Are Genetic Tests Useful Part 3

We diverge, however, on a marker for risk taking—Kevin is a bigger risk-taker. He also has a gene marker often found in sprinters, while I have the version of the same marker associated with athletic endurance.

Then there is one of my favorites—a marker associated with rapid caffeine metabolism (as I suck down another latte). I have a genetic variation linked to being able to drink coffee all day with no added risk of heart attack. Poor Kevin has a variant that links caffeine consumption to an increased risk of heart attack. (If heroin doesn't get him, a double espresso will.)

About half of these traits get 23andMe's top 4-star rating, though even this rating includes studies with only 1,000 people tested to make a link between a genetic marker and a trait or a disease. Most geneticists consider a test group of only 1,000 people to have a low statistical strength compared with studies in which thousands or tens of thousands of subjects were tested.

Analyzing too few people means that random outliers—those who have or don't have a gene or a disease—can overly influence the results by causing the risk factors to be too low or too high. Imagine polling 100 people in Harlingen, Texas, about their choice for president: You would get a skewed result compared with a poll in a larger or more statistically relevant population.

23andMe's rating criteria:

Established Research These topics meet our criteria for findings that are very likely to reflect real effects. 4 stars: At least two studies that examined more than 1,000 people with the trait/condition, or smaller studies where there is a consensus that the effect is real. Preliminary Research Includes results of studies that still need to be confirmed by the scientific community. 3 stars: More than 1,000 people with the trait/condition were studied. However, the effect has not yet been confirmed in a second independent study of similar size. 2 stars: Fewer than 1,000 people with the trait/condition were studied. 1 star: Fewer than 100 people with the trait/condition were studied.

"I am interested in finding out how to quantify who I am as an individual," Kevin tells me. "That's why I'm doing this. It's not useful if this information is incomplete or inaccurate, but the best way to fix this is with more and better information."

None of the sites are saying how many people are paying $1,000 (the price that 23andMe and DeCodeMe charge) or $2,500 (Navigenics' price) and getting their results, though I suspect it's not a huge number. Some people argue that genetics now is where cell phones were in the mid-1980s: Remember how rare it was then to see someone using one of the first clunky mobile phones? Then cell phones got smaller, sleeker, and more useful, and now they're practically ubiquitous.

One's genes, though, are not cell phones or computers. They are part of what makes us who we are and can give us clues to how we will live and die. That's why it's crucial to get this right.

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Next week (the fourth and final part of this series): Why the online genetic testing companies are important.

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