The Pathogenesis of Down’s Syndrome Essay -- Science Medical Genetics

The Pathogenesis of Down’s Syndrome Down’s syndrome (DS) is the most common cause of mental retardation in the United States. It occurs with a frequency of one in 700 live births. The disease is caused by the presence of three copies of chromosome 21 as a result of chromosomal mutation (95% nondisjunction, 5% translocation) during cell division, leading to a total of 47 chromosomes instead of the normal number, 46. There are no individuals with the clinical signs of DS who do not have at least partial trisomy of chromosome 21. Conversely, there are no cases of people with trisomy 21 who do not have DS (Patterson, 1987). Patients suffer from a variety of physical and mental problems. Physically, the disease manifests itself in epicanthic folds of the eyes, flattened facial features, unusual palm creases, muscular flaccidity and short stature (Patterson, 1987). Many are born with congenital heart defects and increased risk for cataracts, leukemia and Alzheimer’s disease. In addition to the anatomical abnorm alities, DS patients suffer from biochemical imbalances including elevated levels of purines - a condition that can by itself lead to neurological impairment, mental retardation, and immunodeficiencies. The life expectancy for DS patients is approximately 30 years. However, with advancing medical care and therapy more patients are living to the age of 50. All individuals with DS over the age of 35 develop the same kind of abnormal microscopic plaques and neurofibrillary tangles in the brain as people who die from Alzheimer’s disease, the major cause of presenile dementia. Although a vast amount of literature exists on DS, little is known about why the presence of an extra chromosome causes mental retardation. In addition to ... ...ogy and Experimental Neurology, 49: 509-518. Ferrer, I., Gullotta, F. (1990): Down’s Syndrome and Alzheimer’s Disease: Dendritic Spine Counts in the Hippocampus. Acta Neuropathol, 79: 680--685. Mann, D. M. A., Brown, A., Prinja, D., Davies, C. A., Landon, M., Masters, C. L., Beyreuthers, K. (1989): An Analysis of the Morphology of Senile Plaques in Down’s Syndrome Patients of Different Ages Using Immunocytochemical and Lectin Histochemical Techniques. Neuropathology and Applied Neurobiology, 15: 317-329. Patterson, D. (1987): The Causes of Down Syndrome. Scientific American, 255: 52-60. Takashima, S., Ieshima, A., Nakamura, H., Becker, L. (1989): Dendrites, Dementia and the Down Syndrome. Brain Development, 11: 131-133. Wisniewski, K., Bobinski, M. (1991): Hypothalamic Abnormalities in Down Syndrome. The Morphogenesis of Down Syndrome., 153-167. The Pathogenesis of Down’s Syndrome Essay -- Science Medical Genetics The Pathogenesis of Down’s Syndrome Down’s syndrome (DS) is the most common cause of mental retardation in the United States. It occurs with a frequency of one in 700 live births. The disease is caused by the presence of three copies of chromosome 21 as a result of chromosomal mutation (95% nondisjunction, 5% translocation) during cell division, leading to a total of 47 chromosomes instead of the normal number, 46. There are no individuals with the clinical signs of DS who do not have at least partial trisomy of chromosome 21. Conversely, there are no cases of people with trisomy 21 who do not have DS (Patterson, 1987). Patients suffer from a variety of physical and mental problems. Physically, the disease manifests itself in epicanthic folds of the eyes, flattened facial features, unusual palm creases, muscular flaccidity and short stature (Patterson, 1987). Many are born with congenital heart defects and increased risk for cataracts, leukemia and Alzheimer’s disease. In addition to the anatomical abnorm alities, DS patients suffer from biochemical imbalances including elevated levels of purines - a condition that can by itself lead to neurological impairment, mental retardation, and immunodeficiencies. The life expectancy for DS patients is approximately 30 years. However, with advancing medical care and therapy more patients are living to the age of 50. All individuals with DS over the age of 35 develop the same kind of abnormal microscopic plaques and neurofibrillary tangles in the brain as people who die from Alzheimer’s disease, the major cause of presenile dementia. Although a vast amount of literature exists on DS, little is known about why the presence of an extra chromosome causes mental retardation. In addition to ... ...ogy and Experimental Neurology, 49: 509-518. Ferrer, I., Gullotta, F. (1990): Down’s Syndrome and Alzheimer’s Disease: Dendritic Spine Counts in the Hippocampus. Acta Neuropathol, 79: 680--685. Mann, D. M. A., Brown, A., Prinja, D., Davies, C. A., Landon, M., Masters, C. L., Beyreuthers, K. (1989): An Analysis of the Morphology of Senile Plaques in Down’s Syndrome Patients of Different Ages Using Immunocytochemical and Lectin Histochemical Techniques. Neuropathology and Applied Neurobiology, 15: 317-329. Patterson, D. (1987): The Causes of Down Syndrome. Scientific American, 255: 52-60. Takashima, S., Ieshima, A., Nakamura, H., Becker, L. (1989): Dendrites, Dementia and the Down Syndrome. Brain Development, 11: 131-133. Wisniewski, K., Bobinski, M. (1991): Hypothalamic Abnormalities in Down Syndrome. The Morphogenesis of Down Syndrome., 153-167.