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"I thought, 'Oh my God. Am I really a man?' " said Denise Weinrich, 48, of St. Peters, Mo. "I thought, 'What's the matter with me? I'm not who I thought I was. How am I going to tell my children?' DNA doesn't lie."

DNA does not lie, but its truth is often elusive. Weinrich was one of 87 people who received incorrect results last month because of a laboratory mix-up involving customers of 23andMe, a testing company backed in part by Google. The Mountain View, Calif., testing company says it regrets the incident and noted that it spotted the mistakes quickly, notified the clients and has taken steps to prevent future errors.

But the blunder has fueled a debate over whether the government should more aggressively police the proliferating tests. Critics say that too many make claims that go far beyond the science, yield results too complicated for people to interpret on their own or are just plain wrong. Others, however, fear that more federal oversight will make the tests too expensive and hard to get.

"If you have things completely unregulated, then you have a Wild West of commercial interests around medical information," said Robert C. Green, director of Boston University's Center for Translational Genomics and Health Outcomes. "If you over-regulate, you run the risk of stifling innovation in a very dynamic industry."

Genetic testing has become one of the flash points in the larger question raised by new technologies that are fueling a movement toward more unfettered access to information: When does government intervention cross from prudent and necessary to intrusive and paternalistic?

Dozens of companies offer tests that claim to tell people everything from what foods they should eat to live longer and what cosmetics they should use to whether they are at risk for cancer, Alzheimer's and other ailments. Many think that genetic testing is key for the future of "personalized medicine," which tailors cures to people's genes. But few tests have undergone stringent scientific validation.

Mounting concerns have prompted the Food and Drug Administration, which has long resisted calls to regulate the field, to begin stepping in. In May, the agency scuttled plans by Pathway Genomics of San Diego to sell genetic tests in Walgreens stores. Several weeks later, the FDA sent letters to five companies that were selling tests over the Internet, declaring that their kits are medical devices and must undergo federal scrutiny. Next week, the agency is convening a public hearing to debate what regulatory role it should play.

"It's come to the point where really there's a need for some oversight," said Alberto Gutierrez, who heads the FDA's Office of In Vitro Diagnostics. Results from questionable tests can be unnecessarily alarming, Gutierrez said, adding that some women have undergone surgery, for example, based on tests that purport to gauge the risk for ovarian cancer.

"We know of reports of people who have found a test, found a doctor that is willing to order the test since they are so afraid of the disease, and even removed ovaries based on questionable results," Gutierrez said.

'My nightmare scenario'

What's more, without a genetic expert to interpret the often-nuanced results of valid tests, patients who test negative might be falsely reassured, critics argue. Women might think they are safe from breast cancer, for example, and stop getting mammograms without realizing that they might still be in danger because of genes not included in the test or other factors.

"That's my nightmare scenario," said Hank Greely, director of Stanford University's Center for Law and the Biosciences. Even when the results are accurate, public perceptions often exaggerate the current power of genetic testing, many experts say.