Tuesday, 22 May 2012

Down Syndrome

           Down syndrome or Down’s syndrome (also known as Trisomy 21) is a genetic development disorder (Martin & Fay 2009) occurred due to incorrect number of chromosome inside DNA cell nucleus while undergoing replication. Down syndrome was named after an England physician, Dr. John Langdon Down who is the first person categorized this syndrome as a disorder in 1866 (Davies & Holloman 2001). Down syndrome may happen due to maternal age (Alan n.d.) especially maternal age around 35 year old (Serene 2011) and also due to radioactive contamination in environment that causes cell mutation.
 
            The chromosome number of a Down syndrome individual is different compared to normal people. This can be indentified in the 21st of chromosome pair which have an extra chromosome. Normally, a healthy individual has 2 chromosomes in 21st chromosome pair but Down syndrome’s individual has 3 chromosomes in 21st chromosome pair. This means that Down syndrome’s individual will have 47 chromosomes instead of 46 chromosomes (included sex identical chromosomes) inside their gene. (Khan et al. 2008)
            There is few factors cause wrong insertion of chromosome in 21st chromosome pair. The main factor is due to gene mutation called aneuplooidy. Aneuploidy means changes in number of chromosome in pair. These changes may not cause the individual to death but some impairment may occur. Besides, Down syndrome can also be described through the concept called nondisjunction which occurs when mature egg or sperm cell of parental cell have less than two or more than two copies (two copies is considered as normal, other than that is considered as abnormal). This may happen due to error occurred during cell cycle in either meiosis I or II. During cell replication, the chromosome is unable to pair or separate properly.

There is another cause which can describe the occurrence of Down syndrome is mosaicism. It happens in either zygote or embryonic egg by forming an extra copy of chromosome in 21st chromosome pair. Lastly, Down syndrome will also occur when translocation happens within two different chromosomes which happened hereditary. One of the extra copies of chromosome will be transferred to either 14th chromosome pair or 21 chromosome pair (Trisomy 21). Individual who has this translocation of Down syndrome can be a carrier who only has 45 chromosomes in the gene. (Martin & Fay 2009)

            Individuals with Down syndrome can be identified easily based on specified facial characteristics such as large tongue (Belfer 1980), round face, small chin (Weiss 1994), small ear and mouth (MacLean et al. 2006), epicanthic fold of eyelids, shorter limbs, almond shape eyes, board neck, epicanthic fold of eyelids, having single transverse palmer crease on one or both hands and the distance between big and second toe are large. Besides, they also having some health issues such as poor muscle tone, mental retardation, having higher risk of getting cardiovascular diseases, lost of hearing, gastroesophageal reflux disease, obstructive sleep apnea, obesity and leukemia (MacLean et al. 2006).

References:

Alan E. Guttmacher n.d., Down Syndrome (Trisomy 21), viewed 15 March 2012, < http://www.genome.gov/Glossary/index.cfm?id=54>.

Davies M & Hollman A 2001, ‘Down Syndrome’, in Heart, vol 86, no. 2, pp 130, viewed 15 Mar. 2012, < http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1729839/pdf/v086p00130.pdf>.

Evans-Martin, F. Fay 2009, Down Syndrome, e-book, accessed 14 March 2012, <http://uql.eblib.com.au.ezproxy.library.uq.edu.au/patron/FullRecord.aspx?p=456977>.

Khan, Q, Masood, QF, Tariq, A, Khan, S & Tirmizi, M 2008, ‘Down Syndrome’, in Encyclopedia of Stem Cell Research, SAGE, Thousand Oaks, CA, pp. 175-7, viewed 14 March 2012, <http://sage-ereference.com.ezproxy.library.uq.edu.au/view/stemcell/n82.xml?rskey=E9FDwh&result=1&q=down%20syndrome>.

MacLean, William E., null, and Sigan L. Hartley, ’Down Syndrome.’ Encyclopedia of Human Development. Ed. . Thousand Oaks, CA: SAGE, 2005. 395-97. SAGE Reference Online. Web, viewed 15 March 2012, <http://sage-ereference.com.ezproxy.library.uq.edu.au/view/humandevelopment/n204.xml?rskey=D6ab4C&result=1&q=down syndrome>.

Meira Weiss, 1994, Conditional love: parents' attitudes toward handicapped children, pp 94, viewed 15 March 2012,<http://books.google.com/?id=a62J5GPHd3cC&pg=PA94&lpg=PA94&dq=%22down%27s+syndrome%22+chin+face>.

Myron Belfer, MD, book by Gottfried Lemperie, MD, and Dorin Radu, MD, 1980, ‘Facial Plastic Surgery in Children with Down's Syndrome (preview page, with link to full content on plasreconsurg.com)’, pp 343, viewed 15 March 2012 , <http://scholar.google.com/scholar?q=info:Nt6asksVAiYJ:scholar.google.com/&hl=en&output=viewport>.

Serene, T 2011, Chapter 2 Pregnancy, PowerPoint slides, UCSI University, Kuala Lumpur.

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