Genetic Testing
Current Issues in Genetic Testing
Types of Genetic Tests
Genetic technology has led to the development of a number of different types of ‘genetic’ tests. These include:
Screening tests are important public health measures. The goal of screening tests is to identify early disease (prior to onset of symptoms) or individuals at high risk of a disease in order to provide treatment and to reduce death or disability. Screening tests do not provide a definite diagnosis but are used to determine if further testing is warranted. The Prenatal and Newborn programs (the Guthrie test) are examples of screening tests.
Diagnostic tests are used to diagnose a genetic condition and determine prognosis. Results provide confirmation of a diagnosis. Amniocentesis is considered a diagnostic test.
Carrier testing is used to determine the presence of a gene variant that will not affect the individual’s health, but may increase their chance of having children with a particular condition. An example is carrier testing for the recessive genetic condition cystic fibrosis.
Predictive tests are ones that are used to identify a risk of future disease in a currently healthy person. An example is the test for Huntington’s disease. Onset of disease is not until 40 or 50 years of age, but a genetic test will be able to inform an individual whether or not they have inherited the gene for the disease.
Susceptibility tests are used to identify susceptibilities to common diseases for which preventive care is often available. These tests can identify individuals at increased risk for a certain disease, but cannot predict future disease with absolute certainty. This type of testing aims to make individuals aware of their risk and allow them to modify their lifestyle to reduce the risk as much as possible. An example is testing for the BRCA1 and BRCA2 gene variants that are associated with an increased risk of breast cancer. Carrying these variants does not indicate with certainty that an individual will develop cancer, but they are considered at greater risk than individuals without the variant. Knowledge of this increased risk however, can allow the individual to undertake preventive measures, such as more frequent mammography screening or surgery.
DNA fingerprint tests include those that are used to determine paternity or identify a criminal suspect. DNA samples from a number of individuals are chemically treated and then compared to identify similarities.
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