HUMAN GENOME PROJECT: Scientists Decode Chromosome 21
Scientists with the Human Genome Project announced yesterday they have mapped the smallest human chromosome, Chromosome 21, the AP/Philadelphia Inquirer reports. The achievement comes after last fall's decoding of Chromosome 22 and "eventually could point the way to treatments for a host of illnesses" associated with Chromosome 21, including Down syndrome, epilepsy, Lou Gehrig's disease and Alzheimer's disease. Francis Collins, chair of the publicly funded effort, said, "Now we really have to roll up our sleeves and assess what these genes are doing there, what role they play in causing disease." The German- and Japanese-led research team that decoded the chromosome encountered a surprise, discovering that it contains only 225 genes, "far fewer" than expected. Chromosome 22, the second smallest chromosome, has 545 genes (Callahan, 5/9). Kathleen Gardiner of the Eleanor Roosevelt Institute in Denver, which helped analyze the research, explained, "We were expecting 500 to 1,000 [genes]." She added, however, that the smaller number "makes sense," since "[i]t's probably the reason that humans born with a third set of Chromosome 21 can live at all, even though their condition, Down syndrome, limits their ability to learn" (Scanlon, Denver Rocky Mountain News, 5/9). Professor Andre Rosenthal of the Institute for Molecular Biotechnology in Jena, Germany, said the lower number of genes in Chromosome 21 may mean the total sum of genes in human DNA is not 100,000 or more, as previously thought, but less than 40,000 (AP/Philadelphia Inquirer, 5/9). According to Johns Hopkins School of Medicine geneticist Robert Reeves, "We will not have a gene therapy tomorrow as a result of finding the sequence today. But it will allow the research community to greatly focus on a small set of genes as the primary cause of what goes wrong in Down syndrome" (Jacobs, Los Angeles Times, 5/9). The map of Chromosome 21 also could help explain why those with Down syndrome have very low rates of breast, lung and gastrointestinal cancers, Rudolph Tanzi, professor of neurology at Harvard Medical School, said, noting that an extra copy of the chromosome could have "tumor-suppressing qualities." A report on the Chromosome 21 map, which is only 99.7% complete due to technical limitations, will be published this Thursday in Nature (Callahan, AP/Austin-American Statesman, 5/9).This is part of the California Healthline Daily Edition, a summary of health policy coverage from major news organizations. Sign up for an email subscription.