If shown to be effective in larger trials, the first drug to prevent dementia could be available in just a few years.

"The results of this clinical study make us optimistic that we can potentially make a great step forward in treating Alzheimer's disease," said Prof Roger Nitsch, at the Institute for Regenerative Medicine at the University of Zurich.

“In the high dose group the amyloid has almost completely disappeared. The effect size of this drug is unprecedented.

“Despite it being a small sample there appeared to be a slowing of cognitive decline and functional decline. The group with a high degree of amyloid removal were basically stable. If we could reproduce this it would be terrific.”