Until recently, only one of the approximately 30,000 genes in the human genome has been linked to risk of late-onset Alzheimer's disease (AD). Now, a new NIH-supported study in the Nov. 19, 2007, issue of "NeuroReport" (now online) used a publicly shared genome dataset to strongly support findings that variation in the sequence of the SORL1 gene may be a second risk factor gene for late-onset disease.
Identifying the genes involved in AD ultimately may help determine who may be at greater risk and enable researchers to zero in on pathways to develop new treatments.
The National Institute on Aging (NIA), part of the National Institutes of Health (NIH), funded the study, along with the Canadian Institutes of Health Research and a number of private foundations in the U.S., Canada and Japan.
Three mutated genes - amyloid precursor protein (APP) and the presenilins (PS1 and PS2) - have been shown to cause rare, early-onset, familial forms of the disease which mostly occur in middle age. A gene variant - apolipoprotein e4 (APO-e4) - was the first confirmed risk factor for the common form of late-onset AD, which typically occurs after age 65.
Earlier this year, researchers first linked variations in the gene SORL1 to late-onset AD. The analysis involved 14 collaborating institutions in North America, Europe and Asia, and 6,600 people who donated blood and tissue for genetic typing.
This new study confirms those findings and in a novel way. Lindsay A. Farrer, Ph.D., of the Boston University School of Medicine and colleagues accessed data from a genome-wide association study (GWAS) recently made publicly available online by the Translational Genomics Research Institute (TGen).
GWAS involves rapidly scanning for markers across the complete set of DNA of many people to find genetic variations related to a particular disease. By analyzing TGen's data on the DNA of 1,408 cases and controls, Dr. Farrer's study replicated the findings of the earlier studies that linked SORL1 data to late-onset AD.
"These results are especially remarkable since this gene was not a focus of the original TGen study which generated the data used to test our hypothesis," Farrer said.
"This is the first example of publicly available data from a genome-wide association study to confirm the identification of a risk factor gene," said Marcelle Morrison-Bogorad, Ph.D., director of the Neuroscience and Neuropsychology Program at NIA. "This shows the tremendous benefit of highly collaborative interaction and rapid data sharing. Sample sharing greatly increases the likelihood of finding new risk factor genes relatively quickly and inexpensively."