Extra dose of protein limits blood vessel formation that tumors need Surplus production of a cancer-suppressing protein may explain in part why people with Down syndrome seldom get cancer, a study in the May 21 Nature shows. People born with Down syndrome have an extra copy of chromosome 21, instead of the usual two copies — one from each parent. The third chromosome causes genetic aberrations that result in the mental retardation and telltale physical traits that define the condition. But chromosome 21 carries 231 genes, including some that may well suppress cancer. In the new study, researchers provide evidence...