Down's Syndrome - Heritable Trait?

Is Down’s Syndrome a heritable trait? What causes it? Genetic or environmental factors? Any sources/information would be appreciated.

Here’s a UK web site:

This is a very informative site on the subject-

Here’s one more. A Google search turned up a lot.

Thanks All!!!

I haven’t read the links, so forgive me if I repeat somthing. I’m sure they covered the normal way of getting Down syndrome, but there can be familial Downs. This happens when most of the 23rd chromosome gets translocated onto the end of the (I think) 17th chromosome. In families with this condition, Downs occurs regularly.

THe 17:23 form of Down’s occurs in something like 4% of the cases IIRC. SOme people are also probably more likely to form trisomies, most of which take care of themselves.