Down's syndrome is a genetic condition involving an extra chromosome, this change occurs around the time of conception. A person with Down's syndrome has forty-seven chromosomes instead of the usual forty-six. A relatively common genetic disorder, Down's strikes 1 out of 600 babies. In 95 percent of all cases, the disorder originates with the egg, not the sperm, and the only known risk factor is advanced maternal age-at age 35, a woman has 1 chance in 117 of having a baby with Down's; at 40, her odds are 1 in 34.
(Graves, 1990)
People with Down's syndrome all have a certain degree of learning disability . This means that they develop and learn more slowly than other children. However, most children with Down's syndrome today will walk and talk, many will read and write, go to ordinary school, and look forward to a semi-independent adult life. (Platt and Carlson, 1992)
Facts on Down Syndrome
*Down syndrome is not a lethal anomaly. One to two percent of persons born with this disorder have uncorrectable heart defects at birth. The average life expectancy for all others is now beyond age 55 years.
*Today less than 5% of persons with Down syndrome have severe-to-profound mental retardation. The majority are on the border of mild-to-moderate mental retardation, and some are exhibiting normal IQ scores today.
*The average reading level for persons with Down syndrome is 3rd grade, with many reading at 6th-12th grade levels today.
*The vast majority of adults with Down syndrome today can be expected to live semi- or totally independently and many enter the work force with today's supported employment programs and some are competitively employed.
Some medical conditions that demand special attention for people with Down syndrome include:
*Congenital Heart Disease: usually in the form of endocardial cushion defects, affects 40% of babies and should be screened for by echocardiography soon after birth as it may well be difficult to detect.
* Gastrointestinal disorders: the most common congenital abnormality of the gastrointestinal tract associated with Down syndrome is duodenal atresia, although pyloric stenosis, Hirschsprung's disease and tracheo-oesophageal fistulae have all been reported.
* Vision: Three percent of newborns with Down syndrome will have dense congenital cataracts which should be removed early. Glaucoma is also common.
* Congenital Hypothyroidism: This condition is slightly more prevalent in babies with Down syndrome. It should be detected by the routine heelprick screen performed on all babies.
*Congenital dislocation of the hips: Joint laxity and hypotonia can combine to increase the incidence of hip dislocation, although true congenital dislocation is quite rare.
* Sensory deficits: Significant hearing impairments occur in the majority of children with Down syndrome. Annual audiometry and specialist consultation is recommended.
* Atlantoaxial instability: Up to 15% of children with Down syndrome will have evidence of instability of the atlantoaxial joint but in only a handful of cases will this instability result in an impingement on the spinal cord with resultant neurological signs.
* Physical growth: Physical development is invariably delayed in children with Down syndrome. A tendency towards obesity requires special attention to healthy diet and exercise habits in this group.
* Dental care: The teeth of children with Down syndrome tend to be small, irregularly spaced and misshapen. Early and frequent dental care is required to ensure adequate dentition for adult life.
* Psychiatric disorders: Psychiatric illnesses occur in people with Down syndrome with much the same frequency as in the rest of the population.
*Dementia: Much recent attention has been focused on the association between Down syndrome and Alzheimer's disease. There appears to be a gene-dose effect where having an extra chromosome 21 gives an individual a higher chance of developing Alzheimer's disease. (Newton, 1992)
A significant amount of research has been conducted on Down syndrome, in particular many methods to detect Down syndrome in fetuses have been developed. This is a controversial issue for researchers and for families who have Down syndrome children and adults. The following is a discussion of some of the detection methods for Down syndrome, and the facilities in which they were developed.
Jones Institute
Scientists at Norfolk's Jones Institute for Reproductive Medicine say they have overcome most technical hurdles to screening embryos for Down syndrome and many other chromosomal defects before the embryos are implanted in a woman's uterus.
The institute, part of Eastern Virginia Medical School, hopes to try out the technique with a handful of high-risk couples who come to the institute for in-vitro fertilization, in the near future. (www #1)
Eventually, all couples who go through the Jones Institute may have the option to screen for Down and most of the other conditions caused by an extra chromosome on one of 23 pairs that make up the normal complement. The technique has been developed in part to help parents avoid a difficult moral decision - what to do if the fertility techniques cause the mother to become pregnant with many children at once. At the same time, it opens up a host of other ethical questions for parents and society as a whole, say people who have children with Down. (www #1)
According to Kingsley and Levitz (1994), in-vitro fertilization (IVF), is a technique in which eggs are removed from a woman's ovaries and combined with sperm in a dish. The resulting embryos are transplanted into the woman's uterus. Before transplant, a single cell will be removed and exposed to probes made up of genetic material treated with fluorescent dye. Each probe has been designed to attach to a specific chromosome in the nucleus. Using a special microscope, a scientist can count the dots of various colors. Three of a specific color means that there is one extra chromosome of that type.
The institute will test five pairs that account for most chromosomal defects. The first cases will be done for free. When the procedure becomes common, the procedure will add about $2,000 to the cost of IVF, about $7,500. The Chairman of reproductive endocrinology at the Jones Institute said the procedure was developed primarily to avoid the multiple births that sometimes happen with IVF. (www #1)
Most transplanted embryos, and many naturally conceived ones, never take root and grow because they have the wrong number of chromosomes. In IVF, doctors try to improve the odds by implanting three or more, assuming that some will be lost. But sometimes, many or all of the embryos are viable. The parents then must decide - do they selectively abort some, or do they take on the hugely demanding task of having many babies at once? If doctors could screen the embryos, he said, they could limit themselves to implanting two and still enjoy a high probability that the embryos will survive.
Nevertheless, the ability to screen out embryos with Down syndrome still worries families of people with the condition. (www #1)
The option not to have a child with Down already exists. Tests during pregnancy can detect the condition. Parents may choose an abortion. Parents of children with Down syndrome, say that other parents who choose to discard an embryo in a laboratory are further removed from the implications of their decision. Doctors at the medical center say that they want very much for people confronting the decision to understand that having a child with Down syndrome can be very fulfilling. They says the Jones Institute isn't trying to devalue people with Down syndrome by offering the test. But they say this information has such important ramifications for the family, if we have that information, we would give it to them and they make the choice.
Polar Body Analysis
Physicians at Illinois Masonic Medical center have discovered that they can determine if a woman will have a baby with Down's syndrome before she gets pregnant, provided she is willing to undergo in-vitro fertilization. Using an experimental technique called polar body analysis, the genetic material of an egg can be checked before laboratory fertilization, helping some women avoid abortions.
Chicago researchers at Masonic reported on a yearlong study involving 100 women who underwent the polar body procedure, they say that several women already have delivered healthy babies, and more than 20 are pregnant with no sign of Down's.
But the possibility exists that the Masonic patients could have achieved the same results without genetic testing. The majority of women who have conventional in-vitro fertilization are older and have normal pregnancies. Dr. Charles Strom, director of medical genetics at the hospital said that, polar body work gives a 35-year-old female the same chance of conceiving a chromosomally normal baby that a 21-year-old has. He said at least half the women in the in-vitro fertilization program are 35 or older. (www #2)
Polar body analysis hinges on basic biology. During normal development, the human egg contains a sac of excess chromosomes called the polar body before it gets ready to be fertilized by a male's sperm. Since this sac, is a mirror image of the egg, the genetic content of the egg itself can be determined through this procedure. (www #3)
Without such testing, about 30 percent of the Down's pregnancies resulting from in-vitro fertilization would have miscarried naturally, and others could have been picked up by the standard prenatal testing techniques, chorionic villi sampling and amniocentesis.
In-vitro fertilization is expensive, labor intensive and often disappointing. The polar body test would add another $2,000 to $2,500 to its costs. (www #2)
The Triple Screen
The "triple screen for Down syndrome" has been in existence for over five years. However, just this past year, the American College of Obstetricians and Gynecologists officially recommended that this test be offered to all pregnant patients of all ages. This implies a legal mandate to practicing physicians who cannot afford the liability of not offering such a test after a national recommendation has been made. This "mandate" has been met with great controversy. (www #3)
The "triple screen" actually involves drawing maternal blood to test for serum levels of three hormones: human chorionic gonadotropin (HCG), alphafetoprotein (AFP), and estriol (E3). The pattern of the levels of these hormones predicts the presence of Down syndrome in the fetuses in up to 60-70% of pregnancies affected. By using computer formulas, the hormonal levels can be found that are predictive for a risk of Down syndrome in the fetus that approximates 1 in 190 - which is the same risk that a pregnant woman has at age 35. Thus, the test has been recommended now for women at all ages. If it is "positive", it should be followed by ultrasonography and then amniocentesis to make a definitive diagnosis. (www #3)
Some uses of the triple screen are seen as positive by all. If the test is negative, these results can prevent further unnecessary ultrasonography, or amniocentesis, or chorionic villus sampling - for women 35 or over; or for the woman with a previous fetus with Down syndrome. Normally these more expensive and invasive tests would have been recommended in those settings.
It is the use of the test for all pregnant women that begins to stir controversy.
Only one such serum test has ever been recommended so widely before - the serum (AFP) alphafetoprotein screen. It is a screening test for multiple types of fetal defects that affect the "neural tube" in the fetus. These defects include such problems as anencephaly, holoprosencephaly, or einencephaly, as well as many levels of spina bifida. Down syndrome is certainly not the same as the wide range of anomalies termed "neural tube defects," but the Triple Screen makes it seem an equal to many lethal defects.
The triple screen actually detects many more fetal anomalies than Down syndrome, including the AFP-related anomalies mentioned above and several lethal trisomies, such as Trisomy 18. The Triple Screen is called a screen "for Down syndrome" for marketing reasons, as much as for scientific accuracy.
The Triple Screen is, in fact, a very poor screen, identifying only about 65% of fetuses with Down syndrome in utero. No other screen with such low validity has been universally recommended for all pregnant women. Such a recommendation means billions of dollars for the genetics industry and the researchers involved. (www #3)
The screening tests establish the probability of pregnant women having children with Down Syndrome or Spina Bifida and other neural tube defects. It is possible the widespread use of genetic screening for the purpose of identification and abortion of fetuses with Down Syndrome may adversely affect the quality of life for all persons with Down Syndrome in the community.
Many groups representing people with Down syndrome have expressed their feelings about this issue, the following is a summary of some of the wishes they have expressed.
1. The primary goal of prenatal genetic testing should not be to reduce the
birth prevalence of Down Syndrome in the population. Its use should be
directed towards the provision of improved health care. 2.Prenatal genetic
testing should be voluntary. The woman or couple should receive counseling
that is comprehensive and provided in a language that is easily understood by
them. Prior to reviewing written consent for prenatal testing, the couple
should be given accurate and up-to-date information on all relevant issues
surrounding prenatal genetic testing and Down Syndrome. This information
should be provided in a balanced manner. Each woman or couple should
be allowed to decide whether prenatal genetic testing is appropriate for
them based on informed choice. An appropriate period of time should be
allowed between receiving information and deciding, with written
consent whether or not to proceed with the test. 3. Following a test result
which implies that the fetus may have a probability of a chromosone
abnormality such as Down Syndrome, the woman or couple should be
provided with detailed, balanced information regarding the options
available to them. This information should be provided by a
knowledgeable and qualified health care provider such as those found
in accredited genetic centres. Balanced information should be so
recorded for the woman or couple to review at their leisure.
Opportunities to have the woman or couple speak to parents of
children with Down Syndrome should be offered. (www #4)
It is evident that the debate over screening for Down syndrome is far from settled. It is also evident that people with Down syndrome can make an important contribution to our society. I think if parents are not prepared to take on the challenges of a child with Down syndrome they should have options, should one of these options be abortion?
I would have a hard time supporting someone's decision to abort, especially having spent some time with a young boy who has Down syndrome.
There are many support groups for families who have children with Down syndrome, there are also many families willing to adopt. The programs at school for these children are very adaptable to the needs of the individual. Most children with Down syndrome can go to school and get along well, they make a valuable contribution to the classroom and their fellow students. The decision is a difficult one and I think that there are many options that need to be explored before anyone can make an informed decision.
References
Cooley, W. and Graham, J. (1991). Down syndrome - an update and review for the primary paediatrician. Clin Paed 30 (4): 233-253.
Graves, P. (1990). The intellectually disabled child in Robinson MJ practical paediatrics 2nd ed. Melboune: Churchill Livingstone.
Kingsley, J. and Levitz, M. (1994). Count us in: Growing up with down syndrome.
New York: Harcourt Brace & Company.
Newton, R.(1992). Down's syndrome. London: Optima.
Platt, L. and Carlson, D.(1992). Prenatal diagnosis - when and how? NEJM 327 (9):636-638.
Pueschel, S.(1990). Clinical aspects of down syndrome from infancy to adulthood. Am J Med Gen Supp 7: 52-56
Pueschel, S. and Pueschel, J. (Eds) (1992). Biomedical concerns in persons with down syndrome. Baltimore: Paul H Brookes Co.
Pueschel, S. (1992). A longitudinal study of atlanto-dens relationships in asymptomatic individuals with Down syndrome. Paediatrics 89 (6) pg. 1194-1198.
Selikowitz, M.(1990). Down Syndrome - the facts. Oxford:Oxford University Press.
Stray-Gundersen, K. (Ed.) (1995). Babies with down syndrome: A new parents' guide (2nd edition). Rockville, MD: Woodbine House.
Tingey, C. (Ed.) (1988). Down syndrome: A resource handbook. Boston, MA: College- Hill Press.
www #1. http://www.erms.edu/jones/depthome.htm
www #2. http://ptolemy.eess.edu/ds.html
www #3. http://wwwpino/ds/prenata/nsdcapf.html
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