Circumstantial
evidence for the transmission of Alzheimer’s from one person to another through
surgery, medical procedures is growing.
Once again, scientists have raised the specter of
Alzheimer’s as an infectious disease, theorizing it could be transmitted
through some medical procedures and surgeries. Though this possibility is
purely theoretical, the “circumstantial evidence for such transmission” is
growing, say Swiss and Austrian researchers.
Their new study focuses on patients with Creutzfeldt-Jakob
disease, who, many years before their deaths, had received surgical grafts of
dura mater, the membrane that covers the brain and spinal cord. During
autopsies, researchers discovered amyloid-β protein, the hallmark of
Alzheimer’s disease, in the grey matter and blood vessels of their brains. Such
results seemed unusual in patients so young — they were between the ages of 28
and 63 — especially since none had a family history of early-onset dementia.
For comparison purposes, then, the scientists performed
another round of autopsies on 21 control patients who died of Creutzfeldt-Jakob
disease at similar ages but had not received surgical grafts. However, none of
these 21 comparison cases had the pathological signs associated with
Alzheimer’s disease.
Based on this outcome, the researchers say it is
“plausible” that the Alzheimer’s pathology may have resulted when small seeds
of amyloid-β protein, a hypothesized trigger for dementia, were transferred
from the grafts and transplanted in the patients' tissues. The grafts having
been prepared from human cadavers provides added weight to this theory.
“Yet, alternative explanations are also possible,” wrote
the team in their published paper. Despite this caveat, their research echoes a
previous study published this past September.
Sterilized
Surgical Instruments May Be Contaminated
In September 2015, University College London scientists
theorized that the signature Alzheimer’s proteins had spread via a hormone
treatment prepared from cadavers based on their own autopsy results. Here, the
British researchers conducted autopsies, including extensive brain tissue
sampling, on eight patients with Creutzfeldt-Jakob disease.
While all the brains revealed the signature signs of
Creutzfeldt-Jakob, six exhibited the amyloid-β pathology associated with
Alzheimer’s as well. At death, these patients had been between the ages of 36
and 51. Once again, these patients were unusually young to display even the
earliest signs of Alzheimer’s, yet none had a genetic history of early-onset
Alzheimer’s.
One thing they did have, though, was a shared history of
treatments with human growth hormone extracted from cadaver-sourced pituitary
glands. The hormone treatments began in 1958 and ceased by 1985 following
reports of Creutzfeldt-Jakob disease occurring among recipients — some of the
treatments had been contaminated with prions, the infectious agent linked to
that disease.
Analyzing the data, the British scientists hypothesized
Alzheimer’s may be transmissible in a manner similar to Creutzfeldt-Jakob
disease. Potentially, the proteins found in the brains of Alzheimer’s patients
could be spread to others by way of contaminated surgical instruments because
the proteins are able to survive sterilization with formaldehyde.
Blood transfusions may also be a route of transmission,
the scientists said, as is the case with Creutzfeldt-Jakob disease.
However, the scientists warn their findings are hypothetical.
Strictly speaking, if transmission did occur, that only happened by way of the
cadaver-derived human growth hormone injections, no longer in use.
Cadaver-derived hormones and membranes have since been replaced with synthetic
growth hormones and synthetic membranes.
Earlier Study
Earlier, 2015, a potentially explosive study has provided
the first evidence that the devastating condition can, like mad cow disease,
spread through 'medical accidents'. The British researcher, Professor John
Collinge, said we 'need to rethink our view of Alzheimer's and evaluate the
risk of it being transmitted inadvertently to patients'. Following the second
case, he told Nature 'Our results are all consistent.
'The fact that the new study shows the same pathology emerging
after a completely different procedure increases our concern.'
Neither study implies that Alzheimer's disease could ever
be transmitted through normal contact with caretakers or family members, the
scientists emphasize.
One of the UK's leading brain surgeons warned that we
don't know if the techniques used sterilize medical instruments are effective
and said that the research 'must be taken seriously'. However, others urged
caution, saying the study was small and it does not prove that Alzheimer's
disease is contagious.
Professor Collinge, of University College London stumbled
on the link with Alzheimer's when inspecting the brains of eight people who had
died from CJD, the human form of mad cow disease. They had caught CJD after
being given injections of human hormones as children to treat growth problems.
To his great surprise, he found a protein that is a hallmark of Alzheimer's in
the brains of seven of the eight of the patients. In four of them, levels of
the memory-robbing amyloid beta protein were 'severe'.
Writing in the prestigious journal Nature, he said that
those studied were aged between 36 and 51 and such brain damage is 'simply not
seen' in people of that age. With no evidence that CJD somehow triggers the
build-up of the protein, Professor Collinge said the most likely answer is that
it, like the CJD, had been lurking in the hormone injections. None had actually
developed full-blown Alzheimer's but they may have done if they had lived
longer.
What does it mean
for me?
It raises concerns that the Alzheimer's amyloid beta
protein can be passed between people in the same way as CJD. This means that it
could potentially be spread via blood transfusions, brain surgery and corneal
transplants.
Even dentistry may be a risk. Lead researcher Professor
John Collinge stresses that his study provides no evidence that dental work is
dangerous. However, he also said such possibility may need to be considered.
But aren't medical
instruments sterilized?
Yes but the amyloid beta protein clings to metal and is
resistant to boiling water and formaldehyde.
Some experts say more research is needed but the
Department of Health says there is no cause for concern and that the NHS has
'extremely stringent' procedures to minimize infection risk from surgical
equipment.
Many dental instruments are only used once and the study
doesn't mean Alzheimer's can be caught by everyday contact such as kissing or
by caring for someone with the disease.
Addressing the recent findings, the Government Chief
Medical Officer, Dame Sally Davies, said: “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”.
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