Down Syndrome and Mutations




This picture was taken from the following website:
https://cornellbiochem.wikispaces.com/file/view/
downsyndrome1.jpg/66756907/downsyndrome1.jpg

 
Recently in class, we have been talking about mutations. We were assigned to do a project on a specific disease, and I chose to do mine on Down syndrome. This is an abnormality caused by nondisjunction in fertilization, or the failure of homologous chromosomes to separate as they should during reproduction, resulting in an extra copy of a chromosome. This is a mutation in the sense that, normally, only two chromosomes would develop in a zygote, whereas three chromosomes develop with this syndrome. A picture of a child with Down syndrome is posted above.

One of our class textbooks, "Mutants" by Leroi, describes two noteworthy details about mutations. First, our faces seem to be the most vulnerable body part in displaying mutation's effects (Leroi). This was apparent to me because one of my sources for my project was MedLine Plus, an online journal. On this website, symptoms of Down syndrome are listed, but nearly all of them are facial disfigurements. It describes an abnormally shaped head, a flattened nose, separated brain sutures, small ears, a small mouth and upward slanting eyes (MedLine Plus). Also, it stated that Down syndrome is mainly apparent to doctors at birth because of its distinct physical abnormalities (MedLine Plus). I had noticed this during my project, but as I read from my textbook, it became more apparent to me. So my question is this: why are our faces so vulnerable to mutation? What about our faces makes mutations almost attract the area? Is there a genetic reason for this? Does the environment play a role?

The other detail Leroi suggests in his coverage of mutations is that "more than 70% of spontaneously aborted fetuses bear severe chromosomal abnormalities" (Leroi). Leroi adds, "it is now widely supported that miscarriage is an evolved device that enables mothers to screen for, and rid themselves of, genetically impaired progeny." Also while doing my project, I found that it was very common for mothers to have abortions, or miscarriages, after they got positive results from testing their babies for Down syndrome. If more than half of spontaneous abortions occur because of genetic abnormalities, such as the one that causes Down syndrome, why does it not account for fetuses with this anomaly? This suggests that spontaneous abortion must have sort of a "cut-off point," in which it can no longer occur. If not, at least some of these fetuses would have spontaneously aborted, especially more than enough to allow Down syndrome to be the "most common single cause of human birth defects" (MedLine Plus). This also peaked my interest. We have answers to the more basic questions concerning spontaneous abortion, such as how and why it happens, but we still do not have all the answers. When does it take place during the pregnancy? Does it stop after a certain point? Are there other criteria? Does the mother have to have specific qualities that allow this process to continue in her? Or is it normally built in to every female? Does it stop after the female reaches a certain age?

These questions, along with those above have yet to be answered and are useful for more research in the scientific world.

The book "Mutants" is a scientific book written in 2003 by Armand Marie Leroi as a means of finding a "direct way into the human genome and the human body" through the discovery of mutants. Leroi is an evolutionary developmental biologist, and thus, has ample experience and knowledge to write such a book. It is informative and does not take sides. Rather, it seeks to provide a new way of thinking: all humans are mutants, not merely those with severe physical disfigurements that we may more often assume. This is, therefore, a trustworthy source.

The other source I used is from an online, peer-reviewed, scientific, medical journal, and as such, does not give a specific author's name. The website is the following: http://www.nlm.nih.gov/medlineplus/ency/article/000997.htm and again, the source is informative. It does not take sides, but merely seeks to inform the public, or whoever may read this journal, of the symptoms of this disease. This website is a service of the United States National Library of Medicine, and the National Institutes of Health. Therefore, all the information posted on this site are reviewed by individuals of appropriate authority in terms of knowledge on the subject. This also, therefore, is a trustworthy source.