Explanation

Down's syndrome is a genetic condition that you are born with. You usually have it because you have an extra chromosome in all of the cells of your body. You have three copies of chromosome 21, rather than two, so you might also hear Down's syndrome being called trisomy 21.

The extra chromosome changes the balance of your body while you are growing in your Mum's tummy. This leads to problems when you are born. No one knows why you get Down's syndrome, it can happen to anyone, and it is not something that you can catch or give to other people.