People may be able to contract Alzheimer’s disease during certain medical procedures in the same way that Creutzfeldt-Jakob disease (CJD) is transmitted, suggest researchers from University College London.
Autopsy studies of the brains of people who died from CJD have revealed tell-tale signs of the pathology associated with Alzheimer’s disease, in addition to the damage caused by CJD.
John Hardy, a molecular neuroscientist at UCL:
This is the first evidence of real-world transmission of amyloid pathology. It is potentially concerning.”
However, the researchers stress that the findings are not conclusive and Alzheimer’s cannot be “caught” by coming into contact with people who have the condition.
The team studied the brains of eight people who had died from CJD, which they had contracted through treatment with contaminated human growth-hormone (hGH) given to them decades previously. In six of the brains, there was evidence of the protein misfolding that is observed in Alzheimer’s disease, which has raised concerns that thousands of other people previously treated with hGH may develop Alzheimer’s in the future. Furthermore, some scientists are worried that Alzheimer’s could potentially be contracted in the same way as CJD, through contaminated surgical instruments or blood transfusions, for example.
CJD is one of several neurodegenerative diseases caused by the presence of an abnormally folded protein referred to as a prion (PrP). Once these misfolded prion proteins appear, they aggregate to form clumps that lead to neuronal loss and the other brain damage seen in CJD. Researchers now believe that Alzheimer’s may share a similar pathology and in this case, it is the peptide amyloid-β that is misfolded and forming clumps or “plaques.”
None of the patients studied had any clinical symptoms or family history of Alzheimer’s disease and they were only aged between 36 and 51 years when they died. Yet, in four of the six brains, the amyloid-β pathology was widespread. Since this pathology is rare in people of such young ages, the scientists suspected that the hGH injections received by the patients were contaminated not only with CJD, but with amyloid “seeds,” which the plaques then grew from.
Further analysis showed that none of the patients carried genes that predispose to Alzheimer’s or other neurodegenerative diseases. The researchers also looked at patients of a similar age who had died of CJD or other prion diseases but who had never been treated with hGH and among those patients, no evidence of the amyloid pathology was observed.
John Collinge, one of the paper’s authors and neurologist at UCL said:
We think that the most plausible explanation for the occurrence of the amyloid pathology is that it had been transmitted by particular hGH extracts that happened to be contaminated with amyloid-β seeds as well as the CJD prions.”
If this were the case, amyloid-β would have been present much more frequently in the different hGH batches than PrP, because Alzheimer’s is such a common disease.
Collinge has contacted the Department of Health to see whether any old stores of hGH can be checked for the amyloid seeds. However, he says he does not believe there is any need for concern and that no one should avoid or delay surgery because of this.
As Eric Karra, director of Research at Alzheimer’s UK points out:
While the findings sound concerning, it's important to remember that human-derived hormone injections are no longer used and were replaced with synthetic forms since the link to CJD was discovered in the 1980s."
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