Oct 15, 2012 - Research

Using Genetics and Family History for Health

For decades, a patient’s family health history has been a keystone to any wellness plan.

A simple record of medical conditions your siblings, your parents, aunts, uncles and grandparents struggled with can help you and your doctor know what to watch for to keep you healthy. Like family health histories, genetic testing also offers people insights they otherwise might not have about their own health.

Unfortunately there has often been a false division between family health histories and genetic testing where the approaches are portrayed as opposing alternatives. It’s an odd argument. No one would juxtapose the utility of a stethoscope against a thermometer. They are both useful in their own way.

A new paper in PLoS Genetics by 23andMe shows that neither family health histories nor genetic testing is perfect in predicting health risks, but they each have their strengths.

More importantly using them together improves upon the risk prediction by capitalizing on the situations where each method is at its strongest. Along with making comparisons between family health history and genetic testing to make risk prediction, the paper describes a model to combine the two methods together to assess risk.

Lead author and 23andMe scientist Chuong “Tom” Do, Ph.D, worked with our senior medical director Uta Francke, MD, and scientists David Hinds, Ph.D., and Nicholas Eriksson Ph.D. to make a comprehensive comparison of family health histories and genetic testing to assess risk for 23 different conditions.

“We show that family history is most useful for highly common, heritable conditions,” Tom said.

So for relatively common diseases that may have many genetic and environmental factors – coronary artery disease, for instance – knowing that your father had the disease is helpful at predicting whether or not you might be at risk for the same condition.

But for less common diseases with many genetic factors influencing them, knowing your family history seldom helps in making a risk prediction, said Tom.

In part, that’s because these diseases are uncommon enough that they would rarely show up in the health history of your immediate family. When family histories are uninformative, genetic testing may still reveal the genetic variants that would put you at a higher or lower risk for the condition. So for example Crohn’s disease might not show up in a family history, but the risk prediction from a genetic test is relatively strong. As an aside there is also the issue of people who simply don’t know their family health history. And we’ve written about how genetic testing can alert them to risks they wouldn’t have otherwise suspected.

To be fair, even though new genetic discoveries are being made every day, only a fraction of the genetic contributions to whether or not a person develops a disease is currently known in many cases. But even after accounting for this, existing genetic testing – that use single nucleotide polymorphism (SNP)-based methods to determine risk for some rare complex diseases – are already as good at predicting risk as family histories for common heritable conditions.

“These results indicate that for a broad range of diseases, already identified SNP associations may be better predictors of risk than their family history-based counterparts, despite the large fraction of missing heritability that remains to be explained,” Tom writes in the paper.

Finally, it’s important to remember that having a family history for a disease is generally not the same as a diagnosis. Just because your mom had diabetes doesn’t mean that you will get it too.  But knowing that you’re at increased risk based on family history can be a motivating factor in helping you to make appropriate lifestyle changes.  In much the same way, knowing your genetic risks can also be useful in helping you live healthier.

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