The findings provide the first evidence of dementia transmission in humans via microscopic protein fragments.
Health officials and experts were quick to reassure the public after the highly controversial research was reported in the journal Nature. However the findings prompted speculation about the safety of some medical procedures, including dental treatments. Blood donations are not considered a meaningful risk, but should be investigated, said the researchers.
University College London (UCL) scientists stumbled on the discovery while investigating a rare form of “iatrogenic” Creutzfeldt Jakob Disease (iCJD), a brain-destroying condition known to be spread by contaminated surgical instruments and procedures. They inspected the brains of eight patients who died from the disease after receiving pituitary growth hormone extracted from cadavers.
Unexpectedly, six bore a clear molecular hallmark of Alzheimer’s - sticky clumps of fragmented protein called amyloid beta that form among neurons and on the walls of blood vessels. In four cases, the amyloid deposits were widespread and only one patient was not affected at all.
All eight individuals were relatively young, aged 36 to 51, and none had genetic variants associated with early-onset Alzheimer’s disease.
The evidence points to the hormone carrying “seeds” of the Alzheimer’s protein into the patients’ brains as well as CJD.
Since the prion proteins responsible for iCJD can be transmitted in other ways - for instance, by neurosurgery - experts are not ruling out the possibility that the same is true for the Alzheimer’s molecule.
Lead scientist Professor John Collinge, of the Medical Research Council Prion Unit at UCL, said there was increasing evidence that neurodegenerative diseases including Alzheimer’s might, in rare circumstances, be “acquired”.
He said: “You could have three different ways you have these protein seeds generated in your brain. Either they happen spontaneously, an unlucky event as you age, or you have got a faulty gene, or you’ve been exposed to a medical accident. That’s what we’re hypothesising.” He pointed out that, like CJD prions, amyloid beta protein fragments stick to metal surfaces and resist conventional sterilisation.
Dr Tara Spires-Jones, Reader and Chancellor’s Fellow at Edinburgh University’s Centre for Cognitive and Neural Systems, said the study was “scientifically important” but there was no evidence that the disease was transmissible through dental procedures.
Previous experiments on laboratory mice and monkeys had already shown that transmission of the Alzheimer’s protein is theoretically possible.