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Trisomy 21
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- This is a common genetic condition in which a variety of abnormalities of chromosome # 21 can result in the same syndrome in which the patient's intelligence is likely below average, to some degree.
- The patient usually has a typical facial appearance with the following:
- A special kind of eyelid fold in the corner of each eye where it meets the nose
- Distinctive spots on the irises of the eyes
- The back of the head is flat.
- Usually the child is hypotonic at birth, has developmental delay, and is small for age, lifelong.
- Many Down syndrome children have congenital heart disease.
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- As listed above, mainly developmental delay, a tendency toward impaired intellect to some degree, hypotonia, and certain other physical characteristics.
- Many of the patients have symptoms of congenital heart disease, Hypothyroidism, joint symptoms, and other physical problems that need attention.
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- An abnormality of chromosome # 21, which is one of the autosomal chromosomes governing the body in general, and not one of the sex chromosomes (see definition of "autosomal," below).
- Most but not all of the Down syndrome patients have three separate units of the # 21 chromosome instead of the normal two units of this. In other cases, the genetic material of the extra # 21 chromosome is attached to another autosomal chromosome, so one does not see three separate units of # 21 under the microscope.
- Some patients have this duplicated genetic material in only some of their body cells, but they still have the clinical features of Down syndrome.
- Autosomal chromosomes are those that are found paired in both a normal male and a normal female; each of whom will have two identically-shaped # 21 chromosomes. The sex chromosomes are different: normal males have what is called an X and Y, but normal females have two of the X's.
- The normal person has 23 sets of paired chromosomes and the sex chromosomes are numbered as pair # 23. The # 23 "pair" in a male is XY, but in a female is XX. The chromosome pair affected in Down syndrome is numbered # 21.
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- The diagnosis is proven by the combination of the physical findings and the positive chromosomal analysis, which shows particular findings in chromosome # 21.
- Some cases may be suspected during the mother's current pregnancy, by running certain chemical tests on maternal blood. If these blood tests show the mother is at high risk for a Down syndrome baby with this pregnancy, an amniotic fluid sample musct be taken. Then, a chromosome analysis is done on fetal cells that are shed into the amniotic fluid, to look at material from fetal chromosome # 21. It is also possible to collect fetal cells from the fetal portion of the placenta, to look at fetal chromosome # 21. These tests have a small possibility of error.
- The tests on the maternal blood are alpha-fetoprotein (AFP); unconjugated estriol (uE3); and human chorionic gonadotropin (hCG). Results of these 3 tests are coupled with the maternal age and the estimated fetal age, to calculate the mother's risk of a Down syndrome baby.
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- Advanced maternal age increases the risk of Down syndrome.
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- Surgical repair, or other treatment, of the congenital heart defect
- Special education, physical therapy, occupational therapy, and speech therapy, may all be of great help.
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- Complications of individual organ systems may occur, because of congenital abnormalities.
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- Contact your physician for assessment and chromosomal analysis. Discuss with your physician what physical characteristics suggest Down syndrome: unusual eyelid folds, spots on the irises, flattening of the back of the head, delayed development.
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- Hypotonic infants with certain facial characteristics might resemble patients with Down syndrome.
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