When Lukas Hartmann, 29, signed up for 23andMe's at-home genetic testing service, there were no surprises in his results. The Berliner learned he would probably die from a mix of heart attack and prostate cancer, he wrote on a friend's blog, but nothing special there. Then a few months ago, he received an update from the company. Hartmann's genetic code showed two mutations that are linked to limb-girdle muscular dystrophy, he says the site told him. Some people with limb-girdle muscular dystrophy lose the ability to walk and suffer from serious disability, his results page read. This ca n't be true, he thought. It must be an error. Genetic testing can be a powerful tool. It can offer information about your family history, tell you how your body might respond to different drugs and identify your risk factors for disease. It can also be misleading. The Food and Drug Administration on Monday ordered 23andMe to stop sales of its $99 home genetic testing kits, saying the Google-backed company has not proven the validity of its product. The FDA warned that customers who received inaccurate results could suffer from undue mental anguish or undergo unnecessary medical procedures. The government agency has asked 23andMe to revise its marketing strategy to comply with federal regulations. The action triggered outrage among some of 23andMe's supporters. So GMOs, aspartame, artificial