Genetic Counseling
Definition, Purpose, Precautions, Description, Preparation, Aftercare, Risks, Normal results, Abnormal results
Genetic counseling aims to facilitate the exchange of information regarding a person's genetic legacy. It attempts to:
- accurately diagnose a disorder
- assess the risk of recurrence in the concerned family members and their relatives
- provide alternatives for decision-making
- provide support groups that will help family members cope with the recurrence of a disorder
Purpose
Genetic counselors work with people concerned about the risk of an inherited disease. The counselor does not prevent the incidence of a disease in a family, but can help family members assess the risk for certain hereditary diseases and offer guidance. Many couples seek genetic counseling because there is a family history of known genetic disorders, infertility, miscarriage, still births, or early infant mortality. Other reasons for participating in genetic counseling may be the influences of a job or lifestyle that exposes a potential parent to health risks such as radiation, chemicals, or drugs. Any family history of mental retardation can be of concern as is a strong family history of heart disease at an early age. Recent statistics show a 3% chance of delivering a baby with birth defects. An additional 2% chance of having a baby with Down syndrome is present for women in their late thirties and older.
Precautions
Amniocentesis, one of the specific tests used to gather information for genetic counseling, is best performed between weeks 15 and 17 of a pregnancy and an additional one to four weeks may be required to culture skin cells and analyze them. Thus, these test data are not available to assist prospective parents in decision-making until the second trimester of the pregnancy. Individuals who participate in genetic counseling and associated testing also must be aware that there are no cures or treatments for some of the disorders that may be identified.
Description
With approximately 2,000 genes identified and approximately 5,000 disorders caused by genetic defects, genetic counseling is important in the medical discipline of obstetrics. Genetic counselors, educated in the medical and the psychosocial aspects of genetic diseases, convey complex information to help people make life decisions. There are limitations to the power of genetic counseling, though, since many of the diseases that have been shown to have a genetic basis currently offer no cure (for example, Down syndrome or Huntington's disease). Although a genetic counselor cannot predict the future unequivocally, he or she can discuss the occurrence of a disease in terms of probability.
A genetic counselor, with the aid of the patient or family, creates a detailed family pedigree that includes the incidence of disease in first-degree (parents, siblings, and children) and second-degree (aunts, uncles, and grandparents) relatives. Before or after this pedigree is completed, certain genetic tests are performed using DNA analysis, x ray, ultrasound, urine analysis, skin biopsy, and physical evaluation. For a pregnant woman, prenatal diagnosis can be made using amniocentesis or chorionic villus sampling.
Family pedigree
An important aspect of the genetic counseling session is the compilation of a family pedigree or medical history. To accurately assess the risk of inherited diseases, information on three generations, including health status and/or cause of death, is usually needed. If the family history is complicated information from more distant relatives may be helpful, and medical records may be requested for any family members who have had a genetic disorder. Through an examination of the family history a counselor may be able to discuss the probability of future occurrence of genetic disorders. In all cases, the counselor provides information in a non-directive way that leaves the decision-making up to the client.
Screening tests
Screening blood tests help identify individuals who carry genes for recessive genetic disorders. Screening tests are usually only done if:
- The disease is lethal or causes severe handicaps or disabilities
- The person is likely to be a carrier due to family pedigree or membership in an at-risk ethnic, geographic or racial group
- The disorder can be treated or reproductive options exist
- A reliable test is available.
Genetic disorders such as Tay-Sachs disease, sickle-cell anemia, and thalassemia meet these criteria, and screening tests are commonly done to identify carriers of these diseases. In addition, screening tests may be done for individuals with family histories of Huntington's disease (a degenerative neurological disease) or hemophilia (a bleeding disorder). Such screening tests can eliminate the need for more invasive tests during a pregnancy.
Another screening test commonly used in the United States in the alpha-fetoprotein (AFP) test. This test is done on a sample of maternal blood around week 16 of a pregnancy. An elevation in the serum AFP level indicates that the fetus may have certain birth defects such as neural tube defects (including spina bifida and anencephaly). If the test yields an elevated result, it may be run again after seven days. If the level is still elevated after repeat testing, additional diagnostic tests (e.g. ultrasound and/or amniocentesis) are done in an attempt to identify the specific birth defect present.
Ultrasound
Ultrasound is a noninvasive procedure which uses sound waves to produce a reflected image of the fetus upon a screen. It is used to determine the age and position of the fetus, and the location of the placenta. Ultra-sound is also useful in detecting visible birth defects such as spina bifida (a defect in the development of the vertebrae of the spinal column and/or the spinal cord). It is also useful for detecting heart defects, and malformations of the head, face, body, and limbs. This procedure, however, cannot detect biochemical or chromosomal alterations in the fetus.
Amniocentesis
Amniocentesis is useful in determining genetic and developmental disorders not detectable by ultrasound. This procedure involves the insertion of a needle through the abdomen and into the uterus of a pregnant woman. A sample of amniotic fluid is withdrawn containing skin cells that have been shed by the fetus. The sample is sent to a laboratory where fetal cells contained in the fluid are isolated and grown in order to provide enough genetic material for testing. This takes about seven to 14 days. The material is then extracted and treated so that visual examination for defects can be made. For some disorders, like Tay-Sachs disease, the simple presence of a telltale chemical compound in the amniotic fluid is enough to confirm a diagnosis.
Chorionic villus sampling
Chorionic villus sampling involves the removal of a small amount of tissue directly from the chorionic villi (minute vascular projections of the fetal chorion that combine with maternal uterine tissue to form the placenta). In the laboratory, the chromosomes of the fetal cells are analyzed for number and type. Extra chromosomes, such as are present in Down syndrome, can be identified. Additional laboratory tests can be performed to look for specific disorders and the results are usually available within a week after the sample is taken. The primary benefit of this procedure is that it is usually performed between weeks 10 and 12 of a pregnancy, allowing earlier detection of fetal disorders.
Preparation
Genetic diagnosis requires that a couple share information about inherited disorders in their background with the genetic counselor, including details of any genetic diseases in either family. A couple undergoing genetic counseling also reports any past miscarriages and discusses the possibility of exposure to chemicals, radiation (including x rays), or other occupational environmental hazards. The couple also needs to disclose information about personal habits before or during pregnancy such as drug or alcohol abuse and the use of prescription or over-the-counter drugs taken by the mother since the beginning of pregnancy. The genetic counselor explains the procedures used in any testing that will be done and describes what each test can and cannot reveal.
Aftercare
Genetic counseling provides couples with information that can help them make decisions about future pregnancies. It also gives couples additional time to emotionally prepare if a disorder is detected in the fetus. The counselor discusses the results of any testing and informs the couple if a problem is apparent. The doctor or genetic counselor also discusses the treatment options available. Genetic counseling is done in a non-directive way, so that any treatment selected remains the personal choice of the individuals involved. Genetic counseling can provide information essential for family planning and pregnancy management, thus maximizing the chances of a positive outcome.
Risks
Because prenatal testing, such as amniocentesis and chorionic villus sampling, is invasive and carries a 1% risk of miscarriage it should never be considered routine.
Normal results
Screening tests and/or prenatal tests reveal no birth defects or genetic abnormalities.
Abnormal results
A birth defect or genetic disorder is detected. The early diagnosis of birth defects and genetic disorders allows a greater number of treatment options. Some disorders can be treated in utero (before birth while the fetus is still in the uterus), while others may require early delivery, immediate surgery, or cesarean section to minimize fetal trauma. Prior warning of fetal difficulties allows parents time to prepare emotionally for the birth of the child. In some instances, termination of the pregnancy may be chosen. Whatever the test results, this information is essential for family planning and pregnancy management.
Resources
BOOKS
Banasik, Jacquelyn L. "Genetic and Developmental Disorders." In Perspectives on Pathophysiology by Lee-Ellen C. Copstead. Philadelphia: W. B. Saunders Co., 1994.
Milunsky, Aubrey. Choices Not Chances: An Essential Guide to Your Heredity and Health. Boston: Little Brown, 1989.
Pierce, Benjamin A. The Family Genetic Sourcebook. New York: John Wiley & Sons, 1990.
ORGANIZATIONS
American Medical Association. 515 N. State St., Chicago, IL 60612. (312) 464-5000. <http://www.ama-assn.org>.
American Society of Human Genetics. 9650 Rockville Pike, Bethesda, MD 20814-3998. (301) 571-1825. <http://www.faseb.org/genetics/ashg/ashgmenu.htm>.
March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. (914) 428-7100. <http://www.modimes.org>.
OTHER
"Genetic Screening Before or During Pregnancy." InteliHealth Page. 19 June 1998 <http://www.intelihealth.com>.
Jeffrey P. Larson, RPT
Additional topics
- Genetic Testing - Definition, Purpose, Precautions, Description, Types of Genetic Testing, Applications for Genetic Testing, Preparation, Aftercare, Risks
- Generalized Anxiety Disorder - Definition, Description, Causes and symptoms, Diagnosis, Treatment, Prognosis, Prevention
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