The Critical Region in Trisomy 21

Down syndrome caused by trisomy of human chromosome 21 is one of the most common genetic diseases, occurring in 1 out of every 700 live births. In their Perspective, [Nelson and Gibbs][1] discuss a new mouse model of Down syndrome ([ Olson et al .][2]), which shows that triplication of a segment of human chromosome 21 containing 33 critical-region genes does not result in the craniofacial abnormalities typical of the disease. The authors point out that this mouse model refutes the notion that triplication of the 33 critical-region genes is directly responsible for the craniofacial abnormalities of Down syndrome. [1]: http://www.sciencemag.org/cgi/content/full/306/5696/619 [2]: http://www.sciencemag.org/cgi/content/short/306/5696/687