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Down syndrome refers to a genetic disorder caused by an additional 21st chromosome. John Langdon Down described the condition hence named after him. Statistical studies about downs syndrome reveal that it affects 1 of 800 live births and this is the major causative factor for cognitive impairment. Children having mild to moderate learning disabilities, low muscle tone, distinctive facial characteristics and growth retardation are most likely suffering from the disorder. Individuals with Down syndrome also suffer from leukemia, Alzheimer’s disease, heart defects and gastrointestinal problems. Down syndrome’s indicators range from mild to severe. Formerly, individuals affected by Down syndrome have a shorter life expectancy compared to the current life expectancy which is averagely 55 years. This paper discusses the aspects of Down syndrome.
The characteristics of Down syndrome are linked to genes present in the additional copy of chromosome 21. A normal human cell contains 23 pairs of varying chromosomes and every chromosome has its own genetic materials. The genetic materials are necessary for maintenance and development of the human body. During conception, both parents contribute 23 chromosomes. Unfortunately, one can inherit an extra chromosome from mother or father. Frequently, individuals inherit two copies of chromosome 21 from the mother and one copy from the father. The inheritance of the three chromosomes 21 causes Down Syndrome, and that is why it is also known as trisomy 21. An estimation of about 95 per cent of children and adults affected by this disorder has the whole chromosome 21.
Apparently, scientists have not clarified how the extra genes on chromosome 21 cause Down syndrome. However, they believe that the additional genes interrupt the relations between the actual genes of the chromosome 21 and other genes. As a result, the activity of some genes will be more than usual or below the usual. The severity of the condition depends on the types and number of extra genes inherited by an individual. Various scientific studies are attempting to identify the specific gene or genes from chromosome 21, present in the three copies inherited from parents, which causes Down syndrome. Presently, approximately 400 chromosome 21 genes have been recognized, but their functionality is still a mystery. Human and animal studies are also playing a critical role in understanding the functions of the identified genes.
Maternal age is a risk factor for conceiving a child affected with Down Syndrome. The older the mother is at the time of conception, the greater the vulnerability of conceiving a child suffering from Down syndrome. For mothers at 25 years, 1 in every 1250 conceives a child with Down syndrome and for mothers at 45 years, 1 in every 30 conceives a child with Down syndrome. This affirms that the older the mother, the higher rate of exposure. A risk of 1 per cent also exists for parents who have conceived a child having Down syndrome. Parents who are carriers of chromosome 21 translocation have the highest risk of 100 per cent of conceiving a child with Down syndrome.
Many individuals with Down syndrome have identifiable physical symptoms, though these symptoms depend on the severity. Some of the features include flattened nose and face, small mouth and occasionally long tongue, small ears, short neck and slanting eyes having small skin folds. People with Down syndrome also have white spots on the iris. They have short and broad hands with short fingers. Presently, various prenatal screening tests, such as alpha-fetoprotein (AFP) and nuchal translucenc, are available for Down syndrome. AFP involves measuring the three hormones namely unconjugated estriol, inhibin-A and chorionic gonadotropin in the mother's blood, from which the disease can be detected.
In conclusion, Down syndrome is a genetic disorder caused by an additional twenty first chromosome. The disorder affects 1 of 800 live births and the dominating causative factor for cognitive impairment. The symptoms of Down syndrome are linked to genes present in the additional copy of chromosome 21. Maternal age and previous conceptions of children affected by Down syndrome are risk factors for conceiving a child with the disorder.