Down syndrome is a collection of features that are caused by trisomy for human
Chromosome 21. While elevated transcript levels
of the more than 350 genes on the
chromosome are primarily responsible, it is likely that multiple genetic mechanisms underlie the numerous ways in which development and function diverge in
individuals with trisomy 21 compared to euploid individuals. We consider genotypephenotype interactions with the goal of producing working concepts that will be useful for approaches to ameliorate the effects of trisomy.