Rare case of human-to-human transmission of Alzheimer’s found in recipients of banned treatment

London, United Kingdom

A new study suggests that Alzheimer’s can spread from human to human after an odd case involving five patients emerged in the United Kingdom, but the researchers have stressed that this happened only after a rare medical accident and the disease cannot spread through everyday activities. 

About the study

The study, published in the journal Nature Medicine, on Monday (Jan 29), addresses the first reported evidence of medically acquired Alzheimer’s disease in what appears to be the result of contaminated injections that the patients received as children decades ago. 

According to the study, all five patients received injections of human growth hormone from donors’ pituitary glands – located at the base of the brain – who developed early onset Alzheimer’s.

However, it seems like what the scientists did not realise at the time is that in some cases another substance was extracted as well which contaminated the batches with another substance – amyloid-beta protein, which is a key component of Alzheimer’s disease when it forms plaque in the brain. 

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Notably, abnormal buildup of the protein amyloid beta in the brain is associated with Alzheimer’s disease. However, in this particular case, researchers cannot explain how being exposed to these proteins could trigger the creation of plaque in the brain.  

“We’re not suggesting for a moment you can catch Alzheimer’s disease. This is not transmissible in the sense of a viral or bacterial infection,” said Professor John Collinge, lead of the study and director of the Medical Research Council (MRC) Prion Unit at University College London (UCL) as quoted by The Guardian. 

He added, “It’s only when people have been accidentally inoculated, essentially, with human tissue or extracts of human tissue containing these seeds, which is thankfully a very rare and unusual circumstance.”

In the study, researchers said five people who got Alzheimer’s due to a now-banned treatment were among the 1,848 patients in the UK, between 1959 and 1985, who received human growth hormone extracted from the pituitary glands of cadavers. 

The practice was banned in 1985 following the deaths of some participants who died after some hormone samples were found to be contaminated with Creutzfeldt-Jakob disease (CJD)-causing proteins.

Why is this study important?

So far, scientists have been able to categorise Alzheimer’s cases into two groups, first, the cases caused by genetic mutations and second, those that develop in people over 65 due to a number of risk factors. 

Since the patients did not fit into either criterion the study suggested a third way for Alzheimer’s to develop, through contaminated medical products. 

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“I should emphasise these are very rare occurrences, and the majority of this relates to medical procedures that are no longer used,” Collinge said at a news briefing, as quoted by CNN. 

The authors of the study also noted that while other patients who received cadaver-derived hormones are at higher risk of Alzheimer’s they do not expect to see a wave of cases. 

“The actual risk of transmission of Alzheimer’s disease in this context is really very low and these are probably going to be very rare cases,” said the lead author as quoted by NBC News. 

(With inputs from agencies)