Who Should Be Concerned About Chromosome Abnormalities? How

Down syndrome is the most What if the screening result common chromosome abnormality is abnormal? in newborns, with an incidence of Further testing should be considered. However, it is approximately 1 in 800 births. The very important to realize that most women who screen positive are carrying normal, healthy babies. chance for having a baby with They simply have a higher chance of carrying a baby with a chromosome abnormality than women who Down syndrome increases with the have a negative result. age of the mother, but chromosome Definitive prenatal diagnosis, either by amniocentesis abnormalities can occur at any age. (at 15-20 weeks gestation) or chorionic villus sam- A variety of screening and prenatal pling (at 10-12 weeks gestation), is highly accurate. Each procedure has a very small risk (primarily of diagnostic options are available to miscarriage) to the pregnancy. The Genetics Center is a full service genetics address this important issue early in Genetic counseling is available to help women make facility which provides clinical genetics, laboratory Some doctors recommend both first and second an informed decision about prenatal diagnosis. In pregnancy. genetics, and genetic counseling in a comfortable trimester screening. When the two screening tests addition to testing for chromosome abnormalities, are considered together, this is called sequential or prenatal diagnosis is available for many genetic and private office setting. Established in 1991, The Who should be concerned about integrated screening. On average, 95% of women metabolic disorders, including, but not limited to, Genetics Center offers a full range of genetic will be “screen negative” and have low risks for cystic fibrosis, Tay-Sachs disease, hemophilia, chromosome abnormalities? services, including prenatal genetics, prenatal carrying babies with either Down syndrome or Duchenne muscular dystrophy, and sickle cell trisomy 18, another serious chromosome anemia. diagnosis by amniocentesis, genetic risk evaluation Every pregnant woman should be. Most babies with abnormality. for cancer and other inherited conditions, and med- chromosome abnormalities have serious birth What is the role of a geneticist? ical evaluations for adults or children who have, or defects and significant developmental disabilities. In the unlikely event that a woman is carrying a Amniocentesis used to be offered mainly to women baby with Down syndrome, the chance of being Geneticists are medical specialists who help may have, genetic disorders. The Genetics Center age 35 or older, but 80% of babies with Down “screen positive” is greater than 85%. By contrast, couples deal with genetic issues. The team of participates in many managed care plans. Our syndrome are born to women under age 35. ultrasound examination in the second trimester a clinical geneticist (who is a physician) and a services are covered by health insurance and are fails to detect any signs of Down syndrome 50% of genetic counselor (who has a graduate degree the time. typically reimbursed as any other medical How does screening work? in genetic counseling) diagnose genetic diseases, assess risks for couples to have a specialist’s services are. Why bother with screening for child with a genetic disorder based on personal First trimester screening (at 11-13 weeks gestation) and family history, explain options for consists of a blood test and a specialized ultra- chromosome abnormalities? addressing abnormal results of first and/or sound examination of the fetus to measure the second trimester screening, and arrange nuchal translucency. In the second trimester (14-22 Screening is important because Down syndrome genetic and prenatal diagnostic testing. weeks gestation) only a blood sample is necessary; can occur at any age. A negative screening result typically three or four chemicals (“markers”) in the is reassuring, and particularly for women who A comprehensive explanation of genetic issues blood are analyzed, hence this is often referred to might have considered amniocentesis. A positive (genetic counseling) is one of the priorities for as triple or quadruple marker screening. Second result is important information for younger women, the genetics team and is an integral part of any trimester screening is also known as the alpha- who may not otherwise have considered definitive genetic consultation. fetoprotein (or AFP) test, since AFP is one of the prenatal testing. markers analyzed. Terminology Genes - Segments of DNA responsible for our Genetics Alpha-fetoprotein (AFP) - A protein made by unique and common characteristics. There are the fetus and found in the maternal circulation an estimated 20-30,000 genes in humans, each during pregnancy. Abnormal values are encoding a protein that is necessary for Prenatal associated with increased risks for spina bifida, controlling cellular functions. With few Down syndrome, and trisomy 18. exceptions we have two copies of all of our & genes, one inherited from each parent. Amniocentesis - A procedure for prenatal Diagnosis diagnosis in which about an ounce of amniotic Genetic Counselor - A specially trained fluid surrounding the fetus is obtained using a professional with expertise in genetics. Most very fine needle that is guided by ultrasound. genetic counselors have a Master's degree The 60 to 90 second procedure is nearly in genetic counseling, and some are certified painless, and the risk for miscarriage from the by the American Board of Genetic Counseling. procedure is less than 0.5 %. Geneticist - A doctor specializing in genetics Aneuploidy - An abnormal number of who either is a physician and/or has a PhD. chromosomes (fewer or greater than 46). This Geneticists are eligible for certification by the is a common reason for miscarriage, and American Board of Medical Genetics. Down syndrome is the most common aneuploidy found in liveborn babies. Nuchal translucency (NT) - A structure at the back of the fetal neck, which is visible at Chorionic villus sampling (CVS) - A prenatal 11-13 weeks gestation. The NT tends to be the genetics center, inc. diagnostic procedure that is performed earlier larger in fetuses with Down syndrome and in than amniocentesis, and carries a risk for certain chromosomal and non-chromosomal miscarriage that is modestly higher than for conditions. amniocentesis. Spina bifida - A type of birth defect in which Chromosomes - Microscopic structures in the the structure and function of the spinal cord nucleus of each cell, which contain and are abnormal. The most severe form of spina organize all of an individual's genetic material. bifida is anencephaly, a condition in which the skull and brain do not form properly. Down syndrome - A condition caused by an extra chromosome 21. Individuals with Down Trisomy 18 - A chromosome abnormality due syndrome have distinctive facial features and to an extra chromosome 18. Very severe birth mental retardation, and often have congenital defects are nearly always present. Most heart defects and/or other birth defects. fetuses do not survive to term, and most 48 Route 25A, Suite 205 liveborn babies die shortly after birth. DNA - The molecule inside of our cells that Smithtown, New York 11787 contains instructions for how our bodies grow Ultrasonography - The use of sound waves to 631-862-3620 and develop. In humans, DNA is bundled into examine internal body structures, such as the www.thegeneticscenter.com 23 pairs of chromosomes. The nucleus of fetus inside the uterus. This is also called Straightforward answers each cell contains a complete set of these sonography, or referred to as an ultrasound or instructions. sonogram. Copyright 2009 The Genetics Center, Inc. to important questions