Should You Get Your Genome Mapped?

Back in early 2010, molecular geneticist Michael Snyder, then a trim 54-year-old, decided to put his genetic blueprint under the microscope and make the results public. Swabbing saliva from his cheek with a sterile sponge and drawing blood to obtain his DNA samples, the Stanford scientist became the subject of one of the first clinical studies to analyze the blueprint of a healthy individual rather than someone known to be sick.

Snyder's study took advantage of recent technological advances that have now made it possible to rapidly and much less expensively sequence a genome--the instruction manual, contained in virtually every cell of a person, for making a human being. Containing some 3.2 billion pieces of genetic information, the genome determines a broad spectrum of human traits such as eye color, height, general health, and whether someone might be more likely to be a basketball player or a biologist.

What the Stanford researcher found surprised him. His genetic tests showed that he had a higher-than-average risk for developing adult onset, or type 2, diabetes even though he wasn't overweight, nor did he have any known family history of the disease. But during the 14-month study, in which Snyder's health was closely monitored using a battery of tests, his glucose levels spiked and remained high following a respiratory infection. Only after six months of increased exercise and a change in diet did Snyder's glucose levels drop back to normal, he and colleagues reported in the March 16 issue of the journal Cell.

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The $1,000 mark. Without the genetic testing, Snyder says, he would not have known of his diabetes risk or been able to address it so quickly. And with the cost of genome mapping already as low as a few thousand dollars and likely to reach a much-ballyhooed benchmark of $1,000 by next year, Snyder and other scientists see the procedure as a crucial part of medicine for everyone, not just the affluent or the curious.

Many experts, though, like Eric Topol, director of the Scripps Translational Science Institute in San Diego, caution that science is only in the embryonic stage of understanding the composition and inner workings of the human genome. Essentially, each person carries two copies of each gene--one from each parent--in every cell (except mature red blood cells). Within these cells, genetic information is divided into 23 pairs of smaller packages, called chromosomes, that store the 20,000 or so genes in the human body, along with other bits of genetic information. The genes in turn are made up of deoxyribonucleic acid, or DNA, molecules whose two strands wrap around each other like vines, forming the iconic double helix structure. Using a four-letter alphabet, scientists have identified and labeled the four building blocks, or bases: adenine (A), thymine (T), guanine (G), and cytosine (C), which combine in each DNA molecule according to precise rules, somewhat like the rungs on a ladder. An A must always seek out a T on its partner strand, while a G must always pair with a C.

If the bases are the musical notes that make up the genome's keyboard, then their exact ordering determines whether the genetic symphony is harmonious or discordant. Just as extra or missing notes can wreck a musical passage, an extra or missing A or T can increase a person's risk of developing a particular disease or, in rare cases, cause an incurable illness.

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The challenge with genome mapping is that large portions of the map reflect uncharted territory. Researchers understand the role of genes in the body fairly well: They dictate how proteins--the compounds necessary for building and repairing muscles and other tissue--are made. But protein-coding genes account for only 1.5 percent of the human genome. A lot of the action appears to be happening in the other 98.5 percent. Once referred to as "junk DNA," this vast but little-explored portion of the genetic blueprint is now believed to play a critical role in regulating gene activity and carrying out unidentified functions that contribute to a person's being predisposed to a disease.

"People will need to be prepared for the fact that these tests are so new that the physician may have limited ideas of what to make of it and what to do with it," says genetic counselor Barbara Biesecker of the National Human Genome Research Institute in Bethesda, Md.

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Should You Get Your Genome Mapped?