What is Down?s syndrome?
Understanding the implications for your child if they are Down's Syndrome
The word syndrome means a collection of signs or characteristics. The name Down comes from Dr John Langdon Down, who first described the condition in 1866. In 1959 Professor Lejeune proved that Down's syndrome is a genetic condition caused by the presence of an extra chromosome.
There are more differences between people with Down's syndrome than there are similarities. They will have many of their families' distinctive characteristics and will therefore resemble their brothers and sisters. As well as these individual characteristics however, they will have physical features shared by others with Down's syndrome.
They will also have learning difficulties. This means they have greater difficulty learning than the majority of people the same age.
Downs syndrome has its origins in the genes. Every cell contains a number of chromosomes. These are tiny particles which carry the blueprint for all the characteristics that we inherit. Normally there are 46 chromosomes in every cell; half of these come from our mother, half from our father. The person with Down's syndrome has an extra chromosome 21 making 47 in all. This results in a disruption to the growth of the developing baby.
This extra chromosome can come from either the mother or the father, and is present because of a genetic accident when the egg or the sperm is made or during the initial cell division following conception.
There are three different types of Down's syndrome. Ninety-five per cent of people with Down's syndrome have the type known as standard trisomy 21. This type of Down's syndrome is always an accident of nature. It can happen to anyone and it is not known why it occurs. Approximately one in 100 people have the second type of Down's syndrome. They inherit the condition from their mother or father because of a genetic anomaly called a translocation. The third type of Down's syndrome, also rare, is known as mosaic Down's syndrome, in which an extra chromosome 21 appears in only some of the cells.
For reasons not yet understood, the chance of any woman having a child with Down's syndrome increases with her age, particularly after 35 years. The age of the father appears to be less significant.