Mikey's Homepage
Major: Pre-Med
 |
My favorite thing about college is the diversity of people. |
|
|
My favorite food is macaroni with sauce. |
|
|
I am most proud of my family. |
|
|
I would like to be a successful intern in a metropolitan hospital. |
|
|
"One day you are going to look back on life and realize you have lived more days then you have left." |
|
|
The most important thing that needs to be changed in the world today is peoples ignorance towards one another.
|
Down syndrome
Down syndrome is the most common genetic disorder among children. 1 out of every 1,000 is diagnosed with what is more commonly known as DS (Leshin, 2000). DS was first observed in 1866 by John Langdon Down, an English physician. However, only speculation existed on what caused this debilitating disease. In 1959, Jerome Lejeune and Patricia Jacobs discovered the true cause. It is trisomy of the 21st chromosomes that causes DS and the debilitating characteristics along with it (Leshin, 2000).
Chromosomes are string like structures that contain DNA and other compounds. They are the information center of living organisms. DNA can be broken down into smaller parts called genes, which contain traits of the individual. A human cell has forty six chromosomes, which can be grouped into 23 pairs. However, in sex cells, the sperm and egg [gametes] only contain 23 chromosomes. This happens because of a cell division process called meiosis, where one cell splits into two cells, each containing half the original cell’s DNA. It is during this process where complications can occur (Leshin, 2000).
During meiosis the chromosomes, after forming a tetrad, separate and go to opposite sides, to form alleles. This is called disjunction. This event does not always happen with 100% accuracy. In some cases a chromosome does not split and still moves to one side. Therefore, the resulting mutation, called nondisjunction, causes one of the two gametes to have an extra chromosome; one having twenty four and the other twenty two chromosomes. When the mutated sperm or egg fertilizes a normal gamete of 23 chromosomes, it results in an egg with an abnormal number of chromosomes. 95% of all cases of DS result from this mutation (Leshin, 2000). One cell has two 21st chromosomes; subsequently, the fertilized egg has three 21st chromosomes, and therefore the scientific name trisomy 21 (Leshin, 2000).
The 21st chromosome holds 200-250 genes, which is considered to be the smallest chromosome in terms of genes (Leshin, 2000). However, the abundance of these genes causes overexpression, which simply means that there is an overabundance of “products” coded by the 21st chromosome. Only a small portion of the alleles present in the chromosome produce the effects of DS. These portions, however small, occur in several areas along the strand called the Down Syndrome Critical Region (Leshin, 2000). There are a diverse amount of traits caused by trisomy 21.
The brain is greatly affected by DS; not only in development, but in its overall structure. When compared to a normal brain, an affected brain has a considerably lower weight and the brain stem and cerebellum are small with respects to the cerebral hemispheres (CChem, 2003) Other abnormal characteristics include a round shape, foreshortened, steep rise of the occipital lobes, extreme narrowing of the superior temporal gyri and incomplete opercularization with exposure of the insular cortex, and reduced secondary sulcal development (CChem, 2003). These abnormalities are causes of diminished and malformed growth of the frontal and temporal lobes secondary to impaired neuronal differentiation (CChem, 2003). The severe changes in the brain cause irregular development of the individual.
Development of children with DS is closely observed to see how far off they are, with respect to time, from normal children. Development is categorized into five different components - gross-motor movements, fine-motor movements, personal and social development, language and speech development, and cognitive development, for ease of description. (Selikowitz, 29-62)
Gross-motor movements are standing, walking, jumping, crawling, etc. The parts of the brain that control these functions are the cerebral cortex, the frontal lobe, the subthalomus, and the cerebellum. (Selikowitz, 29-62)
Fine-motor movements are the tasks in life which require more co-ordination such as the manipulation of one’s fingers along with writing, block-building and so on. The cerebellum and temporal lobe of the brain control these functions. Also, the hippocampus, which is located in the temporal lobe, is where long term memory is stored. Therefore, it is possible, that as time progresses, afflicted individuals could possibly forget important people or information from the very near past. (Selikowitz, 29-62)
Personal and social developments are the next area of focus. This includes areas along the lines of recognition of family members over strangers, using a toilet, reactions to people/stimuli, etc.. Many parts of the brain take part in this region of development. The entire right hemisphere of the brain (cerebral cortex, temporal and limbic lobes), when altered, causes this underdevelopment. (Selikowitz, 29-62)
Language and speech development is probably the most difficult. To learn how to speak and understand takes ample time, patience, and practice. Grammar structure and understanding language is greatly affected. Both the left and right hemisphere of the brain and the cerebral cortex are the areas which control these functions. (Selikowitz, 29-62)
And lastly is cognitive development. This is ability to grasp the world. Trouble in reasoning, thought processes, problem solving, concepts, and overall general knowledge occurs. The associated brain parts affected are the frontal, parietal, and temporal lobes which in turn affects the entire brain. Also, mental retardation is associated with about 90% of all cases of DS. Mental retardation ranges from learning disabilities to those who need twenty four hour supervision. (Selikowitz, 29-62)
Children and adults who have Down’s syndrome are people just like you and I. Through research, government funding, and their tenacious will, they are living normal and healthy lives. They are getting married, finding jobs, and competing in athletics. The debilitating affects of Down’s syndrome no longer hold these people to sheltered lives. They deserve the rights and respect of every other human being.
Works Cited
Berg, Linda R., Diana W. Martin, Edlra P. Solomon. Biology. Ed. Nedah Rose. 6th ed. USA: Thomas Learning Inc., 2002.
Leshin, Len MD, FAAP. “Trisomy 21: The Story of Down Syndrome.” Down Syndrome: Health Issues. 2000. 14 October 2003 < http://www.ds-health.com/trisomy.htm>
CChem, Lubec G., Dr., FRSC. Riverbend Down Syndrome Parent Support Group. 19 March 2003 <http://www.altonweb.com/cs/downsyndrome/index.htm?page=lubec.html>
Selikowitz, Mark. Down Syndrome The Facts. New York: Oxford University. 29-66