Two discoveries have moved scientists toward solving the riddle of what causes Alzheimer's disease, which devastates memory and personality among an estimated 4 million Americans.
A Boston research group said yesterday that it has found a gene variant that more than triples a person's risk of developing late-onset Alzheimer's compared with siblings without the gene. Thirty percent of the U.S. population may carry the newly discovered gene, called A2M-2.
The discovery suggests the possibility of a drug mimicking the gene's normal function, scientists said, protecting susceptible individuals against brain damage or perhaps even reversing it.
Meanwhile, researchers at the University of Texas in San Antonio have revised scientists' understanding of the only other established gene for late-onset Alzheimer's, called apoE-4. That gene, carried by 4 percent to 8 percent of Americans, does not determine whether an individual is likely to develop the disease, as scientists thought. But those who have it are likely to get Alzheimer's symptoms at a somewhat earlier age.
"The apoE-4 gene affects 'when' and doesn't affect 'whether,' " said Dr. Deborah Blacker of the Massachusetts General Hospital, a member of the group that discovered the new late-onset gene. On the other hand, A2M-2 affects "whether" but not "when."
Reports on both findings will appear in the August issue of the journal Nature Genetics. The findings were released early to coincide with presentations at an international Alzheimer's meeting in the Netherlands.
Much of scientists' excitement about the new late-onset Alzheimer's gene stems from the fact that scientists already know a good deal about its normal function and the protein it makes. Often when researchers find a disease-linked gene they don't know what it does, and sometimes they can't even identify a specific gene but only a "region of interest" on the chromosome where the gene resides -- the equivalent of locating the haystack but not the needle.
"This is very exciting," commented Dr. Steven Moldin of the National Institute of Mental Health, "because it implicates a precise part of a specific gene."
Pub Date: 7/23/98