As the number of genetic testing options has grown exponentially in recent years, so have the different types of genetic testing methodologies used. Depending on the type of anomaly being measured, there are three main categories of genetic tests available: cytogenetic tests, biochemical tests, and molecular tests. Newborn screening tests are done shortly after birth to identify genetic disorders that can be treated early in life. For example, all babies in the UK are tested for cystic fibrosis as part of the heel prick test.
Diagnostic tests are used to identify or rule out a specific genetic disorder if a baby or person has symptoms that suggest a particular genetic disorder (for example, Down syndrome). Carrier testing is used to identify people who carry one copy of a genetic mutation (a genetic change) that, when present in two copies, causes a genetic disorder (such as sickle cell anemia). This type of test can be useful in providing information about a couple's risk of having a child with a genetic disorder. Predictive testing is used to detect genetic mutations associated with disorders that appear after birth, often later in life.
These tests may be useful for people who have a family member with a genetic disorder, but who has no characteristics of the disorder itself at the time of the test (for example, breast cancer associated with the BRCA1 gene). Predictive testing can identify mutations that increase a person's risk of developing genetically based disorders, such as certain types of cancer. Therefore, before undergoing predictive testing, it is essential that a specialist thoroughly discuss with you the risks of being affected by the disorder, how the disorder would affect you, and the benefits and risks of having a genetic test to detect the disorder. Certain genetic conditions are associated with specific chromosomal changes, and a chromosomal test may be used when one of these conditions is suspected.
However, genetic testing has limitations, as it is only useful if a specific genetic mutation is known to cause a certain condition. A variety of genetic tests can be purchased individually, many of them now on the Internet, which usually consist of scraping the inside of the cheek to obtain some cells for analysis. The genetic material (DNA and chromosomes) in the cells is tested for the disorder known in the family history. However, sometimes the copying mechanism makes mistakes or other problems with genetic material.
Too much activity (overexpression) or too little (underexpression) of certain genes can indicate the presence of certain genetic disorders, such as many types of cancer. Abnormalities in these substances may indicate that there are changes in the DNA that underlie a genetic disorder. People from families at high risk of suffering from a genetic disease have to live with uncertainty about their future and the future of their children. These types of tests are offered during pregnancy if there is an increased risk of the baby having a genetic or chromosomal disorder.
Genetic test results can confirm or rule out a possible genetic condition or help determine a person's chances of developing or transmitting a genetic disorder. Gene expression tests look at which genes are turned on or off (expressed) in different types of cells. The information you get from genetic testing can have a big impact on your life, so you may be referred to a genetic counselor. Genetic counseling is available to anyone who undergoes any type of genetic testing or is thinking of undergoing any type of genetic testing.
There are thousands of genetic tests available to help doctors diagnose and treat many diseases.
