DNA Testing

Genetic Testing is also referred to as DNA testing (singular - a DNA test). If a doctor is ordering a DNA test, it is typically done to establish or confirm if a health condition is due to an alteration in the DNA of a patient. If a person is doing what is known as a Direct-To-Consumer (DTC) test, then most of the time it is done to get a good picture (profile) of someone’s overall health condition and if lifestyle changes should be made. A good number of people consider ancestry analysis using DNA as a genetic test as well. In our discussions here, we will not consider ancestry analysis as genetic tests but more as an application of genome analysis that is of interest to the public.

Genetic tests can also help determine if a person has a chance of developing a genetically influenced disease (some cancers like breast cancer can be genetically influenced) or is capable of passing the condition on to their children (like color blindness). Technologies for evaluating DNA have become so good that millions of tests (millions of datapoints) can be generated in one attempt. Whatever it is, it is good to keep in mind that just because someone has an altered DNA in a gene being tested or if a result shows or tells that you are pre-disposed to a disease like cancer, it does not necessarily mean that someone is going to get the disease. There are certain ways genes work within our cells and a basic understanding of Genetics is necessary before you worry about getting a disease of any type. See Genetics, DNA and Genes before you do a genetic test so that you know how different results can be understood and appreciated. Also, if questions are there, it is best to talk to your family physician or find a genetic counselor near you. Most hospitals have them, and a list of Genetic Counselors in each State in the US can be found at the National Society of Genetic Counselors (NSGC) website:

https://findageneticcounselor.nsgc.org/

Types of Genetic Tests

Different types of genetic tests are done for different reasons. The reasons are described along with examples so that you can know how clinicians (doctors) might use these tests. What is listed below are tests that are mostly ordered by doctors.

Carrier testing. This is a term used to describe a test to detect a genetic condition that is passed along from one generation to another. Some conditions are very well understood in a family and some conditions are well understood within certain ethnic groups. Cystic fibrosis, sickle cell anemia, Tay-Sachs Syndrome, Marfan syndrome, color blindness etc. are well understood as good options to test before having children. This is also an example of a direct-to-consumer testing option that several marriage partners use today. With DTC options, a wide variety of genetic diseases can be screened to determine if you and your partner are carriers for the same conditions (particularly, autosomal recessive conditions).
Diagnostic Genetic Test. If you have symptoms of a disease that may have an underlying genetic basis, then the doctor might order a very specific genetic test. This will tell the doctor if you have the suspected disorder. For example, if someone shows symptoms of cystic fibrosis, then it can be confirmed with a genetic test.
Newborn screening. Newborn screening is used to identify certain genetic, endocrine, and metabolic disorders as well as hearing loss and critical congenital heart defects (CCHDs). There are typically about 50 diseases that are screened and this is done so that treatment and care can begin early.
Pharmacogenetic Testing. If in the past you found that some medication you used worked better than another for the same condition, then it was your genetic makeup that mostly determined the effectiveness of the drug used. This type of genetic testing looks at multiple genes that are involved in drug efficacy and drug metabolism and may help determine what medication and dosage will be most effective and beneficial for you. This is mostly ordered by physicians in hospital settings.
Prenatal testing. This is done mostly when someone is pregnant and, in the past has involved collecting amniotic fluid. These tests can detect abnormalities like Down syndrome and trisomy 18 syndrome. Now, cell-free DNA testing of the mother’s blood will allow detection of the baby’s DNA, making it easier and safer.
Pre-symptomatic and predictive testing. If during a regular visit to your doctor you indicated family history of a genetically influenced condition (like certain types of colorectal cancer or breast cancer), the doctor might order a genetic test before you showed any symptoms. This will show if there is a risk of you developing that condition and what if any preventive measure or lifestyle changes can be made.

General Information About Genetic Tests

In 1865, Gregor Mendel, the father of modern genetics described inheritance as an observable trait through experiments done on plants. By the 1930s, DNA was confirmed as the genetic material that was responsible for the traits being observed. The first breakthrough for DNA testing came about in the 1970s in the form of DNA sequencing. Then came the discovery of restriction enzymes. These are enzymes that cut DNA at specific sites. By the 1980s, many restriction enzymes were discovered that were able to cut at specific sequences. These enzymes were quickly used in a technique called Restriction Fragment Length Polymorphism (RFLP) analysis where the ability to cut or not cut at a site allowed the mapping of mutations. So, the first set of DNA tests were all based on this method. In the 1990s, Polymerase Chain Reaction (PCR) based DNA testing was introduced which allowed the use of small amounts of DNA as well as different types of samples (blood, tissue, biopsies, swabs etc.). PCR is a method that allowed amplification of DNA (see DNA Sequencing section on how DNA is amplified). Most of the time, DNA tests with PCR included the amplification of DNA followed by RFLP analysis. With DNA sequencing and other genotyping methods becoming more established, genetic tests started becoming popular and now covers a wide range of applications. For more information see:

https://www.genome.gov/FAQ/Genetic-Testing

How is DNA Testing Done

Most doctor’s office will collect blood or some tissue sample (cheek cells or biopsies in serious cases) and send them to a laboratory. If you use a direct to customer home test kit, most will ask you to collect a saliva sample in a special collection tube. Some companies (like GenoTypica) will ask you to swab your cheek inside your mouth with a swab and send the swab in for testing, also in a special collection tube.

Is there any risk in doing a Genetic Test?

There is hardly any physical risk in collecting a sample, particularly if the sample is a cheek swab and you follow instructions that come with the kit. The goal is to get a good sample.

There is emotional risk if you receive unexpected results. Even if a test is ordered by a physician, once you get an unexpected result, it could be difficult. You may feel scared, angry or anxious. Also, there are financial risks. Some tests might cost thousands of dollars. If testing is ordered by a doctor, insurance may cover the cost. If testing is done by the DTC (direct-to-consumer) route, then it may be in the hundreds of dollars. Note that all genetic conditions may not be caught in the test and not all variations for a particular genetic disease may be detected in the test that was run. No test may be 100% accurate but most genetic tests done in hospitals and reputed companies will be close to 98% accurate and that is actually, very accurate. This does not mean that sample mix-up and other unexpected errors and omissions may not happen. So, it is always best to get a second opinion if you are not sure of the results or were not expecting the results that were received.

Results and Follow-Up

What is mentioned below is the typical format of a result. This does not mean all labs and all companies report results this way. Generally speaking, even if millions of data points are generated in a single effort for a variety of conditions; for a single test, a simple explanation may be provided by your doctor or genetic counselor as given below.

Positive: This typically means the lab found a genetic mutation known to cause a specific disease that the test was ordered for. This may identify you as a carrier of the disease or confirm a diagnosis or may determine that you have an increased risk.
Negative: This typically means that the lab did not find a genetic mutation in your DNA known to cause the disease that the test was ordered for. This means your DNA sequence is the normal sequence and the suspected disease could not be confirmed as a genetic disease and so the physician may have to look for another cause.
Uncertain or No Result: This typically means the lab could not confirm the genetic mutation or the normal sequence in your DNA for the test that was ordered. Either the signal was not strong enough or the sample was not good enough to get a clear result. In such cases, the lab will request a resubmission of a new sample. This is why collecting the sample carefully by following instructions are very important.

How accurate are Genetic Tests?

If a genetic test is done in a hospital lab or in a well managed and professional lab of a reputable company, certain standard guidelines are followed. These are standards that most labs follow and there are Federal as well as state standards. This also may mean that the test has been validated analytically and also clinically. In such cases, analytical validity looks at how accurately the lab can detect a specific mutation. Clinical validity means this mutation has been clinically established as being related to a specific disease or condition. Most if not all DTC tests are done with established methods (provided by vendors of the instrument systems used for testing) and validated markers (published papers), that accuracy is in the 98% to 99% rate. No test is 100% accurate and one should be skeptical if anyone makes such claims. Anything at or above 98% accuracy is considered sufficient in most clinical situations. Keep in mind that some of the OTC antigen testing kits that you can find in a pharmacy are only 80% accurate but are considered acceptable. DNA testing is almost all the time more precise and reliable.

In Summary

Genetic tests (DNA tests) are useful and provide a lot of different types of information depending on what you are trying to do. From single gene tests to whole genome scans, from doctor ordered test to direct-to-consumer offerings, it can help you determine if you have a specific genetic condition or if you are likely to develop a genetically influenced condition. It has its benefits and it also comes with risks and limitations. If Genetic Testing of any type is of interest to you, it is best to start first with your healthcare provider. They can refer you to a genetic counselor who can provide you with a lot more information about all types of testing and how it can benefit you. Additionally, once you receive a test result or a test report, it is best to sit down with your genetic counselor and evaluate the information. No testing company can provide you or should provide you with directions on next steps. Genetic tests provide actionable information but you will need advice from a trained professional – your doctor or your genetic counselor. Most hospitals have them, and a list of Genetic Counselors in each State in the US can be found at the National Society of Genetic Counselors (NSGC) website: