The Causes and Effects of Down Syndrome

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Down syndrome, also known as trisomy 21, occurs when a child is born with three copies chromosome 21, as you can see in Figure 1. This can be caused by three different processes; nondisjunction, mosaicism, or translocation. Nondisjunction occurs during the reduction of chromosomes, from 46 to 23, after the egg and sperm have combined, causing one parent to pass on 24 instead of 23. In the case of Down syndrome, the extra chromosome is chromosome 21. Mosaicism is a rare occurrence, happening “in approximately one to two percent of Down syndrome cases” (Johnson, 2013). Initially, the correct number of chromosomes is passed on from the parents, but during the phase following fertilization, when the cells are dividing quickly, one cell divides irregularly, creating a group of cells with an extra copy of chromosome 21. A child with this type of Down syndrome has two kinds of cells, those with 46 chromosomes and those with 47, and usually has less severe signs and symptoms of Down syndrome. Translocation also occurs quite rarely, and happens during cell division when chromosome 21 breaks and attaches to another. All cells continue to have 46 chromosomes, but the broken part of chromosome 21 results in signs and symptoms of Down syndrome. Along with Down syndrome come many types of defects. According to A. Johnson, “Approximately 30-50% of all children with Down syndrome are found to have heart defects” (2013). Several different types of heart defects are common within people with Down syndrome, but all cause irregular blood flow patterns to the heart, meaning that less oxygen is pumped through the body, resulting in “fatigue, a lack of energy, and poor muscle tone” (Johnson, 2011). In addition, 5-7% of children with Down syndrome hav... ... middle of paper ... References Down syndrome stuttering can be treated [Photograph]. (n.d.). Retrieved from Johnson, A. P. (2011). Down syndrome. In L. J. Fundukian (Ed.), The gale encyclopedia of medicine. Retrieved from Gale Science in Context database. (Accession No. DU2601000443) Johnson, A. P. (2013). Down syndrome. In S. L. Blachford (Ed.), The gale encyclopedia of genetic disorders. Retrieved from Gale Science in Context database. (Accession No. JOSDOQ663865759) Karyotype of a boy with Down syndrome [Photograph]. (n.d.). Retrieved from Sie Whitten, M. (n.d.). The story of two syndromes. Retrieved January 19, 2014, from Global Down Syndrome Foundation website:

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