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Should you test your genes?

By Elizabeth Cohen, CNN Senior Medical Correspondent
Many services have sprouted up offering to use genetics to improve your health.
Many services have sprouted up offering to use genetics to improve your health.
  • Home genetic testing is increasingly available but has limits, says expert
  • FDA has asked five companies to submit their tests for review
  • If you do home testing, identify a genetic counselor to help interpret, expert says

(CNN) -- Like anyone else, Dr. Rachel Zahn loves a deal, so when a friend e-mailed her a link to an internet site offering $99 genetic testing -- usually it costs $499 -- she figured, "Why not?" and sent away for the test.

Now she's thinking -- Why?

Zahn is having, if not buyer's remorse, at least some very strong doubts about the wisdom of her decision to get genetic testing. "I did it out of curiosity," she says.

"But then I wondered if I'd leapt into it too quickly. It made me wonder if there was a downside I hadn't considered."

Her first doubts crept in when, shortly after she ordered the test, Walgreen's postponed its plans to sell personal genetic test kits after the Food and Drug Administration intervened, warning consumers to be skeptical about the tests, which aren't approved by the FDA.

"The test arrived, and it sat on my counter for a very long time. But then I said ... 'I'm going to do this,' " Zahn says.

After sending in her saliva test, Zahn had another wave of doubt when she found out that last week, the FDA sent letters to five genetic testing companies, warning that they must submit their at-home genetic tests for review or discuss with officials why their products do not require FDA approval. In its letter to 23andMe, the testing service Zahn used, the FDA said it wants to prevent customers from being "misled by incorrect test results or unsupported clinical interpretations."

Also last week, 23andMe announced it recently had determined that "a number of 23andMe customer samples were incorrectly processed" by their contracted lab.

"But now I'm worried about the accuracy," Zahn says.

Adam Isserlis, a publicist for 23andMe, told CNN no one from the company would be able to comment for this report.

Many services have sprouted up offering to use genetics to improve your health. In his book, "Outsmart Your Genes," Dr. Brandon Colby advocates for extensive genetic testing to help prevent disease.

"A lot of studies show that genetically tailored prevention can fight a lot of diseases now, like cancer and heart disease," he says.

Zahn, a pediatrician in San Diego, says when she gets her results in a few weeks, she'll blog about it on her website,

Before choosing to do genetic testing on your own through an online service, here are some questions experts say you should ask yourself:

1. Do I want genetic testing because I'm worried about a rare disease?

Let's say, for example, you're thinking about having a baby, and some relatives have cystic fibrosis. While you might choose to do genetic testing online without the assistance of a health professional, if the results are positive, only a professional, such as a doctor or genetic counselor, could help you determine the risk of passing on the disease to your child.

"At the very least, before you do online testing, you should identify a genetic counselor in your area who could help you interpret the results," says Ellen Matloff, director of the Department of Genetics at the Yale Cancer Center.

2. Do I want genetic testing because I'm worried about something common?

Some online services offer tests for one particular gene to see if you're likely to have a heart attack. Geneticists say the results of that test will be of limited value since your likelihood of having a heart attack isn't determined by any one gene. A large number of genes -- many of which haven't been identified yet -- plus non-genetic factors such as diet and lifestyle, determine whether you'll have a heart attack.

For more discussion on genetic testing and heart attacks, see this blog.

3. What will I do if I have negative results?

Matloff says she's concerned people will take a negative result to mean there's no chance they could get a certain disease or pass it along to their children, when that's often not the case. For example, 23andMe indicates it doesn't test for every possible mutation in the cystic fibrosis gene.

"You could be told you're not at a high risk for cystic fibrosis when actually you are," Matloff says.

For more common diseases, a negative result doesn't mean you're in the clear, because so many genes and other factors come into play, geneticists say.

"If you don't have the one gene they're testing for, you might say to yourself, 'Oh, my risk is low. I'm not concerned," says Mark Bouzyk, director of Emory University's Biomarker Service Center.

CNN's John Bonifield contributed to this report.