The (Un)Predictability of Risk

Just because we know someone may carry a genetic variant, it doesn't necessarily mean we can confidently predict whether that person has an increased risk for disease, says Genomes Unzipped's Katherine Morley. With polygenic traits in particular, she adds, test results categorize people as low- or high-risk, but give no further detail. The sensitivity and specificity of the tests give an idea of how discriminatory they are, but that doesn't say anything about its validity as a screening test in the general population, Morley says. Negative predictive value and positive predictive value also come into play, but can be improved for each test. "What does this mean for personal genomics?" Morley asks. Despite the complexity of predicting risk, she says it doesn't mean DTC genetic tests are useless. Their sensitivity and specificity aren't at the level of diagnostic or screening tests, but their predictive capacity will increase as more genetic variants for disease are identified, she says. "The important thing is to keep concepts such as PPV and NPV in mind when you look at DTC test results and remember that for complex diseases, the results you get are always probabilistic not deterministic," Morley adds.