Co-founder of Google, Sergey Brin, and wife Anne Wojcicki attend the Allen & Company Sun Valley Conference in 2012. Wojcicki launched the genetic testing company, 23andMe, in 2006. (Kevork Djansezian/Getty Images)

The Food and Drug Administration has ordered the maker of a popular genetic-testing kit to halt sales of its heavily marketed product, saying the mail-order tests haven’t been proven effective and could dangerously mislead people about their health.

The move came in a sharply worded letter to 23andMe, a California start-up backed by Google. The company says that its Personal Genome Service can detect more than 240 genetic conditions and traits, flagging a person’s vulnerability to heart disease, breast cancer and other illnesses. The privately held company, founded in 2006, is headed by biologist and businesswoman Anne Wojcicki, who is separated from Google co-founder Sergey Brin.

The FDA said the company repeatedly has failed to provide the scientific data necessary to prove that its test works as advertised.

Perhaps more significantly, the agency’s action underscores its unease about the potential consequences of direct-to-consumer genetic tests, which can provide people with detailed information but not necessarily the context necessary to interpret what it means or how they should proceed.

It also highlighted a contentious debate that has unfolded in recent years over how and whether the government should police an individual’s access to information about his or her genes.

In its letter, which was dated Nov. 22 but posted online Monday, the FDA said it was concerned about 23andMe’s direct-to-consumer test “because of the potential health consequences that could result from false positive or false negative assessments,” which could lead people into unnecessary or ineffective treatments. The agency also said that the company had failed to support its claims despite “more than 14 face-to-face and teleconference meetings” with FDA officials, as well as “hundreds of e-mail exchanges” and “ample detailed feedback.”

“Since July of 2009, we have been diligently working to help you comply with regulatory requirements,” the FDA said. “However, even after these many interactions with 23andMe, we still do not have any assurance that the firm has analytically or clinically validated the [test] for its intended uses.”

23andMe isn’t the only firm offering direct-to-consumer genetic testing, but it’s the largest and best known. About half a million people have used the company’s DNA kit, which costs $99 online and requires customers to submit a saliva sample via mail. The company then sends recommendations, such as suggesting that a customer track the amount of gluten in his diet if his DNA shows an increased risk for celiac disease.

In a statement Monday, 23andMe confirmed that it had received the FDA’s warning letter. “We recognize that we have not met the FDA’s expectations regarding timeline and communication regarding our submission. Our relationship with the FDA is extremely important to us and we are committed to fully engaging with them to address their concerns.”

The company has 15 days to detail how it will go forward, or else it could face other regulatory actions such as civil fines or injunctions.

David Kaufman, director of research at the Genetics and Public Policy Center at Johns Hopkins University, said the FDA’s scathing warning to 23andMe ultimately could be a positive development for the company and the genetic-testing industry, which until now has operated virtually without oversight.

“In some ways, the industry has been both terrified and has been waiting for this day,” Kaufman said. “The companies want to know what they need to do. . . . It’s good that the feds are thinking about this actively.”

He added that 23andMe had taken care not to be too specific when reporting results, but rather to explain to customers when they have an elevated risk for certain conditions based on their DNA. In addition, he said that the company’s quest for FDA approval, while clearly an effort that has been rocky, also is helping to create a regulatory structure that will govern such tests in the future.

“There are a lot of fly-by-night operations out there, and this isn’t one, in my opinion,” Kaufman said. “I think they’re trying to do it the right way.”

The FDA’s move toward regulating genetic tests marketed directly to consumers ramped up in 2010, when the agency sent letters to 23andMe and several other companies declaring that the tests are medical devices that must receive government approval. The agency also convened a public hearing on the matter.

In the past, even as 23andMe sought the FDA’s blessing, Wojcicki and other company officials have spoken often about the democratization of health care and the right of people to their genetic information.

“If you look back a few decades, people were not told about their diagnosis of cancer, and it was thought [that] we need to protect them from that information. Now, that seems ridiculous,” Joanna Mountain, 23andMe’s senior director of research, told The Washington Post in 2010. “The same thing goes for genetic information. We have many, many people who are very, very curious and want to know and are capable of handling this information.”

In interviews Monday, FDA officials said they understand how rapidly the field of genetic testing is evolving and noted that the agency has approved a range of genetic tests for everything from bladder cancer to cystic fibrosis. Last week, the FDA approved several “next generation” gene-sequencing devices that will speed up testing and allow doctors to diagnose patients more quickly.

But the agency has tread carefully when it comes to consumers taking at-home tests and receiving complex results without the help of a medical professional.

“We don’t have any bias against genetic testing at all,” said Elizabeth Mansfield, director of personalized medicine in the FDA’s medical-device center. “We’re just very concerned about these tests that consumers can buy themselves, and their only interpretation [of the results] may come from a company.”

The agency might eventually approve such tests, but only after it feels confident that they are accurate and that consumers understand the limitations.

“We do believe there is a place for this. We think people have a right to their genetic information,” said Courtney Lias, director of the FDA’s division of chemistry and toxicology devices. “But when a company is providing these types of tests where they interpret the results, we need to understand that the test actually works and the information they provide is correct. . . . The majority of genetics is not so black and white.”