Google founder Sergey Brin's investment in his wife's genome-screening company has gotten even more personal: the product has revealed he carries a genetic mutation linked to Parkinson's disease.

Brin writes on his blog that the genome scan of his saliva from 23andMe told him he has a mutation on the LRRK2 gene, a variation called G2019S, which ups the risk for Parkinson's in some families. Brin's mother has  the neurodegenerative disorder and the mutation, he writes.

"When my wife asked me to look up G2019S in my raw data … I viewed it mostly as entertainment," Brin recalls in the blog. "But, of course, I learned something very important to me."

He adds: "The exact implications of this are not entirely clear. Nonetheless it is clear that I have a markedly higher chance of developing Parkinson's in my lifetime than the average person. In fact, it is somewhere between 20 percent  to 80 percent depending on the study and how you measure."

Whole genome screens like those offered by 23andMe are marketed as informational, not diagnostic. And while Brin doesn’t have Parkinson's disease, the fact that his test revealed a heightened risk for so serious a condition underscores concerns of New York State health authorities, who have sent letters to three dozen DNA-screening companies informing them that it's illegal to offer medical tests in the state without a license, the New York Times recently reported. Earlier this summer, California health officials sent cease-and-desist letters to 11 companies, telling them they needed licenses to operate as medical labs and that only licensed physicians can order such tests; 23andMe and another company, Navigenics, were awarded licenses to operate last month.

It's not clear from Brin's blog when he found out that he carried the Parkinson's gene. "I feel fortunate to be in this position," he writes, noting that exercise could help protect him from the disease. Just last week, he told SciAm editors at a 23andMe "spit party" in New York that it's useful to know one's own genetic code.

"It's a really good thing to know," Brin said. "It can help you out in any number of things. Whether it's lactose intolerance — stay away from cheese — or don't accidentally marry your cousin."

Apparently the disclosure did not hurt Brin's company. Quite the contrary: Google stock was up 12 points at 1 p.m. today.

The pros and cons of genetic testing – not to mention those done by private companies -- have been hotly debated. President Bush signed a measure into law in May that bars insurance companies and employers from discriminating against anyone because of the findings of genetic testing. There's also a push to pass legislation that prevents insurance companies from refusing to cover or charging higher rates for pre-existing conditions.

You can listen to SciAm's entire interview with Brin below, along with the editors' chat with 23andMe co-founder Linda Avey.

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(Image of Sergey Brin by James Duncan Davidson/O'Reilly Media, Inc.)