dining room table. A creative parent had donned a headscarf and extravagant earrings, and soon a line of toddlers were waiting to hear about the magic of their future. Given the state of the science a decade later it’s highly possible that this fortune telling was just as reliable as the high tech horoscopes arising from the marketing of genetic tests for common diseases.

When the US Government Accountability Office recently ran a covert operation on genetic tests for 15 common conditions, including Alzheimer’s disease, breast cancer, and restless legs syndrome, it uncovered the most extraordinary mess.1 It found that identical DNA samples produced wildly contradictory results. One donor was told by four different firms that he was at below average risk, average risk, and above average risk of having high blood pressure and prostate cancer.

Its report concluded that genetic tests marketed directly to the public were “misleading and of little or no practical use.” Yet hundreds of thousands …