The cause of the Down’s Syndrome might be a heredity handicap. The Down’s syndrome is “Trisomy 21” on the picture above. A baby with the Down’s syndrome has three chromosomes instead of two, at the chromosomes couple number 21. That’s why it’s called “trisomy 21”. Tri means three and, ‘somy’ is from chromosome.

You can find the heredity properties like the colour of your hair and eyes in chromosomes. So a baby with the Down’s syndrome has 47 chromosomes instead of 46. A baby without the Down’s syndrome has two times 23 chromosomes per cell. One half comes from the ovum of the mother and the other half from the semen of the father. Scientists still don’t know exactly what goes wrong during the fertilisation, and how the third chromosome arise. Most of the time the parents have the normal amount of chromosomes. It doesn't always mean that babies are born with the Down’s syndrome due to heredity handicap. It might be due to a ‘mistake’ during the development of the baby in the womb.

Three kinds of Trisomy:
1. Normal trisomy 21
This is the most common form (95%). Here the ovum or semen gets two chromosomes 21. The fertilised ovum has three in stead of two chromosomes 21 now. This mistake might happen before the fertilisation or during the first division of the fertilised ovum. One cell gets just one chromosome 21 and dies. The other stays and has three chromosomes 21 and grows into a foetus with an extra chromosome 21.

2. Translocation
This means that a part of a chromosome passes itself to another chromosome. When this happens without any lose of heredity information, the child will be normal. But the person might give it to her or his child. This is called balanced translocation.

When there is a loss of heredity information it might cause the Down’s Syndrome as reaction. This is called an unbalanced translocation. In some cases one of the parents have a ‘handicapped’ chromosome too, without knowing this.

Parents who get a baby by translocation – trisomy are mostly tested genetically to decide the risk for more children.

3. Mosaicism
This is a odd type of Down’s Syndrome which happens during the first division of cells from the fertilised womb. The baby has normal cells with two chromosomes as cells with three chromosomes 21.

Characterstics:
The physical characteristics of the Down’s Syndrome are present from birth:

• (sometimes) A right line over the palm of the hand.
• A smaller head or a flat back of the head
• Small upwards slant-eyes which
• (sometimes) A skin crease at the inside of the eyes.
• A low muscle tension
• A wide space between first and second toe.
• The mouth and ears are smaller in comparison with normal babies, and the tongue is sometimes swollen.
• The neck, arms and legs are relative shorter.
• Mostly less hair.

People can confirm the diagnose with a blood test in which people can control the chromosomes. This can take a couple of weeks.

Health problems
Children with the Down’s syndrome can get health problems.
• Heart condition: In 35 á 40 % of the cases a child with the Down’s syndrome has serious bad heart conditions. Most of these can be helped by operations.
• Infections: There is a high risk for infections.
• Leukaemia: Higher risks to some types of leukaemia but it’s odd.
• Intestinal problems: There might be a narrowed oesophagus or duodenal
This can be helped by operations.
• Eyes: Due by muscle weakness the co-ordination of the eyes might be a bit slow.
In other words they are cross-eyed. Other eye problems are also common, that’s why regular control is very important.
• Ears: It’s common that one or both ears have a bad hearing. This is due to slow down language development. Ear infections are common too.
• Teeth: Slow down or disturbed development of the set of teeth. Frequently controls are necessary.
• Back: Sometimes swathes between the first two cervical vertebra’s are loose. This causes shifting which occurs easily and can harm the spinal cord.
• Figure: Persons with the Down’s Syndrome are most of the time smaller than ‘normal’ people from their age. They have the tendency to have an overweight. This is the reason why it’s important to give attention to a equally diet and to adapted physical exercises.
The health problems are common in the first years of their life. This is the reason why they can’t see at birth how old the child will become. When the first (critical) years are passed, the average life expectancy is about 50 à 60 years.

Read about Trisomy 21 in different languages:
german:
www.m-ww.de
www.medizin-netz.de
french:
www.caducee.net
www.doctissimo.fr
spanish:
www.healthsystem.virginia.edu
www.elcaminohospital.org
english:
www.ds-health.com
dutch:
www.erfocentrum.nl