PARIS (AFP) - Scientists said Sunday they had uncovered five genes linked to the onset of Alzheimers disease, doubling the number of genetic variants known to favour the commonest form of dementia. The findings, published in the journal Nature Genetics, may provide clues on the causes of this incurable and complex disease and help doctors predict who is most at risk, they said. In the largest such studies to date, some 300 scientists in two consortia combed the genomes of 54,000 people - some afflicted, others not - to tease out the newly identified genetic variations. The two projects started out independently but later swapped their data, enabling each group to confirm the overall findings. Prior to these studies, there were five accepted late-onset genes, said Gerard Schellenberg, a researcher at the University of Pennsylvania School of Medicine and the main architect of one of the studies. Now there are five more - MS4A, ABCA7, CD33, EPHA1 and CD2AP, he said in an email exchange. Identifying which snippets of DNA contribute to Alzheimers boosts our understanding of the role of inheritance in its onset, Schellenberg said, adding that others surely remained to be found. But, he added, the biggest contribution will be in helping to understand the underlying mechanism that causes Alzheimers. These genes highlight new pathways that are critical to the disease process. Over the course of the illness, unwanted proteins form plaque in some areas of the brain, ultimately destroying neurons and leading to irreversible brain damage. Typically, symptoms include memory loss, erratic behaviour and eventually full-on dementia.