I’ve been hearing more and more about friends and family having genetic testing done. Many of them have done at-home genetic testing (e.g. 23andMe, AncestryDNA, Helix, etc.) to determine their ancestry or to look for genetic abnormalities. I wondered how this type of testing differed from clinical genetic testing and genetic counseling. Caitlin Troyer, a pediatric genetic counselor at UVA, agreed to share her expertise with me.
What is Genetic Testing?
We all get two sets of genes: one set from our mother and one from our father. There are over 20,000 different genes, made up of 3 billion “letters” of DNA. In genetic testing, the lab reads through those genes looking for “typos” or mutations – essentially, differences in that person’s genes that don’t typically occur in healthy people. Then, they work to determine if that difference is known to cause a health concern or if it’s a normal, harmless genetic variation. Variations typically fall into one of two categories:
- Common, benign genetic variations: These are the differences that make you and I different from one another. They do not cause a disease or an increased risk for a health condition.
- Variations (sometimes called mutations) that cause disease or the risk for disease: These differences impact the function of the gene, causing health implications.
A harmful genetic mutation can be inherited from either a child’s mother or father. Some mutations are only harmful if the child receives a mutation from both parents; that is, both sets of their genes carry a disease-causing typo.
However, not all genetic conditions are inherited from a parent. Random genetic mutations occur, too.
How Does Clinical Genetic Testing Work?
First, a patient meets with a genetic counselor. The genetic counselor reviews the patient’s history and determines if they’re a candidate for genetic testing. They identify a condition or a group of related conditions for which to test. (It’s not feasible to test a patient’s entire set of genes at such a detailed level – the genetic counselor must identify a starting point based on medical and family history.) Once the results come back, the genetic counselor interprets the findings and shares them with the patient.
Benefits of Genetic Testing
Genetic testing can help:
- Connect the patient with the right specialist
- Provide information for patients and families about what to expect for the future
- Determine additional screening or surveillance a patient should receive
- Identify a condition by name, so families can connect with others dealing with the same condition
Drawbacks of Genetic Testing
- A concrete diagnosis won’t necessarily impact a patient’s treatment plan
- Psychological impact of what to expect from the condition in the future
- Psychological impact of learning the chance of passing the condition on to offspring, and/or risks to other relatives
Additionally, results can impact rates and eligibility for certain types of insurance. GINA (Genetic Information Non-Discrimination Act) prohibits employers and health insurers from denying employment or health insurance based on results from genetic testing. However, other types of insurance such as life insurance and long-term care insurance are not subject to the same limitation, and genetic testing results can impact rates and the ability to get coverage.
A Typical Genetic Counseling Patient
The typical patient seen for genetic testing has some sort of developmental or medical issue going on, and doctors have been unable to pinpoint exactly what it is.
Troyer explained that there is a tremendous amount of uncertainty in genetic testing, and oftentimes the patient won’t get a simple yes/no answer about the cause of their condition. This is partly because the field of genetics is still a young and developing one, and discoveries are being made all the time. The roles of many of those 20,000 genes aren’t yet understood, so if an abnormality is found in one of those little-understood genes, geneticists can’t always be certain about its effect.
Interested in having clinical genetic testing done?
While UVA accepts self-referrals for genetic counseling, the best way to get started is to speak to your or your child’s primary care provider, or to a specialist you’re already seeing, about getting a referral.
Sometimes a patient has a genetic typo so uncommon that geneticists can’t yet determine its effect. This is referred to as a “variant of uncertain significance.” It can still be worthwhile to patients to have their testing done, even knowing the results may be inconclusive. As more patients’ genes are studied and the field of genetics matures, geneticists will better understand those variations. As newer tests are developed, those patients may get the confirmation they’re looking for.
Common Genetic Disorders Identified Through Genetic Testing
UVA’s pediatric genetic counselors see a lot of patients from developmental pediatrics, and they’re able to identify genetic disorders in about 40 percent of those children. Those genetic conditions can include chromosome disorders, (chromosomes are where our genes are located, and sometimes people are born with a missing or duplicated piece of a chromosome) or single gene disorders (these are often random mutations rather than inherited abnormalities).
Genetic testing for cancer is also a growing field. These tests look for other variations that may indicate an inherited, increased risk of developing cancer. These are generally done for patients with personal or family histories of specific cancers. BRCA1 and BRCA2 (specific variations of these genes are associated with inherited breast and ovarian cancers) are commonly known genes that are tested for abnormalities. However, there are many other genes that are associated with a hereditary cancer risk. Confirmation of variations like these can provide valuable information about the type and frequency of screening a patient should receive over her lifetime.
Direct-to-Consumer Genetic Testing vs. Clinical Genetic Testing
Clinical genetic testing isn’t the same as what is offered by sites like 23andMe, which are often targeted toward healthy individuals, Troyer says.
There are two main types of direct-to-consumer DNA testing. The first is ancestry-based genetic testing, which looks at genetic markers to estimate the composition of someone’s ethnic background. The second is health-related testing which looks for common polymorphisms (genetic variants common in the population) to provide a risk estimate (high, moderate, low) of developing a particular condition in adulthood.
Direct-to-consumer tests don’t work the same as clinical genetic testing, according to Troyer. Since at-home tests look for polymorphisms in order to assign risks to variations, they aren’t as detailed or focused as clinical genetic screenings.
Troyer shared that sometimes genetic counselors are wary of direct-to-consumer tests, not because they’re bad tests, but because of peoples’ tendency to misinterpret the results. Just because a person’s results indicate they have a genetic typo and are high risk for a certain condition does not mean that they already have the condition. They may not ever develop that condition.
According to Troyer, “It’s important to consider what information you’re trying to learn from the test. It can be fun and interesting, but I would caution about how the results are interpreted. There is the potential for results to be confusing and taken out of context. The at-home tests are accurate. I have no issue with people ordering them, as long as they have a good understanding of what they are and aren’t getting from that test. It’s not a definitive guide to the future of your health.”