Alzheimer’s disease is now considered a “prion disease” by some scientists.
Prions, short for proteinaceous infectious particles, are misfolded proteins that carry the ability to trigger further proteins to misfold, leading to debilitating brain disorders, including:
- Bovine spongiform encephalopathy (BSE or mad cow disease).
- Creutzfeldt-Jakob disease (CJD), the human form of mad cow disease.
- Scrapie in sheep.
Prions are unique in being an infectious agent without any genes, unlike viruses or bacteria. They are extremely tenacious, sticking to metal surfaces of surgical instruments and surviving the high temperatures and chemical agents that kill off infectious viruses and microbes.
A new scientific study found that Alzheimer’s disease can be a transmissible infection, albeit rare, which is inadvertently passed from one person to another during certain medical procedures.
Steve Connor reports for the UK Independent, Sept. 10, 2015, that a study of eight people who were given growth hormone injections when they were children, has raised the disturbing possibility that Alzheimer’s can be transmitted under certain circumstances when infected tissues or surgical instruments are passed between individuals.
The eight adults, aged between 36 and 51, all died of Creutzfeldt-Jakob disease (CJD), aka the human form of mad cow disease, after receiving contaminated hormone injections as children. Autopsies on their brains also revealed that seven of them had the misfolded proteins associated with the early stages of Alzheimer’s disease. It is unheard of for people in this age group to have such proteins.
The scientists did not find the “tau” protein tangles associated with the later stages of the disease, which means the seven individuals did not have full-blown Alzheimer’s, although they may well have developed it had they not died of CJD.
The study, published in the journal Nature, eliminated other possible reasons for the presence of these so-called amyloid-beta (A-beta) proteins and came to the conclusion that they were most probably transmitted as protein “seeds” in the growth-hormone injections.
The findings have raised questions about the safety of some medical procedures, possibly including blood transfusions and invasive dental treatment, which may involve the transfer of contaminated tissues or surgical equipment. It is well-established that the prion proteins behind CJD and Alzheimer’s stick to metal surfaces, such as metal surgical tools, and can survive extreme sterilization procedures such as steam cleaning and formaldehyde.
There is also the question of whether Alzheimer’s disease could be passed on in blood transfusions, given that animal experiments have shown this to be possible. Professor Collinge said:
“Epidemiological studies have been done in the past looking for links between Alzheimer’s disease and blood transfusions and they have not shown an association. Certainly with vCJD, which is the form of CJD associated with mad-cow disease, there is infectivity found in the blood and there have been four documented cases in the UK of vCJD from a blood donor who went on to get vCJD, so it can occur. Certainly there are potential risks in dentistry where it is impacting on nervous tissue, such as root-canal treatments and special precautions are taken for that reason… If you are speculating whether A-beta seeds are transmitted at all by surgical instruments one would have to consider whether certain types of dental procedures might be relevant.”
But in a statement issued later, Dr. Collinge clarified that more research was needed before any conclusions could be drawn about any potential risks in current medical or dental treatments:
“Our findings relate to the specific circumstance of cadaver-derived human growth hormone injections, a treatment that was discontinued many years ago. It is possible our findings might be relevant to some other medical or surgical procedures, but evaluating what risk, if any, there might be requires much further research. Our current data has no bearing on dental surgery and certainly does not argue that dentistry poses a risk of Alzheimer’s disease.”
Between 1958 and 1985 some 1,848 people in Britain, mostly children, received growth hormone injections made from tens of thousands of homogenized pituitary glands derived from the brains of human cadavers. The NHS switched to synthetic growth hormone in 1985 when scientists realized that pituitary-derived hormone could be a route for transmitting CJD. Up to 2000, there were 38 known cases of “iatrogenic” CJD resulting from growth hormone injections in the UK, but this figure is likely to rise further because of the exceptionally long incubation period of the disease.
Dame Sally Davies, the Government’s Chief Medical Officer, played down the significance of the research on transmissible Alzheimer’s saying that it was a small study on only eight samples: “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. I can reassure people that the NHS has extremely stringent procedures in place to minimize infection risk from surgical equipment, and patients are very well protected.”
Doug Brown, director of research at the Alzheimer’s Society, concurred with Davies: “While these findings are interesting and warrant further investigation, there are too many unknowns in this small, observational study of eight brains to draw any conclusions about whether Alzheimer’s disease can be transmitted this way. Injections of growth hormone taken from human brains were stopped in the 1980s. There remains absolutely no evidence that Alzheimer’s disease is contagious or can be transmitted from person to person via any current medical procedures.”
But UCL Professor of Neuroscience John Hardy disagrees. He said: “I think we can be relatively sure that it is possible to transmit amyloid pathology by the injection of human tissues which contain the amyloid of Alzheimer’s disease. Does it have implications for blood transfusions? Probably not, but this definitely deserves systematic epidemiological investigation.”
Scientists emphasised that the new evidence is still preliminary and should not stop anyone from having surgery. They have also stressed that it is not possible to “catch” Alzheimer’s by living with someone with the disease.