Researchers have identified a gene that appears to increase a person’s risk of developing late-onset Alzheimer's disease. Late-onset Alzheimer's strikes after age 65 and accounts for the vast proportion of the estimated 5.3 million people with Alzheimer's in the United States, and many more cases worldwide.
Dozens of genes are under investigation as possible contributing factors to Alzheimer's disease. Only one, called the APO-E4 gene, has been confirmed as a strong risk factor for late-onset disease, though not everyone who inherits this gene ends up with Alzheimer's. About 40 percent of those who develop late-onset Alzheimer's carry the APO-E4 gene.
“Only recently have common variants in genes other than APOE been convincingly shown to be associated with a person’s risk of developing late-onset Alzheimer’s disease,” said Margaret Pericak-Vance, Ph.D., the lead author of the study. Dr. Pericak –Vance is Director of the University of Miami Miller School of Medicine’s John P. Hussman Institute for Human Genomics in Florida.
Scientists hope that better understanding of the genetic mechanisms underlying Alzheimer's will help to clarify what goes wrong in the brains of those with the disease and one day lead to more effective treatments, or even a cure. The research will be presented as part of the late-breaking science program at the American Academy of Neurology’s 62nd Annual Meeting in Toronto.
The gene, called MTHFD1L, was isolated after researchers sifted through the genomes of more than five thousand men and women. This feat would not have been possible a few years ago, without the technology and data that grew out of the sequencing of the first human genome -- an undertaking known as the human genome projec). By comparing the genes of those who had Alzheimer's with those who did not have the disease, they identified variations in an area of chromosome 6.
The study found that individuals with a particular variation in the MTHFD1L gene may be almost twice as likely to develop Alzheimer’s disease as people without the variation. “We are hopeful our identification of MTHFD1L as a risk gene for Alzheimer’s disease will help us to better understand how this disease develops and potentially serve as a marker for people who may be at increased risk,” said Adam Naj, Ph.D., with the University of Miami Miller School of Meidicine’s John P. Hussman Institute for Human Genomics in Miami and the first author of the abstract reporting the discovery.
“Identifying this gene is important, because the gene is known to be involved in influencing the body’s levels of homocysteine, and high levels of homocysteine are a strong risk factor for late-onset Alzheimer’s disease,” Dr. Pericak-Vance said. High homocysteine levels have also been linked to cardiovascular disease.
Homocysteine is a substance made by the body that circulates in the blood. High levels of this substance can damage the heart and blood vessels, including the blood vessels that nourish the brain. Some studies in animals also suggest that high levels of homocysteine may make brain cells more vulnerable to damage from beta-amyloid, the toxic protein that builds up in the brains of those with Alzheimer's. Homocysteine itself may also be directly toxic to brain cells, research suggests.
Scientists hope that continued research into genes and their effects on the brain and memory could one day lead to new drugs that help to modify the course of Alzheimer's. But Alzheimer's is a complex disease and researchers have a long way to go before fully understanding the disease becomes possible. In addition to genetic factors, lifestyle factors like diet and exercise, mental and social stimulation, advancing age, and other environmental components may all play a role in its onset. It will likely take years of continued research to understand the roles of MTHFD1L and other genes in memory and Alzheimer's.
By ALZinfo.org, The Alzheimer's Information Site. Reviewed by William J. Netzer, Ph.D., Fisher Center for Alzheimer's Research Foundation at The Rockefeller University.
Source: American Academy of Neurology’s 62nd Annual Meeting in Toronto, April 10 – 17, 2010.