Common Questions and Answers

What is genetic counseling?
Who should consider genetic counseling?
What is genetic testing?
What are the different types of genetic tests?
Why would a physician offer genetic testing?
What is advanced maternal age?
What is maternal serum screening?
What is chorionic villus sampling (CVS)?
How is CVS performed?
Does CVS have any risks?
What is amniocentesis?
How is amniocentesis performed?
Does amniocentesis have any risks?
What is a teratogen?
What is Cystic fibrosis (CF) screening?
Why is my family history important?
What is Jewish Heritage screening?
How are traits inherited?

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What is genetic counseling?
Genetic counseling was originally defined in 1975 by the American Society of Human Genetics:

"Genetic counseling is a communication process which deals with the human problems associated with the occurrence or risk of occurrence of a genetic disorder in a family. This process involves an attempt by one or more appropriately trained persons to help the individual or family to: (1) comprehend the medical facts including the diagnosis, probable course of the disorder, and the available management, (2) appreciate the way heredity contributes to the disorder and the risk of recurrence in specified relatives, (3) understand the alternatives for dealing with the risk of recurrence, (4) choose a course of action which seems appropriate for them in view of their risk, their family goals, and their ethical and religious standards and act in accordance with that decision, and (5) to make the best possible adjustment to the disorder in an affected family member and/or to the risk of recurrence of that disorder."¹ (American Society of Human Genetics, 1975)

Genetic counseling is an important process in learning about, coping with, and managing the risk of genetic disorders in a family. Genetic counselors are usually board-certified specialists with a master's degree in genetics or genetic counseling or physicians who have specialized in medical genetics. Genetic counseling may also be provided by specially trained nurses, social workers, and physicians.¹

Genetic counselors follow a code of ethics that is non-directive and respects the values, beliefs, autonomy, individuality and freedom of their patients.¹

Genetic counseling may employ electronically assisted media, including telephones, the Web, video tapes, and other interactive media.

References

1. Baker DL, Schuette JL, Uhlmann WR. A Guide to Genetic Counseling. New York, NY:John Wiley & Sons, Inc. 1998.

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Who should consider genetic counseling?

• Women who are pregnant or are planning to become pregnant at or above the age of 35 (advanced maternal age). ¹
• Women/couples who have been told their pregnancy is at an increased risk for a birth defect or genetic condition based on the results of maternal serum screening. ²
• Women/couples who have been told their pregnancy is at an increased risk for a birth defect or genetic condition, such as an open neural tube defect, Down syndrome, or trisomy 18, based on ultrasound findings.
• Couples who are close blood relatives, such as first cousins.
• Women/couples who are pregnant or considering pregnancy who are concerned about an increased risk to the pregnancy due to medical conditions or teratogenic exposures to drugs, alcohol, radiation, chemicals, prescription or over-the-counter medications.
• Couples who would like to discuss testing for conditions that occur more frequently in a specific ethnic group.
• Women/couples who have had two or more miscarriages or unexplained infant deaths.²
• Individuals/couples who have family history of an inherited condition, mental retardation, or a birth defect.³
• Those interested in assessing their genetic risks.

References

1. Ledbetter DH. Prenatal Cytogenetics: Indications, Accuracy, and Future Directions. Essentials of Prenatal Diagnosis. In: Simpson JL, Elias S, eds. Essentials of Prenatal Diagnosis. New York, NY: Churchill Livingstone; 1993;9:165-166.
2. March of Dimes Birth Defects Foundation. Genetic Counseling.
3. Baker DL, Schuette JL, Uhlmann WR. A Guide to Genetic Counseling. New York, NY: John Wiley & Sons, Inc. 1998.

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What is genetic testing?

Genetic testing is a specific type of laboratory testing performed on body tissues or fluids, such as blood. The tests help a physician determine if a person has a genetic disorder, is a carrier of a genetic disease, or has a predisposition to develop a genetic problem.

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What are the different types of genetic tests?

Genetic testing can look at chromosomes, genes, or proteins. There are four main categories of testing and your physician may order one of these types of tests depending on your specific condition.

Cytogenetic Testing:This means "chromosome study". Cytogenetic testing allows a scientist to look at the number or shape of chromosomes present in a patient's sample. Cytogenetic testing is useful when looking at the chromosomes as a whole, but it does not provide any information about specific genes or proteins that may be associated with a genetic disease.^1,2

An example of cytogenetic testing is a blood analysis to look for an extra chromosome. Down syndrome is a disorder caused by an extra chromosome 21. However, a chromosome test will not pick up a genetic disease caused by a single gene change, like cystic fibrosis.

Fluorescence in situ hybridization (FISH) Testing: Fluorescence in situ hybridization, also called FISH, is a technique that uses a specific protein, called a probe, that has been designed to "stick" to unique DNA in a cell. These probes are fluorescent, meaning they glow with a special dye. Laboratory personnel can then examine the cells under a microscope. FISH is currently used to detect the common chromosome problems caused by an extra chromosome (aneuploidy), such as Down syndrome (trisomy 21), and in prenatal diagnosis when results are needed rapidly. FISH can also be used to detect subtle chromosome rearrangements, identify marker chromosomes (extra pieces of unidentified chromosomal material), and test for common syndromes caused by duplication or deletions of large pieces of DNA.³

Pregnancy management decisions and diagnosis of problems should not rely on FISH alone, but should also take into account results of the full chromosome analysis and clinical findings.⁴

Biochemical Testing: Genes make proteins and enzymes that are present in blood or other tissues.² Proteins and enzymes carry out the work of the body, such as digesting fat or making energy available to muscle. Biochemical testing measures the level of protein or enzyme present in a patient's sample to help determine if the gene that produces that protein is functioning properly.⁵

An example of a biochemical test is enzyme analysis for Tay-Sachs disease. Tay-Sachs disease is an inherited disorder that causes neurological deficits, developmental delay, and death by age 4. It is caused by the lack of an enzyme called hexoseaminidase A (hex A). By measuring levels of hex A in the blood, it can be determined if a person is affected by Tay-Sachs disease or is a carrier.

Indirect (linkage) Testing: Not all of the genes have been located yet. For some genes, scientists know approximately where the gene is on a chromosome, but not exactly. This is like knowing the street someone lives on but not knowing the address. Indirect testing requires blood from several family members, including those that are known to be carriers or affected with a specific condition. Laboratories then compare genetic material between family members and determine who is most likely to be a carrier or affected.¹

In some families with hemophilia A, a genetic disorder resulting in excessive bleeding after injury or surgery, the gene mutation causing the disease cannot be identified with common laboratory test methods. Because DNA contains pieces, called markers, that are unique to individuals and families, laboratories can find the markers unique to a hemophilia family near the hemophilia gene. The markers from at least two affected family members are compared to the marker in the family member in whom the diagnosis or carrier status is being questioned. If the unique sequences from an affected family member are present in the person being tested, that individual is predicted to be affected or a carrier. Linkage can also be done for prenatal diagnosis.⁶

Direct Testing: Direct gene testing can be performed when scientists know exactly where a gene is located on a chromosome and what changes in the gene cause a specific disease. When they know this information, the scientists can look for the disease-causing gene changes in a person who is either suspected of having a genetic disease, or who may be a carrier for the disease.⁵

An example of direct testing is mutation analysis for cystic fibrosis. Cystic fibrosis (CF) is an inherited disease that causes lung and digestive problems. Common mutations (gene changes) in the cystic fibrosis gene have been identified. The American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Genetics (ACMG) recommend that CF carrier screening be offered to all couples when at least one member of the couple is Caucasian and pregnant or considering pregnancy.⁷ Carrier screening consists of direct detection for the 25 most common CF mutations. It is further recommended by ACOG and ACMG that CF screening be made available to individuals of other racial and ethnic groups.⁷

References

1. Thompson MW, McInnes RR, Willard HF. Thompson & Thompson Genetics in Medicine. 5th ed. Philadelphia, Pa: W.B. Saunders Company; 1991.
2. Milunsky, A. Heredity and Your Family's Health. Baltimore, MD. The Johns Hopkins University Press. 1992
3. The American College of Obstetricians and Gynecologists. Fluorescence In Situ Hybridization. Genetics in Obstetrics and Gynecology. ACOG; Washington, DC: 2002.
4. American College of Medical Genetics. Technical and Clinical Assessment of Fluorescence In Situ Hybridization: policy statement. Gen in Med 2000;2(6):356-361
5. Harper PS. Practical Genetic Counseling. Oxford, England; Butterworth-Heinemann Ltd; 1994:102.
6. Johnson MJ, Thompson AR. Hemophilia A. www.genetests.org. [Cited January 28, 2004].
7. American College of Obstetricians and Gynecologists, American College of Medical Genetics. Preconception and Prenatal Carrier Screening for Cystic Fibrosis: Clinical and Laboratory Guidelines. Washington, DC: ACOG; Oct 2001

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Why would a physician offer genetic testing?

There are several reasons why a genetic test may be offered:

Carrier Screening

Carrier screening is the most common type of genetic testing performed today.¹ There are several common disorders where either one parent or both parents must be carriers of a certain gene or mutation to have an affected child, such as cystic fibrosis. In these circumstances, the carrier has no symptoms of the disease, but may have a baby with the disease if the other parent is also a carrier. It has become a standard medical practice to offer couples who are expecting a baby or planning a pregnancy screening for some of these diseases, most of which are listed on the Common Disorders page. Some types of carrier screening are not definitive; negative genetic test results mean the likelihood that a person is a carrier is reduced, but cannot entirely eliminate the possibility.

It is important to note that carrier screening is not recommended for minors.²

Diagnostic Testing

Diagnostic testing may be offered to a person when a physician suspects that the patient has a specific genetic disease. For example, if a patient has the symptoms associated with a specific genetic disease, the physician may choose to offer a genetic test to definitively diagnose or rule out that specific disease.

Prenatal Screening

Some tests are available that can screen for certain types of birth defects in a baby before it is born. This type of testing performed during a pregnancy cannot diagnose birth defects, it can only determine if a fetus is at increased risk for certain genetic disorders.⁴ If the fetus is identified to be at an increased risk, the parents may be offered additional testing.⁵

Maternal serum screening is an example of prenatal screening. AFP X-tra is a maternal serum screening test that identifies pregnancies at increased risk for open neural tube defects, Down syndrome, and trisomy 18. The blood test is a screening test and does not provide a definitive diagnosis.

Prenatal Diagnostic Testing

Prenatal diagnostic testing is available during a pregnancy to determine if a baby has a specific disease. The results of this type of testing are conclusive enough to diagnose or rule out a genetic condition before the baby is born. Testing is usually performed on amniotic fluid or chorionic villi samples.⁴

Amniocentesis is an example of prenatal diagnosis. In this test, a small amount of amniotic fluid (fluid surrounding the developing baby during pregnancy) is withdrawn. Cells from the baby are found in the fluid and the chromosomes in the cells can be examined. If, for example, an extra chromosome number 21 is seen, a diagnosis of Down syndrome is made.⁴

Pre-implantation Diagnostic Testing

Testing is available for a limited number of genetic disorders on a single cell of an embryo from a procedure called in vitro fertilization. In vitro fertilization is the fertilization of the egg outside the womb in a laboratory. Certain genetic tests may be performed on a single cell removed from an embryo. After testing, selected embryos may then be implanted in the womb. This testing is only available at specialized centers and may be considered experimental.⁶

References

1. Harper PS. Practical Genetic Counseling. Oxford, England; Butterworth-Heinemann Ltd; 1994:102.
2. The American Society of Human Genetics Board of Directors and The American College of Medical Genetics Board of Directors. Points to Consider: Ethical, Legal, and Psychosocial Implications of Genetic Testing in Children and Adolescents. Bethesda, Md: ASHG;1995.
3. Task Force on Genetic Testing. Interim Principles of the Task Force on Genetic Testing of the NIH-DOE Working group on Ethical, Legal, and Social Implications of Human Genome Research. Baltimore, Md: March 1996.
4. Thompson MW, McInnes RR, Willard HF. Thompson & Thompson Genetics in Medicine. 5th ed. Philadelphia, Pa: W.B. Saunders Company; 1991.
5. American College of Obstetricians and Gynecologists. ACOG Education Bulletin: Maternal Serum Screening. Washington, DC. September 1996(228).
6. Nussbaum RL, McInnes RR, Willard HF. Thompson & Thompson Genetics in Medicine. 6th ed. Philadelphia, Pa: W.B. Sounders Company, 2001.

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What is advanced maternal age?

"Advanced maternal age" is a term used to describe a pregnant woman who will be 35 years of age or older on her due date.¹

As a woman's age increases, the chance of having a baby with a chromosome problem also increases.¹ Chromosomes are the genetic structures that we inherit from our parents. Chromosomes contain our genes, which are important in development and body function.² There are a total of 46 chromosomes in 23 pairs. The last pair (the 23rd pair) determines gender; males have one X and one Y chromosome, and females have two X chromosomes.² The egg and the sperm each have 23 chromosomes, one member of each pair.² Errors can occur when cells divide to make the egg and sperm, or when the egg and sperm unite, causing a baby to have an extra or missing chromosome. Since women are born with all of their eggs, the eggs age along with the body. As a woman's age increases, there is an increased chance that an extra chromosome will be packaged into an egg. There is nothing a woman can do to cause or to prevent this occurrence. Some examples of chromosome conditions associated with advanced maternal age are Down syndrome (an extra chromosome 21), trisomy 18 (an extra chromosome 18), trisomy 13 (an extra chromosome 13), triple X syndrome, and Klinefelter syndrome.²

Women who are younger than 35 also have an increasing risk every year that they will give birth to a child with a chromosome problem. However, most physicians use the age of 35 as a "cutoff" at which the risk of having a child with a chromosome problem is high enough to justify having invasive prenatal testing such as CVS or amniocentesis.¹

Maternal Age and Chromosomal Abnormalities at Live Birth³

There are several kinds of screening and diagnostic tests available for advanced maternal age. Maternal serum screening and ultrasound are non-invasive screening tests that may provide information about the risk for certain conditions in a pregnancy. Maternal serum screening and ultrasound are not diagnostic tests and provide only limited information. Chorionic villus sampling (CVS), early amniocentesis, and traditional amniocentesis are invasive medical procedures that may diagnose certain conditions, but cannot rule out all birth defects.⁴

References

1. Ledbetter DH. Prenatal Cytogenetics: Indications, Accuracy, and Future Directions. Essentials of Prenatal Diagnosis. In: Simpson JL, Elias S, eds. Essentials of Prenatal Diagnosis. New York, NY: Churchill Livingstone; 9:165-166.
2. Milunsky A. Heredity and Your Family's Health. Baltimore, Md: The Johns Hopkins University Press. 1992.
3. U.S. Department of Health and Human Services. Chorionic villus sampling and amniocentesis: Recommendations for prenatal counseling. Morbidity and Mortality Weekly Report. 1995; 44 (No. RR-9).
4. Simpson JL, Elias S, eds. Essentials of Prenatal Diagnosis. New York, NY: Churchill Livingstone; 1993.

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What is maternal serum screening?

Maternal serum screening refers to testing performed on a pregnant woman's blood for the purpose of determining if her developing fetus may have an increased risk of having an open neural tube defect (ONTD), Down syndrome, or trisomy 18. Proteins that are produced by the developing placenta and baby enter the mother's blood. The most commonly tested proteins are AFP (alpha-fetoprotein), hCG (human chorionic gonadotropin), uE3 (unconjugated estriol), and DIA (dimeric inhibin A). By measuring the levels of these proteins in the blood, tests determine if a woman has a high or low risk of having a baby with Down syndrome, trisomy 18, or an open neural tube defect. These tests determine the risk a developing baby may have one of these conditions; however, the maternal serum screening tests are not diagnostic. If a maternal serum screening test is positive, meaning an increased chance for a fetal problem, the woman's health care provider may suggest additional diagnostic testing.

There are three types of maternal serum screening tests. The detection rates for these tests are listed in the table below.

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What does it mean if my maternal serum screening test is negative?
A negative test result significantly reduces the risk the baby may have one of the fetal problems screened for by the maternal serum test. (See table above for the available tests and what they screen). Because this test is only a screen it cannot completely rule out the possibility of these problems.

Does a positive maternal serum screening test result mean that my baby has a birth defect?
No. Maternal serum screening is a screening test; it cannot diagnose problems with the baby or pregnancy. The test identifies those women who are more likely to have a baby with an open neural tube defect, Down syndrome, or trisomy 18. Normally, if a test result is positive additional testing may be offered.

What other tests are available if my maternal serum screening test is positive?
Follow-up options are determined privately between a woman and her physician. In general, most women with positive test results are offered genetic counseling, ultrasound, and amniocentesis.

References

1. American College of Obstetricians and Gynecologists. Maternal Serum Screening. Educational Bulletin. 1996; September (228):3,5-8.
2. Haddow JE, Palomaki GE, Knight GJ, Foster DL, Neveux LM. Second trimester screening for Down's syndrome using maternal serum dimeric inhibin A. J Med Screen. 1998; 5(3):115-119.

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What is chorionic villus sampling (CVS)?

Chorionic villus sampling (CVS) is a diagnostic procedure performed during pregnancy to diagnose chromosome abnormalities, some inherited disorders, and certain birth defects in an unborn baby (fetus).^1-3 CVS is most commonly offered when a woman is at an advanced maternal age (35 years and older at time of delivery) because of the increased chance of a fetal chromosome problem.^1,2,4

CVS may also be offered if an inherited genetic (gene) problem that can be diagnosed prenatally is identified in the family.^{1, 3,4} Performed between 10 and 12 weeks of pregnancy (first trimester), CVS can be done in a doctor's office, hospital, or out-patient clinic.^1-4 Ultrasound is used to guide the procedure. Depending on the location of the placenta, CVS will be performed in one of two ways. A thin needle is either inserted through the abdomen or a specially designed catheter is passed through the vagina and a piece of placenta, approximately the size of a few grains of rice, is removed. The placenta contains cells generated by the baby. Approximately 99% of fetal chromosome abnormalities can be diagnosed.^1-3 Unlike amniocentesis, CVS is not able to provide information about open neural tube defects.¹ The risk of miscarriage or serious complication from the test is approximately 1/200 to 1/100 (0.5% - 1.0%)^1,2,4 Controversy exists about the risk of fetal limb defects as a result of the test, though most physicians and researchers feel that if the test is done at 10 weeks of gestation or later, there is little risk of fetal limb defects. Additionally, in approximately 1.0% to 2.0% of CVS cases, follow-up by amniocentesis is needed to clarify results.^2,3

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How is CVS performed?

Depending on the location of the placenta, CVS is performed either transabdominally or transcervically.^1,3 In transabdominal CVS, a thin needle is inserted through the woman's abdomen, and a small piece of the placenta is removed.^1-3 In transcervical CVS, a specialized catheter is inserted into the woman's vagina and a small sample of the placenta is removed.^1-3 The physician uses ultrasound to guide the needle or the catheter toward the placenta and away from the fetus.^1,3 The cells are gently removed from the placenta without requiring anesthetic.¹ A woman may experience a pinch or cramping, or she may not feel any discomfort.¹ The placenta has the same origin as the fetus and usually contains the same genetic material, though rare exceptions may occur.^1,4 By removing some cells, the number and the structure of chromosomes in these cells can be evaluated.⁴

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Does CVS have any risks?

CVS has been performed in this country since 1983.^1,3,4 Thousands of women worldwide have undergone this procedure without injury to themselves or to their fetuses.^1,4 Yet, as with any medical procedure, complications from CVS can occur.⁴ Pregnancy loss or miscarriage is the most common complication.^1,4 The risk of miscarriage from CVS is approximately 1/200 to 1/100 (0.5%-1%).^1,2,4 The risk of a miscarriage is the same for both types of CVS procedures, the transabdominal and the transcervical.^1,3 Choosing a physician experienced with these procedures may further reduce the risk of complication.^1,3 CVS performed prior to 10 weeks has been associated with causing fetal limb defects, such as underdeveloped fingers or toes, and missing or undeveloped nails.^3,4 Studies indicate that when CVS is performed at 10 weeks and later, the risk for these defects is reduced to approximately one out of one thousand (1/1000) or 0.1%.^1,4 To reduce this risk, confirmatory dating of the pregnancy will be done with an ultrasound to make sure the pregnancy is at least 10 weeks. Other possible side effects include bleeding, cramping, and fluid leakage. These symptoms may be seen after CVS but do not necessarily lead to miscarriage.¹ Nevertheless, the health care provider should be contacted and informed of these symptoms. Certain activities may be restricted for a limited time.¹ Infection rarely occurs, but any fevers or flu-like symptoms in the weeks following the procedure should also be reported to the health care provider.⁴

References

1. March of Dimes Birth Defects Foundation. Chorionic Villus Sampling (CVS). White Plains, NY: March of Dimes Birth Defects Foundation; 1994.
2. Nussbaum RL, MacInnes RR, Willard HF, Boerkel CF. Thompson and Thompson: Genetics in Medicine. 6th ed. Philadelphia, Pa: W.B. Saunders; 2001
3. Kuller JA. Chorionic villus sampling. In Kuller JA, Chescheir NC, Cefalo RC, eds. Prenatal Diagnosis and Reproductive Genetics. St Louis, Mo: Mosby; 1996.
4. Centers for Disease Control and Prevention. Chorionic villus sampling and amniocentesis: Recommendations for prenatal counseling. MMWR. 1995; 44(Nº RR-9):1-11.

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What is amniocentesis?

Amniocentesis is an important test in prenatal diagnosis.^1-3 This test is primarily used to help diagnose fetal chromosome problems.^2,3,4 Amniocentesis can also help diagnose open fetal defects, such as open spina bifida, or abdominal wall defects, and some inherited problems if identified in your family.^1-4

Amniocentesis is performed on amniotic fluid (the fluid that surrounds the fetus), usually between 16 and 18 weeks of pregnancy (second trimester).^1-3 As the fetus grows and sheds cells, those cells may be found floating in the amniotic fluid and used to study the chromosomes.^1-3 Also, a protein made by the fetus, called alpha-fetoprotein (AFP), is released into the amniotic fluid.^1,2,4 Measuring this protein can help screen for birth defects that cause an opening in the spine, such as spina bifida.²

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How is amniocentesis performed?

Typically, an ultrasound is done first.¹ An ultrasound provides images of the fetus using sound waves that (1) determine the age of the fetus and the position of the placenta and fetus and (2) detect a fetal heartbeat and fetal movement.⁵ The physician determines, based on the ultrasound exam, where to insert a thin needle through the woman's abdomen and into the womb (uterus).^2,4 The needle is carefully guided toward a pocket of amniotic fluid and away from the fetus.⁴ Once a small amount of fluid is obtained, usually less than an ounce, the needle is removed and the baby is monitored by ultrasound for a few more minutes.¹ Many women feel little discomfort and report feeling a cramp or pressure for a brief time.¹

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Does amniocentesis have any risks?

Amniocentesis is a procedure that has been performed in this country since the late 1960s.⁴ Women worldwide have undergone this procedure without injury to themselves or to their fetus.¹ Yet as with any medical procedure, complications from the procedure can occasionally occur.¹ Pregnancy loss (or miscarriage) is the most serious possible complication.^1,4 The risk of miscarriage from amniocentesis is estimated at 1/200 (0.5%).^1,2,4 In other words, one out of 200 women will experience a miscarriage after the amniocentesis procedure.^1,2,4 Choosing an experienced physician may further reduce the risk of complication.^1,4 Because the physician typically uses ultrasound to guide the needle in the uterus throughout the procedure, the chance of harm to the fetus is low.^1,4 Other possible side effects include cramping, bleeding, and fluid leakage from the vagina.^1,4 The chance of these symptoms occurring is low and their presence does not necessarily lead to miscarriage.³ The health care provider should also be contacted immediately and informed of these symptoms. Certain activities may be restricted for a limited time.^1,4 Infection rarely occurs, but any fevers or flu-like symptoms in the weeks following the procedure should be reported to the physician.²

References

1. March of Dimes Birth Defects Foundation. Amniocentesis. White Plains, NY: March of Dimes Birth Defects Foundation; 1994.
2. Centers for Disease Control and Prevention. Chorionic Villus Sampling and Amniocentesis: Recommendations for Prenatal Counseling. MMWR. 1995; 44(no. RR-9):1-11.
3. Nussbaum RL, McInnes RR, Williard HF, Boerkoel CF. Thompson and Thompson: Genetics in Medicine. Philadelphia, Pa: W.B. Saunders; 2001.
4. Cabaniss ML. Amniocentesis. In Kuller JA, Chescheir NC, Cefalo RD, eds. Prenatal Diagnosis and Reproductive Genetics. St. Louis, Mo: Mosby; 1996:chap 18.
5. March of Dimes. Quick References and Fact Sheets: Ultrasound. www.marchofdimes.com/professionals/14332_1167.asp [Feb 2003].

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What is a teratogen?

A teratogen is any substance that could cause harm to a developing fetus. For example, certain prescription and over-the-counter medications, recreational drugs, alcohol, smoking, X-rays, and chemicals may cause developmental problems during the pregnancy.¹ For more information about teratogens, or to find a teratogen service in your area, contact http://orpheus.ucsd.edu/otis/

Medication: It is extremely important to inform your physician of any medications you are taking when planning to become pregnant or as soon as you find out you are pregnant. You should inform your physician or genetic counselor of the dates you were taking the medication and the dosage. Your physician or genetic counselor will determine the potential risks associated with the medication and then discuss with you the benefits of the medication versus the potential risk to the developing fetus. You should always consult your physician or genetic counselor prior to taking or stopping any medication during pregnancy.

Alcohol: Discuss with your physician or genetic counselor any alcohol use prior to knowledge of your pregnancy or during your pregnancy. No level of drinking during pregnancy has been proven safe. Fetal Alcohol Syndrome (FAS) is a term used to describe the effects of alcohol use during pregnancy. Babies who are born with FAS may have serious complications, including mental retardation, delayed growth, short upturned nose, flat cheeks, small eyes, thin upper lip, malformed organs, behavioral problems and psychological problems. Fetal Alcohol Effects (FAE) is a term used to describe babies who are born with some, but not all, of the birth defects associated with FAS.²

Smoking: Smoking during pregnancy has been associated with miscarriage, stillbirth, pre-term labor and low birth weight.³ The use of tobacco products during pregnancy is discouraged by most physicians.

Drugs: Many recreational drugs, such as cocaine, are known to cause birth defects. For example, cocaine use during pregnancy can cause miscarriage, stillbirth, preterm labor, limb defects, brain abnormalities and intestinal abnormalities.⁴ It is very important to discuss with your physician or genetic counselor any drug use prior to or during your pregnancy.

Chemicals: Many women are concerned about exposures to chemicals at their place of employment. If you are concerned about any chemical exposures, your physician or genetic counselor can help determine the potential risk to the pregnancy from the chemical exposure.⁵ You may also request a Material Safety Data Sheet (MSDS) from your employer. The MSDS should include any known risks associated with the chemical. Even if there is no known risk associated with a chemical, protective outerwear, gloves, goggles, and good ventilation are highly recommended for these women working in proximity to chemicals during pregnancy.⁵

X-rays: The risk to the developing pregnancy due to radiation exposure depends on the amount of radiation and the timing of the exposure.⁶ If you are exposed to any radiation during pregnancy, you should discuss the exposure in detail with your physician or genetic counselor.

References

1. Illinois Teratogen Service. What is a Teratogen? http://www.fetal-exposure.org/terato.html. Cited January 25, 2002.
2. March of Dimes Birth Defects Foundation. Public health education information sheet- Drinking during pregnancy. New York, NY. 1995.
3. March of Dimes Birth Defects Foundation. Smoking During Pregnancy. www.marchofdimes.com/professionals/14332_1171.asp. Cited January 24, 2002.
4. Organization of Teratology Information Services. Cocaine. www.otispregnancy.org/pdf/cocaine.pdf. Cited January 24, 2002.
5. March of Dimes Birth Defects Foundation. Pre-Pregnancy Planning. www.marchofdimes.com/professionals/14332_1156.asp. Cited January 24, 2002.
6. Robinson A, Linden M. Clinical Genetics Handbook. Chapter 10. Ann Arbor, Mich: Blackwell Scientific Publications, Inc. 1993.

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What is Cystic fibrosis (CF) screening?

Cystic fibrosis (CF) is a common genetic disorder. The American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Genetics (ACMG) have recommended that carrier screening be offered to all couples pregnant or considering pregnancy when at least one member of the couple is Caucasian.¹ CF testing is not required; it is an option for all couples. Couples might choose to have carrier screening if prenatal diagnosis for CF is important to them, or if they want early diagnosis and treatment for their children at risk for CF. Couples of non-Caucasian ethnic groups may also request CF screening.¹ Choosing CF carrier screening is a personal matter that should be discussed in private with health care provider(s) and/or genetic counselor(s).

For additional information on CF.

References

1. American College of Obstetricians and Gynecologists, American College of Medical Genetics. Preconception and Prenatal Carrier Screening for Cystic Fibrosis: Clinical and Laboratory Guidelines. Washington, DC: ACOG; Oct 2001.

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Why is my family history important?

One of the most important tools in determining genetic risks in a family is documenting the relevant history of all members of a family in a family tree, also called a pedigree.¹(See figure below.) A pedigree is a visual representation of the family's medical history and other important historical facts. It outlines biological relationships, diagnoses, and reveals inherited conditions.¹ When a genetic counselor or physician takes your family pedigree, he or she is getting to know your personal and family history to determine if any risk of genetic disease is present for you or your offspring. Occasionally it is necessary to obtain medical records of other family members to confirm a diagnosis and accurately determine genetic risk. Carrier, presymptomatic and diagnostic testing is available for many genetic disorders. An accurate family history may help reveal if such testing would be valuable for you. It is important to discuss all medical problems in a family, even if you do not think they are genetic, because important patterns and information may be revealed.

Pedigree

Reference

1. Robinson A, Linden M. Clinical Genetics Handbook. Ann Arbor, Mich: Blackwell Scientific Publications, Inc. 1993.

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What is Jewish Heritage Screening?

Certain inherited disorders are more common in the Ashkenazi Jewish population than in other population groups. The term "Ashkenazi" refers to people of Eastern European Jewish ancestry. Screening for these disorders in the Ashkenazi Jewish population may help identify couples at risk for having children with some of these problems.
For more information about genetic diseases common in this population, contact your physician or genetic counselor.

For additional information on Jewish Heritage screening.

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How are traits inherited?

When a family's medical history is reviewed, a genetic specialist is looking for conditions or diseases which have a genetic component. Sometimes these conditions follow simple patterns of inheritance such as autosomal recessive, autosomal dominant, or X-linked diseases. Other conditions, which also have a genetic basis, do not follow straightforward patterns. Conditions which tend to cluster in families but do not follow a straightforward inheritance pattern are multifactorial conditions.

Autosomal Recessive
The term "autosomal" means that the disease-causing gene is not on either of the sex-determining X or Y chromosomes.¹ The term "recessive" means that a person must have two copies of a non-working gene to have that particular condition.¹ For example, sickle cell anemia is an autosomal recessive condition. Two parents can each have one sickle cell anemia gene that does not work. Neither parent will have health problems because each parent also has a second copy of the gene which does work and is able to make up for the copy which does not work. Such parents are called "sickle cell carriers" or are said to have "sickle trait." If each parent passes on the non-working copy of the gene that he/she has to the baby, so that the baby has two non-working copies and no working copies, the baby will have symptoms of sickle cell anemia. When both parents are carriers of a gene for an autosomal recessive condition, there is a 25% chance with each pregnancy for a child to be born with the disease.¹ Cystic fibrosis, thalassemia, Tay-Sachs, and Canavan disease are other examples of conditions which are autosomal recessive.¹

Autosomal Dominant
The term "autosomal" means that the disease-causing gene is not on either of the sex-determining X or Y chromosomes. The term "dominant" means that a person only needs to have one copy of a non-working gene to have that particular condition.¹ For example, a specific type of colon cancer called Familial Adenomatous Polyposis, is an autosomal dominant condition.² With Familial Adenomatous Polyposis, there are no carriers. People who have one copy of a non-working gene and one copy of the working gene will have the condition. With this type of inheritance, the non-working copy of the gene is dominant over the working copy.²

X-linked Inheritance
Genes for conditions that are X-linked are located on the X chromosome.¹ An example of an X-linked condition is Fragile X syndrome. Males have one X and one Y chromosome while females have two X chromosomes and no Y chromosome. Because males only have one X chromosome, they are more often affected with X-linked conditions and have more severe effects of those conditions than females.^3,4 This is because if a female inherits one non-working copy of the Fragile X gene from a parent, she will still have a second copy which does work and acts to buffer the effects of the non-working gene.⁴ If a male inherits an X chromosome with a non-working Fragile X gene on it, he will have no working copies of the gene to make up for it and will have symptoms of the condition.^{3, 4}

Multifactorial Inheritance
One of the most complicated mechanisms of inheritance is "multifactorial" inheritance.¹ An example of a multifactorial condition is diabetes. With multifactorial conditions, it is known that some genetic component exists but that other environmental factors also contribute to the onset of such a condition.¹ For example, if a member of your family has diabetes, your risk of having diabetes is higher than someone who does not have a family history of diabetes.¹ However, your risk of developing diabetes can be reduced if you eat well-balanced meals and exercise regularly.^5,6

References

1. Robinson A, Linden M. Clinical Genetics Handbook. Ann Arbor, Mich: Blackwell Scientific Publications, Inc. 1993.
2. O'Sullivan M, McCarthy TV, Doyle TC.. Familial Adenomatous Polyposis: From bedside to benchside. Am J Clin Path. 1998;109:521-526.
3. McIntosh N, Gane LW, et al. Genetic Counseling for Fragile X Syndrome: Recommendations of the National Society of Genetic Counselors. J Genet Counseling. 2000;9(4):303-321.
4. American College of Medical Genetics. Fragile X Syndrome: Diagnostic and Carrier Testing. Policy Statement, Bethesda, Md. ACMG; 1994. http://www.faseb.org/genetics/acmg/pol-16.htm. Cited May 24, 2001.
5. U.S. Department of Health and Human Services. Diet and exercise dramatically delay type 2 diabetes, diabetes medication metformin also effective. 2001. http://www.hhs.gov/news/press/2001pres/20010808a.html. Cited October 5, 2001.
6. Centers for Disease Control. News & Information: CDC Statements on Diabetes Issues. http://www.cdc.gov/diabetes/news/docs/dpp.htm. Cited October 5, 2001.

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