A genetic test can help identify if there is a faulty gene or chromosome that might cause a genetic condition. It is usually a blood or tissue test. There are a number of reasons why a person might take a genetic test.
Some of the reasons are listed below:
It will not always be necessary to have a genetic test. They may be able to diagnose a genetic condition through a clinical examination, or tell you about your risk by looking at a detailed family history. Depending on the purpose of the test, genetic tests can be categorised as diagnostic tests, carrier tests or predictive tests.
Diagnostic testing is used when someone is already experiencing symptoms to identify or confirm the genetic cause of these symptoms, if there is one. A doctor may already have a strong belief that the symptoms are caused by a specific condition, and use genetic testing to confirm this and identify the genetic fault causing the condition. In other cases the doctor may look at a large number of genes which can cause a particular set of symptoms, in the hope of finding out which gene or mutation is responsible. Knowing the molecular basis of a condition can sometimes help doctors target their treatment so that it is more appropriate to the patient.
For some genetic conditions that need two copies of a faulty gene to cause a condition (recessive conditions), someone who only has one copy is called a carrier. Carriers of most conditions are themselves unaffected because the working copy of the gene overrides the faulty copy, but they can pass on a copy of the faulty gene to their children. Carrier testing allows you to know whether or not you and your partner carry a faulty copy of a gene, in order to make informed choices about having children in the future.
For chromosome translocations, a carrier is a person who has a balanced translocation whereby no chromosome material is lost or gained and is not usually affected by it.
A predictive test can provide information about whether or not someone will develop or is likely to develop a specific condition, usually at a later stage in life. If a late onset genetic condition runs in your family, then you might decide that you would like to know whether or not you have inherited the faulty gene. We talk more about predictive testing here, as there are lots of factors to consider when deciding whether or not to have a predictive test.