What is Genetic Analysis?
Genetic analysis refers to examination or study of a sample of your DNA (deoxyribonucleic acid), the chemical database that carries instructions for your body's functions, to check for changes (mutations) that may increase your risk for disease or affect the way you respond to treatment.
Our genetic makeup (DNA, chromosomes, genes, and proteins) is what makes each of us unique. Many diseases are caused by changes or mutations in certain genes. A gene is the basic physical and functional unit of heredity. Genes are made up of DNA and are passed from parents to offspring. They contain the information required to specify biological and physical traits. Genetic analysis helps to determine whether you are at an increased risk of a genetic disorder. For example, genetic analysis can provide a diagnosis for a genetic disorder such as Fragile X or information about your risk of developing cancer.
Indications for Genetic Analysis
Genetic analysis is recommended to identify abnormalities in the genetic makeup of a person, which may cause illness or disease. In general, genetic analysis may be performed to:
- Diagnose genetic conditions
- Detect the correct medication and dosage required for a particular medical condition
- Test for genetic conditions before symptoms surface, especially if you have a family history of genetic condition
- Identify genetic diseases in unborn babies
- Screen newborns for certain gene abnormalities that cause specific conditions, so that immediate treatment can be planned
- Ascertain if you carry a gene for a disease that may pass on to your children
- Screen in vitro fertilized embryos for genetic abnormalities before implantation
What Does Genetic Analysis Involve?
There are several types of genetic tests that are performed as part of genetic analysis. These include:
- Molecular tests: Molecular tests check for mutations in one or more genes. These types of tests establish the order of DNA building blocks (nucleotides) in an individual's genetic code, a process referred to as DNA sequencing. These tests can differ in scope:
- Whole genome sequencing/whole exome sequencing: These tests examine the bulk of an individual’s DNA to identify genetic variations. Whole genome or whole exome sequencing is usually utilized when a single gene or panel testing has not provided a diagnosis, or when the suspected condition or genetic cause is not clear. Whole genome or whole exome sequencing is commonly more time- and cost-effective than doing multiple single gene or panel tests.
- Gene panel: Gene panel tests check for variants in more than one gene. This type of test is commonly used to identify a diagnosis when an individual has symptoms that may fit a great variety of disorders or when the suspected disorder can be caused by variants in many genes. For instance, there are hundreds of genetic causes of epilepsy.
- Single gene: Single gene tests check for any genetic variations in one gene. These tests are generally used to rule out or confirm a specific diagnosis, especially when there are numerous gene variants that can cause the suspected disorder.
- Targeted single variant: Targeted single variant tests check for a particular variant in one gene. The chosen variant is known to cause a condition (for instance, the particular variant in the HBB gene that causes sickle cell disease). This type of test is commonly used to test family members of someone who is known to have a specific variant, to establish whether they have a familial disorder. In addition, direct-to-consumer genetic testing companies usually examine a number of particular variants in specific genes (rather than detecting all the variants in those genes) when providing health or disease risk information.
- Chromosomal tests: Chromosomal tests examine entire chromosomes or long lengths of DNA to find out extensive changes. Changes that can be detected include a missing or an extra copy of a chromosome (monosomy or trisomy, respectively), a large segment of a chromosome that is missing (deleted) or added (duplicated), or rearrangements (translocations) of pieces of chromosomes. Certain genetic disorders are connected with specific chromosomal changes, and a chromosomal test can be utilized when one of these disorders is suspected (for instance, Williams syndrome is caused by a deletion of a segment of chromosome 7).
- Gene expression tests: Gene expression tests look at which genes are turned on or off (expressed) in different types of cells. When a gene is turned on (active), the cell makes a molecule called mRNA from the instructions in the genes, and the mRNA molecule is utilized as a blueprint to produce proteins. Gene expression tests study the mRNA in cells to establish which genes are active. Too little activity (underexpression) or too much activity (overexpression) of certain genes can be indicative of specific genetic conditions, such as many types of cancer.
- Biochemical tests: Biochemical tests do not directly examine DNA, but they study the activity level or the number of proteins or enzymes that are made from genes. Irregularities in these substances can suggest that there are mutations in the DNA that underlie a genetic condition (for example, low levels of biotinidase enzyme activity are indicative of biotinidase deficiency, which is caused by BTD gene variants.)
How is a Genetic Analysis Performed?
Genetic analysis is performed using samples collected from blood, cheek tissue, amniotic fluid (protective liquid in which the unborn child develops), or chorionic villus (finger-like extensions of the placenta). These are then sent to the laboratory for analysis.
- Blood sample: Your healthcare team member will collect the blood sample by placing a needle into a vein in your arm. For newborn genetic screening, a blood sample is obtained by pricking the heel of your baby.
- Cheek swab: For some genetic analysis, a swab sample from the inside of your cheek is taken for testing.
- Amniocentesis: This is a prenatal genetic analysis that involves the insertion of a hollow, thin needle through your abdominal wall and into the uterus to obtain an amniotic fluid sample for testing.
- Chorionic villus sampling: In this prenatal genetic test, your physician obtains a tissue sample from the placenta. The sample may be obtained through your abdominal wall and uterus utilizing a thin needle or with a tube (catheter) through your cervix.
Results of Genetic Analysis
Depending upon the type of test done, it can take weeks or even months for the results to become available. Although genetic testing may give you an insight into the disease you may develop, it does not always necessarily mean that you will develop a certain condition if your genetic test comes positive (mutated gene was detected). It may show that with a particular gene abnormality, your chances of getting a particular disease are higher. Similarly, it does not necessarily mean that if you get a negative result (mutated gene was not detected), you will never develop a genetic disorder in the future. In some cases, a genetic test may not provide helpful information about the gene in question. These are termed as inconclusive results. In such situations, periodic reviews or follow-up testing of the gene over time may be required.