Down Syndrome: What It Is, What Causes It, And Associated Problems
Human beings are our genes, both at the individual and species level. It is estimated that the human genome contains about 25,000 different genes with 3.2 billion base pairs of DNA. As astronomical as this figure may seem, the reality is far from it: only 1.5% of all our genetic information is made up of exons that code for specific proteins.
70% of human DNA is extragenic and the remaining almost 30% is part of sequences related to genes. Of all this extragenic DNA (formerly known as junk DNA), seven out of 10 sections correspond to dispersed repeats, so about half of our genome is composed of repeated nucleotides without functionality (or whose functionality has not yet been elucidated). .
Within this vast genetic conglomerate, it is expected that mutations will occur from time to time. Some are heritable, others appear de novo throughout the life of the individual and others are manifested through epigenetic mechanisms, that is, by the regulation of gene expression through certain mechanisms influenced by the environment. Today we come to bring you all the information you should know about Down syndrome, one of the most widespread genetic conditions in the world. Do not miss it.
First of all, it is necessary to lay certain foundations that will govern the rest of the article. As indicated by the Spanish Down Syndrome Federation (Down España) This condition should not be considered, at least on a social level, as a disease This is one of the first steps necessary to end the stigma that has discriminated against non-neurotypical people for centuries.
According to the World Health Organization (WHO), pathology is the alteration or deviation of the physiological state in one or several parts of the body, manifested with characteristic symptoms and with a more or less predictable evolution. A person with Down syndrome does not have to be sick, despite having a lower content of brain neurons and synapses between them. It is possible to be healthy even with this condition, and the fact that people with it live 60 years on average supports this.
So that, Doctors do not “treat” Down syndrome, but rather address the possible pathologies that a person with this genetic condition may develop, such as heart disease, celiac disease, sensory deficits, hypothyroidism and others. Thus, we conclude this initial section by saying that we are not dealing with a disease, but rather a condition, or what is the same, one more variant within the possible normality.
Its causes and genetic bases
Beyond social terminology, Down syndrome is a really interesting event from a genetic perspective. We begin by pointing out that human beings are diploid (2n), that is, we have two sets of the same chromosome, one inherited from the father and the other from the mother. The diploidy that characterizes each and every one of our somatic (body) cells means that we have 23 pairs of chromosomes within each nucleus which makes a total of 46.
Within these 23 pairs, it should be noted that 22 of them are autosomal and one is sexual. This concept will sound familiar to you, since biology lessons emphasize that the last two chromosomes are those that represent our biological gender: XX corresponds to females and XY to males. The rest of the chromosomes are listed based on their size and shape, with chromosome 1 being the largest of all (with 245,522,847 base pairs, 28% of the DNA) and 21 the smallest (47,000,000 base pairs). of bases, with only 1.5% of human DNA).
When gametogenesis occurs, germ cells divide by meiosis instead of mitosis, giving rise to eggs and sperm with half the genetic information than the rest of the cells. These are considered haploid (n), and this should be the case for the following reason:
Meiosis is essential in sexual reproduction, because without it, each time the zygote resulting from fertilization would have more and more chromosome pairs (4n, 8n, etc.). More simply put, if gametes “split” their genetic information in half, they form a complete cell when they join together. Thus, the fetus recovers the diploidy that will determine each of its non-sexual cells for the rest of its life.
The problem is that, sometimes, this “partitioning” of the genome during meiosis is not done very well. Thus, Monosomies (lack of a chromosome), trisomies (an extra whole or partial copy of a chromosome in a pair) or even tetrasomy may eventually arise the presence of four copies of a chromosome where there should be only two.
Down syndrome is considered a trisomy 21, or in other words, within the pair of chromosomes 21 (one male and one female) there is one more copy than there should be, making a total of three. It is not the only trisomy that can occur, since for example there are also trisomy 13 and 18, although these conditions are much more associated with abortions and death of the newborn (almost 70% of abortions present alterations in the number of chromosomes).
Why does Down syndrome occur?
At this point, we have already learned that Down syndrome is a trisomy 21, that is, chromosome 21 has one more copy than necessary (2+1). In 90% of cases, this condition arises sporadically, as an unprecedented error occurs in meiotic division: When an egg or sperm is forming, sometimes instead of chromosome 21, the entire pair inherits it. Then, when joined with their other gamete, they give a total of 3 chromosomes 21 (2+1), making a total of 47 chromosomes instead of 46.
In a very small percentage of cases, translocations occur, events that receive the common name of “familial Down syndrome.” We are not going to go into their particularities due to the genetic complexity they report, but it is enough for us to know that there are some accessory mechanisms beyond the common error during gametogenesis.
The future of people with Down syndrome
People with Down syndrome are more present in society than it seems, because This genetic condition occurs in up to one in every 700-1,000 live births and around 8 million people around the globe live with it. The average life expectancy is 60 years (while a few decades ago this figure was less than 10 years), so the number of people with trisomy 21 is expected to increase in the world.
Unfortunately, professional medical sources show a very different paradigm when we talk on a case-by-case basis. According to the study The Efficiency of Motor Activities Programs in Fighting the Social Exclusion of Children and Young People with Down Syndromeinfants with Down syndrome are often classified in classrooms as “disabled” and, therefore, their inclusion in social activities is prevented and they tend to be marginalized.
The employment situation is not much more favorable, since Down España tells us that Almost 95% of people with this genetic condition of legal age are unemployed in this country. Curiously, the majority of contracts made to these people in large companies end with their inclusion in the workforce indefinitely: like all human beings, they are capable of showing methodicality, rigor and commitment.
A final thought
As interesting as it is to dissect the genetics of syndromes, we must not forget that we are talking about people at all times. Therefore, we urge readers to look inside themselves and ask what normality is. In a world where biological gender does not determine identity, where the life expectancy of people with genetic conditions is increasingly higher, and where expression is valued above all, We increasingly realize that the “norm” does not exist
Therefore, something that deviates from the midline should not be considered a pathology, whether the underlying condition is genetic, emotional, physical, or whether or not it is shown externally. As long as it does not imply death and/or illness per se, every condition that defines the individual must be considered as one more variant than expected in the enormous spectrum that we human beings are. Only in this way will we let the rest live without preconceptions and prejudices.
