Human Chromosomes and Down Syndrome

All the information about our body’s structure and function is stored inside tiny threads called the DNA within the cells' nuclei. These DNA threads come together to create X or Y-shaped structures called chromosomes. Nature does an amazing job in compressing huge amounts of information inside a tiny space. It wouldn't be an exaggeration to say that nature was ‘zipping’ files before it was cool. Every chromosome contains between 50 to 300 megabytes of data. Only 15 years ago, we needed huge hard disks to carry around this amount. Considering the minuscule size of chromosomes, it is difficult not to be amazed by this.

Cells in the human body contain 23 ‘pairs’ of chromosomes, which makes 46 chromosomes for each cell. The only exceptions to this are sperm and egg cells, the reproductive cells that contain only 23 chromosomes without the pairs. This makes sense since, during fertilization of the egg by the sperm, the chromosomes from the mother and the father unite so that the progeny carries 46 chromosomes in total. If that were not the case, the number of chromosomes in a species would have doubled for every offspring and constantly increased.

If instead of having a pair, there is a third conjugate to a chromosome pair, this situation is called a ‘trisomy.’ In Down syndrome, Chromosome number 21 has three chromosomes instead of two, hence the condition's scientific name: ‘Trisomy 21!’ That is also why March (3rd month of the year) 21st is celebrated as World Down Syndrome Day.

Down syndrome is the most common chromosomal abnormality that is found in the human species. It is estimated that 1 out of every 1000 babies born in the world is born with Down Syndrome. This syndrome is named after John Langdon Down, who defined the condition in the 19th century. Before discovered the genetic basis, the term ‘mongoloid’ was used to refer to the condition but was dropped later because of misleading connotations of the term. The cause of Down Syndrome is yet to be discovered. Although the mechanism of the disease is clear, the factors that play a role mostly stay elusive. One established association is maternal age. The chances of having a baby with Down Syndrome increase with maternal age.

People with this syndrome have some physical characteristics, such as flattened nasal bridge, slanted eyes, smaller than a usual chin, and single palm crease. Also, patients with this condition have some mental and neurological problems. Most of the affected individuals have stunted growth which means that they reach developmental milestones later compared to their peers. Unfortunately, they are also more prone to potentially life-threatening conditions such as leukemia.

Because it is a genetic condition rather than an acquired disease, there is currently no cure for Down syndrome. There are screening tests offered to every pregnant woman to look for signs of Down Syndrome before birth. An increase of some blood molecules may signal that the condition may be present in the fetus. In addition to that, during routine Ultrasonographic examination of the fetus, some findings such as increased fluid in the neck area may alert the clinician or technician. If these screening tests suggest that the condition might be present, a biopsy of the placental membranes or samples taken from the fluid around the fetus might help with the definitive diagnosis.

Individuals with this condition have to face many physical and mental challenges throughout their lives. Perhaps the most difficult part is to deal with the misconceptions in the community regarding this condition. It should be noted that these individuals can have education, join the workforce, and be productive community members. Widespread awareness of these simple facts can benefit them greatly. Increased life expectancy, involvement with the community, and employment rates of people with Down Syndrome in recent years serve as testimonies of this fact. As people are more aware of the situation and more tolerant towards their differences, it is obvious that everyone in society benefits from this.  

Dr. Egehan Salepçi

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