The long and winding journey to the roots of Alzheimer's disease, the most common form of dementia, has turned up three new genetic clues—the first major ones in 15 years.

Two separate groups of researchers—one based in Wales and the other in France—have confirmed links between the degenerative dementia and three specific genetic variations in humans. The French team, led by Philippe Amouyel, of the Pasteur Institute de Lille, pinpointed the genes CLU and CR1, and the Welsh team, led by Julie Williams, a professor of psychological medicine at the Cardiff University School of Medicine, found genes called Picalm and CLU.

"We didn't know before we finished the studies that we had the same genes," Amouyel told Bloomberg News. "The chance of that happening by accident is very low."

Smaller studies have turned up possible genetic links in the past, but these large projects—each testing more than 10,000 people, both with and without the disease—provided a new level of confidence for the association.

The results were published online in two separate papers on Sunday in Nature Genetics (Scientific American is part of the Nature Publishing Group).

Although other factors, such as a person's lifestyle or environment, may play a role in the onset of the disease, many researchers think genetics is the biggest factor. The new lineup of suspected genes all play a role in protecting the brain, and experts hope that as they learn more about how Alzheimer's is intertwined with genetics, they will "be able to triangulate down onto specific biological processes," Michael Owen, director of the Center for Neuropsychiatric Genetics and Genomics at Cardiff University and a senior investigator on the Welsh study, said at a press briefing. And that knowledge should bring them closer to devising better detection and treatment.

In all, estimate the lead authors, if these genes could be amended to function properly, they could reduce the number of people who develop the disease by 20 percent. The links aren't, however, frequent or adequately understood enough to have diagnostic or treatment value yet.

Aside from the three genes the groups uncovered, Williams said at the press briefing, "we found strong evidence that other genes play a role in disease risk." Those genetic traces have prompted researchers to follow up with an even larger study, one that will include 60,000 subjects.

The findings have also validated gene-hunting as a fruitful pursuit in the study of Alzheimer's. "It's a bit like we've been fishing with a fishing net and we've pulled out some fish, so we know that there are fish in the lake," Owen said at the briefing. "We now know that a number of fish are slipping out," he said, citing the fact that each group missed one of the other's top hits. "With a finer mesh net [a bigger study], we can catch them."

Image courtesy of Wikimedia Commons/NIH