Alzheimer's Disease and Down's Syndrome Essay

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Alzheimer and Down's Syndrome

Down?s Syndrome, Trisomy 21, or Mongolism is one of the most common causes of mental retardation. The majority of Down?s Syndrome patients have a moderate retardation although it can range from mild to severe. Trisomy 21 occurs in about 1 in 800 live births. This incidence increases markedly as the age of the mother increases over 35. The prevalence in children born to young mothers is 1 in 1000, while it increases to almost 1 in 40 in children born to mothers over 40. Most individuals with Down?s Syndrome have characteristic features such as upward slanted eyes, broad flattened face, short neck, and a prominent tongue. Muscle coordination is often impaired in these individuals, resulting in uncoordinated
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This remained only a hypothesis as the exact number of chromosomes had not yet been identified. During the 1950?s the number of chromosomes was identified as forty-six, and Bleyer?s hypothesis was soon supported, as it was verified that individuals with Down?s Syndrome did in fact have 47 chromosomes.

In Down?s Syndrome one pair of chromatics fail to separate during reproductive cell division, resulting in a daughter cell with two chromatics, and the other with none, which then dies. This error is referred to as nondisjunction, and usually occurs during Anaphase I or Anaphase II. It is a result of the failure of spindle fibers to pull the chromatics to their respective poles. Nondisjunction usually occurs on chromosome 21, the smallest of the chromosomes. This abnormal gamete then is then fertilized by the male gamete, resulting in an offspring with chromosome 21 in triplicate, hence the name Trisomy 21.

About three to four percent of patients with Down?s Syndrome have translocation, a slightly different chromosomal abnormality. A portion of chromosome 21 attaches itself to another chromosome during cell division. This results only in part of chromosome 21 being in triplicate, but the offspring once again manifests Down?s Syndrome.

The brain?s of Down?s Syndrome patients show morphological differences when compared to normal individuals. Via magnetic resonance imaging and post mortem examinations it has been determined

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