Down syndrome is a condition in which a baby is born with an extra chromosome. Chromosomes are small “packages” of genes in the body that determine how a baby’s body forms during pregnancy and how, as the baby grows in the womb and after birth, the baby’s body functions.
Down syndrome is caused by an error in cell division that results in an extra 21st chromosome. Normally, each human cell contains 23 pairs of different chromosomes. Each chromosome carries genes, which are needed for proper development and maintenance of our bodies. At conception, an individual inherits 23 chromosomes from the mother (through the egg cell) and 23 chromosomes from the father (through the sperm cell). In Down syndrome however, an individual most often inherits two copies of chromosome 21 from the mother and one chromosome 21 from the father for a total of three chromosomes 21. This is why Down syndrome is also known as Trisomy 21.
This genetic disorder occurs in approximately 1 of 800 live births. Through a series of screenings and tests, Down syndrome can be detected before and after the baby is born. Prenatal screening tests currently available include the expanded alpha-fetoprotein (AFD) screening test, the nuchal translucency test, and additional ultrasound screens which look for changes in certain anatomical features of the fetus. While these screening tests can assess the risk of Down syndrome, they cannot confirm Down syndrome with certainty.
Down syndrome is associated with mild to moderate learning disabilities, developmental delays, characteristic facial features, and low muscle tone in early infancy. It is also the leading cause of cognitive impairment.
Exactly how the extra genes from chromosome 21 lead to Down syndrome is still not clear. Scientists believe that the increased presence of specific genes alters the interaction between these and other genes. Some genes will become more active and others less active than normal, leading to changes in the development and maintenance of the body. Why some individuals are more severely affected than others might have to do with how many and which specific extra genes were inherited.
The only well known risk factor for conceiving a child with Down syndrome is advanced maternal age. The older the woman is at conception, the greater the risk of having a child with Down syndrome. Research shows this rather interesting statistics:
|Mothers age at conception||Risk of Down syndrome|
|25 years||1 in 1,250|
|30 years||1 in 1000|
|35 years||1 in 400|
|40 years||1 in 100|
|45 years||1 in 30|
According to research carried out by CDC (Centre for Disease Control and Prevention), the number of babies with Down syndrome seems to be increasing, especially among mothers older than 35 years of age. However, because younger women are more likely to have babies than older women, 80% of babies with Down syndrome are born to women younger than 35 years of age. While there is currently no way to prevent Down syndrome, mothers can take steps before and during pregnancy to have a healthy pregnancy. Steps include taking a daily multivitamin with folic acid (400 micrograms), not smoking, and not drinking alcohol during pregnancy.
Parents who have conceived a child with Down syndrome have a 1% increased risk of conceiving another child with Down syndrome. If a parent is a carrier of a chromosome 21 translocation, the risk can be as high as 100%. Women with Down syndrome have a 50% risk of conceiving a child with Down syndrome. If the father has Down syndrome, the risk of conceiving a child with Down syndrome is also increased.
Although the severity of Down syndrome ranges from mild to severe, most individuals with Down syndrome have widely recognisable physical characteristics. These include:
- Eyes that have an upward slant, oblique fissures, epicanthic skin folds on the inner corner, and white spots on the iris.
- A flattened face and nose, a short neck, a small mouth sometimes with a large, protruding tongue, and small ears.
- The hands are short and broad with short fingers, and with a single deep crease across the centre of the palm.
- Small stature.
- Large space between large and second toe.
- A single flexion furrow of the fifth finger.
- Poor muscle tine and loose ligaments are also common
- Development and growth is usually delayed and often, average height and developmental milestones are not reached.
TO BE CONTINUED……………
Jessica B shares a three part series on her experiences with living with a beloved brother with Down syndrome. She hopes to raise awareness on down syndrome throughout Africa.This is part 2 of a three part series on Down Syndrome. Check out part 1 here
Heyn, S.K. (PhD) et al. DOWN SYNDROME Retrieved from http://www.medicinenet.com/down_syndrome/article.htm
CENTRE FOR DISEASE CONTROL AND PREVENTION, 2011 FACTS ABOUT DOWN SYNDROME Retrieved from http://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.html
MEDICAL NEWS TODAY, 2009 WHAT IS DOWN SYNDROME? WHAT CAUSES DOWN SYNDROME? Retrieved from http://www.medicalnewstoday.com/articles/145554.php