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Example research essay topic: Percent Of The Cases Genetic Disorders - 1,268 words

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Down syndrome, the most common genetic birth defect associated with mental retardation, occurs equally across all races and levels of society. The effects of the disorder on physical and mental development are severe and are expressed throughout the life span. The individual's family is also affected emotionally, economically, and socially (Bellenir 1996). Characteristics associated with Down syndrome include: epicanthus folds, unilateral squints, a flat saddle nose, flat jaw bones, large fissured tongue (macroglossia), hypotonic lower lip (cheilosis), receding chin (micronesia), protruding flat ears, dry and cracked lips, dry skin, delays in skeletal maturation, shorter than average stature, delays in motor skill acquisition, flat feet, intellectual disability, delayed language abilities, and numerous others (Whitaker 1998). It has only been known since as recently as 1959 that Down syndrome, first described in 1866 by Langdon Down, is caused by extra genetic material carried on the 21 st chromosome. All normal cells in the human body, except for eggs and sperm cells, have 46 chromosomes.

These being 44 autosomes and two sex chromosomes. Normal reproductive cells contain one half of that number- 22 autosomes and one sex chromosome. The genetic effect associated with Down syndrome is the presence of extra material on the chromosome pair 21. This extra material in chromosome pair 21 is usually another chromosome. This is called Trisomy 21 (see figure 1). It occurs in 95 % of all Down syndrome cases.

Trisomy 21 results from as error in cell division during the development of the egg or sperm, or during fertilization (Bellenir 1996). Translocation is an interchange of chromosomes or parts of chromosomes which may result in a mismatched pair. Translocation occurs in about four percent of the cases. Children with translocation Down syndrome have an extra number 21 chromosome that has broken and become attached to another chromosome (Bellenir 1996).

In a few cases, a person can carry a broken chromosome 21 without showing any symptoms of Down syndrome because the correct amount of genetic material is present, just out of place. Accounting for about one percent of the cases of Down syndrome is mysticism. Affected persons have cells with different chromosome counts (for example, 46 in some cells and 47 in others) (Bellenir 1996). Essentially this is a fraction of an extra chromosome 21 attached to one of the existing chromosomes. Mosaicism is not carried in the parents' chromosomes; it is accidental, resulting from an error in cell division of the fertilized egg.

Being that only some of their cells have an abnormal number of chromosomes, babies with mosaic Down syndrome may have only some of the features of the disorder. Although surveys are all different the incidence of Down syndrome is around 1 in 800 live births. However, the risk of bearing a child with the disorder increases dramatically with advancing maternal age. For example, the incidence is less than one in 1, 000 live births to women under 30, increasing to one in 35 to mothers aged 44. Below is a table of the relationship between mothers age to the incidence of Down syndrome. It was taken from the Genetic Disorders Source Book.

Mother's age Incidence of Down syndrome Mother's age Incidence of Down syndrome under 30 less than 1 in 1000 39 1 in 135 The sharp rise in the incidence of babies with Down syndrome born to older women may occur for several reasons. Although males produce new sperm continually, women are born with all the oocytes they will ever have. An oocyte remains in a state of incomplete development until the process begins that results in ovulation. Thus, a 35 -year-old woman has 35 -year-old oocytes (Bellenir 1996).

Many body functions decline with age, and oocytes in the older woman simply may be past their prime. Or they may have been exposed through the years to damaging internal and external influences, including medications, radiation or other harmful agents. Until recently, the mother was believed to be the source of the extra genetic material. However, new laboratory techniques, have demonstrated that in about 25 percent of the studied, the father is the source of the extra chromosome. Because older fathers have been associated with increased incidence of other genetic disorders, researchers are looking more closely at the possible effect of the father's age on the incidence of Down syndrome.

In one project, involving only a small number of cases, a paternal age effect for fathers over 55 was reported (Bellenir 1996). In most cases, the first medical exam identifies the newborn with Down syndrome. Expecting a normal infant, most parents are intensely disappointed when the physician explains their new baby's condition to them. Parents generally experience an initial period of shock, follows by denial, grief, anger, adjustment and finally acceptance. Faced with an abrupt change in their hopes and plans for the child, parents need early counseling and guidance to help the cope with the situation and plan for their child's future. The presence of a retarded child in the home is not necessarily detrimental to the happiness and welfare of siblings or to the family as a whole.

With professional guidance, and accepting community attitude and the help of parent support organizations, a loving home atmosphere can evolve. All children, but especially those with Down syndrome, benefit from loving and caring homes. Since stereotypes of Down syndrome persist, early and sound information for new parents and other family members is very important. In the past, most physicians recommended placing the infant in an institution immediately upon discharge from the hospital nursery (Bellenir 1996). New developments in care and treatment mow permit other courses, but, unfortunately, parents are mot always made aware of these approaches or to other alternatives to institutionalization, such as the parents raising the child. There are several techniques for the early detection of the disease in fetuses.

The newest being an fetal nucl translucency test, which is done using ultra sound. Modern ultrasound imaging can identify and measure small subcutaneous collections of fluid behind the necks and backs of fetuses during the late first trimester. Several reports link the increased thickness of such "fetal nucl translucency" with chromosomal abnormalities (Neilson 1997). Amniocentesis is another way to test for Down syndrome. It is performed by piercing the amniotic sac and drawing out some of the fluid surrounding the baby. Amniocentesis offers mos patients 11 - 14 weeks LMP with 99 percent detection by acetylcholinesterase (AchE) testing.

Health and developmental problems occur in the child during the first years of life, close monitoring is necessary throughout this period. Medical management and surgical correction, when indicated, of the life-threatening congenital defects frequently associated with Down syndrome are essential to assure the child's optimal health and well-being. Children with Down syndrome are more susceptible to infections than normal children and, as a result often suffer chronic respiratory infection, recurrent pneumonia and repeated bouts of tonsillitis. Researchers believe that children have a deficient immune response. According to several studies, they not only have fewer of the cells needed for normal immunologic response to infection, but the cells they have do not function well (Bellenir 1996). Development delays are evident from the early months of life.

Infants are slow to turn over, sit stand, speak and respond. This may be due to the mental retardation caused by the disease. Studies on infants with Down syndrome show that the brain is virtually normal size and structure for at least a few months after birth. Infants with the disease later become retarded, largely because of the over-expression of the gene for the enzyme, Superoxide dismutase (SOD).

The result of this over expression is the productio...


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Research essay sample on Percent Of The Cases Genetic Disorders

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