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November 14, 2011
Down syndrome is the most common cause of mental retardation
Down syndrome is the most common cause of mental retardation. It is caused by the presence of an extra chromosome. Chromosomes contain sequences of DNA called genes that represent the genetic information that exists within a cell. Twenty-three distinctive pairs of chromosomes which is 46 in total. They are located within the nucleus (a region of the cell that is bounded by a specialized membrane, and which houses the genetic material). When a sperm cell fertilizes an egg cell, the newly created zygote normally receives 23 chromosomes from each parent. The contribution of genetic information from each parent is what makes each baby a distinctive blend of both characteristics. In Down syndrome a mistake during division of the sperm or egg cell produces a cell with an extra chromosome 21. This event occurs during cell division and is referred to as nondisjunction, or the failure of all chromosomes to separately properly resulting in retention of one of the chromosomes in one of the two new daughter cells. This is also called trisomy 21 and is accounted for 95% of all Down syndrome patients. A rare number of Down syndrome cases the original egg and sperm cells begins with the correct number of chromosomes but shortly after fertilization during the phase where cells are dividing rapidly a single cell can divide abnormally creating a line of cells with an extra chromosome 21.It’s called a cell line mosaicism. The individual with this type of down syndrome has two types of cells: some 46 chromosomes which is the normal number and some with 47. Individuals who are mosaic for trisomy 21 typically have less sever sign and symptoms of the disorder. Another are location that can cause down syndrome is called a chromosome translocation. This is an even that unlike the numerical abnormally causing trisomy 21, there is a structural abnormality. Exchange of material from two different chromosomes during the production of sex cells can take place such that there is a whole chromosome 21 attached to another chromosome but the chromosome number is normal. These types of translocation involving chromosome 21, occur in about 3-4% of cases of Down syndrome. Ancient cultures, such as those in Greece, Rome, and Egypt, put disabled infants to death. Compassion toward the disabled was awakened by the early Christian church, but its charitable influence waned during the middle ages. Down syndrome also affected this people due to no one really caring about what was going on with the ill children. Down syndrome has a lot of causes and this is normally what some parents want to know is why their child is born with this syndrome. Most times this is why they tell you while you are carrying your child you need to watch very closely and look for all signs of genetic disorders with pregnant. Down syndrome is a chromosomal disorder as I said before. A baby is usually identified at birth through observation of a set of common physical characteristics. Babies with Down syndrome tend to be overly quiet. When I say that I mean less responsive with weak floppy muscles. With that being said a number of physical signs might be present. This includes a flat bridge of the nose which is smaller than normal. It’s a low set nose. They will tend to have a small mouth with a protruding tongue, upward slanting eyes and also extra folds of skin located at the corner of each eye, near the nose. They will have small outwardly rotated ears and small hands as well. Usually they have an unusual deep crease across the center of the palm and a malformed fifth finger. They will have a wide space between the big and the second toes and unusual creases on the soles of the feet. They also experience shorter than normal height later on in their childhood. Before genetic testing became available, Down syndrome was...
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