What is the cause of the genetic disorder – a genetic mutation, inheritance of a recessive or dominate gene, etc.?
Down syndrome is a genetic disorder that results in an abnormal cell division leading to an additional complete or partial copy of chromosome 21. A majority of cases of Down syndrome are a result of trisomy 21, where every cell in the human body bears three copies of chromosome 21 rather than having the usual pair of chromosome 21. Also, less commonly, Down syndrome is known to occur when a part of chromosome 21 is translocated or attached to another chromosome at a time when the reproductive cells of humans in a parent are formed or during the early stages of development of the fetus. Typically, affected persons carry a pair of normal chromosome 21 copies, and in addition, carry an extra material from chromosome 21, which is attached to another chromosome. As a result, such persons have three copies of material carrying genetic information from chromosome 21. The individuals who experience this genetic alteration are said to have translocation Down syndrome. In another case of Down syndrome, which also occurs in a very small proportion of individuals with Down syndrome, an extra copy of chromosome 21 tends to be present in some cells within the body and not all cells, as is the case with trisomy 21. The condition in this group of individuals is called mosaic Down syndrome (Brill, 2007).
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Does the trait for the genetic disorder run in families? Can you pass the gene for the disorder to your children? If so, is it more prevalent in males or females?
According to research, the majority of the cases of Down syndrome (trisomy 21) are not acquired through inheritance. Regarding the case of trisomy 21, for instance, the abnormality evidenced in chromosomes occurs randomly during the formation of ovaries and sperms cells. Normally, the defect occurs in egg cells, but it can also happen in sperm cells on some occasions. An error recorded in a cell division process, termed as nondisjunction, leads to the formation of a reproductive cell having an abnormal number of chromosomes. For example, either reproductive cell may gain an additional copy of chromosome 21. In cases where the atypical reproductive cells carry genetic material forming part of the child's genetic make-up, the child will bear an additional chromosome 21 in every cell within the body. Down syndrome can also be inherited. Individuals with translocation Down syndrome can acquire the condition through inheritance from an unaffected parent. The parent carries altered genetic material between chromosome 21 and a different chromosome. This alteration is termed as a balanced translocation. Usually, there is no loss or gaining of genetic material during a balanced translocation. The balanced translocation can become unbalanced when it is to the following generation, and individuals inheriting the unbalanced translocation involving chromosome 21 may acquire additional genetic material contained in chromosome 21, and thus acquire Down syndrome. Like the case of trisomy 21, mosaic Down syndrome is also not acquired through inheritance, but rather, it develops as a random occurrence during cell division in a developing fetus (Brill, 2007).
Is the disorder Dominant or Recessive – Autosomal or Sex-linked or a Mitochondrial disorder?
Down syndrome is a genetic disorder, but cannot be classified as either dominant or recessive. It is termed as a chromosomal condition. There is no genetic marker designated for Down syndrome, and therefore, there is nothing to be passed to the next generation. Based on this fact, since there is no genetic information to be passed from one generation to another regarding Down syndrome, there is certainly nothing to be inherited. Thus Down syndrome is neither dominant nor recessive (Brill, 2007).
What are the statistics of the disorder in the general population? (How many people have the disorder?)
Down syndrome is the most widespread genetic disease in the world. It is estimated that the global probability of an infant being born with Down syndrome is one in every 400 to 1500 births. In the United States, prevalence stands at 1 in every 800 births. The United Kingdom has a lesser rate with statistics indicating that prevalence stands at approximately 10.3 cases in every 10000 births (Jensen & Davis, 2012). Annually, 600 children are born with the condition in the US. Down syndrome is also directly linked with a mother’s age with studies indicating that older mothers have a high probability of giving birth to children with Down syndrome than younger mothers. Age factored demographics indicate that by 2002, one in every 1000 children was living with Down syndrome while one in every 1,200 adults had the condition in the US. (Parker et al., 2010). With increased research and better medication, the survival of patients with Down syndrome has tremendously increased. In the United Kingdom, the rate of survival in children born with Down syndrome has sharply increased from 50% to 90% within the last five decades with the median death age shifting from 25 to 49 years (Jensen & Davis, 2012).
Is the disorder fatal? Are there treatments (or cure) available?
Down syndrome is highly fatal with the probability of succumbing to the condition remaining higher in children. The mortality rate of Down syndrome remains considerably high despite major improvements noticed in the last 50 years. From 1983 to 2003, 7% of babies born with Down syndrome died within 12 months of birth while 12% succumbed before reaching 20 years in the United States. Persons who survive beyond 20 years have a median death age of 60 years, which is way below the current life expectancy of 78 years in the United States (Kucik, 2012). Down syndrome has also been associated with development of other serious ailmentsin children such as pulmonary hypertension (Bush et al., 2018). Currently, no medical treatment is availably capable of curing the Down syndrome condition. However, there are procedures for prevention in expectant mothers and screening for early detection. Prevention is done during prenatal by performing amniocentesis and chorionic villus sampling (CVS). The two procedures are effective in the prevention of Down syndrome even though miscarriage is a common side effect after their administration. Ultrasound screening between week 14 and week 24 of pregnancy detects risks of a fetus getting Down syndrome . This may be followed by a diagnosis called cytogenic analysis. Notably, children born with Down syndrome have varying needs. Proper management of Down syndrome is vital in ensuring the patient’s life expectancy is prolonged. The patient may, therefore, require services from a cardiologist to check heart defects which are common among Down syndrome patients and a clinical geneticist for counseling. Checking of respiratory infections and the condition of the nervous system is also vital. Frequent visits to a child psychiatrists offer patient and family therapies as well as evaluations on the trend of Down syndrome symptoms. Therapists and language experts and audiologists are also essential in the management of Down syndrome . The three ensure physical development and communication patterns are monitored and development in children with Down syndrome condition (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015).
Some genetic disorders appear immediately – some have an onset later in life – which category does your genetic disorder fall into?
Down syndrome appears in children. Affected children, as well as adults, have distinct facial features. These may include a flattened face, small head, protruding tongue, short neck, small ears, broad and short hands, short fingers, poor muscles tone and excessive flexibility. Affected children and adults are also short in height.
Describe any social issues associated with the testing, transmission or treating of the disorder.
Screening and testing for diagnosis of Down syndrome is usually done during pregnancy. In the U.S, it is offered a routine part of prenatal care. Pregnant women whose age is over 35 years, and the father of the baby is over 40 years are encouraged to get an evaluation. It is worth noting that some women may decide not to go through the various tests to ascertain presence of Down syndrome because of the associated fear of pregnancy loss. Rather, they may decide to just have a baby with Down syndrome. Presently, the lifespan of individuals with Down syndrome has improved has been extended, with the possibility of reaching an average of 50 to 60 years.
References
Asim, A., Kumar, A., Muthuswamy, S., Jain, S., & Agarwal, S. (2015). Down syndrome: an insight of the disease. Journal of Biomedical Science , 22 (1).
Brill, M. T. (2007). Down syndrome . New York: Marshall Cavendish Benchmark.
Bush, D., Galambos, C., Ivy, D. D., Abman, S. H., Wolter-Warmerdam, K., & Hickey, F. (2018). Clinical characteristics and risk factors for developing pulmonary hypertension in children with Down syndrome. The Journal of Pediatrics, 202, 212.
Jensen, K. M., & Davis, M. M. (2012). Health care in adults with Down syndrome: a longitudinal cohort study. Journal of Intellectual Disability Research , 57 (10), 947-958. doi:10.1111/j.1365-2788.2012.01589.x
Kucik, J. E., Shin, M., Siffel, C., Marengo, L., & Correa, A. (2012). Trends in survival among children with Down syndrome in 10 regions of the United States. Pediatrics , 131 (1), e27-e36.
Parker, S. E., Mai, C. T., Canfield, M. A., Rickard, R., Wang, Y., & Meyer, R. E. (2010). Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Research Part A: Clinical and Molecular Teratology , 88 (12), 1008-1016.
