Alzheimer’s disease is not infectious (part 2)
If you have been following our blog you probably saw a similar post only a few months ago. But, since very similar headlines re-appeared last week, I thought it was worth discussing once again the news telling us that Alzheimer’s disease is infectious. The headlines were quite dramatic: “Alzheimer’s can be transmitted from one person to another” in the Independent, or “Can you CATCH Alzheimer’s? Fresh fears emerge amid claims of a second case of transmission from a transplant” in the Daily Mail.
These pieces follow a recent study conducted by a team of researchers in Switzerland and Austria who describe autopsy results consistent with the possibility of Alzheimer’s being transmitted during specific medical procedures. These findings represent a completely independent replication of what was reported by a UK study published in Nature last September.
Both studies analysed brains from patients who died of the rare Creutzfeldt–Jakob disease (CJD) contracted after treatment with contaminated batches of growth hormone, which was derived from human cadavers. In addition to the pathology CJD, markers associated with Alzheimer’s disease were also detected (in particular, insoluble protein aggregates called amyloid).
The growth hormone injection was a procedure applied mainly to children with atypical growth rates, but it was stopped in 1985. Some of the preparations were contaminated with CJD prions, and at least 200 people died of this disease decades after receiving the injections. CJD has a long incubation time and number of cases are likely to become higher. None of the individuals showing amyloid aggregates in their brain had Alzheimer’s disease, but this also has a long incubation and it is possible symptoms were not visible before dying of CJD.
Both studies are interesting because they describe a new route leading to development of a pathology considered to be causative of Alzheimer’s.
In summary, both studies show that an outdated procedure conducted with contaminated material has caused CJD and brain damage similar to what is observed in Alzheimer’s. Conversely, none of the studies showed directly that this procedure has caused Alzheimer’s, or, most notably, that Alzheimer’s can be transmitted from person to person. But of course, the “person-to-person transmission” makes a catchy headline and a strong story, and this is what the media have focused on, in spite of what happened a few months ago.
In fact, the alarmist headlines we saw in September prompted the release of high profile statements to explain the meaning of the original findings. For example, the Chief Medical Officer Professor Dame Sally Davies said: “There is no evidence that Alzheimer’s disease can be transmitted in humans, nor is there any evidence that Alzheimer’s disease can be transmitted through any medical procedure.” Following this statements most of the news outlets published new articles to correct themselves. The Independent said “Claims Alzheimer’s can be caught are ‘misleading and unnecessarily concerning for the public‘. So it is ironic to see the present headlines that contradict these clarifications.
I do not want to repeat myself to describe the significance of this story as I have already discussed it in a previous post, but I would like to highlight one more time how these studies have been misinterpreted and how the media focused on what is newsworthy, which was not described in the scientific papers. For example, the use of phrases like “new evidence supports Alzheimer’s transmission” is totally incorrect. While the results described in both studies are consistent and the second study indeed shows new evidence supporting the original findings, none of them have actually shown that you can catch Alzheimer’s as you would catch the flu!
Frontzek, K. et al. (2016). Amyloid-β pathology and cerebral amyloid angiopathy are frequent in iatrogenic Creutzfeldt-Jakob disease after dural grafting. Swiss Medical Weekly. DOI: 10.4414/smw.2016.14287
Jaunmuktane, Z. et al. (2015). Evidence for human transmission of amyloid-β pathology and cerebral amyloid angiopathy. Nature. DOI: 10.1038/nature15369