Genetic testing is a transformative technology with many applications in medicine and legal frameworks. For example, genetic testing can tell if someone is at risk of developing a genetic disorder like Fragile X. Fragile X is a genetic defect that causes developmental problems like cognitive impairment and learning disabilities. So, genetic testing results significantly reduce uncertainty and help people make better decisions about their health care.
Genetic testing has greatly evolved from single-gene tests to more sophisticated ones that examine multiple genes. This article extensively covers the concept of genetic testing from its definition, preparation, procedure, and types and reasons for testing. I will also explain the meaning of various genetic testing types and their associated benefits, risks, and limitations.
Keep reading till the end of this article to uncover every aspect of genetic testing.
What is genetic testing?
Genetic testing can also mean DNA testing. Genetic testing examines an individual’s DNA to determine genetic differences or susceptibility to certain disorders or diseases. It identifies variations or mutations in the human body’s protein, chromosome, or gene sequences.
Genetic tests provide much information about an individual’s genetic makeup. They can determine if one has certain mutated genes to be passed down to the offspring. It also shows if one has a higher risk of developing certain genetic diseases or disorders. They can also verify if one has or does not have certain health conditions.
How Do You Prepare for Genetic Testing
Before seeking a genetic test, one should first understand the procedure, benefits, shortcomings, and consequences of the test results. The aspect of informed consent applies where the subject should be fully aware of the test.
The information on the family’s medical history is critical in this process. After gathering family medical history, one proceeds to discuss the family and personal medical history with the genetic counselor to clearly understand the associated risk. When testing conditions that cut across families, you should share the decision to perform the test with your family. This helps to predetermine the family’s reaction to the test results.
How is Genetic Testing Carried Out?
Genetic testing usually happens during a genetic consultation with a physician. The process begins by preparing the DNA collected from a test sample. A test sample can be hair, skin, amniotic fluid, blood, or other applicable tissue.
The lab technicians examine the samples to detect the specific variations in the DNA, proteins, or chromosome structure. They use different detection ways depending on the suspected condition and the doctor’s order. The lab performs sequencing tests to identify the abnormalities in the DNA. Sequencing tests provide detailed information about specific genes or the whole genome.
A DNA sequencer is the machine technicians load part or whole DNA sample to sequence it. The DNA sequencer reads the DNA and collects data as short “reads,” representing tiny parts of the DNA sequence.
Computerized systems analyze the short “reads” that compare the DNA to the human reference genome (all human DNA). These computers relay the report, listing any DNA, chromosome, or protein variations. All humans have DNA variants, but not all can cause a disease or increase the risk of developing a disease. The technicians then present the report to the doctor, genetic counselor, or patient upon request.
Summary of Different Types of Genetic Testing
Different types of genetic tests examine variations in genes, chromosomes, or proteins. The doctor decides the type of testing based on the suspected condition and the different signs of the condition. The common types of genetic testing are molecular, chromosomal, gene expression, and biochemical tests.
Molecular Tests
Molecular genetic tests look for gene variations to determine nucleotide arrangement in a person’s genetic makeup through DNA sequencing. The subtypes of molecular genetic tests include the following:
- Single gene testing: These tests help identify genetic variations in a single gene to clarify a certain diagnosis in case a gene has multiple genetic changes that can cause the suspected condition.
- Targeted single variant: These tests help find specific variants in a single gene when testing family members of a person with a particular variant to see if the condition runs in the family.
- Gene panel: This test looks for changes in more than one gene to help determine what’s wrong with a person whose symptoms could be caused by more than one disease or changes in many genes.
- Whole genome/exome sequencing: This is the most economical and easy way to test a large amount of a subject’s DNA to identify genetic changes. It is applied when the suspected genetic condition or cause is unknown.
Biochemical Tests
A biochemical genetic test indirectly analyzes DNA by studying the variations in the enzymes or proteins the genes produce.
Gene Expression Tests
Doctors conduct gene expression tests by looking at the genes expressed (turned on/off) in various cell types. These tests study the mRNA released from expressed (active) genes during protein formation to identify the active genes. Overexpression or underexpression of particular genes suggests the presence of a particular condition or risk of developing a given condition.
Chromosomal Tests
They look at the whole chromosomes or long DNA strands to find big changes like translocations, duplications, or missing segments.
Why Do You Need Genetic Testing
Genetic testing helps doctors determine the likelihood of developing a certain disease, its presence, and treatment options. The above types of genetic testing are performed for different reasons, as discussed below:
- Diagnostic testing: This test helps confirm the presence of a condition that is thought to be present based on signs and symptoms.
- Newborn screening: This is the most common reason for genetic testing. All US states require genetic testing for newborns to ascertain the presence of certain genetic or metabolic abnormalities that may cause specific conditions like sickle cell or hypothyroidism. The tests are conducted at birth to identify genetic conditions treatable earlier in life.
- Presymptomatic and predictive testing: This test is applied to individuals with a family history of a genetic disease to do a genetic test before the symptoms start showing up if they are at risk of developing the condition.
- Carrier testing:Â People who have a family history of a certain genetic disorder or come from an ethnic group that is more likely to get it need this test to see if they have one copy of the mutated gene that, when expressed in two copies, causes a genetic disorder like sickle cell anaemia.
- Prenatal testing: Doctors can also perform genetic testing during pregnancy to look for variations in the fetus’s genes, proteins, or chromosomes and determine if the baby is at high risk for developing specific genetic disorders like Down syndrome and trisomy 18 syndromes.
- Pharmacogenetics: This test helps find the best medicine and dose for a health problem.
- Preimplantation testing, Also called preimplantation genetic diagnosis, minimizes the risk of having a child with a certain genetic condition. People use it when trying to have a child through assisted reproductive techniques like in-vitro fertilization (IVF) to identify genetic variations in created embryos. Ultimately, doctors will screen the embryos for any genetic mutations and only implant embryos free of any genetic abnormalities.
- Forensic testing: Unlike the above reasons for genetic testing (finding gene mutations linked to diseases), forensic genetic testing looks at DNA sequences to find proof for the law. It can be used to find out who the father of a child is, to confirm that a suspect committed a crime, or to find out who the victims of a disaster are.
What Do the Results of the Genetic Test Mean?
During genetic testing, always discuss and decide on the (expected) results with the genetic counselor, medical geneticist, or doctor. Genetic testing results are not always direct, making them challenging to interpret and understand. Doctors determine the results based on the type of genetic test and the person’s family and medical history. Usually, there are three types of genetic testing results: positive, negative, and inconclusive.
Positive Results of a Genetic Test
Positive results in genetic testing mean that genetic variations were present. Usually, what you do with the results depends on why you did the genetic testing in the first place. For instance, the positive results may indicate higher risks of developing a condition, show that a person is a carrier for a particular condition, confirm a medical diagnosis, guide the physicians on medication and dosage, or insinuate more testing.
However, a positive result for a presymptomatic or predictive genetic test does not mean one should or is at risk of developing the genetic disorder. The presence of breast cancer genes indicates higher risk of developing breast cancer later in life. Still, it does not ensure the person will develop the condition. Though, having gene variations relating to certain diseases like Huntington’s disease means the disease will certainly occur. Still, doctors cannot rely on a positive test result to predict the severity pattern of a genetic condition.
Again, though rarely, false-positive genetic testing results are also possible. False positive results happen when a test shows a disorder or a higher chance of getting a disorder when this is not true. For example, it is common that non-invasive prenatal testing (NIPT) may result in false positive results because the analyzed fetal DNA has a placental origin. Also, false results can result from chromosomal abnormalities in additional embryonic tissue missing from the fetal tissue (placental mosaicism), giving discordant, hence invalid results.
Negative Results of a Genetic Test
Negative results on a genetic test mean that the test didn’t find the suspected gene change(s), which can be reassuring. Still, suggesting the individual lacks genetic variation is not 100% reliable. The accuracy of genetic tests to find gene changes depends on the condition being studied and whether or not the targeted genetic abnormalities have been seen in the family before.
Still, not having a specific gene change doesn’t mean a person will never get the related disease. In particular, research has shown that many breast cancer cells have occurred in individuals without cancer genes. Also, genetic testing may fail to identify all genetic defects, resulting in false negative results (which happen rarely and mean the results show the genetic defect is missing when the subject is at risk or affected). Further testing and re-testing could confirm the results if they are negative.
Inconclusive Genetic Test Results
Inconclusive, ambiguous, indeterminate, or uninformative test results do not tell us anything useful about the genetic variations being studied. These results happen because all individuals have similar, innate mutations in their DNA sequence called polymorphisms that pose no health risk to them.
However, it is not always easy to differentiate between harmless gene defects and gene variations related to the risk of developing or worsening an existing disorder. Gene abnormalities yet to be confirmed to cause or relate to any genetic disorder are called a variant of uncertain significance. However, this does not mean these gene variants do not cause disorders. Instead, there are limited scientific findings to rule out or confirm, or there are conflicting scientific research findings.
So, inconclusive genetic test results won’t prove or disprove a certain diagnosis, nor the likelihood of developing the defect. Sometimes, more tests on affected and unaffected relatives may help clear the uncertainty. In addition, follow-up tests and regular assessments of the genes could also help.
What Are the Advantages of Genetic Testing?
Genetic testing results can still be useful, whether negative or positive.
Whereas negative results provide reassurance, positive results allow people to prepare and decide how to live sustainably with the genetic disorder. The results provide ideas of individuals’ prognoses and allow doctors to be more certain about how they respond to the patient. Positive results inform treatment, monitoring, and prevention plans at the early stages of the genetic disorder. Therefore, positive results improve the affected people’s life expectancy and general quality of life.
Genetic test results help individuals decide their future lives, such as having children. This applies when the test results show a low risk of passing a genetic defect on to children. But positive results will discourage people from having children because of the high risk of their children inheriting genetic disorders.
What Are the Risks of Genetic Testing
Usually, genetic testing poses little physical risk to the parties involved. For instance, blood and cheek swab tests may not be risky to the subject. However, prenatal tests, which may require the collection of test samples from the fetus, such as the amniotic fluid (amniocentesis), may carry a considerable risk of losing the pregnancy or causing miscarriages.
Another common risk of genetic testing relates to financial, social, emotional, and psychological risks. There is a high likelihood that the results will make individuals guilty, depressed, and angry. In other cases, genetic testing results in family friction because the results may reveal details about other relatives and the subject of their genetic defects. Socioeconomic effects such as discrimination at places of employment and on insurance plans may arise because of certain positive genetic testing results.
What Are the Limitations of Genetic Testing
Despite its broad spectrum of applications, genetic tests also have limitations. For instance, it is unlikely for genetic testing to give all information about an individual’s condition, such as the possible symptoms or projection of severity of the condition.
Before undertaking a genetic test, one should always discuss and seek clarity on the limitations and risks with physicians and genetic counselors. This will make you well-informed about the process before taking part.
Conclusion
Genetic testing helps people determine if they have a genetic defect or their likelihood of developing one in the future. It looks for mutations or abnormalities in the genes, chromosomes, or protein sequences. Anyone can seek genetic testing to understand their state of health in relation to genetic disorders such as cystic fibrosis, sickle cell anemia, and Down syndrome. Besides medication and checking of gene variants, genetic testing is also applied in legal systems to provide evidence on paternity tests and determine whether a given suspect is connected to a crime.
Genetic testing gives individuals peace of mind whenever it returns a negative result. But still, a positive result can help them seek preventive, monitoring, and treatment plans as soon as possible to manage the severity of the condition. It also comes with the risks and limitations discussed above.
Therefore, one should consult their doctor before taking a genetic test to understand the benefits and process.
Thank you for reading this article. Please comment below if you have any questions or concerns about genetic testing. Also, if you found this article interesting, please comment below.
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