In addition, few data suggest that knowledge of one’s genomic status is effective in changing behavior. Moreover, even if it is, genomic data also could be a double-edged sword, said Evans, if individuals forgo healthy diets and exercise because of a perceived decreased risk of developing a disease.

“I know what almost everybody in this room is going to die of,” said Evans. “We are going to die of heart disease or cancer.… We are all at high risk for these maladies regardless of our [genomically determined] risk. And many at decreased risk for heart disease will still die of heart disease. So we are all going to benefit from interventions that lower heart disease. We don’t really need to target people. It doesn’t do anyone much good to tweak our estimation of an individual’s relative risk for common diseases which we are all at high absolute risk of developing anyway.”

A possible application of genetic testing in healthy people is finding the relatively rare individuals in a population who are at high risk of preventable diseases—what another workshop participant called “newborn screening of adults.” Risk assessment will always be most valuable when the identified risks are high. For example, about 0.2 percent of the population carries deleterious mutations that cause Lynch syndrome (Hampel et al., 2008), placing them at extraordinarily high risk for colorectal cancer, which is a preventable disorder. Today these individuals are identified only after numerous family members have developed cancer or died. Genomic testing could make it possible to do population screening for such disorders. Altogether, perhaps 1 percent of the population might harbor genetic variants that create dramatically increased risk, Evans estimated. “That is not small change. The number needed to treat for a lot of interventions, like statins for high cholesterol, is around that number for primary prevention,” he said.

Preemptively identifying genetic variants that influence the effects of drugs in individuals is another promising application of genomic testing. Still, this application will probably be useful for a minority of drugs, Evans said. Even today, after years of development in pharmacogenomics, few loci have demonstrated unequivocal value in improving outcomes or reducing costs. Genetic testing to inform the use of abacavir (Mallal et al., 2008) is an exception to this generalization. But for other promising variants, data still are being collected regarding whether testing benefits patients. Furthermore, such testing may not require a genomic approach. Targeted genotyping at the point of care rather than advance knowledge may be preferable because pharmacogenomic information is only needed when a drug is prescribed. And retesting may be necessary for high-stakes decisions because test results can be wrong and because the tests themselves improve over time.

Genomic testing as an adjunct to newborn screening also holds consid-



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