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personal genomics

In Gattaca‘s opening scene, a doctor predicts, at the time of Ethan Hawke’s character Vincent’s birth, the likelihood that Vincent will suffer from a variety of diseases (“Manic depression: 42% probability…Heart disorder: 99% probability”), and determines his life expectancy to be 30.2 years.

While monthly flights to the moon and dating Uma Thurman remain science fiction (or science fantasy) for most, this type of genetic palm reading is now entering the realm of modern-day reality. You can get “sequenced” on the cheap, and at home, with personal genomics – retailed kits that provide users, after they’ve sent a saliva sample back to the company for analysis, with a range of personal genetic information.

But, as in Gattaca, where Vincent beats the odds of his genetic “fate,” a question remains: How useful and predictive are the results of these personal genome tests? Some doctors say the results are not as relevant as one might think.

Last month, Navigenics dropped the price of its personal genome scanning service from $1000 to $400, matching the price of its primary competitor, 23andMe (started by Anne Wojcicki, wife of Google co-founder Sergey Brin, and partially funded by Google). Navigenic’s service offers a “genetic snapshot of your predisposition” to ten common health conditions, including breast cancer, prostate cancer, Crohn’s disease, glaucoma and macular degeneration. So, for around the price of an iPod touch, you can get a set of custom Gattaca-style disposition percentage-predictions for ten diseases.

Many believe the low cost and predictive value of these personal genomic tests will revolutionize health care, since people will be more aware of their own risks and take either preventative measures or better plan for future diseases. Time Magazine named 23andMe’s “Retail DNA Kit” as its 2008 Invention of the Year, noting that celebrities such as Rupert Murdoch, Warren Buffet and Ivanka Trump are customers. But as they become more popular and affordable, these personal genetic kits are also gaining detractors in the medical profession who question the validity of their predictive results.

The tests identify single nucleotide polymorphisms (SNPs, or singular variations in the standard genetic code for a gene) that are typically associated with common diseases. For example, if the standard sequence for a specific gene starts “GATTA” but yours begins “TATTA” then you have an SNP for that gene. If that SNP is associated with a higher incidence of a particular disease, then you are at higher risk for contracting it.

But what does “higher risk” really mean? The predictive problem occurs because the onset of many of these diseases depends on a range of factors, both genetic and environmental, that are unaccounted for in these results. So even if someone has the higher-risk SNP gene sequence for macular degeneration, there is only a 30% chance that this person will actually develop the disease. Further, doctors do not know which 30% of those “higher risk” individuals will go on to develop the disease, or why. Most of the diseases tested by these personal genomic companies are still ambiguous in this way – actually contracting the diseases depends on a variety of genetic and environmental factors.

If all that these tests reveal is that you have a higher risk of being in a subset of people with an increased chance (30%, in the case of macular degeneration) of getting a disease, what exactly is the takeaway lesson for the consumer?

Some in the medical profession argue there is very little. In an interview with MedPage Today, Dr. Daniel Weeks, an expert geneticist at the University of Pittsburgh noted that, while SNP tests are very important in studying the causes and treatment of diseases, “they’re not ready for diagnostic prime time” in applying their results to individuals in good health.

The tests provide an array of percentage dispositions for a variety of diseases. But when many of these diseases are dependent on factors beyond genetics that are not fully understood, the test results may be both difficult to interpret and limited in accuracy. Does it really help to know you may have a 15% chance of contracting a disease that normally occurs at a rate of 5% in the general population? While the knowledge of additional risks may motivate a person to live a healthier lifestyle, the stress of knowing about all of these risks (such as in this graphic ad) could have the opposite effect. Think about it, if the person ends up not making better lifestyle choices, the stress of learning the test results (30% greater chance of glaucoma! I am a good candidate to contract gout!) could actually be more detrimental to your health than helpful.

Despite these criticisms, it is important to note that genetic testing performed by a doctor does play an effective and vital role for predicting the onset of many diseases whose predispositions are primarily genetic (e.g., the BRCA1 and BRCA2 breast cancer genes have significant and proven predictive value). Moreover, as medical research improves our understanding of both the genetic and environmental factors that influence diseases, these at-home personal genetic tests will become more accurate. Personal genomics also has non-medical utility in helping families chart their genetic history (23andMe provides this service).

So while personal genomics may be hot right now (If Google believes in it, it must be true!), sit tight; its reputed crystal-ball abilities regarding your health may be premature. And, regardless of what your sequence says, Uma Thurman will still not go out with you.

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