Although scientists have known for several years that the presence of the 4 form of the gene known as apolipoprotein-E (APOE), or APOE- 4 allele (gene variation), is associated with an increased risk of Alzheimer’s disease among whites, the risk posed by the gene has not been so clear-cut among African Americans and Hispanics.
Now, researchers from Columbia University College of Physicians & Surgeons have discovered that African Americans and Hispanics have an increased risk of Alzheimer’s disease whether or not they carry the APOE- 4 allele.
The discovery could lead to a better understanding of other genes or risk factors that may contribute to Alzheimer’s disease. The study, published in the March 11 issue of the Journal of the American Medical Association, reports that African Americans and Hispanics with the APOE- 4 allele have approximately the same risk of Alzheimer’s disease as do whites with the allele. But African Americans without the APOE- 4 genotype had four times the risk of developing Alzheimer’s disease than did whites without the genotype, and Hispanics had 2.5 times the risk.
“This indicates that either there are genes that modify APOE- 4 or there are different genes involved,” says Dr. Richard Mayeux, senior investigator, Gertrude H. Sergievsky Professor of Neurology, director of the Sergievsky Center, and co-director of the Taub Center for Alzheimer’s Disease Research. “It suggests that there is probably a whole new way to approach the etiology of Alzheimer’s disease.”
The study was funded by the National Institute on Aging and the Alzheimer’s Association. Dr. Ming-Xin Tang, lead author and assistant professor of biostatistics in the Gertrude H. Sergievsky Center, and colleagues determined the genotypes of approximately 1,000 elderly volunteers, all residents of Washington Heights.The researchers then monitored the health of the volunteers over five years to assess them for signs of Alzheimer’s disease (all volunteers were free of any signs of disease at the start of the study).
The researchers controlled for other factors that might affect the risk of the disease, such as education levels. And to reduce the likelihood that the results might be swayed by a misdiagnosis of Alzheimer’s, the researchers also calculated their results only among those who developed severe disease. The researchers are not certain what causes the increased risk among the two minority groups.
“It could be genetic or it could be due to environmental factors,” says Dr. Tang. “More broad-based studies are needed.” The researchers are now proposing a follow-up study. Notes Dr. Mayeux, “This research highlights an important point: When something is found to be true among the white population, we can’t automatically assume it will be true for other ethnic groups as well.” The study’s other authors were Drs. Yaakov Stern, Karen Marder, Karen Bell, Barry Gurland, Rafael Lantigua, Howard Andrews, Lin Feng, and Benjamin Tycko.