15 October 2009

Genetic testing not always useful

Are commercial genetic tests worth taking? Experts cautious about validity, usefulness of some on the market.


Peter Orszag, the 40-year-old head of the White House Office of Management and Budget, is reported to drink so much tea, hot and iced, that he took a genetic test to see if his body could metabolise his voluminous intake of caffeine.

According to the results, his body is perfectly suited to the task, and Orszag can easily go about his busy day, according to published reports.

Like Orszag, droves of people are flocking to get genetic tests -- which are now marketed direct-to-consumer -- ranging from the $179 CaffeineGen to assess caffeine metabolism to those that claim to gauge risk for Alzheimer's disease. There's also a $79 HomeDNA Home Paternity Testing System that includes, for an additional $25, lab services for the "alleged" father and one child.

But whether or not the commercially available genetic tests currently entering the market actually provide any useful information is another question.

Most genetic tests only for rare conditions
According to Dr Muin J. Khoury, director of the Office of Public Health Genomics at the US Centres for Disease Control and Prevention, some 1 800 to 2 000 genetic tests have been developed, most of which are relevant only to rare genetic conditions that don't affect too many people.

"A growing number of these tests are suggested to be used to target interventions [pharmacogenetics], and to do early detection or susceptibility testing," Khoury said.

Khoury participated in a recent conference hosted by the National Academy of Sciences in Washington, DC, that looked at direct-to-consumer marketing of genetic tests. Among other things, panellists discussed how valid and useful these tests are. Probably some will prove useful, and some will not, the experts said.

"With very few exceptions, we still have some big gaps in evidence," said Dr Marc S. Williams, director of clinical genetics at the American College of Medical Genetics and director of Intermountain Healthcare, Clinical Genetics Institute, in Salt Lake City. "Do we really know if this works or not?"

"We don't know what they do to help people or hurt them," Khoury added.

Cannot predict drug effectiveness
Some are tried and true, such as those to detect the BRCA 1 and 2 genes, which heighten a woman's risk for breast and ovarian cancer, or specific tests to figure the risk for Lynch syndrome, a hereditary form of colon cancer.

But take the example of several much-hyped genetic tests to help determine what type or what dose of antidepressant would be effective for different individuals.

"Researchers have found that even clinically available tests that are supposed to inform someone about specific doses or specific medications use virtually no evidence. We don't even know what to do with the results of tests in terms of dosing, etcetera," Williams said.

"People are promoting this test to choose which SSRI [selective serotonin reuptake inhibitor] they should use, and at what dose with almost no evidence. We'd love to be able to predict which drug to use, but the evidence just isn't there to support that."

And results could be alarming to some people, said Sandra Soo-Jin Lee, senior research scholar and medical anthropologist at the Stanford University Centre for Biomedical Ethics, although one recent study reported that people who discovered they had a higher risk for Alzheimer's through a genetic test were not psychologically distressed by the results.

Perhaps they kept in mind that genes are only one factor that determine risk. The environment also has a lot to do with it.

Some companies working in ‘no-man’s land’
For instance, "there is a fairly robust history of research around genetic variations a population might express in terms of how they take up those chemicals. So, in terms of caffeine metabolism, there may be some individuals that are fast metabolisers of caffeine so it goes through their system fairly quickly," Lee said.

"But there may also be other things about that person and that person's environment that affect how they metabolise caffeine. For now, we just don't know what's what in terms of tests and results," she added.

"Right now, the direct-to-consumer genetic testing companies are working in an unregulated space. It's sort of a no man's land," Lee said.

"But I think there are some indications that we are moving in a direction of creating some hopeful policies. One of the first steps is making sure all the stakeholders come together and discuss what would be helpful in terms of regulation. That not only means health-care providers and patients, but companies themselves."

Attempts to reach several makers of the tests for comment were unsuccessful. – (HealthDay News, October 2009)

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