Downs syndrome is the commonest identifiable cause of intellectual disability, accounting for around 15-20% of the intellectually disabled population. It is believed that people with Downs syndrome have always existed. However, it was not until 1866 that the English doctor, John Langdon Down, first described the condition, which subsequently took In 1959 Professor Jerome Lejeune, a geneticist in Paris, discovered that Downs syndrome occurred as a result of a trisomy of chromosome 21. This means that instead of the usual 46 chromosomes in the cells of the body, there is an extra chromosome 21, making 47 chromosomes in all. Since then, other forms of the condition, which are much rarer, have been discovered, such as Translocation and Mosaicism. Approximately 94% of people with Downs syndrome have standard trisomy 21, 4% have a translocation and 2% mosaic Downs syndrome. In the vast majority of cases, Downs syndrome is not hereditary. What causes Downs syndrome? As yet we do not know what causes the presence of an extra chromosome 21. It can come from either the mother or the father, but most commonly from the mother. There is no way of predicting whether a parent is more likely to produce an egg or sperm with 24 chromosomes. There is a definite link with advanced maternal age for reasons yet unknown. However, most babies with Downs syndrome are born to women under the age of 35, as younger women have higher fertility rates. Nothing done before or during pregnancy can cause Downs syndrome. It occurs in all races, social classes and in all countries throughout the world. It can happen to anyone. Incidence For every 1,000 babies born in the UK, one will have Downs syndrome. This means that about 600 babies are born with Downs syndrome each year in the UK. Downs syndrome affects people of all ages, races, religious backgrounds and economic situations. It is estimated that there are around 60,000 people with Downs syndrome living in the UK, but since Downs syndrome has never been a notifiable condition, accurate figures are difficult to obtain. How is Downs syndrome diagnosed? The diagnosis of Downs syndrome is usually made soon after the birth of the baby because of the babys appearance. There are many physical characteristics associated with the condition, which may lead a parent or midwife, or other medical professional, to suspect that the baby has Downs syndrome. Some of the features include: Reduced muscle tone which results in floppiness (hypotonia); A flat facial profile, flat nasal bridge, small nose; Eyes that slant upwards and outwards, often with a fold of skin that runs vertically between the lids at the inner corner of the eye (epicanthic fold); A small mouth which makes the tongue seem slightly large; A big space between the first and second toe (sandal gap); Broad hands with short fingers and a little finger that curves inwards. The palm may have only one crease across it (single palmar crease); A below average birth weight and length at birth; Many of these features are found in the general population. Therefore a chromosome test (karyotype) would need to be carried out before a positive diagnosis could be made. This is done by analysing the chromosomes in the blood cells.
Posted on: Tue, 15 Jul 2014 19:07:57 +0000
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