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 (see diagram below) or during the initial cell division following conception, (ie when the egg and sperm fuse). There are 3 different types of Down's syndrome. 95% 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 there is no known reason why it occurs. Faulty distribution of chromosome 21 in the egg leading to standard trisomy 21. Approximately 1 in 100 people with Down's syndrome have inherited the condition from their mother or their 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. Again, for reasons not 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. Risk and maternal age - the chance of having a baby with Down's syndrome.
The majority of babies with Down's syndrome are still born to younger women, since the overall birth rate is higher in younger women. The chance of parents of one child with Down's syndrome having a second child with the condition can be greater than that of the general population. Down's syndrome is normally suspected soon after the birth, because a doctor, nurse, or sometimes a parent recognises the characteristic features. Chromosome tests are then carried out to confirm the diagnosis. The features which people look for include: Eyes that slant upwards and outwards. They often have a fold of skin that runs vertically between the two lids at the inner corner of the eye. A head which is rather flat at the back with a hairline that is low and ill defined at the nape of the neck, often with rather loose skin in this area.
