Writer: Sabrina Samidon
Introduction
Down syndrome, referred to in medical terms as trisomy 21, is a genetic disorder that results from an extra copy of chromosome 21. This chromosomal dysfunction leads to a wide array of physical and intellectual disabilities and increases the chances of developing certain health conditions. Examining the role of trisomy 21 in causing Down syndrome is crucial to break down its manifestations, potential interventions, and the ongoing research aimed at improving the quality of life for those affected.
Genetic Base of Trisomy 21
To begin with, typical human development involves individuals inheriting 23 pairs of chromosomes, half from each parent, which total to 46. Down syndrome occurs when there is a full or partially extra copy of chromosome 21. As a result, there are three copies produced instead of the usual two. This condition is defined as trisomy 21. Consequently, extra genetic material disrupts the normal development process, leading to certain physical features and health issues associated with Down syndrome.
The majority of Down syndrome cases (approximately 95%) are caused by complete trisomy 21. This means that every cell in the body contains the extra chromosome. The cause of this is from nondisjunction, where an error in cell division during the formation of egg or sperm leads to an embryo with three copies of chromosome 21. Other cases of Down syndrome may occur from a Robertsonian translocation or mosaicism. [1][4]
Impact of Trisomy 21 on Development
Furthermore, the extra genetic material from the additional chromosome 21 affects various bodily systems. This ultimately leads to a range of developmental and health challenges. First, individuals with down syndrome commonly have physical features such as a flattened facial profile, upward slanting eyes, a single deep crease across the palm, and reduced muscle tone. Mentally, Down syndrome also brings out mild to moderate intellectual disability, with delays in speech and motor skills.
Next, trisomy 21 increases the risk of several medical conditions. Congenital heart defects occur in nearly half of all infants with Down syndrome. This calls for immediate medical intervention from an early age. Furthermore, gastrointestinal anomalies, such as duodenal atresia and Hirschsprung disease, may also be more prevalent. Endocrine disorders, including hypothyroidism, spark as a regular occurrence. Finally, respiratory infections, leukemia, and early-onset Alzheimer’s disease may come into effect. [2][3]
Recent Research Advancements
In regards to scientific exploration, research into the mechanisms of trisomy 21 has been ongoing. Recently, studies focusing on potential therapeutic interventions have brought out astonishing breakthroughs. One example of this is the application of gene-editing technologies, such as CRISPR-Cas9, to target and remove the extra chromosome in affected cells. This was tested by researchers in PNAS Nexus. These researchers were able to utilize this technology to successfully eliminate the extra chromosome 21 in cultured cells. Though these initial findings may be basic, their early results pave the way for future research that may lead to advanced therapeutic strategies to combat the effects of trisomy 21. [3][4]
Conclusion
In conclusion, Trisomy 21 plays a central role in the production of Down syndrome, which results in a range of physical and cognitive traits and prompts research for advancements in genetic research that offer promising insights into potential therapies. As research progresses, it remains crucial to balance the pursuit of medical breakthroughs with high regard for the dignity and individuality of those with Down syndrome.
Sources & Works Cited:
[1] “Down Syndrome (Trisomy 21)”, February 2024, Merck Manual: https://www.merckmanuals.com/home/children-s-health-issues/chromosome-and-gene
[2] “The Causes of Down Syndrome”, August 1987, Scientific American: https://www.jstor.org/stable/24979443
[3] “Trisomy 21 and the Brain”, 1 July 2004, Journal of Neuropathology and Experimental Neurology: https://academic.oup.com/jnen/article-abstract/63/7/679/2916484
[4] “Trisomic rescue via allele-specific multiple chromosome cleavage using CRISPR-Cas9 in trisomy 21 cells”, 18 February 2025, PNAS Nexus: https://academic.oup.com/pnasnexus/article/4/2/pgaf022/8016019?utm_source=chatgpt.com
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