Why Does Down's Syndrome Occur?

Down's syndrome is a genetic condition that happens because of the presence of an extra chromosome. It was first described in 1886 and is not classed as a disease as children do not suffer from Down's syndrome. Although children with Down's syndrome will have specific physical characteristics there are more differences than similarities amongst children with Down's syndrome. This syndrome occurs in all social, economic, cultural, religious and racial backgrounds.
Children with Down's syndrome have a learning disability and they may also have associated physical difficulties such as heart problems, thyroid diseases, extra coughs and colds and hearing or visual impairment.

Although there are three different types of Down's syndrome the effects on the child are all similar. The first type of Down's syndrome is standard trisomy and 95% of children with Down's syndrome have this type, which is always an accident of nature. Standard trisomy occurs when a child inherits an extra chromosome either from the mother or the father so instead of having the usual forty-six chromosomes in twenty three pairs the child has forty seven chromosomes in total.

There is also a type of Down's syndrome known as translocation. This is a rare condition and occurs in approximately 2% of children with Down's syndrome. In translocation the parents pass on an abnormal chromosome 21, which contains extra material, as well as the normal chromosome 21, so the child has the usual total of forty-six chromosomes.

There is also an extremely rare form of Down's syndrome called Mosaic Down's syndrome and this occurs in 2 to 5 % of children with Down's syndrome. A child with this will have the usual forty-six chromosomes and some abnormal cells will have forty-seven. Mosaic Downs syndrome has less severe effects and there are fewer characteristic facial features and disproportionately less learning disabilities.

The chromosomal abnormalities can cause some health difficulties and a disruption to the growth of the developing baby. A child with Down's syndrome may have hearing problems due to the child's vulnerability to catch frequent colds which can cause glue ear. These children may have affected vision and there is often a squint or other associated difficulties.

A child with Down's syndrome may have physical development problems and will be smaller than her peers. There will be poor muscle tone initially, due to the floppiness which affects children with Down's syndrome, which will cause a delay in developing gross motor skills. There will also be a tendency to gain weight.

An underdeveloped immune system will leave her vulnerable to illnesses, especially in the early years.

Approximately 40% of children with Down's syndrome will have heart problems some of which will be serious and require surgery.

It is important to understand that shared physical characteristics are not an indication of future capability or capacity to learn and not all children with Down's syndrome will have all the associated health problems and even if some are present they will vary in severity.

Source - Good Practice in Caring for Young Children with Special Needs - Angela Dare and Margaret O'Donovan