This is expected to provide scientists with a much clearer route to developing new treatments.

The team shared their data with another French-led study, which has revealed compelling evidence for a third gene associated with Alzheimer's called CR1.

The paper's lead-author, Julie Williams, professor and chief scientific adviser to the Alzheimer's Research Trust, said: 'This research is changing our understanding of what causes the common form of Alzheimer's disease and provides valuable new leads in the race to find treatments and possibly cures.'

These findings were published in Nature Genetics.