Gene May Explain 5% of Inherited Alzheimer's Disease Cases
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Reviewed By Laura J. Martin, MD
April 14, 2010 (Toronto) -- A newly identified gene appears to increase a person's risk of developing late-onset Alzheimer's disease, the most common type of Alzheimer's disease.
People with a particular variation in the gene, dubbed MTHFD1L, may be nearly twice as likely to develop Alzheimer's disease as people without the variation.
Still, the absolute risk of developing Alzheimer's will be "very small" for any given individual that carries the variant, says Margaret Pericak-Vance, PhD, director of the University of Miami Miller School of Medicine's John P. Hussman Institute for Human Genomics.
The study was presented at the annual meeting of the American Academy of Neurology.
Gene May Explain 5% of Inherited Alzheimer's Disease
The search for new genes that predispose people to Alzheimer's disease has been quite slow, Pericak-Vance tells WebMD.
It's been nearly two decades since researchers discovered the variants in the ApoE gene that are associated with an increased risk for late-onset Alzheimer's disease, which affects people 60 and older.
A mixture of genetic and environmental factors is thought to cause late-onset Alzheimer's disease. About 60% to 80% of the disease is attributable to genetics, and about 40% of that genetic effect is attributable to the ApoE4 variant.
MTHFD1L may help explain another 5% of inherited cases of the disease, Pericak-Vance says.
What makes this discovery "so exciting" is that the gene is known to be involved in the metabolism of folate, which in turn influences the body's levels of homocysteine, she says.
High levels of homocysteine, which are associated with too little folate in the diet, have been shown to be a risk factor for Alzheimer's disease, she says.
"A lot of the time we find a gene and have to figure out how it ties in to the disease. This finding melds the genetics with the biology," Pericak-Vance says.
Genome-Wide Technique Aids Finding of New Alzheimer's Gene
Pericak-Vance says the discovery was made possible by a technique known as a genome-wide association study (GWAS) that lets scientists look throughout the entire genome for small differences, or variants, in long stretches of DNA that are more common in people with a particular disease.
For the new study, the researchers used GWAS to look for gene variants in about 1,100 people with late-onset Alzheimer's disease and 1,000 people without the disease.
About 9% of those with late-onset Alzheimer's had the MTHFD1L variant on chromosome 6, compared with only 5% of those who did not have Alzheimer's.
The researchers then replicated the findings in 2,500 people, about 1,300 of whom had the disorder.
That replication gives "us more confidence" the finding is real, says Ron Peterson, director of the Mayo Alzheimer's Disease Research Center in Rochester, Minn.
Several other research teams have reported homing in on gene variants involved in Alzheimer's over the years, he says, but the findings often could not be duplicated.
"It's also always nice if the genetics make sense with the biology of the disease," as is the case here, Peterson tells WebMD.
Having genes that can help pinpoint who will develop Alzheimer's disease before symptoms develop will be even more beneficial once drugs to prevent or slow the course of the disorder become available, he says.
Few people have opted to be tested for the ApoE gene, even though testing is available, according to the Alzheimer's Association.
The World Health Organization estimates that there are 18 million people worldwide with Alzheimer's disease, a figure projected to nearly double to 34 million by 2025. There are more than 5 million Americans living with Alzheimer's disease.
The study was supported by the National Institutes of Health and the National Institute on Aging.
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Margaret Pericak-Vance, PhD, director, John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine.
Ron Peterson, director, Mayo Alzheimer's Disease Research Center, Rochester, Minn.
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