Down syndrome (also known as Trisomy 21) is a condition in which a person has an extra chromosome. There is more information about chromosomes below.
Down syndrome occurs naturally – there is no known cause.
Around 1 in every 800 babies will be born with Down syndrome.
All living things have chromosomes.
Chromosomes act like an instruction manual that defines how our bodies look and how they work. For example, they say what colour our eyes will be or how tall we will grow.
Most people have 23 pairs of chromosomes – 46 in total.
People with Down syndrome have an extra chromosome added onto the 21st pair – 47 in total.
People who have Down syndrome usually have an intellectual disability. This is different in each person.
Some health conditions are more common in people with Down syndrome. You can find information about these on our child health and adult health pages.
