Genetic tests are done by analyzing small samples of blood or body tissues. They determine whether you, your partner, or your baby carry genes for certain inherited disorders.
Genetic testing has developed enough so that doctors can often pinpoint missing or defective genes. The type of genetic test needed to make a specific diagnosis depends on the particular illness that a doctor suspects.
Many different types of body fluids and tissues can be used in genetic testing. For deoxyribonucleic acid (DNA) screening, only a very tiny bit of blood, skin, bone, or other tissue is needed.
For genetic testing before birth, pregnant women may decide to undergo amniocentesis or chorionic villus sampling. There is also a blood test available to women to screen for some disorders. If this screening test finds a possible problem, amniocentesis or chorionic villus sampling may be recommended.
Amniocentesis is a test usually performed between weeks 15 and 20 of a woman's pregnancy. The doctor inserts a hollow needle into the woman's abdomen to remove a small amount of amniotic fluid from around the developing fetus. This fluid can be tested to check for genetic problems and to determine the sex of the child. When there's risk of premature birth, amniocentesis may be done to see how far the baby's lungs have matured. Amniocentesis carries a slight risk of inducing a miscarriage.
Chorionic villus sampling (CVS) is usually performed between the 10th and 12th weeks of pregnancy. The doctor removes a small piece of the placenta to check for genetic problems in the fetus. Because chorionic villus sampling is an invasive test, there's a small risk that it can induce a miscarriage.
A doctor may recommend genetic counseling or testing for any of the following reasons:
Although advances in genetic testing have improved doctors' ability to diagnose and treat certain illnesses, there are still some limits. Genetic tests can identify a particular problem gene, but can't always predict how severely that gene will affect the person who carries it. In cystic fibrosis, for example, finding a problem gene on chromosome number 7 can't necessarily predict whether a child will have serious lung problems or milder respiratory symptoms.
Also, simply having problem genes is only half the story because many illnesses develop from a mix of high-risk genes and environmental factors. Knowing that you carry high-risk genes may actually be an advantage if it gives you the chance to modify your lifestyle to avoid becoming sick.
As research continues, genes are being identified that put people at risk for illnesses like cancer, heart disease, psychiatric disorders, and many other medical problems. The hope is that someday it will be possible to develop specific types of gene therapy to totally prevent some diseases and illnesses.
Gene therapy is already being used studied as a possible way to treat conditions like cystic fibrosis, cancer, and ADA deficiency (an immune deficiency), sickle cell disease, hemophilia, and thalassemia. However, severe complications have occurred in some patients receiving gene therapy, so current research with gene therapy is very carefully controlled.
Although genetic treatments for some conditions may be a long way off, there is still great hope that many more genetic cures will be found. The Human Genome Project, which was completed in 2003, identified and mapped out all of the genes (about 25,000) carried in our human chromosomes. The map is just the start, but it's a very hopeful beginning.
|Sickle Cell Disease Association of America This group provides education, advocacy, and other initiatives to promote awareness of and support for sickle cell disease programs.|
|National Human Genome Research Institute (NHGRI) The leader in the Human Genome Project, the NHGRI aims to improve human health and fighting disease through genomic research.|
|CDC: Genetic Counseling The CDC's site has up-to-date information on genetic counseling.|
|American Society of Gene & Cell Therapy Learn about the latest gene and cell therapy clinical trials.|
|National Society of Genetic Counselors This organization represents the genetic counseling profession through research, advocacy, and education.|
|National Down Syndrome Society (NDSS) NDSS strives to ensure that all people with Down syndrome have the opportunity to achieve their full potential in community life. Call: (800) 221-4602|
|March of Dimes The March of Dimes seeks to prevent birth defects, infant mortality, low birthweight, and lack of prenatal care.|
|Birth Defects Birth defects are relatively common. Some are minor and cause no problems; others cause major disabilities. Learn about the different types of birth defects, and how to help prevent them.|
|Gene Therapy and Children Gene therapy carries the promise of cures for many diseases and for types of medical treatment most of us would not have thought possible.|
|Down Syndrome Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, both physically and mentally.|
|Newborn Screening Tests Newborn screening tests look for harmful or potentially fatal disorders that aren't apparent at birth. Find out which tests are done and which disorders they're designed to detect.|
|All About Genetics Read the basics about genetics, including how certain illnesses, or increased risks for certain illnesses, pass from generation to generation.|
|Genetic Counseling Genetic counselors work with people who are either planning to have a baby or are pregnant to determine whether they carry the genes for certain inherited disorders. Find out more.|
|FAQs: Prenatal Tests Find out what tests are available to keep you informed of your -- and your baby's -- health throughout pregnancy.|
|Prenatal Tests: First Trimester Find out what tests may be offered to you during the first 12 weeks of pregnancy.|
|Prenatal Tests: Second Trimester Find out what tests may be offered to you during weeks 13 through 26 of pregnancy.|
|Prenatal Tests: Third Trimester Find out what tests may be offered to you during weeks 27 through 40 of pregnancy.|
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