About one in 600 babies are born with Down syndrome in developing countries and one in 1000 in developed countries. It is caused by an abnormality in the genetic material. More specifically, the most common type of Down syndrome is an extra number 21 chromosome and is called Trisomy 21.
How does it happen?
Each person’s cells contain 23 pairs of chromosomes. When an egg or sperm cell is formed, only one half of the pair is contained within. Once conception takes place the fertilised egg again contains 23 pairs. In the case of Down syndrome the split of the chromosomes takes place incorrectly and the egg or sperm cell ends up with 24 chromosomes. With conception the fertilised egg will contain an extra chromosome, resulting in Down syndrome.
The most important thing to remember is that nothing that the parents did or didn’t do is responsible for this condition.
Down syndrome characteristics
Babies with Down syndrome look different from other babies and can therefore be identified at birth. Some of the typical characteristics include the following:
• Eyes that slant upwards
• Small folds in the inside corners of the eyes (Epicanthic folds)
• Small white spots on the iris of the eye (Brushfield spots)
• A small nose with a broad flat bridge
• A small mouth, and tongue that looks too big
• Small ears situated low on the head
• A single fold in the palm of the hand
• Short fingers and hands
• Pinkies that turn in towards the hand
• A bigger gap between the big toe and the next
• A slightly flat appearance at the back of the head
Other signs include:
• Unusually loose joints
• Low muscle tone (Hypotonia), that makes the baby feel floppy
• Loose skin at the back of the neck
• Heart defects in approximately 50% of all cases
• Eye defects in about 60% of cases
• Hearing problems may occur and can affect speech
• Developmental delay (intellectual disability can be mild to moderate)
Not all of these characteristics will be present in all the children. Like other kids, children with Down syndrome look like their parents, for example hair and eye colour, but they will also have some of the above characteristics. Each child is a unique individual and can differ greatly in appearance, temperament and ability. Remember that appearance doesn’t have anything to do with intelligence. This means that if someone has more of these characteristics it does not mean that they are more intellectually disabled.
Down syndrome is diagnosed with more than just these characteristics. A chromosomal analysis is done in a laboratory before it is an accepted fact.
Where does the name "Down syndrome" come from?
Down syndrome is named after Dr Langdon Down, who described the characteristics of the condition for the first time in 1866. The word ‘syndrome’ means the collection of specific characteristics and symptoms that are found in combination.
Source: Step by Step into the future. An Introduction to Down syndrome, Published by the Department of Health.
Read this mother's account of having a Down syndrome baby in Diagnosis: Down syndrome.
Or bust your own beliefs about Down syndrome. Read about Down syndrome myths.
The Down Syndrome Association can be contacted on (021) 919 8533 or email@example.com