Down's syndrome is caused by the presence of an extra chromosome 21 in a baby's cells. It occurs by chance at conception and is irreversible.
Down's syndrome is not a disease. People with Down's syndrome are not ill and do not "suffer" from the condition.
People with the syndrome will have a degree of learning difficulty. However, most people with Down's syndrome will walk and talk and many will read and write, go to ordinary schools and lead fulfilling, semi-independent lives.
Around one in every 1,000 babies born in the UK will have Down's syndrome.
There are 60,000 people in the UK with the condition.
Although the chance of a baby having Down's syndrome is higher for older mothers, more babies with Down's syndrome are born to younger women.
Today the average life expectancy for a person with Down's syndrome is between 50 and 60. A considerable number of people with Down's syndrome live into their 60's.