They've actually narrowed down the genetic pathway responsible they think. What's interesting is the correlation between maternal (and to some extent paternal) age and Downs is also found between age and blood homocysteine levels. The thought is that older mothers risk of Downs could be attenuated with proper supplements. Which would be wonderful. (nothing against your nephew, i'm sure he's a great kid, most Downs kids are).
Yes I read all of that 24 years ago. It has long been a given that children of older women were at greater risk for Downs. I swear, they get more government funding to come up with the same "new" results! LOL!
And yes my nephew is a great kid. I call him our 250 lb. 4 year old. He is unfortunately unemployable and operates on the most simple terms. But sometimes, in our complicated world, I find that very refreshing. :-)