Individual Characteristics of Down Syndrome - Case Study Example

Down syndrome Down syndrome is a genetic condition and was first identified in 1860 by Dr Landon Down, who noticed a number of people in shad similar physical characteristics. Down syndrome is caused by the presence of an extra chromosome 21, hence the classification Trisomy 21 (Leshin, 1997). Trisomy of human chromosome 21 is one of the most frequent aneuploidies in humans and results in Down syndrome, affecting approximately 1 in 700 live births. Down syndrome is a major cause of mental retardation and congenital heart disease in humans. Besides a characteristic set of facial and physical features, Down syndrome is associated with congenital anomalies of the gastrointestinal tract, an increased risk of leukemia, immune system defects, and an Alzheimer-like dementia (Korenberg, et al. 1994). A Down syndrome child will have several individual characteristics. The following are a few of these characters: the eyes of a Down syndrome child have an upward and outward slant; there is a fold of skin on the inner side of the eye (epicanthal fold); the eye slit is narrow and short; small, white patches can be seen on the edge of the iris; the face has a flat appearance; the head is smaller than average; the soft spots on the head (fontanels) are larger than normal because the baby is growing more slowly; the ears are smaller and lower-set; the mouth is small and the lips are thin which leads to the tongue sticking out because the inside of the mouth is smaller; the neck appears slightly short and loose folds of skin are seen at the back and sides (these go away as the baby grows); the legs and arms are short in relation to the body; the hands are broad and flat with short fingers, the little finger slants inward, and there is a single crease across the palm; the feet are broad with short toes and there is a larger space than normal between the big toe and the other toes ; there is poor muscle tone (hypotonia) and loose-jointedness (hyperflexibility); and reflexes tend to be weaker and the cry is weak. 1 Several studies show that the risk of chromosome disorders like Down syndrome, trisomy 13 and trisomy 18 increases with maternal age. All individuals with Down syndrome have extra chromosome 21 material. There are 3 genetic mechanisms for trisomy 21. The first and most common, is called non-disjunction, where there is an entire extra chromosome 21 in all cells (Fig. 1). The second is mosaic Down syndrome, where trisomy 21 cells are mixed with a second cell line, usually "normal" (46,XX or 46,XY). Individuals with this form of Down syndrome are frequently a bit milder in their presentation, depending on the proportion of normal cells. The third is a translocation Down syndrome, about 3-5% of the total, where part or all of chromosome 21 is translocated to another chromosome, usually 14 (Fig. 2). Translocation Down syndrome does not vary with age. Children with translocation Down syndrome are indistinguishable from individuals with the usual form of Down syndrome. "Translocation" refers to one type of rearrangement of chromosomal material; in Down syndrome almost all translocations are Robertsonian translocations, named for Dr. Roberts, an Australian chromosome expert who originally described this type of translocation. In about one-fourth of translocation Down syndrome individuals, the translocation is inherited. When it runs in families, the carriers are usually unaware they have a translocation because there are no problems for the balanced translocation carrier. Only with the birth of a Down syndrome child or Down syndrome fetus by miscarriage, does the couple find out one parent is a translocation carrier (Benke, et al., 1995). In trisomy 21, the presence of an extra set of genes leads to overexpression of the involved genes, leading to increased production of certain products. For most genes, their overexpression has little effect due to the bodys regulating mechanisms of genes and their products. But the genes that cause Down syndrome appear to be exceptions. Genes that may have input into Down syndrome include: Superoxide Dismutase (SOD1)-- overexpression may cause premature aging and decreased function of the immune system; its role in Senile Dementia of the Alzheimers type or decreased cognition is still speculative COL6A1 -- overexpression may be the cause of heart defects ETS2 -- overexpression may be the cause of skeletal abnormalities CAF1A -- overexpression may be detrimental to DNA synthesis Cystathione Beta Synthase (CBS) -- overexpression may disrupt metabolism and DNA repair DYRK -- overexpression may be the cause of mental retardation CRYA1 -- overexpression may be the cause of cataracts GART -- overexpression may disrupt DNA synthesis and repair IFNAR -- the gene for expression of Interferon, overexpression may interfere with the immune system as well as other organ systems Other genes that are also suspects include APP, GLUR5, S100B, TAM, PFKL, and a few others. Again, it is important to note that no gene has yet been fully linked to any feature associated with Down syndrome (Leshin, 1997). There have been accumulated evidences by the analysis of DNA polymorphism, they allow to affirm that the first molecular correlation of the human non disjunction is the altered recombination, the meiosis I errors start with a reduced recombination and the meiosis II errors with an increase of the recombination in the non disjunctive chromosomes. So the meiotic maternal errors of the chromosome 21 start in meiosis I. The evidences that the chromosomic alterations occur in all ages, suggest that there are two types of mechanism operating in the production of errors in the non disjunction, some dependent and others independent from the maternal age (Martínez, 2000). Prenatal screening for Down syndrome is available. There is a relatively simple, noninvasive screening test that examines a drop of the mothers blood to determine if there is an increased likelihood for Down syndrome. This blood test measures the levels of three markers for Down syndrome: serum alpha feto-protein (MSAFP), chorionic gonadotropin (hCG), and unconjugated estriol (uE3). While these measurements are not a definitive test for Down syndrome, a lower MSAFP value, a lower uE3 level, and an elevated hCG level, on average, suggests an increased likelihood of a Down syndrome fetus, and additional diagnostic testing may be desired (NICHD, 2006). Down syndrome is caused by a chromosome problem that is present when pregnancy occurs. Therefore, there is no way to prevent Down syndrome in a person who has already been born. Some women may want to have their child screened for Down syndrome during early pregnancy. If screening detects Down syndrome in the child, some women may elect to have an abortion. Genetic counseling is also useful for the families of affected children (Jorgenson, 2000). The outlook for a therapy that negates the influence of the extra genes in Downs syndrome is certainly moving ahead by leaps and bounds. Even Doctors will assume that the extra genes are mapping the childs life from the moment it is conceived. While some of the genes may map the outcome there is no common pathology for Downs syndrome, variation is the norm. Environment including the provision of a good healthy diet, loving parents and a stimulating existence results in a better outcome for every child and the same rule applies when the child has Downs syndrome. Downs syndrome is a collection of medical and developmental abnormalities easily catalogued, but not so easily understood. Perhaps too easily brushed aside by doctors with the comment "Its normal for Downs syndrome". But the sum total of these "abnormal" medical conditions is what define the syndrome, the genes only predispose towards that abnormal risk situation,  at the moment there is no certainty that the genes positively map the outcome.  There is such variability in the outcome from one patient to another patient that there is a good opportunity to do more research in this area to find out why some patients do so much better (or worse) than other patients (Elliott, 2001) .  Future research in the areas of stem cell, gene therapies may have solutions for Down syndrome. However as of now there is no complete cure for Down syndrome. Surgeries may be performed for congenital heart problems and other individual problems however there is no complete cure. Results from research on stem cell may offer solutions for Down syndrome. These cells have the potential to create any one of many different specialized cells in the body such as brain cells.  These stem cells are present within the bone marrow and they are perfectly matched to the individuals’ genetic code so there is no chance of rejection. Medical researchers are trying to use these cells to find a cure for certain disorders. References Benke, P.J., Carver, V. and Donahue, R., (1995) Risk and Recurrence Risk of Down Syndrome [Online]. Available from: [Accessed 27 January 2006]. Elliott, P. (2001). Will there ever be a cure for Downs syndrome? Available from: < http://www.dsrf.co.uk/ds_cure.htm > [Accessed 28 January 2006]. Jorgenson, R.J. (2000). Down syndrome Available from: [Accessed 28 January 2006]. Korenberg, J.R., Chen, X.N., Schipper, R., Sun, Z., Gonsky, R., Gerwehr, S., Carpenter, N., Daumer, C., Dignan, P., Disteche, C., et al. (1994) Down syndrome phenotypes: the consequences of chromosomal imbalance. Proc Natl Acad Sci U S A. 91(11): 4997–5001. [Online]. Available from: [Accessed 27 January 2006]. Leshin, L. (1997). Trisomy 21: The Story of Down Syndrome. [Online]. Available from: [Accessed 27 January 2006]. Martínez, M.H. (2000) Risk Factors Associated To The Down Syndrome Ocurrence. Cuban Journal of Human Genetics Volume 2, Number 1. National Institute of Child Health and Human Development (NICHD) (2006) Facts About Down Syndrome. Available from: [Accessed 28 January 2006]. Read More