Wednesday January 27 2016
Proteins may have spread into the brain during surgery
"Researchers have reported a second case that suggest [sic] Alzheimer's can be transmitted during medical treatments," the Mail Online reports.
Researchers carried out autopsies of seven people who died from Creutzfeld Jakob Disease (CJD) after a procedure called a dural graft, which is often used to repair severe head injuries and treat brain tumours.
This involved taking a section of the dura – the membrane surrounding the brain – from a person who had recently passed away. Unfortunately, in these seven cases, the tissue was contaminated with the CJD prion. Dural grafting is also now done using artificial material, not material derived from human brains.
In five out of the seven cases, researchers also found abnormal proteins associated with Alzheimer's disease. These are called amyloid beta proteins, which have been described as the "seeds" of Alzheimer's.
The question is: could the grafting procedure have introduced amyloid beta protein, as well as prions? And could this have theoretically caused Alzheimer's disease if they had not died of CJD?
The research was carried out after a previous study in 2015 unexpectedly found amyloid protein in brains of some people in the UK who had died of CJD after being infected by injections of contaminated human growth hormone.
Neither study proves that Alzheimer's disease is caused by amyloid beta proteins, or that they can be passed on by surgery.
Some experts have raised the issue that amyloid beta protein are very "sticky" and if they can be passed on, that more stringent sterilisation procedures of surgical instruments may be required.
Where did the story come from?
The study was carried out by researchers from University Hospital Zurich and Medical University Vienna. It had no specific funding.
The study was published in the online peer-reviewed journal Swiss Medical Weekly, and is available on an open-access basis, so it is free to read online.
The quality of the reporting in the Mail Online and the Daily Mirror was accurate, balanced, and in the case of the Mail, particularly informative. Unfortunately, these factors were undermined by unnecessarily alarmist headlines.
The Mail's headline, asking: "Can you catch Alzheimer's?" and the Mirror's question: "Is Alzheimer's passed from person to person?" suggest that people might get the disease directly from being in contact with or caring for someone with dementia. This is completely untrue and could cause unnecessary fear and distress.
What kind of research was this?
This was a case-controlled study, involving post-mortem pathological investigations of the brains of patients who had died from CJD caused by brain surgery. CJD related to surgery is known as iatrogenic CJD. Iatrogenic CJD is now extremely rare in the UK, due to a greater understanding of the underlying risks.
Observational studies such as this can compare groups to see whether something is more common in one group than another, but cannot show the reasons.
What did the research involve?
Researchers looked at the brains of seven people who had died of CJD, years after having dural grafting surgery. They tested the brains for the presence of two proteins linked to Alzheimer's disease – amyloid beta protein and tau protein. They compared the results to tests on brains of people who had died of CJD not caused by medical accidents (sporadic CJD).
Each of the seven brains was compared to three brains of people the same age, who had died of sporadic CJD. The researchers also tested a series of 81 cases of sporadic CJD, not matched for age but in a similar age range. They looked for amyloid beta protein in the blood vessels of the brain (cerebral amyloid angiopathy) and as plaques in the brain's grey matter.
The researchers wanted to see whether amyloid beta protein was more common in the brains of people who had got CJD after dural grafting surgery, compared to people who got CJD without having been infected by a medical accident. They looked to see whether people's age, or the length of time since they'd had surgery before dying of CJD, made any difference to the results.
What were the basic results?
Five of the seven (71%) brains of people who'd died of CJD after dural grafting contained amyloid beta proteins. All of these had amyloid proteins, both in blood vessels in the brain and as plaques.
Among the brains of people the same age, who'd died of sporadic CJD, one had amyloid beta in brain blood vessels (5%) and five had amyloid plaques (24%). Among the big group who'd died of sporadic CJD, 11% had amyloid beta in either blood vessels or plaques in the brain. Statistical analysis showed that amyloid protein was far more common among people with CJD who'd had dural grafts.
The people who'd had dural grafting and also had signs of amyloid beta were aged 28, 33, 47, 52 and 63. They'd had dural grafting more than 20 years before their deaths. The two people who did not show signs of amyloid beta were aged 51 and 59, and had received dural grafts 11 to 12 years earlier.
None of the brains studied showed signs of tau, the other protein linked to Alzheimer's disease.
How did the researchers interpret the results?
The researchers said: "The presence of amyloid beta pathology in young individuals who present with neither a family history of early-onset dementia or prominent AD-related tau pathology is highly unusual and suggests a causal relationship to the dural grafts."
In other words, they say, it is "plausible" that the amyloid proteins in the brains had not arisen naturally as part of ageing, or because people had genes predisposing them to Alzheimer's disease, but that they had been deposited in the brains during the dural graft surgery.
They say there are other possible explanations – for example, that the head injury or brain tumour which led to the dural graft surgery could also have led to the presence of amyloid beta in the brain. They point out that we don't know whether potential transmission of amyloid beta protein into the brain could actually cause Alzheimer's disease.
However, they call for a "critical re-evaluation" of decontamination procedures for surgical instruments and drugs derived from human tissue, to prevent possible contamination being passed on during medical treatment.
This latest research adds some evidence to the possibility that amyloid beta proteins could have been passed on during certain types of treatment, which introduced substances derived from donor brains or pituitary glands into the body. However, these types of treatment are no longer used.
The theory is far from certain, and other possible causes need to be investigated. Even if the theory was proven, we don't know that having these proteins introduced into the brain in this way would cause Alzheimer's disease. All the evidence showing amyloid protein in the brain after medical treatment has come from studies of the brains of people known to have been infected with prions causing CJD. None of these people actually showed outward signs of Alzheimer's.
There is absolutely no need to worry about "catching" Alzheimer's disease through day-to-day contact with people who have the disease, whether you are a carer or a family member.
There is no reason to think the condition has been passed on through routine surgery or blood transfusions. However, doctors will want to look at how instruments are decontaminated, to ensure that the precautions now taken against passing on prion diseases are also adequate to protect against possible transmission of amyloid beta protein.