Fig 1. Isogenic trisomic-disomic mosaic Down syndrome study design.

An individual with mosaicism for trisomy 21 has both trisomic and disomic cells that originated from a single zygote as a constitutional finding. Thus, these trisomic and disomic cells have identical genetic backgrounds (except for the trisomy 21 imbalance) and identical environmental exposures. By measuring trisomic compared to disomic cellular attributes, individual genetic “background” variation is eliminated to allow for direct assessments of trisomy 21-specific influences.