What is Down's Syndrome? Down's syndrome is a genetic condition (i.e. something you are born with, which is present in the baby from the moment of conception) caused by the presence of an extra chromosome. Chromosomes are tiny particles, which are present in every cell in every tissue in our bodies. They carry the 'blueprint' for all the characteristics we inherit. This blueprint is carried in the form of a coded message in a chemical substance called DNA. There are 23 pairs of chromosomes in each cell, hence 46 altogether. One of each pair comes from the father, one from the mother. In 1959, a French geneticist, Professor Jerome Lejeune, discovered that Down's syndrome was caused by the presence of an extra copy of chromosome 21, making 47 chromosomes in all. A 'syndrome' is a collection of signs or characteristics. The name 'Down' comes from the English doctor, John Langdon Down, who first described the syndrome in 1866, nearly 100 years before the extra chromosome was discovered. Everyday in the UK, between one and two babies are born with Down's syndrome, which means that one baby in 1000 has the condition. People with Down's syndrome all have a certain degree of learning disability (mental handicap). The degree of disability varies from person to person and it is impossible to tell at birth what that degree will be. We know that babies born to older mothers have a higher chance of having Down's syndrome, but we do not know why.