Genetic marker, any alteration in a sequence of nucleic acids or other genetic trait that can be readily detected and used to identify individuals, populations, or species or to identify genes involved in inherited disease. Genetic markers consist primarily of polymorphisms, which are discontinuous genetic variations that divide individuals of a population into distinct forms (e.g., AB versus ABO blood type or blond hair versus red hair). Genetic markers play a key role in genetic mapping, specifically in identifying the positions of different alleles that are located close to one another on the same chromosome and tend to be inherited together. Such linkage groups can be used to identify unknown genes that influence disease risk. Technological advances, especially in DNA sequencing, have greatly increased the catalogue of variable sites in the human genome.
Genetic Check-up involves examining your DNA, the chemical database that carries instructions for your body’s functions. Genetic testing can reveal changes or alterations in your genes that may cause illness or disease.
Although genetic testing can provide important information for diagnosing, treating and preventing illness, there are limitations. For example, if you’re a healthy person, a positive result from genetic testing doesn’t always mean you will develop a disease. On the other hand, in some situations, a negative result doesn’t guarantee that you won’t have a certain disorder.
Talking to your doctor or a genetic counselor about what you will do with the results is an important step in the process of genetic testing.
What is tested?
- Disease Susceptibility (Multifactorial Disorders)
- Genetic Diseases Carrier State
- Personal Response to Drugs (10 Drugs)
Purpose of Test
Your doctor may order a genetic test for any number of reasons related to diagnosis, prevention, and treatment. Genetic testing can also be used in legal investigations. There are even direct-to-consumer tests able to trace your ancestry.
How Genetic Tests Work
Nearly every cell in your body contains DNA, genes, and chromosomes. Each serves a specific and interrelated function:
• DNA (deoxyribonucleic acid) is a double-stranded molecule that contains all the genetic information about you as an individual. DNA is made up of four substances known as adenine (A), thymine (T), cytosine (C), and guanine (G). The unique sequence of these substances provides the “programming code” for your body.
• A gene is a distinct portion of DNA that contains the coded instructions on how and when to build specific proteins. While a gene is meant to perform in a standard way, any flaws in its DNA coding can affect how those instructions are delivered. These flaws are referred to as genetic mutations.
• A chromosome is a bundled unit of genes. Every human has 46 genes, 23 of which are inherited from the mother and father, respectively. Each chromosome contains between 20,000 to 25,000 genes.
Since the early 1900s, scientists have understood that specific genetic variations (genotypes) translate into specific physical characteristics (phenotypes). In recent years, advances in technology and a broader understanding of the human genome have allowed scientists to pinpoint which mutations confer to certain illnesses or characteristics.
Types of Genetic Tests
Genetic tests have far-ranging applications in medical and non-medical settings. They include:
• Diagnostic testing to confirm or rule out a genetic disorder
• Carrier testing done prior to or during pregnancy to see if you and your partner carry a gene that may cause a congenital defect
• Prenatal diagnosis to detect abnormalities in a fetus’s genes before birth to identify congenital disorders or birth defects
• Newborn screening to routinely screen for 21 inheritable disorders, as mandated by law
• Preimplantation testing used to screen embryos for abnormalities as part of the in vitro fertilization (IVF) process
• Predictive diagnosis to estimate your risk (predisposition) of developing a genetically influenced disease, like breast cancer, later in life
• Pharmacogenetics testing to determine whether your genetics may influence your response to drug therapies, particularly genetic resistance to viruses such as HIV
Non-medical uses of genetic testing include paternity test (used to identify inheritance patterns between individuals), genealogy testing (to determine ancestry or heritage), or forensic testing (to identify an individual for legal purposes).
Risks and Contraindications
The physical risks of genetic testing are small. Most require a blood or saliva sample or a swab of the inside of your cheek (known as a buccal smear). Depending on the aims of the test, it may only require a few drops of blood (such as for newborn screening or paternity testing) or several vials (for cancer or HIV testing).1
If cancer is suspected, a biopsy may be performed to obtain cells from a solid tumor or bone marrow. The risks of biopsy can vary depending on how invasive the procedure is, ranging from localized pain and bruising to scarring and infection. A novel liquid biopsy for cancer gene mutation can be done substitute tissue biopsy to make diagnosis via circulating tumor cells .
Before the Test
A genetic test does not require much preparation on your part. The only exception may be prenatal tests, which sometimes require food and/or fluid restrictions.
Timing
Depending on the purpose of the investigation, a genetic test may take as little as a few minutes to perform.
With the exception of direct-to-consumer ancestry kits, most genetic tests will involve some level of pre-test counseling. Even if your doctor orders the test as part of an ongoing investigation, expect to spend no less than 15 minutes at the lab or clinic (not including the wait time).
Prenatal tests may take anywhere from 30 to 90 minutes to perform, depending on whether amniocentesis, transabdominal CVS, or transcervical CVS is ordered.
Biopsies may take longer, particularly those involving bone marrow or the colon. While the procedure may take only 10 to 30 minutes to perform, preparation and recovery time may add another hour if an intravenous (IV) sedative is used.
Interpreting the Results
Depending on the test and testing facility used, it can take anywhere from one to four weeks to get your test results. Commercial labs tend to be faster than institutional or research labs.
If the test was performed for diagnostic purposes, the results will generally be reviewed with you by the doctor who ordered the test. One such example is an HIV specialist who orders genotyping to determine which drugs will be most effective based on the genotype of your virus or cancer as precision medicine.
If the test is used for predictive or screening purposes, a genetic counselor may be on hand to explain what the results mean and do not mean.
For the most part, single-gene tests will deliver a positive, negative, or ambiguous result. By definition:
• A positive result indicates that a “deleterious mutation” (also known as a “pathogenic mutation”) was found. A deleterious mutation is one in which your risk of a disease is increased, but not necessarily certain.
• A negative result means that no gene mutation was found.
• An ambiguous result, often described as a “variation of uncertain significant” (VUS), describes a mutation with unknown impact. While many such mutations are harmless, some may actually be beneficial. Consult our specialist @ www.drorawan.com
