Fragments of sticky proteins found in the brains of people with Alzheimer’s disease could potentially be spread to others via contaminated surgical instruments and other medical procedures, scientists warn.
Researchers called for further work into the possibility that metal instruments used in medical procedures could pick up harmful proteins which survive conventional sterilisation with formaldehyde.
The concern comes after scientists found that a small number of people who died from Creutzfeldt-Jakob disease (CJD) after being treated with growth hormone taken from cadavers, developed brain changes seen in Alzheimer’s disease.
Doctors examined the brains of eight CJD patients who had received pituitary growth hormone, given predominantly to children with stunted growth until it was stopped in 1985. Six of the brains had an unusual build-up of protein called amyloid beta, which has long been linked to Alzheimer’s disease. The patients were aged 36 to 51 years old, but none carried gene variants that bring about the early onset of dementia.
John Collinge, director of the Medical Research Council Prion Unit at University College London, said the findings suggest that the hormone might have spread tiny pieces, or “seeds”, of amyloid beta, alongside the abnormal proteins, or prions, that gave people CJD. None of the patients developed Alzheimer’s disease, or other brain changes linked to the disease. They may never have done. Or they may have died before the symptoms had time to emerge.
Reporting their findings in the journal Nature, the scientists say the work should drive investigations into whether amyloid beta can be spread through other medical procedures, referred to as “iatrogenic routes” in the study.
“While there is no suggestion that Alzheimer’s disease is a contagious disease and no supportive evidence from epidemiological studies that Alzheimer’s disease is transmissible … our findings should prompt consideration of whether other known iatrogenic routes of prion transmission, including surgical instruments and blood products, may also be relevant to amyloid beta,” the authors write.
Collinge told reporters that his team now suspected people could acquire amyloid beta “seeds” in three different ways: from a spontaneous, unlucky biological event, from a faulty gene or through a medical accident. He said there was no evidence that Alzheimer’s could be transmitted through blood transfusions, but added: “I think it’s not unreasonable to have a look. My concerns would be more to see if there is a risk of seeding from metal surfaces. I think that is something we ought to prioritise.”
Speaking to the journal, John Hardy, a leading Alzheimer’s researcher at UCL, said: “This is the first evidence of real-world transmission of amyloid pathology. It is potentially concerning.”
The findings prompted a wave of reassurance from scientists and doctors who urged people not to delay or cancel surgery out of fear of contracting Alzheimer’s. The chief medical officer, Sally Davies, said there was no evidence that Alzheimer’s disease could be transmitted in humans through any medical procedure.
“This was a small study on only eight samples,” she said. “We monitor research closely and there is a large research programme in place to help us understand and respond to the challenges of Alzheimer’s. I can reassure people that the NHS has extremely stringent procedures in place to minimise infection risk from surgical equipment, and patients are very well protected.”
Treatment with pituitary growth hormone taken from cadavers was stopped in the UK in 1985 after reports of CJD among recipients. Because hormone from different donors was pooled before use, a single patient could receive hormone from a large number of donors, raising the risk of disease transmission. Nearly 2,000 men and women in Britain had injections for stunted growth. Of those, 77 have died from CJD.
David Allsop, professor of neuroscience at Lancaster University, said the build-up of amyloid in the patients’ brains might have another explanation. “It is very well known from other studies that one type of rogue protein, in this case the prion protein, can predispose to accumulation of another, in this case amyloid,” he said. “There is no evidence that Alzheimer’s disease can be transmitted from one person to another, or through use of contaminated surgical instruments, and these results should be interpreted with a great deal of caution.”
Eric Karran, director of research at Alzheimer’s Research UK, said: “Previous research has suggested that the amyloid protein may behave in a similar way to the prion protein responsible for CJD, but this study provides evidence that amyloid could also be passed between humans through contaminated brain tissue.
“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. It’s unusual for people of the ages studied in this research to have amyloid in the brain, but we don’t know whether they would have gone on to develop Alzheimer’s and there is currently no evidence that people who received human-derived growth hormone have a higher rate of the disease.”
In an accompanying article in Nature, Mathias Jucker at the Hertie Institute for Clinical Brain Research, University of Tübingen and Lary Walker at the Yerkes National Primate Research Center in Atlanta, added to the voices of reassurance: “So far, there is no indication that Alzheimer’s disease can be transmitted between people under ordinary circumstances.”
This article titled “Protein linked to Alzheimer’s could be spread during surgery, say researchers” was written by Ian Sample Science editor, for The Guardian on Wednesday 9th September 2015 17.00 UTC