Types of Genetic Tests - GenomeSmart

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There are more than 76,000 different genetic tests available to consumers and health care professionals. To decide whether a genetic test is right for you, it’s a good idea to get comfortable with basics.

Predictive tests (screening tests) vs. diagnostic tests Genetic tests are either: 1. Predictive, sometimes called screening tests, or 2. Diagnostic.

Predictive testing is used to assess a person’s risk for, or likelihood of developing, genetic conditions. This type of test is done before a person develops symptoms for any particular genetic condition. For example, when a cancer runs in the family, family members may use predictive tests to see whether their genetic makeup indicates any risk for the same cancer. Results from a predictive test usually do not give patients a yes or no answer, but they can sometimes help doctors and patients manage, or even prevent, the onset of genetic conditions. On the other hand, diagnostic testing is used to determine a specific genetic cause for an existing

particular condition. This means that the person doing a diagnostic test has already developed symptoms for this condition. If a specific mutation is pinpointed as the cause for a genetic condition, this information may help doctors better manage the disease or advise parents on reproductive decisions.

How testing works: the science behind testing All genetic tests decode your DNA. Your DNA is a code with four main characters: A, C, G, and T. These four characters are arranged in a specific order A, C, G and T represent our nucleotides which are like our genetic alphabet. “A” represents adenine, “C” cytosine, “G” guanine and “T” thymine. Based on data from many people, scientists can often predict whether the order of a certain DNA sequence could cause a genetic condition. Scientists need to know your DNA sequence to decipher it. Genetic tests uncover and decipher your DNA in different ways, depending on the technologies they use.

Many genetic tests use sequencing, or technologies that determine the exact sequence of your DNA. With sequencing, scientists can look at your entire genome or specific parts of your genome, even just single genes. Sequencing methods are designed to detect the smallest changes to your DNA: point mutations or duplications and deletions within a single gene. However, sequencing methods alone often cannot reliably detect entire gene deletions and duplications or chromosomal abnormalities.

Many other genetic tests use a technology

known as a microarray, which analyzes an array of different sequences of interest. A microarray compares a subset of your DNA sequences directly with a subset of DNA sequences from a reference sample. With this method, a microarray can identify variants, or differences, in your DNA compared with the reference DNA. Various microarray-based tests exist for different purposes. For example, chromosomal microarrays can detect chromosomal abnormalities like deletions and duplications, which are regions of DNA which are missing or duplicated compared with the reference DNA. Other microarrays like genotyping tests, also called SNP-based tests, detect very small changes such as a single letter in your DNA. However, unlike sequencing tests, they can identify only a specific set of known mutations. Although microarrays limit the number of DNA sequences that tests can analyze and identify, they are typically cheaper and faster than sequencing.

What testing looks for In addition to using different technologies to decode your DNA, genetic tests may be targeted to different parts of your DNA. Single gene tests only examine one gene of interest. For example, a single gene test looking at BRCA1 will analyze only the BRCA1 gene. It will not determine if you have mutations in any other genes linked to breast and ovarian cancer. Gene panels examine a specific subset of genes of interest. For example, a gene panel test for a breast cancer patient will look at BRCA1, BRCA2, CHEK2, and other related genes. Whole genome sequencing looks for mutations across your entire genome. This kind of testing is unnecessary or too expensive for most patients. However, it can often provide the most information about a person’s genetic makeup but is complex to interpret.

Whole exome sequencing looks for

mutations across your entire exome: the part of your genome that codes for proteins (because a large part of your genome doesn’t code for proteins at all!). It is slightly more targeted than whole genome sequencing, while remaining one of the most extensive genetic testing methods available which is currently used in some special clinical cases.

Evaluate the validity of the method and the utility of the test!

Each of the technologies and methods used for genetic testing have advantages and disadvantages. But, for every test suggested, it’s important to consider both its validity (or accuracy) and its utility—its usefulness for you. GenomeSmart will do its best to pair you with tests that are best suited for you based on your personal and family history.

For example, think about two different genetic tests that each look at your BRCA1 gene.

Test 1 uses a SNP-based microarray and can only identify a few of the BRCA1 variants associated with cancer.

Test 2 uses sequencing technology to identify your precise DNA sequence. As a result, it can identify any possible variants of BRCA1.

Test 1 is quite specific: it could identify the variant you are interested and give you a simple yes or no answer about that variant only. If you are certain that Test 1 looks for a variant that has been passed down in your family and you are curious to know whether you have that exact variant, then this test is a reasonable option for you.

GenomeSmart can empower you with understanding of genetic tests. Use that information to talk with a health care professional and your family to make

informed decisions about genetic testing. For most people, Test 2 is the more useful option. Test 2 is more sensitive and more comprehensive, because it can identify any variant of BRCA1, whether or not you know if a BRCA1 mutation runs in your family. So, before getting a genetic test done, make sure you do your research!

Take the time to consider different tests and take advantage of GenomeSmart to learn more about the best options for you.

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