Researchers say they are closing in on a second gene linked to late-onset Alzheimer’s disease, a gene that could account for 10 percent to 15 percent of cases of the ailment, which causes cognitive impairment and memory loss.
They said Tuesday that the gene functions independent of a gene found in 1993 that also was linked to late onset of the disease, defined as occurring in people age 60 or over. Several additional genes previously have been associated with Alzheimer’s but only with rare, early-onset forms.
In a separate genetics study announced Tuesday, scientists said they may be better able to determine who is most likely to carry a genetic mutation linked to breast and ovarian cancer.
The Alzheimer’s and breast-cancer research results were announced at a news conference in Chicago before the Wednesday publication of the Journal of the American Medical Association, where both studies appear.
This week’s issue of JAMA largely is devoted to genetic research. During the next year, the American Medical Association will be “very much involved” in genetic issues because they increasingly are a part of the daily practice of medicine, said Dr. Reed Tuckson, the association’s group vice president for professional standards. Those issues will include cloning, ethics, testing and test marketing, screening, gene therapy and patents.
Researchers examining genetic links to Alzheimer’s hope that a better understanding of the genetic predisposition to the disease eventually could lead to treatments to delay its onset.
An estimated 4 million people in the U.S. have Alzheimer’s disease, a leading cause of dementia in the elderly. That number is expected to increase significantly in the next century as Baby Boomers age.
The researchers, led by Margaret Pericak-Vance at Duke University Medical Center, haven’t yet isolated the second gene linked to late-onset Alzheimer’s, but they believe they have narrowed it to a section of chromosome 12.
Genes, however, probably are not solely responsible for Alzheimer’s disease. Environmental factors also are believed to be important, interacting with genetic influences in ways that scientists do not yet understand.
The researchers collected information for further study on about 20 factors that may be important, including environmental exposures, head trauma, dietary regimen, smoking history and cardiovascular disease.
In the breast-cancer study, researchers examined 798 people who were in extended families at a heightened risk of breast cancer. These families had multiple cases of the cancer among relatives, someone who developed breast cancer early, someone who had ovarian cancer and other factors.
Researchers suggested the definition of “early” breast cancer be widened to include women in their 40s, not just 20s and 30s.
Lead author Donna Shattuck-Eidens collaborated with 58 colleagues at 20 institutions in the U.S., Italy, Germany, Finland and Switzerland.
As in Alzheimer’s, genetic susceptibility is just one piece of the breast-cancer puzzle. An estimated 5 percent to 10 percent of female breast cancer is attributed to the inheritance of a genetic mutation of one of two genes known as BRCA1 and BRCA2 (for breast cancer 1 and breast cancer 2). In the study announced Tuesday, researchers studied BRCA1 mutations; it was the largest study ever conducted of this gene.
It generally has not been possible, researchers said, for doctors to determine which individuals in high-risk families carry a mutation that would raise their risk of cancer. As a result, some women have taken dramatic steps to decrease their cancer risk, including having their breasts removed before developing the disease.
“This study will assist physicians in determining which patients are at highest risk of having a BRCA1 mutation and will help those women and family members seek care that may save their lives,” said Shattuck-Eidens.
