Alzheimer's disease is thought to afflict up to four million Americans, according to current estimates. And with baby boomers aging, that number stands poised to increase significantly in coming years. Researchers are thus scrambling to identify risk factors for this neurodegenerative disorder and understand the biological mechanisms by which the disease unfolds, in hopes that this information will lead to improved treatment and prevention. So far, a gene on chromosome 19 and perhaps one on 12 appear to be risk factors for late-onset Alzheimer's. Now, following yesterday's announcement of a potential Alzheimer's vaccine, three separate studies described in the journal Science suggest that chromosome 10 may also house a risk factor.

In the first study Alison Goate of Washington University and her colleagues identified a region on chromosome 10 that appears to contain a risk factor and concluded that the Alzheimer's susceptibility gene in this region could be as influential as the apolipoprotein E (APOE) gene on chromosome 19. Michael Hutton and Steven Younkin of the Mayo Clinic in Jacksonville, Fla., led the second study, which pinpointed the same region on chromosome 10. The third report, in contrast, provides evidence of an Alzheimer's locus in a different area of the chromosome. Rudoph E. Tanzi of Harvard Medical School and his colleagues concentrated on chromosome stretches near the gene that makes insulin degrading enzyme, which may also play a role in degrading so-called amyloid beta protein. In fact, all three studies suggest that this newly discovered genetic influence may affect the processing of amyloid beta protein, a peptide important in the formation of the amyloid plaques found in the brains of Alzheimer's patients.

"We still have a long way to go," Younkin says. "The next step will be to find the chromosome 10 gene and to figure out how it works. If things go as they have historically in this field, that will take us to new therapeutic targets."