By Pat Wechsler

Oct. 7 (Bloomberg) -- Navigenics Inc. and 23andMe Inc. both market DNA tests to consumers to uncover genetic predispositions for diseases. The companies don’t always come up with the same answers, according to J. Craig Venter, the genome pioneer.

The two testers agreed only two-thirds of the time when making risk predictions for five individuals on their chances of contracting 13 diseases, including breast cancer and diabetes, Venter and three other genetic researchers said today in an opinion article in the journal Nature.

As scientists including Venter aim to usher in an era of personalized medicine based on individuals’ biological differences, companies such as 23andMe and Navigenics already offer tests that plumb people’s genetic makeup. The article’s authors said “the nascent industry” could improve predictions by developing a consensus on how to do the analyses.

“Genetic testing can improve lifestyle choices and increase preventive screening,” Venter and colleagues wrote in Nature. “However, understanding of the genetic contribution to human disease is far from complete.”

Genes are the basic hereditary units containing information needed by the body to make proteins and sustain life. Researchers look for so-called genetic markers, or sequences of DNA with links to specific traits.

Discrepancies in the analyses arose because the companies focused on different markers when calculating the probability of a person’s developing a particular illness or condition, according to the article. Venter recommended that the companies agree on a core set to achieve more-consistent results.

‘Great Ideal’

The proposal is a “great ideal, but difficult to implement in practice,” said Andro Hsu, 23andMe’s science and policy liaison. He said he has taken part in discussions sponsored by the Personalized Medicine Coalition, a Washington-based nonprofit advocacy group, on which markers and statistical methods to use.

“We had a pretty difficult time agreeing,” Hsu said in an e-mail today. “It would be nice if there were a third-party to score associations,” or assess the strength of links between markers and traits.

“At Navigenics we have always been focused on promoting industry standard setting, and we welcome the input of our industry colleagues,” said Amy DuRoss, Navigenics vice president of business and policy affairs, in an e-mail today. “All of the differences in methodology are transparent and visible on each companies’ websites. Since then, we have continued to work with industry groups and patient advocates to produce industry guides and establish standards.”

Direct to Consumers

Genetic testing companies sell directly to consumers. 23andMe, based in Mountain View, California, was started in 2007 by Anne Wojcicki, wife of Sergey Brin, the cofounder of Google Inc. Google, the operator of the most popular search engine, has invested at least $6.5 million since 2007 in Wojcicki’s company, according to regulatory filings. Brin loaned 23andMe $10 million in June, filings show.

Navigenics, of Foster City, California, also received money from Mountain View-based Google. Other genetic testing competitors include deCode Genetics Inc., based in Reykjavik, Iceland, and Pathway Genomics Corp. of San Diego.

Customers looking to have their DNA analyzed must provide DNA testers with saliva or a cheek swab. The sample is then scanned for 500,000 to 1 million markers, according to the article. This kind of analysis provides data that may be useful in determining the probability of developing diseases and in suggesting drugs or treatments.

Prices

At Navigenics, a comprehensive test costs $999, according to the company Web site. At 23andMe, unlimited access to health, disease and trait reports costs $399, according to its Web site. For $99, a customer can get access to 100 reports.

Venter and the other authors also said users of tests sometimes can make lifestyle changes that decrease the chance of getting a disease for which the genetic analysis suggests a high risk.

Venter is known for developing a technique for discovering and sequencing genes -- and for decoding the human genome. He now pursues his research at the J. Craig Venter Institute, with offices in San Diego and in Rockville, Maryland.

Skeptics in the scientific community doubt the value of the gene-testing services in their current form, said Pauline Ng, the lead author of the Nature article and a researcher at the Venter institute.

In 2008, states including California and New York sought to crack down on genetic testing. California decided to require Navigenics and 23andMe to obtain licenses in order to solicit specimens from customers.

“These are recreational tests and are not meant for diagnostic purposes,” Ng said. “I thought it would be interesting to see if there were differences. I expected the predictions to match.”

To contact the reporter on this story: Pat Wechsler in New York at pwechsler@bloomberg.net.