Introduction
Trisomy 21 is a frequently occurring genetic disorder or chromosomal abnormality that may affect people from various populations all over the world. It traditionally depends on inner failures in genetic processes and causes various physical and intellectual disabilities. Trisomy 21 is a common reason for additional diseases such as hematopoietic disorders, heart defects, various types of dementia, mental retardation, and gastrointestinal anomalies. The purpose of this essay is to describe trisomy 21, its clinical presentation, pathophysiology, genetic causes, types of diagnostics, and possible ways of medical treatment.
Pathophysiology, Clinical Presentation, and Social Perception of Trisomy 21
Trisomy 21 is a genetic disorder widely recognized as Down syndrome. Although the condition had been familiar to people from ancient times, it received its name after John Langdon Down in 1866 for his clinical description of the disorder (Kazemi, Salehi, & Kheirollahi, 2016). This condition is frequently regarded as “one of the commonest disorders with huge medical and social cost” (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015, p. 1).
Down syndrome is a chromosomal aberration that is characterized by the presence of three copies of human chromosome 21. The complex phenotype of the disorder results from the substantial dosage imbalance of genes. Down syndrome causes intellectual disability, physical developmental delays, and multiple severe health issues, such as congenital heart defects, Alzheimer’s diseases, various types of cancer, leukemia, and Hirschprung disease (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015). However, in developed countries, social support and recent advancement in medicine and health care delivery have substantially contributed to the increase of the life expectancy for people with Down syndrome.
Concerning the clinical presentation of trisomy 21, it is necessary to notice that there are various specific features that occur in all Down syndrome population, such as craniofacial abnormality, learning, and physical disabilities. Hypotonia at the stage of early infancy is typical for this genetic disorder as well. The phenotypes of Down syndrome are diverse, and some people with this condition are affected by acute megakaryoblastic or lymphoblastic leukemia and atrioventricular septal heart defects (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015).
Moreover, the majority of individuals with Down syndrome possess a variety of distinctive physical characteristics such as a slanted eye, a small chin, and a flat nasal bridge (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015). Poor muscle tone, the palm’s single crease, and a protruding that is caused by large tongue and small mouth, short fingers with the fingerprint’s abnormal pattern, and big toe are typical for trisomy 21 as well. A prevalent number of patients have a certain degree of intellectual disability and cognitive impairment and frequently demonstrate language delays.
The presence of extra chromosome 21 negatively affects basically all organ systems, increases morbidity, both prenatal and postnatal, and encourages the substantive delays in bone development, maturation, and dental eruption. With age, patients have a substantial risk of dementia and Alzheimer’s disease’s development (“Down syndrome and Alzheimer disease,” n.d.). In addition to cardiac defects, abnormal physiologic functioning provided by Down syndrome affects intestinal malabsorption and thyroid metabolism. People with trisomy 21 have a sufficient predisposition to obesity, eating or digestion disorders, increased insulin resistance, and hyperuricemia. A lack of autoimmunity and impaired immune responses lead to frequent acute respiratory infections for Down syndrome patients as well.
It goes without saying that families with children who suffer from Down syndrome experience a higher level of stress and tension in comparison with families who have children without genetic disorders. Societal values and beliefs, the availability of specific resources, and the attitude of the community towards people with disabilities play an immeasurably important role in the families’ experience of living with trisomy 21 (Choi & Van Riper, 2016).
Unfortunately, not all societies, even in developed countries, express their support to patients with Down syndrome. The research, conducted in 2011 in the United Kingdom, focuses on the interviewing of white British, black African, and black British mothers who have children with trisomy 21 (Choi & Van Riper, 2016). Regardless of the variety of cultural backgrounds, all mothers admitted the existence of intolerance and a negative attitude from society towards their children. The similar results of investigations may be observed in Turkey as well, where parents face with negative social responses that cause severe stress (Choi & Van Riper, 2016).
In Korea, there are three different views on genetic disorders. One group of the society believes that Down syndrome and other genetic disorders are the punishment from Gods for sinners, while another group is more reasonable and “endorses the biomedical view of causation” (Choi & Van Riper, 2016, p. 289). In addition, there are community members who see the reason for Down syndrome in inappropriate and incorrect prenatal care.
Genetic Issues of the Disorder
There is no connection between trisomy 21 and lifestyle, diet, drugs, or economic status. Some scientific evidence suggests that Down syndrome may be connected with Alzheimer’s disease in parents or relatives (“Down syndrome and Alzheimer disease,” n.d.). Although trisomy 21 is not determined by the age of a mother, women after 35 years old have a substantial risk of giving birth to children with this genetic disorder (“Down syndrome and Alzheimer disease,” n.d.). The most scientifically acceptable theory of the trisomy 21’s pathogenesis is the gene-dosage hypothesis that traditionally explains the genetic disorder by an extra copy of chromosome 21.
Candidate genes for the Down syndrome’s phenotypes are not clear. However, data received from laboratory transgenic mice suggests the theory that certain genes products are more predisposed to gene dosage imbalance, and only some genes included in chromosome 21 are involved in the disorder’s phenotypes (Kazemi, Salehi, & Kheirollahi, 2016). Potential gene products include cell adhesion molecules, ligands and the ligands’ receptors, morphogens, transcription transporters and regulators, and the multi-subunit proteins’ components (Kazemi, Salehi, & Kheirollahi, 2016). The dosage imbalance of genes within chromosome 21 is responsible for mental retardation, craniofacial abnormalities, the fifth finger’s clinodactyly, congenital heart defects, and other phenotypes.
According to Asim et al. (2015), the most common reasons for Down syndrome are the presence of the additional copy of chromosome 21, Robertsonian translocation, and an isochromosome or ring chromosome. The term of isochromosome is used by scientists to describe “a condition in which two long arms of chromosome separate together rather than the long and short arm separating together during egg sperm development” (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015, p. 1).
Trisomy is derived from the failure of chromosome 21’s separation during sperm or egg development (Antonarakis, 2017). In the case of Robertsonian translocation, the chromosome’s long arm is attached to chromosome 14 or 15. Down syndrome occurs when the translocated chromosome that possesses the chromosome 21’s extra piece “is inherited together with two common copies of chromosome 21” (Kazemi, Salehi, & Kheirollahi, 2016, p. 127). If a couple has one child with Down syndrome that occurred due to translocation, parents have a substantial risk of this genetic disorder in future pregnancies as well as one of the partners may be a balanced translocation carrier.
Another term related to Down syndrome is mosaicism that is characterized by the misdivision at a certain stage of cell division after fertilization. The chromosome 21’s third copy may be present partially and not in all cells. The mixture may be observed in various cells of similar types, and one type of cells may have ordinary chromosomes, while another type will be the carrier of trisomy 21.
Diagnostics and Treatment
Screening for Down syndrome plays a highly essential role in the diagnostics of this genetic disorder. It is an immeasurably essential part of the women’s prenatal care. The most common method of screening includes the measurement of various factors – multiple serum markers and ultrasonography of the pregnancy’s second trimester and the advanced maternal age. The mother’s age may cause substantial risks for the occurring of trisomy 21 and other chromosomal abnormalities in a child. According to currently accepted medical standards, the advanced maternal age was defined “as age 35 years or older at delivery” (Kazemi, Salehi, & Kheirollahi, 2016, p. 128).
In addition, trisomy 21 is characterized by cardiac defects, brachycephaly, mild ventriculomegaly, duodenal atresia, echogenic bowel, nasal hypoplasia, “shortening of the femur and sandal gap and clinodactyly or middle phalanx hypoplasia of the fifth finger” (Kazemi, Salehi, & Kheirollahi, 2016, p. 128). The diagnostics by screening encourages the observation of the fetus’s potential abnormalities to exclude or confirm Down syndrome.
The first marker of screening that is associated with trisomy 21 is the neck area’s thickening. With the use of nuchal translucency, a process that investigates the fetal vascular and lymphatic development in the neck area and head, more than 80% of Down syndrome pregnancies were identified during the first trimester (Kazemi, Salehi, & Kheirollahi, 2016). The second marker of trisomy 21 is pyelectasis that refers to the measuring of the renal pelvis, diameter.
Renal dilatation frequently occurs among the substantial number of fetuses with aneuploidy. Another highly significant marker of screening that identifies Down syndrome is “the absence of nasal bone in fetus at the 11-14 weeks scan” (Kazemi, Salehi, & Kheirollahi, 2016, p. 129). Despite racial peculiarities and differences in the nose’s length, the sonographic marker of a fetal nasal bone is essential in combination with maternal age and other markers.
However, there are other types of diagnostics that include routine karyotyping, rapid aneuploidy testing methods. The cytogenetic analysis of metaphase karyotype may be defined as a common practice that is applied to identify not only Down syndrome but other balanced translocations and aneuploidies (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015).
In recent years, the innovative methods of the trisomy 21’s detection, such as FISH of interphase nuclei and QFPCR were put into practice worldwide (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015). They use the probes of chromosome 21, or its DNA polymorphic markers are used to investigates the presence or absence of three different alleles.
The treatment of patients with Down syndrome substantively depends on the variability of possible effects. It goes without saying that people with trisomy 21 that exists in every cell have all body systems affected in various ways. Nevertheless, not all children with Down syndrome have identical health issues due to this condition. Parents should “be aware of these possible conditions so they can be diagnosed and treated quickly and appropriately” (Asim, Kumar, Muthuswamy, Jain, & Agarwal, 2015, p. 7).
For instance, time-sensitive and appropriate surgical treatment of cardiac issues during the first months after birth helps to prevent further complications. Appropriate weight and the control under the gastrointestinal system may be established by regular exercise and a balanced diet. Regular visits to certain health care specialists maintain an appropriate level of life for patients with Down syndrome as well.
Conclusion
Trisomy 21 is defined as a genetic disorder or a chromosomal aberration that is characterized by the presence of three copies of human chromosome 21. It is widely recognized as Down syndrome and marked by craniofacial abnormalities, intellectual disability, physical developmental delays, and multiple severe health issues, such as dementia, heart defects, and digestion disorders. The most scientifically acceptable theory of the trisomy 21’s pathogenesis is the gene-dosage hypothesis that traditionally explains the genetic disorder by an extra copy of chromosome 21. The advanced maternal age negatively affects the occurrence of Down syndrome, and women after 35 years old have a substantial risk of giving birth to children with this genetic disorder.
Concerning the types of the trisomy 21’s diagnostics, screening, routine karyotyping, and rapid aneuploidy testing methods may be distinguished. Screening for Down syndrome plays a highly essential role in the diagnostics of this genetic disorder. There are several markers that help to define trisomy 21, such as the neck area’s thickening, pyelectasis, and the absence of a nasal bone. The treatment of patients with Down syndrome substantively depends on the variability of possible effects, and the parents should be aware of their children’s peculiarities for the successful prevention of serious complications in the future.
References
Alzheimer’s Association. (n.d.). Down syndrome and Alzheimer disease. Web.
Antonarakis, S. E. (2017). Down syndrome and the complexity of genome dosage imbalance. Nature Reviews Genetics, 18, 147-163.
Asim, A., Kumar, A., Muthuswamy, S., Jain, S., & Agarwal, S. (2015). Down syndrome: An insight of the disease. Journal of the Biomedical Science, 22(41), 1-9. Web.
Choi, H. & Van Riper, M. (2016). Maternal perceptions to open-ended questions about life with Down syndrome in Korea. The Qualitative Report, 21(2), 288-298.
Kazemi, M., Salehi, M., & Kheirollahi, M. (2016). Down syndrome: Current status, challenges and future perspectives. International Journal of Molecular and Cellular Medicine, 5(3), 125-133.