What Is Genetic Testing?

Genetic testing is the analysis of human DNA, RNA, chromosomes, and proteins, which determine an individual's physical traits, development, and many other characteristics. It can be useful for detecting variations in genes that could increase susceptibility to certain diseases or conditions.

There are several types of genetic tests, including:

• Direct testing: direct examination of the DNA or RNA that makes up a gene
• Linkage testing: examination of "markers" inherited along with a disease-causing gene
• Biochemical testing: examination of proteins or protein products that indicate gene variations
• Cytogenetic testing: examination of chromosomes

Genetic tests may be used for:

• Confirming a suspected diagnosis
• Predicting an individual's susceptibility to a future illness
• Screening unaffected individuals for gene variations that could affect their children (carrier status)
• Prescribing correct medications, or for adjusting the doses

The use of genetic testing has been limited, primarily for rare, heritable conditions in families where there is a strong history of such conditions. However, new genetic tests are being developed to predict susceptibility to a wide range of common diseases too, including cancer, diabetes, heart disease, and mental illness. Researchers in the emerging field of pharmacogenomics are developing tests that may be used to predict a person's response to certain treatments or drugs.

Genetic tests are a powerful medical tool, and they need to be handled with care. The evidence for some tests is preliminary or incomplete. Most tests only predict risks, not certainties, and counseling is important.