Genetic testing

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, genetics 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 in gene 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. Genetics 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 gene alteration but is 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 and Huntington's disease.
• Predictive medicine: determine whether an individual has 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) and colorectal cancer. 
•  Pharmacogenomics: classifies subtle variations in an individual's genetic makeup to determine whether a drug is suitable for a particular patient, and if so, what would be the safest and most effective dose.  Learn more about pharmacogenomics.

How many different types of genetic tests are currently available?

There are >1200 genetic tests available to physicians to aid in the diagnosis and therpay for >1000 different diseases. Genetic testing is performed for the following reasons:

• conformational diagnosis of a symptomatic individual
• presymptomatic testing for estimating risk developing disease
• presymptomatic testing for predicting disease
• prenatal diagnostic screening
• newborn screening
• preimplantation genetic diagnosis
• carrier screening
• forensic testing
• paternal testing  
  

What are genetic counselors?

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

National Cancer Institute - Understanding Cancer Series: Gene Testing

US Department of Health and Human Services - Understanding Gene Testing