The sequence of human chromosome 21 and implications for research into Down syndrome

The recent completion of the DNA sequence of human chromosome 21 has provided the first look at the 225 genes that are candidates for involvement in Down syndrome (trisomy 21). A broad functional classification of these genes, their expression data and evolutionary conservation, and comparison with the gene content of the major mouse models of Down syndrome, suggest how the chromosome sequence may help in understanding the complex Down syndrome phenotype.