Experiments with mice indicate that the genetics of Down syndrome aren’t as simple as has been thought, Johns Hopkins University researchers report.Down syndrome causes mental retardation and abnormalities of the face and skeleton. It is sometimes called trisomy 21 because there are three copies of chromosome 21, rather than the normal two, in people with the disorder. Research has zeroed in on a specific part of that chromosome, which has come to be called the Down syndrome critical region.But mice genetically engineered to have three copies of that region in their chromosome 16 -- which corresponds to chromosome 21 in humans -- don’t have the facial and skeletal features associated with Down syndrome, the study found. The research was led by Roger H. Reeves, professor of molecular biology and genetics, and reported in the Oct. 22 issue of the journal Science.
