50+ health * Mental wellbeing

Two new genetic risk factors for Alzheimer's disease found

new genetic breakthrough in alzheimers Study also found 13 other factors worth investigating

An international team of scientists has identified two more genetic risk factors for Alzheimer's disease.

Prior to this study, only four genes had been definitively associated with Alzheimer's disease. Three genetic mutations have been identified as causes of rare, inherited forms of early-onset Alzheimer's. The fourth gene, APOE4, is the only one previously linked to the more common late-onset form of the disease.

Drawn from the largest ever genetic study involving patients with Alzheimer's disease, the findings identified two new genes that appeared to be involved in elevated risk for Alzheimer's and confirmed the importance of APOE4.

DNA samples were taken from nearly 20,000 older European and U.S. residents, 7,000 of whom had Alzheimer's, the rest having no symptoms of the disease.

The group, led by investigators from the School of Medicine at Cardiff in the United Kingdom and including scientists from Washington University School of Medicine in St. Louis, completed the largest genome-wide association study ever involving patients with Alzheimer's disease. The study pooled DNA samples from more than 19,000 older European and U.S. residents. Seven thousand had Alzheimer's disease, and the others had no clinical symptoms of the disorder.

"There's good evidence that these new genes may be novel risk factors, the first discovered since APOE in 1993," says Washington University researcher and co-author Alison M. Goate, D.Phil. "So it's a very important observation because this study is the first to provide such significant evidence of novel genetic risk factors for the most common form of Alzheimer's disease."

"These genes are both significant, but their effect appears to be much smaller than that of the APOE gene," Goate says. "Using statistical methods, we've been able to estimate the amount of risk attributable to APOE at about 19 or 20 percent. The newly identified genes each come in under 10 percent, so it appears they have a much smaller effect."

The other gene, PICALM, appears to be involved in the breakdown of synapses, structures that allow neurons in the brain to communicate. Some scientists also hypothesize that the gene may be involved in the development of amyloid deposits, but Goate says much more work is required to identify exactly how PICALM elevates Alzheimer's risk.

She expects many more genes also are involved in Alzheimer's risk. In fact, this study identified 13 more gene variants worthy of further investigation.

The study was lead by scientists at the School of Medicine of Cardiff University, and was reported in the online edition of the journal Nature Genetics.

This article was published on Mon 7 September 2009



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