DOWN'S SYNDROME

What is it?

Down's syndrome is a genetic condition caused by the presence of an extra chromosome. Chromosomes are tiny particles which are present in every cell in every tissue in the body. They carry the "blueprint" for all inherited characteristics. This blueprint is carried in the form of a coded message in a chemical substance called DNA. There are 23 pairs of chromosomes in each cell, hence 46 altogether. One of each pair comes from the father, and one from the mother. In 1959, a French geneticist, Professor Jérôme Lejeune, discovered that Down's syndrome was caused by the presence of an extra copy of chromosome 21, making 47 chromosomes in all.

Who gets it?

Every day in the UK, between two and three babies are born with Down's syndrome, which means that about one baby in 1,000 has the condition. It occurs in all races, in all social classes, and in all countries throughout the world.

As yet, the cause of the presence of the extra number 21 chromosome is unknown. It can come from either the mother or the father. The most common type of Down's syndrome is called Standard Trisomy 21 (also known as Primary Trisomy 21 or Regular Trisomy 21), and it always occurs as a result of an accident of nature during the development of the egg or sperm, so that the condition is established during the initial cell division following conception. It is known to occur more frequently among the children of older mothers, but not know why.

Standard Trisomy 21 (or Primary Trisomy 21) is not hereditary. However, after giving birth to one baby with Down's syndrome the chances of having another child with the condition are increased. Overall this chance is between 1 in 100 and 1 in 200, which is considerably less than the chance of having twins. If in doubt, consult a genetic counsellor.

What are the symptoms?

All people with Down's syndrome share certain physical characteristics, though not every child with the condition has every characteristic. The baby inherits physical characteristics from both parents, just like any other child, as well as sharing some of the common signs of Down's syndrome. Each baby is unique. Some parents wonder if there is a link between the number of these physical characteristics and the future development of their new baby. In fact, it is not possible at this early stage to predict the level of ability of the child.

People with Down's syndrome all have a certain degree of learning disability (mental handicap). The degree of disability varies from person to person, and it is impossible to tell at birth what that degree will be.

The extra chromosome means that the baby will be slower to reach milestones and will have a certain degree of learning difficulty, but most children with Down's syndrome do learn to walk and talk, ride a bike, read and write - in fact to do most of the things other children do. It is just that their development is usually delayed.

The common signs of Down's syndrome are:

• the baby may have looser muscles and joints than other babies; this will improve with age
• the baby may have a lower than average birth weight and put on weight at a slower pace than other babies (special weight charts are available for babies and children with Down's syndrome from the national office of the Down's Syndrome Association)
• babies with Down's syndrome often have eyes that slant upward and outward; their eyelids often have an extra fold of skin (an epicanthic fold) which appears to exaggerate the slant; this does not mean there is anything wrong with the eyes, they just look different
• the back of the baby's head may be flatter than average

Many babies with Down's syndrome have a single crease which runs right across the palm of the hand. Doctors often look for this characteristic crease as a sign that a baby may have Down's syndrome. However, some babies who do not have Down's syndrome also have a crease like this.

What tests will the Doctor want to do?

The definitive test is a blood test to check the chromosomes.

What is the treatment?

There is no cure for Down's syndrome however, with much support, there is no reason why the majority of sufferers may not live a full and happy life.