Alzheimer’s can spread from person to person through rare medical accidents, although experts stress that there is no evidence that the disease can be transmitted between people through everyday activities or routine care.
Researchers say a handful of people who received human growth hormone from the pituitary glands of deceased donors developed Alzheimer’s earlier — likely because the hormones used were contaminated with proteins that seeded the disease in their brains.
“We are not suggesting for a moment that you can get Alzheimer’s disease. It is not transmissible in the sense of a viral or bacterial infection,” said Prof John Collinge, co-author of the study and director of the MRC Prion Unit.
“It’s only when people are accidentally inoculated, essentially, with human tissue or extracts of human tissue that contain these seeds, which fortunately is a very rare and unusual circumstance.”
The team says the new work adds weight to the idea that Alzheimer’s has similarities to prion diseases, including in the mechanism by which the proteins in question spread across the brain.
Prion diseases, which include Creutzfeldt-Jakob disease (CJD), curu and BSE, are caused by infectious, misfolded proteins that reproduce in the brain. These diseases typically occur spontaneously, but more rarely they can arise as a result of a genetic mutation, or be transmitted through infected brain or nervous tissue.
Writing in the journal Nature Medicine, Collinge and colleagues report how between 1959 and 1985, at least 1,848 patients in the UK received human growth hormone extracted from the pituitary glands of cadavers.
However, the practice was banned in 1985 after some patients came forward subsequently deceased from CJD due to hormone samples contaminated with CJD-causing proteins.
Of the 80 such cases in the UK, some were also found to have a protein called amyloid-beta in their brains when they died – a hallmark of Alzheimer’s disease. Although it was unclear whether they would develop symptoms of Alzheimer’s, other research showed that amyloid-beta was present in some of the hormone clusters, and that it caused Alzheimer’s-like disease when administered to mice.
Researchers reported findings from all eight people referred to the National Prion Clinic between 2017 and 2022.
All had received human growth hormone from cadavers but did not have CJD. Five had dementia symptoms that met clinical criteria for Alzheimer’s disease, with onset as young as 38 years of age. Three of these patients had brain scans consistent with the diagnosis, while two had biomarkers that met criteria for Alzheimer’s disease.
Of the other three patients, one had mild cognitive impairment, one had self-reported cognitive problems, and one had no such symptoms, with the former showing postmortem results consistent with Alzheimer’s and the latter meeting biomarker criteria for the disease.
Five patients had DNA data, but only one showed a genetic risk factor for late-onset Alzheimer’s, and none had genetic variants known to cause early-onset Alzheimer’s.
The researchers add that the patients showed some symptoms that differ from those typical of Alzheimer’s disease, which either arise spontaneously or are linked to genetic risk, which they claim can either be due to their disease that have a different origin, either due to different “strains” of amyloid-beta.
The results, they say, provide evidence that Alzheimer’s disease may arise as a result of treatment with the contaminated pituitary hormone.
While the cases involved repeated exposure to contaminated human growth hormone over a period of years, Collinge and colleagues say the findings raise the importance of measures such as ensuring effective decontamination of surgical instruments.
However, Andrew Doig, professor of biochemistry at the University of Manchester, said experts were already very cautious about transferring brain tissue between people.
Doig also cautioned that only eight patients were involved in the study, some of whom did not have genetic data, while there was no direct evidence yet for different strains of amyloid-beta.
“While the new type of Alzheimer’s reported here is of great scientific interest as it reveals a new way of spreading the disease, there is no reason to fear it as the way the disease is caused is more than 40 was discontinued years ago,” said Doig. “Disease transmission from human brain to brain in this way should never happen again.”
