What is Down Syndrome?
Down syndrome or Down's syndrome, is a genetic condition that causes delayed development of physical and intellectual aspects of a child. A child, with this condition, has a lower IQ (of 50) and low understanding, reasoning and perception abilities.
In the United States, 1 out of every 691 children is born with this condition. Though, a cure is yet to be found, researches have shown that with special care and recognition in society, the life expectancy of such individuals has increased.
What Causes Down Syndrome?
A human child inherits 23 pairs of chromosome from his parents. 23 chromosomes from the egg cell of the mother and 23 chromosomes from the sperm cell of the father, which make a total of 46 chromosomes. Each chromosome carries genes from each parent. However, sometimes an extra chromosome is inherited by the embryo, from either of the parents. Down syndrome or DS is caused when a child inherits this extra chromosome 21, completely or partially. Out of all the cases that have been studied, 5% fathers have been found as the donor of the added chromosome 21. This additional genetic material alters the overall development of a child.
What are the Chances of a Child Being Born with DS?
Down's syndrome can occur in any person, regardless of the race or any other factor. Although, children born to women of older age are often diagnosed with it. It is the only known risk factor that increases the chances of Down syndrome.
|Maternal Age||Risk of Down Syndrome|
|20||1 in 2,000|
|25||1 in 1,200|
|30||1 in 900|
|35||1 in 350|
|40||1 in 100|
|45||1 in 30|
|50||1 in 10|
Couples, who have conceived a child with Down's syndrome, have an increased risk of conceiving another child with a similar condition.
What are the Types of DS?
There are three kinds of patterns of chromosome, that have known to be the cause of Down syndrome.
Trisomy 21: In Down's syndrome, a child has three copies of the chromosome 21. So, it is also called trisomy 21. Usually, during conception, the embryo has two sets of chromosome 21. But sometimes, an extra chromosome fails to separate itself from either the egg cell or the sperm cell. This chromosome then gets duplicated in every cell of the body. Trisomy 21 is found to be the prominent kind of this syndrome. Almost 95% cases of Down's syndrome are trisomy 21.
Translocation: During cell division in an embryo, sometimes, a part of chromosome 21 detaches and adheres to chromosome 14. This is known as translocation. Although, the number of chromosomes present in each cell is 46, the extra genes from partial chromosome 21 causes the disorders in growth of the embryo, and leads to Down syndrome. 4 - 5% cases of DS are caused due to translocation.
Mosaicism: In genetics, the presence of different genes in one or more cells in an individual, is referred to as mosaicism. In Down's syndrome, it refers to presence of genes of the third chromosome 21 in the cell. There has not been much research on Mosaic DS, but studies have shown that kids with MDS have higher IQ than the kids with the Down syndrome. As, only a small percentage of cells are affected by mosaicism, there are very less characteristics of DS present in the child. However, speech delay is reported as one of the symptoms of this disorder.
What are the Signs and Symptoms?
The major characteristic of DS is neoteny or hindered maturity. Based on the type, an individual with DS may have all or some of these physical traits:
- Unusually small chin
- Poor muscle tone
- Brushfield spots (white spots on iris)
- Single crease on the palm
- Flat nasal bridge
- Broad hands with short fingers
- Small ears
- Loose joint ligaments
- Creases on eyelids
- Protruding tongue
- Flattened face
- Space between big and second toe
How is DS Diagnosed?
Down's syndrome is usually diagnosed at birth. The physical characteristics of the infant, such as upward slant of the eyes and flat facial structure, are the signs that may lead to diagnosis of the disorder. However, there are several chromosomal analysis processes that the doctor may resort to, for positive confirmation. These analysis are called karyotype, where a blood sample from the baby is tested to check for chromosomal anomalies. Another test, FISH (Fluorescence In Situ Hybridization), takes lesser time and helps in faster diagnosis.
There are many prenatal screening tests available, that are absolutely noninvasive. A diagnosis before the baby is born, gives the parents time to prepare and get genetic counseling. However, prenatal screening tests only estimate the chances of the baby being born with DS. AFP or alpha-fetoprotein screening test is the most widely used and reliable test. Blood sample of the expecting mother is taken between 15 - 20 weeks of pregnancy, and checked for higher levels (indicate chances of DS) of AFP and three other hormones. An ultrasound between 11 - 13 weeks of pregnancy, known as nuchal translucency test, is done to check the thickness of fold of the neck. When taken with maternal age, this test has proved to be correct for 80% of the cases.
Apart from the above-mentioned screening tests, there are several other diagnostic tests as well. However, these tests are invasive, and carry a slight risk of miscarriage.
One such test is Amniocentesis, done during 16 - 20 weeks of pregnancy. A small sample of amniotic fluid is extracted via a needle, inserted into the abdominal wall. This fluid is then tested from chromosomal anomalies.
Chorionic Villus Sampling (CVS) is done by extracting chorionic villus cell sample from the placenta, taken either through a needle inserted into the abdominal wall, or catheter in vagina. It is done between 11 - 12 weeks of pregnancy, and the sample is tested for any alterations.
What are the Other Conditions Associated with DS?
The major consequence of DS is cognitive impairment.The ways through which the extra chromosome 21 affects the development of a child's learning and understanding abilities, are still unknown. Also, a number of people with DS have been identified with various heart defects, cancer and other medical conditions that include:
- Hearing loss
- Obsessive Compulsion Disorder (OCD)
- Attention Deficit Hyperactivity Disorder (ADHD)
How to Manage DS?
The cause behind Down syndrome is known - the third copy of chromosome 21. Every chromosome has more than 250 genes. Genealogists have identified almost every gene present on this particular chromosome. However, a cure is yet to be found. Researches and clinical trials are ongoing all over the world, but they are in a very primary stage.
Although, there is no cure for DS yet, however, the conditions associated with it can be treated via organ replacement and other medical procedures. A person with DS must get regular medical check-ups done, as early detection of any other disorder or ailment will assist in the treatment.
Apart from all medical facilities, it is very important that these individuals are considered a part of the society. They must be assured that they belong here, with everyone. Like every other child, they need to be nurtured and encouraged. There are many programs for people with special needs, which concentrate on development of such people. They focus on speech, occupational and physical therapies. These programs have definitely increased and improved the quality of life for people with DS.
Also, as they reach adolescence, it is vital to make them aware of the physical changes that they go through during puberty. Although, girls with DS are not very fertile, they do have regular menstrual periods and can get pregnant. Similarly, there are cases where men with DS have fathered a child. They must be taught about hygiene and sexual development.
With proper care, education and encouragement, kids with DS can flourish well. There are many adults with DS who, with proper training, have achieved paid employment. And often, they live a very happy, healthy and productive life.
Disclaimer: This Buzzle article is for informative purposes only, and should not be used as a replacement for expert medical advice.