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What Causes Down Syndrome?

Last updated date: 16th May 2024
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Define Down Syndrome

Down syndrome disease is a disorder arising because of genetic abnormality and it leads to physical as well as mental disabilities of various kinds. Down syndrome occurs due to the presence of an extra chromosome, chromosome 21. This condition is also known as trisomy of chromosome 21. Down syndrome disease is one of the leading cases of genetic disorder worldwide. It is also a very prominent and very well-known disease. 

Named after the physician Langdon Down, who first observed this disease, down syndrome disease affects not only physical characteristics but mental characteristics as well. Mental retardness is one of the effects of the disease. Along with all these they are also susceptible to other disease conditions like leukaemia (a form of blood cancer) and Alzheimer’s. Unfortunately, there is no cure for down syndrome disease. But the quality of life can be made better by taking extra care and providing training to the individuals to perform better in daily essentials. Noteworthy is that down syndrome can be diagnosed during early screens in pregnancy stages and this can be helpful in decreasing the occurrence of disease. 

Reasons for Down Syndrome

From the above information, it is clear that to define down syndrome the abnormality of the genetic disorder has to be mentioned. So, when asked, is down syndrome genetic, the answer is yes since the disease is caused by the presence of an extra copy of chromosome 21. Thus, it is a chromosomal disorder.

When asked what causes down syndrome one of the most simple reasons for down syndrome is the chromosomal disorder due to the aneuploidy of the autosome. The rate at which the disease is prevalent is 1 in 1800 live births. It is found to be more occurring in cases when the age of the mother has exceeded 35. 

Down syndrome disease is caused due to abnormal cell division. Usually, during the mitotic and meiotic cell division, there is a duplication of the chromosomes and the chromosome pairs are separated so that each daughter cell can get a copy of each chromosome. Sometimes, when they are not able to separate properly, this gives rise to unequal distribution of the chromosomes in each daughter cell. This condition known as nondisjunction gives rise to down syndrome disease. The nondisjunction occurs during the anaphase before all of the replicated chromosomes’ centre points or kinetochores, which are attached to the microtubules originating from opposite ends of the cells, are segregated. Due to this condition, abnormal numbers of chromosomes appear in the daughter cells with one cell receiving one chromosome 21 while the other receiving three chromosomes 21. 

Many times there is the translocation of a part of chromosome 21 to another part of another chromosome. This also leads to down syndrome as even though the number of chromosomes is normal, there is an extra portion of chromosome 21 present in the cells. 

Thus, the down syndrome disease can be characterized not by the absence of any genetic information but the presence of an abnormally extra genetic material from chromosome 21. This causes abnormalities in the physical and mental development of the person. The diagram of the genetic abnormalities of the down syndrome disease is given below:

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As it is clear that down syndrome is genetic, it is also non-inheritable in most cases. In cases where the abnormality is caused due to a problem in genetic translocation rather than an entirely new chromosome being present, down syndrome is inheritable. In such cases, the signs and symptoms of down syndrome may be absent in the parent but can be passed on to the child. The child can go on to live for another 60 years. But this also depends on the number of other health complications present. 

Types of Down Syndrome

Down syndrome disease can be classified into three types. All the three types explained above as part of the theory are distinctly given below in points:

  1. Trisomy of Chromosome 21: 

This is the general case when there is an extra copy of chromosome 21 present in the cells. This makes the total number of chromosomes from 46, the normal case, to 47, the abnormal one. This as explained earlier happens because of the nondisjunction of chromosome 21 during the anaphase segregation of chromosomes. Because of this down syndrome is also known as Trisomy or Trisomy 21. 

  1. Mosaicism: 

This accounts for one percent of the total cases of down syndrome disease. Usually, this case arises when the nondisjunction's happen during the mitotic division of the zygote into blastomeres. It causes some cells to have a normal number of chromosome 21 while some cells have an abnormal number of chromosome 21.

  1. Translocation Down Syndrome: 

As said, this condition arises when a part of chromosome 21 is translocated to another chromosome (usually chromosome 14). It does not end in an extra chromosome 21 copy but some part of the long arm of chromosome 21 as part of chromosome 14. Nevertheless, it can cause down syndrome disease when expressed in a dominant form. The translocation of the down syndrome doesn't have any correlation with the mother’s age. 

Signs and Symptoms of Down Syndrome

There are various physical and mental abnormalities in a person suffering from down syndrome. One example is those that have poor immunity and hence are subjected to many diseases. Their development takes place at an age later than normal. Many of the patients are born with congenital heart defects, thyroid disease, sleep arena, and gastrointestinal defects. They are also susceptible to diseases like leukaemia and Alzheimer’s more than normal people. 

The physical and facial features are the easiest signs of down syndrome. After the child is born, the signs and symptoms of down syndrome start appearing. At first, the infants may be of normal size but when they grow slowly, their height grows much less than those of the same age. The prominent signs and symptoms of down syndrome are:

  • Short height and undersized growth

  • Slanty eyes and folding in the skin above the eye

  • Flattened nose and furrowed tongue

  • Mental retardation

  • Heart deformities

  • Broad and short hand

  • Poor toning of the muscle with excessive flexibility

  • Short neck, small head and abnormal teeth

  • Longer time in developing linguistic abilities

  • Mild or moderate cognitive impairment

FAQs on What Causes Down Syndrome?

1. Can Down Syndrome be Cured?

Ans: There is no cure for down syndrome disease. Although, the quality of life of the patient can be improved by the practice of daily essential skills such as speech, educational and physical attributes.

2. How is Down Syndrome inherited?

Ans: Generally, Down Syndrome is not inheritable. Down syndrome occurs when there is an entire extra copy of chromosome 21, or a part of it present in all the cells, or some cells. These incidents occur as random events during the formation of the reproductive cells.