Five more genes which increase the risk of developing Alzheimer's disease have been identified, scientists say.
It takes the number of identified genes linked to Alzheimer's to 10 - the new genes affect three bodily processes and could become targets for treatment.
If the effects of all 10 could be eliminated the risk of developing the disease would be cut by 60%, research published in Nature Genetics says.
However, the international team warns new treatments could be 15 years away.
The disease is thought to be up to 80% genetic. The first gene linked to the disease, APOE, was discovered more than 17 years ago but no new genes were discovered until 2009.
As Professor Kevin Morgan, from the University of Nottingham, put it: "We were basically clueless."
The newly discovered genes affect three processes in the body: the way it deals with fat and cholesterol; the mechanism by which brain cells process big molecules (endocytosis); and the immune system.
Cardiff University's Professor Julie Williams, who led the international study, said: "What I find exciting is that we have found specific gene processes, we now have precise targets to identify treatments."
She said that if the effect of these genes could be eliminated then the number of cases could be reduced by 60%.
"There are 500,000 people with Alzheimer's [in the UK] so if you could prevent 60% that would be 300,000 people," she said.
Prof Morgan said: "This disease is devastating, people are desperate for any hope or advance. I've no doubt it will come, but the time frame is 10 to 15 years."
The disease is a growing problem because of an ageing population. The Alzheimer's Society predicts the number of people with dementia will reach one million by 2021.
Health economists already believe the cost to the UK of dementia is £23bn every year.
Rebecca Wood, chief executive of Alzheimer's Research UK, which part-funded the study, said: "These findings are a step towards defeating dementia.
"We are yet to find ways of halting this devastating condition, but this work is likely to spark off new ideas, collaborations and more research.
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said: "These two robust studies mark an exciting development for scientists hoping to identify a cause and find a cure for Alzheimer's disease.
"Although these studies will not bring us any closer to being able to predict who might be at greater risk of developing Alzheimer's, they will give scientists clues as to how Alzheimer's might develop, most importantly their identification could also lead to the development of new drug treatments in the longer term."