‘Seeds’ of Alzheimer’s may be transmitted

The paper suggests that the amyloid-beta compounds that herald Alzheimer’s may behave like prions – proteins that cause CreutzfeldtJakob disease.

The trigger for Alzheimer’s disease can be passed between people through contaminated surgical tools, a landmark study suggests.

Until now, scientists believed that the disease was mostly a consequence of old age and partly influenced by genes. The new findings raise the prospect that patients could develop dementia as a result of a hospital operation, a blood transfusion or dental work such as root canal treatment.

The study, published in Nature on Thursday , is the first evidence that the ‘‘seeds’’ of Alzheimer’s – microscopic protein molecules – could be transmitted between humans. The discovery was described by the study’s lead scientist as a paradigm shift in the understanding of how Alzheimer’s develops.

John Collinge, professor of neurology at University College London, said: ‘‘You could have three different ways you have these protein seeds generated in your brain.

‘‘Either they happen spontaneously – an unlucky event as you age – or you have got a faulty gene, or you’ve been exposed to a medical accident. That’s what we’re hypothesising. It’s a paradigm shift.’’

More than 500,000 people in the UK have Alzheimer’s, which accounts for just under two-thirds of dementia cases. It is thought to kill 40,000 people a year and to cost the economy about £16 billion.

The team found no evidence that Alzheimer’s itself was contagious, but said that medical procedures could result in protein build-ups that presage the disease. Experts and the government’s top medical adviser cautioned that the research was at a very early stage and based on a small sample.

The study revealed that several patients who had been treated with human growth hormones derived from dead bodies had advanced physical signs of Alzheimer’s when they died in middle age. The likeliest way this could have happened was if proteins linked to the disease had been transferred from the cadavers and had taken root in the patients’ brains, the authors said.

If the findings are confirmed, it is possible that seeds of the most common form of dementia could spread through tiny remnants of infected tissue. The paper suggests that the amyloid-beta compounds that herald Alzheimer’s may behave like prions – proteins that cause Creutzfeldt-Jakob disease (CJD) and several other lethal brain conditions – and take hold when they are passed from an infected body to a healthy person. The study is the first evidence that this phenomenon can happen in people, building on experiments showing that mice and primates can acquire Alzheimer-like brain changes after being injected with infected human tissue. Collinge said that the mechanism could also be at play in common neurodegenerative conditions such as Parkinson’s, motor neurone disease and other forms of dementia.

He and his colleagues examined eight brains taken from people who had received growth hormones when they were children. Treating short people with pituitary growth hormone from dead donors began in the UK in 1958, but stopped in 1985 after confirmed reports of CJD among recipients.

All eight died of CJD when they were in their 30s or 40s, but the scientists were surprised to find that six of the brains also showed the patterns of amyloid-beta buildup characteristic of Alzheimer’s. The changes were severe in four patients in spite of their youth. Professor Collinge said: ‘‘Alzheimer’s disease is a common disease of the elderly . . . You simply do not see that sort of amyloid deposition in young people.’’

Prion diseases such as CJD can linger on sterilised surgical equipment after brain operations , and he believes that the Alzheimer’s seeds may have a similar resilience. People could even pick up the seeds from eating infected animal tissue, although Collinge thought this unlikely.

Most experts in the field urged caution, emphasising that the patients in the study did not have Alzheimer’s and might never have gone on to develop it.

Roger Morris, professor of molecular neurobiology at King’s College London, said that the Alzheimer’s seeds had spread through a specific medical procedure that had not been carried out in Britain for 30 years.

‘‘Does this Nature paper . . . presage a new era in which Alzheimer’s disease changes from being an isolated disease of each individual as they age to becoming infectious and able to attack everyone, young and hold? No,’’ he said.

Dame Sally Davies, the chief medical officer, assured the public that brain surgery was safe.

‘‘As this research itself states, 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.’’