Genetic Testing
Genetic testing involves examining a person’s blood or other tissues to determinewhether he or she has a change in his or her genetic material. Genetic testing may beuseful in determining whether an individual has a genetic condition or may develop onein the future. The information gained from genetic testing may be helpful in a number ofways such as diagnosing a genetic disease, starting treatment, or initiating preventionstrategies, as well as making life decisions such as career choice and family planning.Several types of genetic testing are available, and this appendix provides an overviewof the genetic testing available, as well as who may be offered such testing.
Why Genetic Testing?
Genetic testing may be offered for a number of different reasons including:
To confirm or rule out a diagnosis in an individual with symptoms of a geneticcondition
For individuals with a family history of or a previous child with a geneticcondition
To locate possible genetic conditions in newborn babies so treatment may bestarted immediately
How Is Genetic Testing Performed?
Genetic testing involves analyzing an individual’s blood, skin, hair, or otherbody tissue to look at his or her DNA, chromosomes, or proteins for a change, ormutation, that is associated with a genetic condition. When a mutation occurs, it mayaffect all or part of a gene and can result in an abnormal function leading to disease.Three major types of genetic testing are available in laboratories: cytogenetic (toexamine whole chromosomes), biochemical (to measure protein produced by genes), andmolecular (to look for small DNA mutations). (See Chapter 2 and Appendix I for more information.)
What Types of Genetic Testing Are There?
Newborn screening is the most widespread use of genetic testing. (SeeChapter 4 for moreinformation about newborn screening.) Almost every newborn in the U.S. is screened forseveral genetic diseases. Early detection of these diseases can lead to interventions toprevent the onset of symptoms or minimize disease severity.
Carrier testing can be used to help couples to learn if theycarry—and thus risk passing to their children—an allele for a recessivecondition such as cystic fibrosis, sickle cell anemia, and Tay-Sachs disease. This typeof testing is typically offered to individuals who have a family history of a geneticdisorder and to people in ethnic groups with an increased risk of specific geneticconditions. If both parents are tested, the test can provide information about acouple’s chance of having a child with a genetic condition.
Prenatal diagnostic testing is used to detect changes in afetus’ genes or chromosomes. This type of testing is offered to couples with anincreased chance of having a baby with a genetic or chromosomal disorder. A tissuesample for testing can be obtained through amniocentesis or chorionic villus sampling.(See Appendix E for moreinformation.)
Genetic tests may be used to confirm a diagnosis in a symptomaticindividual or to monitor prognosis of a disease or response to treatment.
Predictive or predispositional genetic testing can identify individualsat risk of getting a disease prior to the onset of symptoms. These tests areparticularly useful if an individual has a family history of a specific disease and anintervention is available to prevent the onset of disease or minimize disease severity.Predictive testing can identify mutations that increase a person’s risk ofdeveloping disorders with a genetic basis such as certain types of cancer.
Forensic testing is used for identification, not to identify individualsat risk for a genetic disease. Forensic testing is performed for legal purposes such ascriminal investigations, questions of paternity, and identification after catastrophicevents such as Hurricane Katrina.
Who Should Consider Genetic Testing?
When deciding whether or not to get a genetic test for yourself or a family member,several issues need to be considered, both from a medical and an emotional standpoint.Genetic testing may provide a diagnosis and help provide information for symptommanagement, treatment, or lifestyle changes. However, genetic testing has limitations.When a genetic test detects a mutation, the test cannot always determine when or whatsymptoms of the condition may show, which symptoms will occur first, how severe thecondition will be, or how the condition will progress over time. Even if a test isnegative, an individual may still be at risk for a condition.
Due to the complexity of the medical and emotional issues involved in genetic testing, itis important to speak to a health professional such as a genetic counselor to help youunderstand the benefits and risks of genetic testing and to answer any questions you mayhave before and after testing. For information on genetic counseling, preparation for agenetic counseling visit, and sample questions to ask healthcare providers, see Appendix O.
References
American College of Medical Geneticswww.acmg.net.
GeneTests www.genetests.org.
National Society of Genetic Counselorswww.nsgc.org.
U.S. National Library of Medicine: Genetics HomeTesting http://www.ghr.nlm.nih.gov/
