The Pathogenesis of Down’s Syndrome Essay - 1724 Words

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†¦show more content†¦By examining abnormalities in neurons, dendrites, synapses, and neuroglial cells of the CNS much information on the DS brain’s insufficiencies can be elucidated. The typical, gross morphological characteristics of the DS brain are a round cerebrum, shortened fronto-occipital diameter with steep inclinations of both occipital lobes, small superior temporal gyri perpendicularly oriented, simplicity of convolutions, irregularity of the operculum, and small cerebellum and brain stem. In addition, other anomalies have been described including hydrocephalus, holoprosencephaly, hippocampal hypoplasia, and hypoplasia of the anterior commissure (Becker, 1991). Microscopic examination shows many abnormalities including cortical dysmorphogenesis which includes a decrease of 20 to 50 percent in the number of neurons in the cortical layers, precentral cortex, and the granular cell layers of the temporal, parietal, and occipital lobes. In order to determine the pattern of cortical development, examination was done on brains of controls and DS fetuses and infants. By 40 weeks gestation, layers of the visual cortex were well defined in the normal infants, whereas cellular distribution was much more diffuse (less differentiated) in DS infants. At four months of age, the same relations were observed where normal neurons were more in number and maturity, whereas DS cell layers were poorly defined (Becker, 1991). ThisShow MoreRelatedAlzheimer s Disease : Genetic Analysis1129 Words   |  5 Pagesthe links between AD and other disorders; such as Down’s syndrome, will aid researchers in the diagnosis and treatment of AD. Familial Alzheimer ’s disease Familial Alzheimer’s disease (FAD) is the inheritable genetic predisposition to early-onset AD. The known causes of FAD include mutations in the genes that code for amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) (Mak et.al., 2015). The genetic disorder Down’s syndrome also exhibits early-onset AD. 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