A mother testing her adopted child’s genome...
A young woman learning from a spit-and-send test that she is at markedly increased risk for breast and ovarian cancer...
A reporter who sends samples to multiple direct-to-consumer genomics companies, each with unique and variable results...
These are just a few of the stories to surface around the recent warning letter sent by the US Food and Drug Administration to a Direct-to-Consumer (DTC) genomics testing company.
The warning letter stated that the company had not provided adequate evidence that the Personal Genome Service provides accurate assessment of disease risk. This news and related stories have popularized discussions that have been taking place within the walls of genetic medicine for quite some time.
“The variability of results from DTC testing is not exactly a new finding,” says Susan Domchek, MD, executive director of Penn Medicine’s Basser Research Center for BRCA. “Starting around 2010, researchers have illustrated similar discrepancies by sending batches of samples to DTC companies and publishing the results. It is widely understood that each lab looks for slightly different genetic markers and may interpret the same data differently.”What is direct-to-consumer genetic testing? What do the tests look for? What are the risks and benefits to this type of testing?
Basser Center genetic counselor Rebecca Mueller MS, CGC, CCRC explains.
Q: What is direct-to-consumer genetic testing?
Direct-to-consumer- or DTC- genetic testing is genetic testing that is arranged directly between a consumer and a company with no medical professional intermediary. Most of the companies provide saliva sample kits that are mailed in for genetic testing at a company laboratory.
First, many SNPs typically contribute to risk of any given disease and different laboratories may look at different SNPs.
Second, even if two laboratories are looking at the same SNP they may interpret results differently for a variety of reasons. For example, they may have different data about the baseline or average risk for a given disease in a particular population, and the increase or decrease in risk is based off of that data.
Regardless of what the genetic reports say, there are a few more things to consider: We have yet to define all the genetic variations that contribute to disease risks, so every test has important limitations. We also know that there are many non-genetic factors that affect disease risks significantly, so even a hypothetically perfect genetic test would have limitations. For example, you can lack genetic risk factors for obesity but still be obese.
Q: What conditions do DTC tests look for?
DTC tests have been marketed to test for everything from ancestry, to carrier status for recessive conditions, to disease risk, to paternity. Currently, the FDA is concerned about DTC testing for disease risk. These genetic tests for disease risk typically look at what we call SNPs or Single Nucleotide Polymorphisms.Q: What exactly are Single Nucleotide Polymorphisms (SNPs)?
These are small differences in the genome at specific places in the genetic code that are commonly found in people. Through studies of large samples of individuals, scientists have identified many, many SNPs that increase or decrease risk for different diseases within certain populations.Q: Why do reported disease risks vary depending on the company doing testing?
Many things contribute to disease risk—not just genetics. While we know that genetic variation contributes to disease risk, there are several reasons why results vary by laboratory.First, many SNPs typically contribute to risk of any given disease and different laboratories may look at different SNPs.
Second, even if two laboratories are looking at the same SNP they may interpret results differently for a variety of reasons. For example, they may have different data about the baseline or average risk for a given disease in a particular population, and the increase or decrease in risk is based off of that data.
Regardless of what the genetic reports say, there are a few more things to consider: We have yet to define all the genetic variations that contribute to disease risks, so every test has important limitations. We also know that there are many non-genetic factors that affect disease risks significantly, so even a hypothetically perfect genetic test would have limitations. For example, you can lack genetic risk factors for obesity but still be obese.
Q: Are DTC companies doing BRCA testing?
It is important to understand that most DTC companies do not comprehensively sequence genes, meaning they cannot rule out the presence of a mutation with the same precision as the laboratories used in medical settings. For example, one company tested people’s samples for three specific mutations within the BRCA1 and BRCA2 genes that are commonly found in the Ashkenazi Jewish population, but the company did not provide comprehensive genetic testing (also called full sequencing) of the BRCA genes. Individuals might think they had negative BRCA1/2 testing, when in fact they had very limited testing that is insufficient for ruling out a BRCA mutation.Q: Are SNP test results medically useful?
Many things contribute to risk for any given disease. Currently, family history and personal medical history and exposures are the best way to assess risk for many types of cancer. In some individuals, genetic testing of certain genes (not SNPs, but entire genes such as BRCA1 and BRCA2 and genes for hereditary colon cancer) can be very useful. These tests can be ordered by medical providers when indicated to shed more light on inherited cancer risk. Comprehensive testing of these genes is not available through DTC companies.Interested in learning more?
Genetic counselors at the Marian and Robert MacDonald Women’s Cancer Risk Evaluation Program and the Division of Translational Medicine and Human Genetics provide risk assessment and genetic testing for a variety of conditions.
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