Brain cells affected by Alzheimer's have been created artificially for the first time, providing an invaluable new research tool for scientists.
Experts hope improved versions of the "model" cells will lead to greater understanding of the disease and speed up the search for new treatments.
The cells were made by reprogramming skin cells taken from two patients with a rare inherited form of Alzheimer's.
They were turned into induced pluripotent stem cells (iPSCs) with the same properties as stem cells obtained from embryos.
Like embryonic stem cells, iPSCs have the potential to grow into a virtually limitless range of human tissues.
Carefully-selected iPSCs from those created from the Alzheimer's patients went on to develop into neurons displaying biochemical hallmarks of the disease.
The US research appears in the journal 'Nature'. Senior author Professor Lawrence Goldstein, from the University of California at San Diego, said: "The differences between a healthy neuron and an Alzheimer's neuron are subtle. It basically comes down to low-level mischief accumulating over a very long time, with catastrophic results.
"At the end of the day, we need to use cells like these to better understand Alzheimer's and find drugs to treat it."
The research has already yielded some surprising findings.
One of the early changes in Alzheimer's neurons thought to be a triggering event turned out to have little significance. A different early event was shown to play a bigger role.