Chromosomal Abnormalities: Down Syndrome

The human body is made up of trillions of cells. Cells are known as the basic building blocks of life. Every cell has a nucleus that contains genes, which store all of the genetic material (What is Down Syndrome, 2018). Genes are made up of deoxyribonucleic acid (DNA) that is packaged into chromosomes, which are responsible for inherited traits. Humans have 23 pairs of chromosomes, containing one chromosome from dad and one from mom, with a total of 46 altogether. If there is an extra chromosome present or one missing, this chromosomal abnormality is known as aneuploidy.

One of the most common chromosomal abnormalities is trisomy 21, more popularly known as Down Syndrome. An error in cell division, called “nondisjunction” is the typical cause of Down Syndrome. Down Syndrome occurs when there is an extra copy of a partial or full chromosome 21 (What is Down Syndrome, 2018). This means that instead of two chromosome 21’s there are three. The extra chromosome is what leads to all of the developmental and physical traits of Down Syndrome (Down Syndrome, 2018).

Down Syndrome can be categorized into three different types, Trisomy 21, translocation or, mosaicism based on how the extra chromosome presents itself. Usually someone cannot tell the difference between the three because the behaviors, as well as physical traits, are very similar (Facts about Down Syndrome, 2018). One would have to look microscopically at the chromosomal differences to determine which type one would have. The first type of Down Syndrome, accounting for 95% of all cases, is Trisomy 21 (Facts about Down Syndrome, 2018). With Trisomy 21, every cell in the body strictly has three copies of chromosome 21 instead of the typical two copies (Facts about Down Syndrome, 2018). A pair of the chromosome fails to separate in either the sperm or the egg before or during conception. (What is Down Syndrome, 2018). During the development of the embryo the extra chromosome is then replicated in every cell in the body resulting in Trisomy 21 (What is Down Syndrome, 2018). The second type of Down Syndrome is known as Translocation Down Syndrome. This type accounts for a very small population of those with Down Syndrome, presenting in only 3% of cases (Facts about Down Syndrome, 2018). Translocation Down Syndrome occurs when there are three copies of chromosome 21, but the third copy attaches itself to another chromosome, typically chromosome 14, or to other chromosomes such as 13,15 or 22 (Translocation Down Syndrome, 2018). Mosaic Down Syndrome, also known as Mosaicism, is the third type of Down Syndrome and is even more uncommon, accounting for only 2% of cases (Facts about Down Syndrome, 2018). This type occurs when there is a combination of cells, some possess an aneuploidy and some do not. Some of the cells will have three copies of chromosome 21, while other cells only have the normal two copies of chromosome 21 (What is Down Syndrome, 2018). Those individuals with Mosaic Down Syndrome can present with the same features as other individuals with Down syndrome, but may have fewer physical features of the condition because some cells have the normal number of chromosomes (Facts about Down Syndrome, 2018).

All three types of Down Syndrome are genetic conditions relating to the genes, however, only 1% of Down Syndrome cases have a hereditary element (What is Down Syndrome, 2018). Trisomy 21 and Mosaic Down Syndrome are not hereditary, although, in one-third of the cases related to translocation, there is a hereditary factor. Maternal age is not a hereditary risk factor for translocation, these cases are often sporadic and chance events (What is Down Syndrome, 2018).

Although the cause of the extra chromosome in those with Down Syndrome is still unknown, is believed to be passed on from the father or the mother. Approximately 5% of Down syndrome cases have been linked to the extra chromosome coming from the father (What is Down Syndrome, 2018). Down Syndrome can develop in any race, nationality, religion, or socioeconomic class.

Currently, no cure for Down Syndrome exists. Maternal age is the most linked risk factor to the condition. Increased maternal age is a risk factor because older eggs have a greater risk of improper chromosome division, resulting in an extra chromosome 21 (Down Syndrome, 2018). After the age of 35, the odds of having a child with Down Syndrome is 1 in every 350 births (What is Down Syndrome, 2018). After the age of 45, the odds increase considerably to 1 in every 30 births (What is Down Syndrome, 2018). Although, 80% of children born with Down Syndrome are born to mothers under the age of 35 due to higher birth rates in younger women (Facts and FAQ About Down Syndrome, 2018).

Astonishingly the current population of people in the United States with Down Syndrome is currently unknown. According to the Centers for Disease Control (CDC) an estimated number of 1 in ever 691 live births was recorded in 2012 (Facts and FAQ About Down Syndrome, 2018). However, the 2000 US Census estimated the number of individuals with Down Syndrome in the US by taking the 281 million Americans into the frequency of individuals born with Down Syndrome (1 in 691) and estimated the population of individuals with Down Syndrome to be just over 407,000 (Facts and FAQ About Down Syndrome ,2018. Roughly 6,000 babies are born with Down Syndrome in the United States every year (What is Down Syndrome, 2018). Between approximately 1979 and 2003, the number of babies born with Down Syndrome increased by 30% (Data and Statistics, 2017). The current average life expectancy of someone with Down Syndrome is approximately 60 years old. “As recently as 1983, the average lifespan of a person with Down syndrome was 25 years. The dramatic increase to 60 years is largely due to the end of the inhumane practice of institutionalizing people with Down syndrome.”(Facts About Down Syndrome, 2018, p. 3). Today, more and more people with Down Syndrome are living longer, healthier lives because of the advanced healthcare they are receiving.

Since Down Syndrome is considered the most common chromosomal abnormality, and there is no cure, early prenatal screening in high risk pregnancies is crucial in determining if further action is needed by the parents. There are two different types of tests that can be done before the baby is born. One test is the prenatal screen. Prenatal screens can only be used to estimate the chance of the fetus having Down Syndrome (Messerlian, Palomaki, 2018). Prenatal screens do not give you a definitive answer as to if the baby has Down Syndrome or not. Good candidates for prenatal screening would be anyone before 20 weeks’ gestation that have not had prior aneuploidy screenings done. Another type of screening is a diagnostic test which provides a 100% accuracy diagnosis. Good candidates for diagnostic tests are women of any age at high risk for any fetal aneuploidies (Messerlian, et al, 2018). Women who have either had a positive screening test or a previous pregnancy with complications from fetal trisomy, are candidates for diagnostic testing (Messerlian, et al, 2018). There are three very common diagnostic tests used today. “The different types of diagnostic tests include: Chorionic villus sampling (CVS) which examines material from the placenta, an Amniocentesis which examines the amniotic fluid from the sac surrounding the baby and, the Percutaneous umbilical sampling (PUBS) which examines the blood around the umbilical cord” (Facts about Down Syndrome, 2018, p. 3). All of these tests look for changes in the chromosomes that would indicate an abnormality, leading to the diagnosis of Down Syndrome. When counseling patients about the prenatal screening or diagnostic test, it is important to provide straightforward and complete information (Messerlian, et al, 2018). The information given is what will help them to make informed and individualized decisions on how they go about prenatal screening and diagnostic testing (Messerlian, et al, 2018).

All testing is voluntary and should be made clear from the very beginning. The patients should be made aware of the estimated risk of Down Syndrome based on the screening tests results and it should be discussed thoroughly. Referral to a genetic counselor or a medical geneticist can also be beneficial to the parents. These professionals can facilitate more knowledge to help with decision making when it comes to the different tests that are offered. If the patient decides to undergo a diagnostic test and the results come back positive, The National Society of Genetic Counselors have published a list of guidelines recommended for communication of prenatal diagnosis of Down Syndrome to the parents (Messerlian, et al, 2018). “The following is a synopsis of their recommendations: inform parents as soon as possible, ideally the diagnosis should be delivered in person to both parents by a healthcare professional with sufficient knowledge on the condition, provide up-to-date accurate verbal and written information with a balanced perspective and be tailored to the patients knowledge base and emotional needs, provide informational resources including national and local support groups and local medical and educational resources, when appropriate provide referrals to other specialists such as medical geneticists, genetic counselors, cardiologists, neonatologists or pediatric surgeons, discuss pregnancy outcomes such as the increased risk of miscarriage and stillbirth, couples with an affected pregnancy have several options such as continuing the pregnancy, pregnancy termination or giving the child up for adoption” (Messerlian, et al, 2018, p. 7). Depending on how effective the communication and education is will better determine the parents likeliness of seeking additional resources and testing.

The diagnostic testing can predetermine the medical care that the parents will need to seek if the results come back that the child will have Down Syndrome. Once the diagnosis is confirmed, the parents or guardians will then be educated on the complications that can develop over the lifespan. Education is a crucial nursing intervention for parents across the lifespan of the child with Down Syndrome and it starts before birth. Once they are born, patients with Down Syndrome should be monitored for disturbances in growth associated with other disorders and complications such as hypothyroidism, celiac disease, and/or excessive weight gain (Ostermaier, 2018). Those with Down Syndrome will have the typical physical features but not all will have the birth defects or complications that can co-occur with the condition. The physical features that frequently present in a person who has Down Syndrome are flat occiput and flattened facial appearance, small bradycephalic head, epicanthal folds, flat nasal bridge, upward-slanting palpebral fissures, brushfield spots, protruding tongue, small and dysplastic ears and generous nuchal skin. Parents should be educated on the differences in these physical features and the affect they can have on their child. Parents should also be given visual representations of the physical features so they will be familiar with the physical differences. Education then needs to be given on the disease processes that can co-occur as a dual diagnosis with Down Syndrome. The disease processes that can co-occur include: cardiac disease, hearing loss, ophthalmologic disorders, changes in thyroid function, celiac disease, hematology disorders, periodontal disease, sleep apnea, fertility and reproduction, Alzheimer disease and, atlantoaxial instability. Any of these disease processes can have life threatening effects on someone with Down Syndrome if they go untreated. Newborn screenings as well as yearly evaluations are crucial in detecting any co-morbidities, and treatment should be started right away.

Treatment is based on the comorbidities because there is no cure for Down Syndrome in itself. Awareness and education about the disease processes that can co-occur with Down Syndrome are crucial nursing interventions when starting a treatment regimen. While there is no cure, healthcare professionals focus on the pharmacologic treatments based off of their co-morbidities. An important nursing intervention is understanding what the medications are used for and being aware of any interactions possible during pharmacologic treatment overlap. Another important nursing intervention is being able to explain the medications to the patient and any possible side effects or adverse effects to look for. While there is only pharmacologic treatment for the comorbidities associated with Down Syndrome, advancing research is finding pharmacologic treatment to focus on the intellectual disabilities common in Down Syndrome as well. According to the article, Down Syndrome: Management, “The development of Down Syndrome (DS) mouse models has provided an opportunity to study emerging pharmacotherapies that target intellectual disabilities common in DS. The overexpression of many genes found on chromosome 21 contributes to learning deficits. Research has focused on hippocampus function related to memory and learning. Areas of interest include specific gamma-aminobutyric acid (GABBA) receptor inhibitors, N-methyl-D-aspartic (NMDA) receptor antagonist and hippocampal dentate gyrus neurogenesis. Preliminary basic science research shows medications such as pentylenetetrazol (PTZ), memantine, and fluoxetine may enhance learning in the DS mouse model. Further studies and clinical trials are needed to show efficacy and safety of these medications in children with DS.”(Ostermaiser, 2018, p. 5). Overall, the most important nursing intervention for pharmacologic therapies for patients with Down Syndrome is education on the medications used for treatment. Since there is not yet a cure to treat Down Syndrome, treatment of the related comorbidities is the main focus of pharmacologic therapy.

Nonpharmacologic therapy is another treatment that can be utilized by the family as well as the patient with Down Syndrome. Part of the education given as a nursing intervention are the different resources available. Resources such as local and national support or education groups can be very helpful for the family. Along with resources for educational or support purposes, counseling is also available. Nurses as well as healthcare providers can recommend counselors in the field to the families for emotional support. The most important nursing intervention is providing emotional support and motivation to the family and the patient. The families and the patient will need support and guidance from the time the child is born. The overall goal is for the families and patients to feel as if they have the proper resources, education and support behind them at all times.

Managing Down Syndrome is an ongoing process. Undergoing evaluations from healthcare professionals continue to happen across the lifespan for patients. Monitoring current co-morbidities and preventing common illnesses is a part of the lifestyle of someone with Down Syndrome. Since there is no cure for Down Syndrome, managing the underlying disease processes is the main focus of treatment. Providing individuals and their families with the proper resources needed to achieve the optimal level of independence is the overall goal.

References

  1. Data and Statistics. (2017). Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov
  2. Down Syndrome. (2018). Mayo Clinic. Retrieved from http ://www.mayoclinic.org
  3. Facts about Down Syndrome. (2018). Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov
  4. Facts and FAQ About Down Syndrome. (2018). Global Down Syndrome Foundation. Retrieved from http://www.globaldownsyndorme.org
  5. Messerlian, G. M., Palomaki, G. E. (2018). Down Syndrome: Overview of prenatal screening. UptoDate. Retrieved from http://www.uptodate.com
  6. Ostermairer, K. K. (2018). Down Syndrome: Management. UptoDate. Retrieved from http://www.uptodate.com
  7. Translocation Down Syndrome. (2018). Children’s Hospital of Philadelphia. Retrieved from http://www.chop.edu
  8. What is Down Syndrome. (2018). National Down Syndrome Society. Retrieved from http://www.ndss.org
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