How to explain DS to a 7yr old?

[pantsjustpants]

I have big gaps between my children, and as such I have grandchildren whilst my own children are still very young.

My grandson was diagnosed at a few days old with DS. Luckily at 17mths he's very happy and healthy. Up until recently my 7yr old dd just accepted the fact that dgs has ds, but now she's asking lots of questions. I'm not sure how to explain in terms that she can understand, are there any websites or books that anybody could recommend please?

I don't have any website/book suggestions, but a simple explanation could be 'our body is made up of genes. To work properly we need two of each gene. A baby with DS has 3 of one particular gene, which changes some bits of them. It can make it harder to learn.'