Advances in genetics have the potential to revolutionize how physicians diagnose and treat illness. But while the ability to repair defective genes remains far in the future, genetic testing can help patients determine the likelihood of passing on or inheriting certain disorders today. Genetic testing usually refers to the analysis of DNA to identify changes ingene sequence (deletions, additions, or misspellings) or expression levels.Genetic testing can also refer to biochemical tests for gene products (proteins) and for microscopic analysis of stained chromosomes. Genetic testing still is in its early stages, so both patients and experienced physicians may need guidance when it comes to navigating this new and complex territory.

How is genetic testing used clinically? Diagnostic medicine: identify whether an individual has a certain genetic disease. This type of test commonly detects a specific genealteration butis often not able to determine disease severity or age of onset. It is estimated that there are >4000 diseases caused by a mutation in a single gene. Examples of diseases that can be diagnosed by genetic testing includes cystic fibrosis andHuntington's disease.

Predictive medicine: determine whether an individualhas an increased risk for a particular disease. Results from this type of test are usually expressed in terms of probability and are therefore less definitive since disease susceptibility may also be influenced by other genetic and nongenetic (e.g. environmental, lifestyle) factors. Examples of diseases that use genetic testing to identify individuals with increased risk include certain forms of breast cancer (BRCA) andcolorectal cancer.

Pharmacogenomics:classifies subtle variations in an individual's genetic makeup todeterminewhether a drug is suitable for a particular patient, and if so, what would be the safest and most effective dose. Learnmore aboutpharmacogenomics.

Whole-genome and whole-exome sequencing: examines the entire genome or exome to discover genetic alterations that may be the cause of disease. Currently, this type of test is most often used in complex diagnostic cases, but it is being explored for use in asymptomatic individuals to predict future disease. Read more in this article.

How many different types of genetic tests are currently available? There are >2000genetic tests available to physicians to aid in the diagnosis and therapy for >1000 different diseases. Genetic testing is performed for the following reasons:

What are geneticcounselors? Genetic counselors are health professionals with specialized graduate degrees and experience in the areas of medical genetics and counseling. They are an integral part of the healthcare team providing information and support to individuals and families who have members with birth defects, genetic disorders, or may be at risk for a variety of inherited disorders. Genetic counselors also serve as educators and a resource for other healthcare professionals and for the general public.

Additional resources

NIH Genetic Testing Registry

National Cancer Institute - Understanding Cancer Series: Gene Testing

US Department of Health and Human Services - Understanding Gene Testing

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Genetic Testing - American Medical Association

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