Down syndrome (DS), also called Trisomy 21, is a condition in which extra genetic material causes delays in the way a child develops, both mentally and physically. It affects about 1 in every 800 babies.
Children with Down syndrome have a distinct facial appearance.
Common features are:
- Flattened facial features.
- Protruding tongue.
- Small head.
- Upward slanting eyes, unusual for the child's ethnic group.
- Unusually shaped ears.
- Children with Down syndrome may also have:
- Poor muscle tone.
- Broad, short hands with a single crease in the palm.
- Relatively short fingers.
- Excessive flexibility.
- Infants born with Down syndrome may be of average size, but typically they grow slowly and remain smaller than other children of similar age. Children with Down syndrome also have some degree of mental retardation, ranging from mild to moderate.
Causes of Down syndrome:
The cause of Down syndrome is one of three types of abnormal cell division involving the 21st chromosome. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The three genetic variations that can cause Down syndrome include:
- Trisomy 21: More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells. This form of Down syndrome is caused by abnormal cell division during the development of the sperm cell or the egg cell.
- Mosaic Down syndrome: In this rare form of Down syndrome, children have some cells with an extra copy of chromosome 21, but not all. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
- Translocation Down syndrome: Down syndrome can also occur when part of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 stuck to the translocated chromosome. This form of Down syndrome is uncommon.
- Risk factors of Down’s syndrome:
- Advancing maternal age. As a woman's eggs age, there's a greater inclination for chromosomes to divide improperly. So a woman's chances of giving birth to a child with Down syndrome increase with age. By age 35, a woman's risk of conceiving a child with Down syndrome is 1 in 385. By age 40, the risk is 1 in 106. And by age 45, the risk is 1 in 30.
- Mothers who already have one child with Down syndrome. Typically, a woman who has one child with Down syndrome has about a 1 percent chance of having another child with Down syndrome.
- Parents who are carriers of the genetic translocation for Down syndrome. Both men and women can pass the genetic translocation for Down syndrome on to their children.
Tests and diagnosis for Down’s syndrome:
Screening tests during pregnancy:
Various screening tests can help identify whether you have a high risk of carrying a baby with Down syndrome. Blood tests, such as the quad screen. The most effective screening is done in two steps between the 11th and 14th week of pregnancy:
- Ultrasound: The doctor uses ultrasound to measure a specific region on the back of a baby's neck. This is known as a nuchal translucency screening test. When abnormalities are present, more fluid than usual tends to collect in this tissue.
- Blood tests: Results of the ultrasound are paired with blood tests that measure levels of pregnancy-associated plasma protein-A (PAPP-A) and a hormone known as human chorionic gonadotropin (HCG). Abnormal levels of PAPP-A and HCG may indicate a problem with the baby.
- Diagnostic tests during pregnancy:
- Amniocentesis: A sample of the amniotic fluid surrounding the fetus is withdrawn through a needle inserted into the mother's uterus. This sample is then used to analyze the chromosomes of the fetus.
- Chorionic villus sampling (CVS): Cells taken from the mother's placenta can be used to analyze the fetal chromosomes.
- Percutaneous umbilical blood sampling (PUBS): Blood is taken from a vein in the umbilical cord and examined for chromosomal defects. Doctors generally perform this test after 18 weeks of gestation.
- Heart defects.
- Infectious diseases like pneumonia since there is abnormality of the immune systems.
- Other problems like intestinal obstruction, thyroid problems, hearing loss and poor vision.
There's no medical treatment for Down syndrome that will provide a cure..
There's no way to prevent Down syndrome. However, if you're at high risk of having a child with Down syndrome or you already have one child with Down syndrome, you may wish to consult a genetic counselor before becoming pregnant.