Could Alzheimer’s disease be transmitted between people by common medical procedures? Not according to the medical orthodoxy, which says the condition happens due to a build-up of proteins in the brain.
But a controversial idea posits that occasionally those proteins can be passed from one person to another through measures such as bone marrow and organ transplants, or even blood transfusions.
Now, this view has been bolstered by experiments in mice where the animals developed symptoms of Alzheimer’s after bone marrow transplants. Critics say this isn’t yet definitive proof of this route of transmission. So, what does this mean in practice?
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The mainstream view is that Alzheimer’s is caused by the build-up of two proteins, beta-amyloid and tau. While the exact mechanism is unclear, this idea has been strengthened by the recent success of two new medicines that clear amyloid specifically from the brain, although their effects on slowing memory decline are modest.
Some genetic mutations that cause people to get Alzheimer’s in middle age, relatively early in life, directly cause a build-up of amyloid. For almost everyone else, the condition is seen as something that effectively strikes at random, with little that can be done to prevent it, except possibly keeping to a healthy lifestyle to boost general brain health.
The shocking claim that the condition can sometimes be contagious emerged from studies of people who had received injections of growth hormone in childhood between the 1950s and 1980s. The hormone had been obtained from dead people’s brains.
In the UK, small samples of the treatments were in storage, so they were examined to see if they contained a misfolded form of amyloid, which is thought to possibly be involved in triggering amyloid build-up.
Recent research has revealed eight such people had misfolded amyloid in their growth hormone injections. They had all either been diagnosed with Alzheimer’s or had memory problems or signs of the condition on brain scans. But it is still unclear if their childhood treatments were really responsible, as memory deterioration is common in old age and most members of the group have now died, limiting further investigation.
The latest development is an attempt to shed light on the question through animal research. A group at University of British Columbia in Vancouver, Canada, took bone marrow from mice that had been genetically altered to have high amyloid levels in their brains, which cause them to develop memory problems early in life, then injected it into the blood of normal mice. These also developed cognitive impairments at a young age and had amyloid build-up in their brains.
The researchers say this shows that Alzheimer’s disease can be passed on by medical procedures, at least in mice. “The dogma states it is amyloid that is brain-derived that leads to pathology,” says at University of British Columbia. “This is evidence that bone marrow transplants can actually transfer disease.”
Singh’s team is calling for people donating bone marrow or an organ for transplantation to be genetically tested to make sure they don’t have an inherited form of Alzheimer’s that is the human equivalent to the genetically altered mice’s version. This should even be considered for people donating blood, says Singh.
But some researchers are sceptical that the findings should change medical practice. A key issue is that the research has been in animals, not humans, and it is unclear just how well these genetically altered mice exemplify the process that causes Alzheimer’s in people. “While studies like this are important, differences in the physiology, anatomy and metabolism of mice mean this early-stage research cannot be reliably applied to humans,” says at UK stem cell transplant charity Anthony Nolan.
On a practical level, it can already be hard to find someone suitable for bone marrow donation who is genetically similar enough to the recipient. Adding genetic screening for Alzheimer’s would be an additional step and could put potential donors off.
at University College London says that the inherited form of Alzheimer’s is very rare and so any risk to bone marrow recipients seems low. Doctors seeking a bone marrow donor for a particular person have to weigh up multiple factors, he says. “I would put the risk of transferring dementia relatively low down on that list.”
The latest study certainly isn’t conclusive proof that this form of dementia can be passed on by medical procedures, but it is another step along the road to answering the important question of whether Alzheimer’s is indeed transmissible.
Stem Cell Reports
