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About one in one thousand births result in Down’s Syndrome. It is the most frequent form of mental retardation. Some victims of Down’s Syndrome may have a fair intelligence, but usually the IQ is between 20 and 40. Many of the babies born with Down’s Syndrome die before they reach their teens, because they seem to be particularly susceptible to infection. Yet, through research and medical treatment over the later years, victims of Down’s Syndrome are living longer healthier lives.
History of Down’s Syndrome
In 1866, a physician, John Langdore Down first described a set of children with common features who were distinct from other children with mental retardation. Down was superintendent of an asylum for children with mental distinction between children who were cretins (later to be found to have hypothyroidism) and what he referred to as “Mongoloids”. Down based this unfortunate name on his notion that these children looked like people from Mongolia, who were thought then to have an arrested development. This ethnic insult came under fire in the 1960’s, from Asian genetic researchers, and the term Mongoloidism was dropped from scientific use. In 1970, an American reversion of scientific terms changed it simply to Down’s Syndrome.
The first people to speculate that Down’s Syndrome may be due to chromosomal abnormalities were Waardenberg and Bleyer in the 1930’s. Then, in 1959, Jerome Legeune and Patricia Jacobs working independently first determined the cause to be trisomy (triplication) of the 21st chromosome. Causes of Down’s Syndrome due to translocation and mosaicism were described over the next three years (Human Molecular Genetics, 1996, 5:1411-1416).
Down’s Syndrome increases with maternal age, but there are other factors. Some professionals believe those hormonal abnormalities, x-rays, viral infection, immunologic problems, or genetic predisposition may be the cause of the improper cell division resulting in Down Syndrome.
Birth prevalence rates of Down syndrome, plotted by maternal age, form a J-shaped curve, with women 20-24 years of age having the lowest prevalence rates (American Journal Of Human Genetics, 1996, 58:628-633).
With advances in DNA technology it is possible to classify trisomy 21 according to parental origin and the stage of the chromosome error. Exact figures in studies vary, but it is overwhelmingly maternal nondisjunction (86%-95%) that leads to Down Syndrome, paternal nondisjunction is 5%-10% (British Journal of Obstetrics and Gynecology, 1996, 103:1205-1211).
Also DNA polymorphism tells us the meiotic stage of the chromosome error. Errors in meiosis I occur when chromosome pairs fail to separate, and in meiosis II when the chromatids fail to separate. It was found that maternal meiosis I (MMI) errors occurred approximately three times more often than MMII. MMI can occur as early as the mother’s fetal life while MMI occurs around conception. When the extra chromosome came from the father it was found it originated in errors in both meiosis I and meiosis II equally.
A recent study by French researchers found that 0.41% of children born to fathers over 39 had Down Syndrome. This figure is three times higher than that of fathers less than 35 (New Science, 21 Oct. 1995).
Children born with Down’s Syndrome have several identifiable features as follows:
I. Hypotonia (weak muscle tone) in which the muscles appear to relax and feel somewhat floppy. Weak muscle tone affects the baby’s movement,strength, and development. Also, weak muscle tome will affect the skills like rolling over, crawling, standing and walking. Latching onto a bottle is sometimes not that easy, and the acceptance of solid foods is sometimes a chore due to the weak muscle tone around the mouth. Hypotonia can be cured, although the child’s tone will always be somewhat lower than others. Early intervention of a qualified therapist is vital.
II. Facial features that give evidence to Down syndrome is the bridge of the nose, which may be somewhat flattener than usual, and the face may be a little broader. Also, children with Down Syndrome often have smaller noses and therefore the nasal passages will be somewhat smaller and prone to becoming congested more easily. The use of a good cool mist humidifier in the child’s room at night is helpful.
III. The hair is usually very soft, fine, and sometimes sparse.
IV. The chest may be somewhat funnel shaped, or pigeon boned. Yet, neither of the two results in additional medical problems.
V. The skin may be fair, and very sensitive
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Chromosomal abnormalities, Cytogenetics, Syndromes, Antioxidants, Genetic disorders, Edwards syndrome, Down syndrome, Glutathione peroxidase, Selenium, Aneuploidy, Hypotonia, Peroxidase
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