By comparing genome-wide data and brain MRIs from more than 700 people, scientists have confirmed that 4 suspect genes are tied to Alzheimer’s disease. The researchers also linked the disease to 2 new genes, offering unexpected targets for future research.
Alzheimer's disease is an irreversible, progressive brain disease. It starts with mild memory problems and ends with severe brain damage. In most affected people, symptoms first appear after age 60.
Research suggests that Alzheimer's disease is up to 80% heritable, but until recently only one gene, known as APOE, had been linked to disease risk and age at onset. Last year, genome-wide association studies identified 3 additional chromosome regions, or loci, that affect Alzheimer's risk. Still, the underlying causes of the disease remain mostly unknown.
In the new study, scientists searched for connections between gene variants and specific brain changes typical of Alzheimer's disease. The researchers drew on publicly available data collected for the Alzheimer's Disease Neuroimaging Initiative. This research consortium conducts genome-wide analyses and collects neuroimaging and other data on older adults from across North America. The initiative is a public-private partnership funded primarily by NIH’s National Institute on Aging (NIA) and National Institute of Biomedical Imaging and Bioengineering (NIBIB), along with pharmaceutical companies and other organizations.
The scientists analyzed data on 168 Alzheimer's patients, 357 people with mild cognitive impairment (a precursor to Alzheimer's disease), and 215 who were cognitively normal. They scoured MRIs for structural traits in 6 brain regions linked to Alzheimer's disease, including changes in the size of the amygdala and hippocampus.
The researchers found that APOE had the strongest association with clinical Alzheimer's disease and was linked to all the neuroimaging traits except one. The 3 genes identified last year, along with 2 new target genes, had a significant cumulative effect on all 6 neuroimaging traits. The newly identified genes—BIN1 and CNTN5—are known to contribute to neuron function, although their roles are poorly understood.
"The genes we identified, and other genes that they interact with, will provide good targets for drug development in the future," says study coauthor Dr. Alessandro Biffi of Massachusetts General Hospital and the Broad Institute. "Still, with the information we have, we're not able to provide any type of personalized medicine for Alzheimer's disease, mainly because the effects of these gene variants are very weak."
Illustration: National Institutes of Health.
National Institutes of Health News Release (06/21/10)
Abstract (Archives of Neurology; Vol. 67, No. 6, 677-685 (06/10))