Down syndrome is one of the most common and easily recognized genetic disorders.
It is caused by abnormal cell division that involves the 21st chromosome pair of the 23 pairs of chromosome found in all normal human cells. There are three types of these abnormalities, which are non-disjunction, translocation, and mosaicism. Ninety five percent of children born with Down syndrome are a non-disjunction type which is three rather than two chromosome 21s. About three to four percent of cases are because of translocation which is chromosome 21 detaches and attaches to another chromosome. Mosaicism accounts for only one to two percent of births, which is an abnormal cell division with the normal 46 chromosomes while the others have 47 creating a mosaic of normal and abnormal cells (Encarta.
p1). The presence of Down syndrome in children is also due to the age of the mother. A twenty five year old woman’ s chance of having a baby with Down syndrome is 1 in 1,250, but a woman who is thirty five it’s 1 in 378 and a woman 45 it’s1 in 30 (Encarta. p2). Diana Danilenko-Dixon, M.
D. states “As a woman’s eggs age, there is a greater propensity for chromosomes to divide improperly”. Although researchers are studying ways to detect improper cell division, there isn’t a test yet to the likelihood of Down syndrome before conception (Exceptional children p173). One recent study noted that a rise in children born with Down syndrome between 1990 and 1995 because of the old maternal age.
The age of the father does not seem to be a factor. When a woman becomes pregnant, there are screening tests that can be performed to detect Down syndrome beginning at the tenth week of gestation. Of course the test isn’t 100% accurate so you should know a positive result does not mean Down syndrome is present and a normal screening doesn’t mean the baby will be born without Down syndrome; the chance is just reduced. Its very important to know that some screening test may slightly increase the chance of a miscarriage. Tests in utero for identifying Down syndrome include amniocentesis, which is a needle inserted into the uterus and a sample of the amniotic fluid surrounding the fetus is taken out.
Usually used within 14-16 week of pregnancy. This test is 99% accurate, but carries a 0. 5 percent chance of miscarriage. Chorionic villus sampling (C. V.
S. ) is used by taking cells from the placenta through the mother’s abdominal wall or cervix. Performed between tenth and twelfth week of pregnancy, this test is 98 percent accurate and carries a risk of limb deformities and a one to two percent chance of a miscarriage. Karyotyping can be used through the process in which a picture of chromosomal patterns is prepared (Genetic Disorders. p5).
An ultrasound can identify any traits a fetus has such as shortened thighbones or gastrointestinal blockage that can be associated with Down syndrome, but not as accurate to be used as a substitute for C. V. S. or amniocentesis in detecting Down syndrome.
Before the 1970’s Down syndrome wasn’t diagnosed until birth or even later, but due to such early diagnosing and screening this has posed a major dilemma for families and physicians. It allows parents to decide whether or not the pregnancy should be terminated (exceptional child book p176). The physical description of a child with Down syndrome is that they have distinct facial appearance; small round head, with high-flattened forehead, upward slanting eyes dry lips and tongue, and a short stature (Genetic Disorders. p20). Other complications include almost half of children with Down syndrome have congenital heart defects, also a risk for developing gastrointestinal complications, thyroid problems (Encarta.
p3), hearing loss and impaired vision and tend to develop leukemia. Children with Down syndrome can have mental delays, under developed digestive system, and low muscle tone. Intelligence quotient usually ranges between 20 and 60, but with early intervention and proper education some people reach higher levels. Children with Down syndrome tend to be happy, loving, and easygoing.
There may be a behavior problem in some. One in three people with Down syndrome past the age of thirty-five will have increasing senility similar to Alzheimer’s disease. Average life expectancy is 50 years, but it depends greatly on the .
