What is Down’s Syndrome?

Down’s syndrome (Ds) is a genetic condition caused by the presence of a full or partial third copy of chromosome 21 in the body’s cells. Down’s syndrome usually occurs because of a chance happening at the time of conception. It is rarely hereditary and nothing the parents did before or during pregnancy can have caused it. It occurs randomly at the point of conception and affects males and females alike. Approximately one in every 1,000 babies worldwide is born with Down’s syndrome. There are three types of Down’s syndrome: Trisomy 21 (94%), Translocation (4%), and Mosaic (2%).

The most common type of Down’s syndrome (occurring in about 94% of people with Ds) is Trisomy 21, all the cells have an extra chromosome 21. Our bodies are made up of cells that contain genes. Genes are grouped in thread-like structures called chromosomes. These contain detailed genetic instructions for lots of different things, including: how a baby’s cells develop, their gender, and their eye colour. Usually, cells contain 46 chromosomes – 23 from the mother and 23 from the father. Trisomy 21 means there is an extra copy of the 21st chromosome, all the cells have an extra chromosome 21. This causes the characteristics of Down’s syndrome. People with regular trisomy 21 have mild to moderate learning disabilities.

In mosaic trisomy 21 only some of the cells in the body have the extra chromosome. About 2% of people with Down’s syndrome have this type. People with mosaic Down’s syndrome are likely to have milder learning disabilities.

Around 4% of people with Down’s syndrome have translocation. This is when the extra chromosome 21 material comes from one of the parent’s genes. Either parent may have the long arm of chromosome 21 attached to another chromosome. This can lead to an extra chromosome being created during reproduction, producing a child with Down’s syndrome.

The condition is named after a British doctor, John Langdon Down, who identified it in 1886. People with Ds are not all the same; they have more in common with their families than with each other. Down’s syndrome is the most frequently recognised form of learning disability. The learning disability affects a child’s ability to learn compared with other children of their age, it does not mean they cannot learn. But the most important thing to remember is that everyone with Ds is a unique individual.

DS is a lifelong condition and there is no cure; however, there are many ways to ensure that each individual with Down’s syndrome is given the right type and amount of support that they need to develop to their full potential. Today the average life expectancy for a person with Ds is about 60 years old with a small number of people living into their 70s and beyond.