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How is Down Syndrome Inherited?

Posted Mar 14 2013 2:07pm

how is down syndrome inheritedDo you often wonder how is down syndrome inherited Well, this disease really has nothing to do with certain foods or drinks consumed during pregnancy, as perceived by many. This is more of a genetic disease. Each human cell contains 23 pairs of chromosomes, one coming from father and the other from the mother, for each pair. In case of abnormal cell division for the 21st chromosome, the newborn gets affected by down syndrome. In general, down syndrome is inherited by three genetic variations and here are all of the three explained:

How is Down Syndrome Inherited?

In most of the cases, it is not. Only, translocated down syndrome can be passed to the kid from his parent. If the father is the carrier, chances are 3% that the kid may have down syndrome. The same risk increases to 10%-15% if, the mother is the carrier.

Trisomy 21

The term “Trisomy” actually originated from a Greek word which means the “Third Copy.” Trisomy 21 is the most common cause of down syndrome, in fact 90% of the time; this has been identified to be the main reason of a newborn having down syndrome. A child has 3 copies of Chromosome 21, instead of the regular 2, in case he has trisomy 21. During the development of sperm cell, in case, if cells are divided abnormally, trisomy 21 may appear in the newborn.

Mosaic Down syndrome

This is one of the rarest causes of down syndrome. This is caused by abnormal human cell division after the fertilization process is complete. A child in this case, has some cells with the extra copy of Chromosome 21.

Translocation Down syndrome


This genetic disorder may happen before or after the conception happens. In this case, a part of the 21st chromosome gets attached to another chromosome. This is rare and if this happens, the kid does not have an extra copy of 21st Chromosome, unlike other causes of down syndrome. However, the translocated chromosome has some part of the 21st Chromosome attached with it. Only 4% of the total cases of down syndrome are known to be caused by translocation of Chromosome 21.

Risk factors

There are certain risk factors which are regarded as possible causes of down syndrome and here are those explained:


Environmental Factors:

  • Using oral contraception
  • Exposure to any sort of radiation or pesticides during pregnancy
  • Smoking during pregnancy (This is not scientifically proven and these days many scientists are against this concept; that being said, smoking during pregnancy can still have detrimental effects on the new born)
  • Living near the waste incinerators or landfill sites
  • Exposure to virus or any other infectious agents during the time of pregnancy

There is no hard evidence or proven facts about down syndrome that support the aforementioned suggestions. That being said, researches are being conducted all over the world to understand what role these environmental factors may have on down syndrome (If any).

Maternal Age:

This is clearly a risk factor in case of down syndrome. Higher the age of the mother is, higher are the chances of she giving birth to a kid having down syndrome. The risk of the kid having down syndrome actually increases to around 3.5% in case the maternal age is above 45. The same however is less than 0.65% in case the mother is less than 30 years old.

Though it is a fact that no treatment for down syndrome can completely cure this disease, if a person with down syndrome can be taught basic self-help skills, he will surely live a better life.

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