What is Down Syndrome?
Down Syndrome is a genetic disorder caused by an extra chromosome 21 due to abnormal cell division, otherwise known as nondisjunction. It is also known by the name Trisomy 21. This disorder alters the "normal" physical and genetic appearance as well as slowing down certain mental aspects of a person. Down Syndrome is also found in certain animals like tigers.
One in every 691 babies in the United States are born with Down Syndrome making it the most common genetic condition.
Types of Down Syndrome
1. Trisomy 21:
This strand of Down Syndrome is caused by unequal cell division called "nondisjunction" This causes an embryo to have 3 copies of autosome 21 instead of the normal amount, which is 2. As the embryo develops, a copy of this extra chromosome is replicated in every single cell of the body. This strand accounts for 95% of all Down Syndrome cases making it the most popular strand. 2. Mosaicism:
This strand of Down Syndrome occurs again through nondisjunction, but this time only one of the cells has an extra chromosome. This allows for two types of cells in the body. Those containing 46 and those containing 47. This allows for fewer characteristics of Down Syndrome, however this isn't a concrete characteristic. This strand accounts for only 1% of cases. 3. Translocation: In translocation, part of chromosome 21 breaks off during cell division and attaches themselves to another chromosome, autosome 14 being the most popular choice. This allows the number of cells in the body to remain at 46, however characteristics of Down Syndrome are still visible due to the extra chromosome. This accounts for 4% of all cases. |
Brief History of Down Syndrome Research:
Down Syndrome has been around for centuries, but it wasn't until the late nineteenth century that John Langdon Down, an English physician created an accurate description of a person with Down Syndrome. Due to this, he is recognized as the "father" of the syndrome. Recent advances in science and technology has allowed this syndrome to be studied more closely. In 1959, Jerome Lejeune, a French physician, identified Down Syndrome as a chromosomal condition when instead of seeing the regular amount of 46 chromosomes, he identified 47 within a person with Down Syndrome. An international group successfully identified and catalogued all the 329 genes on chromosome 21 in 2001 opening the door for major advances for Down Syndrome research. Research is on-going.
Down Syndrome has been around for centuries, but it wasn't until the late nineteenth century that John Langdon Down, an English physician created an accurate description of a person with Down Syndrome. Due to this, he is recognized as the "father" of the syndrome. Recent advances in science and technology has allowed this syndrome to be studied more closely. In 1959, Jerome Lejeune, a French physician, identified Down Syndrome as a chromosomal condition when instead of seeing the regular amount of 46 chromosomes, he identified 47 within a person with Down Syndrome. An international group successfully identified and catalogued all the 329 genes on chromosome 21 in 2001 opening the door for major advances for Down Syndrome research. Research is on-going.
How does down syndrome occur?
This is a genetic disorder, therefore it is present from birth and cannot be developed afterwards. Both males and females are affected by this disorder. Generally all the strands of the disorder are genetic, occurring through nondisjunction, but only 1% of all cases are due to hereditary. Hereditary is not a problem is Trisomy 21 or Mosaicism, but it occurs in 1% of all translocation cases. Although why nondisjunction occurs is still being researched, scientists have made connections between certain factors to increased rates of Down Syndrome. For example as a woman age she posses when giving birth increases so does the chances of nondisjuntion, however due to birth rates being higher among younger woman 80% of cases are shown in babies birthed by women under the age of 35. The additional, partial, or full copy of the extra chromosome can originate from both parents, however only approximately 5% of all cases have been traced to the father.
Down Syndrome Diagnosis
There are two ways to diagnose the disorder, one before birth and one at birth.
1. Before birth a screening test or a diagnostic test can be taken to determine the chances of the fetus having the disorder. Screening tests are not absolute while diagnostics are almost 100% accurate. With screening tests, If the test is taken during the first trimester of pregnancy, an ultrasound, called a nuchal translucency, is performed where it measures the fluid under the skin of the back of the fetus's neck to determine if the disorder is there or not.
During the second trimester, blood work from the mother is done to determine the disorder. The main type of diagnostic testing is Chorionic Villus testing. This is where during CVS a very small sample of the chorionic villi placenta tissue is taken, it contains the exact genetic make up of the fetus, and examined to determine the disorder. This is an exact test and is done during the 11th - 14th weeks of pregnancy.
2. The second type of diagnostic is done at birth. At birth, the physical characteristics are examined to determine whether the baby has this disorder or not. A karyotype can also be taken for confirmation.
1. Before birth a screening test or a diagnostic test can be taken to determine the chances of the fetus having the disorder. Screening tests are not absolute while diagnostics are almost 100% accurate. With screening tests, If the test is taken during the first trimester of pregnancy, an ultrasound, called a nuchal translucency, is performed where it measures the fluid under the skin of the back of the fetus's neck to determine if the disorder is there or not.
During the second trimester, blood work from the mother is done to determine the disorder. The main type of diagnostic testing is Chorionic Villus testing. This is where during CVS a very small sample of the chorionic villi placenta tissue is taken, it contains the exact genetic make up of the fetus, and examined to determine the disorder. This is an exact test and is done during the 11th - 14th weeks of pregnancy.
2. The second type of diagnostic is done at birth. At birth, the physical characteristics are examined to determine whether the baby has this disorder or not. A karyotype can also be taken for confirmation.
Physical, Development, and Genetic traits
PHYSICAL:
* Low muscle tone (babies appear floppy) *Single deep crease across the center of palm
* Flat facial features, with small noses * Hyper flexibility
* Upward slant of eyes * Fifth finger has only one flexion furrow instead of two
* Small skin folds on the inner corner of eyes * Extra space between the big toe and the second toe
* Abnormally shaped ears * Enlarged tongue, tends to stick out
Genetic: People with down syndrome have an extra autosome 21.
Learning & Development: Most people with down syndrome have mild to moderate learning impairments, but are capable of leading normal lives with special help from a young age. Some cases of this disorder may lead to severe mental incapability, however with therapy they can get help. People with this disorder also have minor speech defects that can be improved through years of speech therapy.
Learning & Development: Most people with down syndrome have mild to moderate learning impairments, but are capable of leading normal lives with special help from a young age. Some cases of this disorder may lead to severe mental incapability, however with therapy they can get help. People with this disorder also have minor speech defects that can be improved through years of speech therapy.
Health Issues
Children with Down Syndrome are more prone to health complications than normal children. Approximately 40% of children with the disorder have congenital heart defects. Some of these heart defects require surgery while others only require monitoring. Children with this disorder also have a higher chance of infection, respiratory, hearing, and vision problems as well as thyroid and other health conditions. Some speech problems may occur as well. However, with proper medical care, children and adults with the disorder all able to live full healthy lives.