You’ve probably seen ads for them online or on television—those genetic tests that promise to help you figure out if you’re related to someone famous and if you’re at risk of some disease. Have you ever wondered how those tests work and how effective they are? If you have, you’re in luck.
Direct-to-consumer (DTC) genetic tests are all the rage. With options like 23andMe and Ancestry.com, do you know which one to choose? According to Jennifer Siettmann, a genetic counselor with Banner MD Anderson Cancer Center, your choice should depend on what you want to get out of the test.
In an Ask the Expert column, Siettmann explained the importance of genetic counseling in helping determine risk for illnesses, such as cancer, heart disease and diabetes. Recently, she also noted that DTC genetic tests have very specific limitations and should never be used in place of comprehensive genetic testing when it comes to determining your risks for serious disease.
How do genetic tests work?
DTC genetic tests and genetic screenings your doctor might order both examine your DNA. To do this, a sample must be collected.
In a typical DTC test, you provide a saliva sample. After your ordered kit arrives, you use a swab to collect a bit of spit. You seal the swab and mail it back in for analysis, which can take between 4 and 6 weeks.
Samples for clinical genetic testing can be collected one of two ways: a saliva sample like the DTC test or by blood draw. Siettmann notes accuracy is the same for both, and most clinical laboratories accept either. A clinical test is typically turned around in about 2 to 3 weeks.
Analysis and reporting
A DTC test may vary depending on the laboratory, notes Siettmann. While some companies may have geneticists or genetic counselors analyze the results, other do not. Additionally, some laboratories may not have Clinical Laboratory Improvement Amendments of 1988 (CLIA) certification.
“CLIA certification requires that laboratories have set quality and privacy standards for a laboratory to meet, and these certifications are constantly renewed,” Siettmann said.
Additionally, not all DTC laboratories are accurate in what they report. Siettmann explains these labs may be accurate for certain parts of their testing but not others, like raw data analysis.
You may receive the results from these tests online with informational videos or data sheets explaining what the information means. While some companies may have genetic counselors on staff to help with interpretations, most of the interpretation and learning is done by the patient.
Things are different with clinical genetic testing, which is analyzed by geneticists and genetic counselors at CLIA-approved laboratories. According to Siettmann, the data is put through stringent quality processes to ensure accuracy.
“Geneticists and genetic counselors at these laboratories work very hard to determine what genetic variants are benign or not causing any problems and which are harmful and may lead to a health problem,” Siettmann said.
The report compiled after the testing is completed explains what genes were analyzed, what mutations—if any—were found, and the test specifications. If a mutation or variant is found, the geneticists and genetic counselors will give information on that gene and mutation.
Finally, the provider who ordered the test reviews and interprets the results within the context of your personal and family history.
What direct-to-consumer genetic tests do
There are a lot of things a DTC genetic test can tell you, but Siettmann notes the information tends to be superficial. For example, it can help you trace your ancestry, find out if you can taste cilantro or determine how caffeine affects you.
“Basically, direct-to-consumer tests are fun and all over the place right now, but they do not replace the genetic testing that a doctor can perform,” Siettmann said. The depth of information a doctor can give you will far outweigh what a DTC genetic test gives you.
A lot depends on the DTC test you choose, according to Siettmann. Some are accurate, CLIA-certified and can be used for healthcare decisions, but most are not. Most of this testing will not be able to be used clinically and usually will not point a physician towards using more accurate testing methods.
“There are exceptions where a specific DTC will require confirmation testing through a CLIA-approved laboratory, but most of the information is meant to be for fun,” said Siettmann.
What direct-to-consumer genetic tests don’t do
If you’re thinking of buying a DTC genetic test to determine your risk for a specific disease, you’ll likely be out of luck. And, while genetic counselors are not against DTC genetic tests, Siettmann says they want people to understand what these types of tests can and cannot do.
For example, while one DTC test looks at the BRCA1 and BRCA2 genes—genes which help produce tumor suppressors—the test only looks at three mutations within the gene, explains Siettmann. In reality, thousands of mutations could be present in these genes.
Another piece Siettmann points out involves Alzheimer’s disease, heart disease and macular degeneration. Instead of doing full gene sequences, some labs may only look at single nucleotide polymorphisms (SNPs). A mouthful, right? So, what are they?
As Siettmann explains, they are a single nucleotide that is substituted for another within a gene, which leads to a change within that gene. SNPs are usually very common and usually benign; however, they can be associated with certain genetic quirks—like how caffeine affects you or if you can taste cilantro.
“So, think of it like a recipe for apple pie,” Siettmann said. “A SNP would be adding an extra dash of cinnamon or being very particular about the kind of apple you use, whereas a true pathogenic mutation would be like substituting vinegar instead of butter.”
Currently, geneticists and genetic counselors consider SNPs to be warning signs and not the cause of a disease. Most DTC testing uses these SNP-based arrays and makes causative leaps about these SNPs that the data does not uphold. Some DTC labs, however, do not use a SNP array and do offer full sequencing, and some use a combination of both, so it’s important to know what the lab uses.
“I’ll tell patients they’re like road signs that tell you to watch for falling rocks,” Siettmann said. “The sign won’t cause rocks to fall, and it won’t even guarantee that the rocks will fall. However, once, rocks fell in this spot, so now a sign is up to warn about it.”
Set your expectations
If you have your heart set on trying a genetic test, make sure you know what you want to get out of it first. The DTC tests can provide basic information, but they won’t answer more serious questions a genetic screening from a doctor can provide.
- If you want a test to trace back your ancestry or some minor things, the direct-to-consumer option may be perfect for you.
- If you are concerned about your risks of getting cancer, Alzheimer’s disease or several other major diseases, a full genetic screening from your doctor may be in order. Talk to your doctor about your options.
Siettmann’s final piece of advice is to be careful. Pay attention to what the DTC test company is doing because some of them sell your data to third parties. Siettmann also suggests considering if the DTC test is CLIA-certified, being aware of who signs off on the report and what their accuracy record is.
“Be a smart consumer and don’t sign up for every DTC that comes across a Google search,” Siettmann said.