Genetic testing is a powerful tool that can provide a diagnosis and help provide information for managing symptoms, treatment, or lifestyle changes. There are several types of genetic tests available, each with its own purpose and implications. Exome sequencing is the most common type of genetic test. It analyzes all the genes in the DNA (whole exome) or only genes related to medical conditions (clinical exome).
Genome sequencing is the largest genetic test and analyzes all of a person's DNA, not just genes. Newborn screening tests are done right 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. Biochemical tests do not directly analyze DNA, but rather study the amount or level of activity of proteins or enzymes that are produced from genes. 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.
In newborns, routine tests for a genetic disorder, such as phenylketonuria, are done as part of the baby's heel prick test when they are about 5 days old. These tests are particularly useful if a person has a family history of a specific illness and an intervention is available to prevent the onset of the disease or minimize the severity of the disease. Genetic testing can also refer to the analysis of RNA to determine gene expression, to biochemical tests to detect the presence of gene products (proteins), and to the microscopic analysis of chromosomes. 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.
When deciding whether or not to perform genetic testing for yourself or a member of your family, several issues must be considered, both medically and emotionally.