What causes Down syndrome?
Try to ignore generalisation as, for examples, children with Down syndrome are gentle and like music. This is certainly not true for all children having this syndrome. People with Down syndrome are very different in their outward appearance, their temperament and their abilities: each of them is an individual.
A syndrome is, generally speaking, a set of symptoms which together indicate a certain disease or abnormal condition. A congenital syndrome as the Down syndrome already exists when the child is born. There care thousands of different commonly named after the person who discovered and described it first. So the Down syndrome was named after Dr. J. L. Down.
Early illustrations of people with Down syndrome ca already be found on an altar form 1505. But until 1866 it does not seem to be recognized as a syndrome with its own individual symptoms. The first person who defined and described the characteristic symptoms was the English physician John Langdon Down (1828-1896), but the did not know how they were caused. Only in 1959 Lejeune and his team in Paris showed that people with Down syndrome have an additional chromosome.
Formerly, people with Down syndrome were called "Mongols", an expression no longer in use and replaced by the name "Down syndrome". So, when you speak of your child, rather say "it has as Down syndrome" or even better "it is a child with Down syndrome. Avoid the term "Down syndrome-child".
First of all it is a child and having Down syndrome comes second.
On average one out of approximately 700 babies has Down syndrome. The older the parents the greater is the risk to have such a child.
After the birth of a baby a doctor can find out if the child has Down syndrome by the following characteristics:
- face: a child with down syndrome usually has a round face an is rather flat in profile
- head: the back of the head is slightly flattened
- eyes: the curve of the eyes of almost all children is pointed upwards. Often a small skin fold runs between the corner of the eye and the nose. The eyes can have white or light yellow spots on the edge of the iris.
- hair: general the hair is soft and sleek
- Neck: new-born babies often have additional skin folds in their necks which usually go away when the child grows
- mouth: the oral cavity is small than average, the tongue slightly bigger. Because of this and less tonus in the muscels some children put out their tongues sometimes.
- hands: the hands are often broad and the fingers short. Many people with Down syndrome have a four-finger hand-line, e. g. a line rung all across the palm
- feet: the feet are often compact and have a rather wide gap between the first and second toe.
- musceltonus: the limbs and necks of small children are often limp. This muscular weakness is called "hypotonic"
- measures: the birth weight and length is often less than average. The find height is mostly below the family average
The human body consists of tiny cells. In every cell, there is the genetic material that all human beings inherit from their parents. Every one of these cells has a nucleus consisting of about 100,000 genes. Every single gene is responsible for the synthesis of a certain protein, and this way it determines one characteristic of the body.
In an adult, only ten per cent of these genes are working at any particular time. But while the fetus (the unborn child) is developing in the uterus, almost half of the genes in all nuclei are active at the same time in order to control the cell functions during this important period of development. That’s why changes in the genetic material often result in the unborn child’s abnormal development.
The genes aren’t lying around individually in the nucleus; but are lined up (like beads on a necklace) on strings called chromosomes. Each human cell has 46 chromosomes, which make up 23 pairs of chromosomes. One chromosome of any given pair comes from the mother the second from the father. Every time a body cell divides, the newly produced cells receive the complete set of 46 chromosomes.
The only human cells that differ from this model are sex cells (egg and sperm): They include only 23 chromosomes, which means only half as many as body cells. During insemination an egg and a sperm cell unite to one single cell. This newly produced cell (the zygote) again has 46 chromosomes (23+23 = 46).
The Genetic Changes Resulting in Down Syndrome:
Down Syndrome is caused by an additional chromosome. The cells of people with Down Syndrome include three chromosomes #21 instead of two. Since all three genes lying on chromosome 21 cause the cell to produce the same kinds of protein, certain kinds of protein are produced abundantly. While the fetus with Down Syndrome is developing, its body cells don’t reproduce as fast as usual. That’s why these babies are smaller than average after birth and their brain is not as big as the brain of other newborn children. If a baby’s brain doesn’t develop properly before birth, the child will learn more slowly than others his or her whole lifetime. Having happened before birth, these changes cannot be reversed or made up. The additional chromosome reduces the survival chance of the fetus; the reason why many pregnancies end with a premature birth.
All children with Down Syndrome possess the chromosome 21 three times. However, there are three different types of Down Syndrome:
- 1. free trisomy (frequency 95 per cent), there is another whole chromosome 21 in addition to the usual pair
- 2. translocation trisomy (frequency 4 per cent), part of another chromosome 21 exists in addition to the usual pair
- 3. mosaic trisomy 21 (frequency 1 per cent), the additional chromosome 21 with the genes responsible for Down Syndrome doesn’t exist in all of a person’s cells.
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page was last updated on 05/11/2016