Down syndrome: better understanding this genetic disorder

Published on 21/03/2019

Down syndrome_ better understanding this genetic_

What is Down syndrome?

Within each human cell is a nucleus that contains the genetic material. Genes pass on the codes for almost all traits inherited either from the mother’s side or the father’s side, and even from the forefathers. In addition to carrying the codes for these inherited traits, genes also cluster together to form a rod-like structure called chromosomes. A typical nucleus consists of a total of 23 pairs of chromosomes that are also inherited half from the father and half from the mother. However, it is possible for a person to have a complete or partial supernumerary copy of chromosome 21.
This extra genetic material is proving to be detrimental to the health of this individual, as it alters development, resulting in various characteristics considered to be associated with Down syndrome. Some of the most common physical characteristics related to this syndrome include short stature, low muscle tone, a single deep crease in the center of the palm, an upward tilt of the eyes, and many other characteristics. Clearly, all people with Down syndrome are considered unique, as they may exhibit these characteristics to varying degrees.
According to statistics from the U.S. Centers for Disease Control and Prevention, Down syndrome affects about 1 in 700 American babies. Thus, Down syndrome is the most common disease associated with chromosomal problems. In addition, the committee also confirms that some 6,000 babies are born each year in the United States with Down syndrome.

When was Down syndrome discovered?

For centuries, people with Down syndrome have been alluded to in the arts, literature and science. However, it was not until the end of the 19th century that John Langdon Down, an English physician, published an accurate description of a person with Down syndrome. It was this scholarly work, published in 1866, that earned John Langdon Down recognition as the “father” of Down syndrome. Although other scientists had already recognized the characteristics of the syndrome, it was Dr. Down who described this anomaly as a distinct and separate entity.
In recent years, scientific advances, particularly in medicine, have allowed researchers to study the characteristics of people with Down syndrome traits. In 1959, a French doctor, Jérôme Lejeune, identified Down syndrome as a disorder primarily affecting the chromosomes. Instead of the 46 normal chromosomes expected in each cell, Jérôme Lejeune found that people with Down syndrome actually had 47 chromosomes. Subsequently, it was discovered that a partial or complete supernumerary copy of chromosome 21 could cause the characteristics associated with Down syndrome. In addition, several researchers have also been able to identify and catalog an approximate number of 329 genes that are believed to be located on chromosome 21. All of these discoveries have led to great progress in Down syndrome research.

The different types of Down syndrome

There are 3 main types of Down syndrome: trisomy 21, translocation, and mosaicism.
Trisomy 21 : These are the most common types of Down syndrome. Trisomy 21 occurs whenever more than two chromosomes 21 are present in each cell of the body. Thus, a person with Down syndrome has 47 chromosomes instead of 46, as is normally the case. This extra genetic material is responsible for altering the developmental course of that person, resulting in the characteristics associated with Down syndrome. Interestingly, Trisomy 21 accounts for about 95% of the cases of people with Down syndrome.
Translocation : Translocation accounts for about 4% of the cases of people with Down syndrome. Translocation is the result of a segment of chromosome 21 that breaks off during cell division in the body and attaches to another non-homologous chromosome. Chromosome 14 is a typical example. While a normal human being has 46 chromosomes, the presence of an extra chromosome 21 results in the characteristics associated with Down syndrome.
Mosaicism : This occurs when there is non-disjunction of chromosome 21 in one of the initial cell divisions, especially after fertilization in women. Whenever this happens, it results in a mixture of two different types of cells; some cells contain 47 chromosomes, and others consist of 46 chromosomes. Mosaicism accounts for approximately 1% of each case of Down syndrome.

What is the impact of Down syndrome on society?

Recently, people with Down syndrome are rapidly strengthening the bonds of integration within communities and organizations in society such as the workforce, schools, health care systems, social and recreational activities, etc. People with Down syndrome will obviously have varying degrees of cognitive delays, ranging from mild to severe.
Due to the rapid development of medical technology, people with Down syndrome are living longer than ever before. In 1910, children born with Down syndrome would probably only reach the age of nine. Subsequently, the discovery of various antibiotics made it possible to extend the life expectancy of children with Down syndrome somewhat, who could expect to live to 19 or even 20 years of age. However, recent medical advances through advanced clinical care, including corrective cardiac procedures, have further increased the average life expectancy of adults with this syndrome to 60 years. Perhaps interestingly, more and more Americans are developing a harmonious relationship with people with Down syndrome, while using this medium to increase public awareness and acceptance.

What is World Down Syndrome Day?

World Down Syndrome or Down Syndrome Day is celebrated on March 21 each year. On this day, people with Down syndrome and those who live and work with them around the world organize and participate in activities and events to raise awareness and create a single global voice for the rights, inclusion and well-being of people with Down syndrome.
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