Alzheimer's is transmissible in extremely rare scenarios

Medical illustration of a neuron, in blue, in the background being surrounded by a plaque of amyloid-beta protein, in yellow with the illustration visualizing how the proteins join together .

For the first time, scientists have identified people with Alzheimer's whose disease was likely triggered by a medical treatment — one that's now been banned for decades. 

Alzheimer's is caused partly by the gradual accumulation of amyloid-beta and tau proteins in the brain, which trigger a cascade of events that lead to the death of brain cells. Now, a new study provides what may be the first clinical evidence that the "seeds" of these proteins can be extracted from one person and planted into another, sparking disease. However, this seed transfer occurred in a very specific and extraordinary medical context.