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Personal Genetics: Testing for Susceptibility

Ask Science talks about genetic susceptibility. What does it mean to be susceptible to a disease? Can susceptibility really be tested? Click to learn more about personal genetic testing.

By
Lee Falin, PhD
4-minute read
Episode #127

In last week's episode, we laid some of the groundwork for understanding the kinds of information you can and can’t get from a personal genetic testing service. This week, we finish up by looking at what genetic susceptibility means, and why these types of tests can’t tell you the whole story.

If you haven’t read or listened to last week’s episode, make sure you do so before continuing..

Confounding Factors

Let’s say that you are a scientist trying to run a GWAS to find SNPs associated with a certain disease. You find a couple of SNPs that seem to consistently occur in the group of people that have the disease, and which don’t occur in the group of people that don’t have the disease. Then you do some more research and discover that all of the people with those SNPs are of Russian ancestry.

So are the SNPs you found really associated with the disease, or are they just associated with a haplotype that is common to people of Russian ancestry? Could there by other SNPs in that haplotype associated with the disease that your test didn’t measure? Could there be other factors that people of Russian descent might have in common, such as diet, environment, or lifestyle?

All of these issues are confounding factors that make it nearly impossible for a GWAS alone to say whether or not a particular SNP is really associated with a particular disease.

Genetic Susceptibility and Odds Ratios

All of these issues are confounding factors that make it nearly impossible for a GWAS alone to say whether or not a particular SNP is really associated with a particular disease.

Typically, when we report on SNPs being associated with a particular condition, such as a disease, we do so using something called an "odds ratio." Let’s say that we do a study of people that have loud sneezes. We find a SNP that seems to be associated with this group of loud sneezers and we look at the possible nucleotides.

We discover that of all of the people with loud sneezes, a large portion of them have a certain nucleotide at this SNP (scientists would say a large portion of them have a certain allele.) However, not all of the loud sneezers have that allele, and not everyone with that allele has a loud sneeze. So we can’t say for certain that this allele causes loud sneezes - we can just say that it is associated with loud sneezes.

So now let’s say you’re looking at your genome report and you see that you have the loud sneeze allele. You start to worry that your sneezes might be louder than you thought. Should you see a doctor about your sneezes? Maybe try some alternative sneeze therapies?

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About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.