The idea was initially seen as medical heresy, but, eventually, it was shown to be completely correct. Mad cow disease arose because, in the UK, cattle feed had started being made with the remains of other animals. When a misfolded version of a molecule called prion protein present in some feed spread through the recipient animals’ brains, it caused progressive neurodegeneration that was inevitably fatal.
Once this was understood, millions of British cattle had to be destroyed, there was a global export ban on British beef for several years and the rules on animal feed were changed around the world.
It also sparked panic over the potential number of human cases. Fortunately, it is now thought that only people with certain variants of the prion gene are susceptible to catching vCJD in this way. Less than 200 people are thought to have been affected, all of whom have sadly died.
But eating contaminated beef turned out not to be the only way vCJD can spread. Until the 1980s, children of very short stature were occasionally treated with injections of growth hormone obtained from the brains of deceased donors. Some of the hormone treatments were unknowingly taken from people who had a natural form of CJD – and several of the recipients went on to get the condition as a result.
Alzheimer’s link
The connection with Alzheimer’s and other conditions arises because CJD isn’t the only condition in which misfolded proteins play a role. Alzheimer’s has long been suspected of being caused by a build-up of a protein called beta-amyloid. It now seems that, at least in some people, misfolding of amyloid could also be involved.
The new study has found suggestions that in eight people who received growth hormone treatments containing misfolded amyloid, all of them either were diagnosed with Alzheimer’s relatively early in life, had signs of it on brain scans or had other forms of cognitive impairment.
You can read about this study here. But as it is based on such a small number of people, it shouldn’t be taken as definite proof that Alzheimer’s is transmissible by misfolded proteins, some experts say. But it should raise our suspicions that this is possible.
Another piece of evidence supporting this idea is that misfolded amyloid in the walls of blood vessels in the brain can cause stroke. It has recently emerged that, in a few people, this was triggered by misfolded amyloid being seeded into their brains during brain surgery, sometimes decades earlier.
If Alzheimer’s and stroke are indeed able to be passed on in this way, it would have some serious consequences. For one thing, some protein-folding disorders can be very infectious if the misfolded proteins are directly introduced into the body. Unlike bacteria or viruses, misfolded proteins may not be destroyed by ordinary procedures for sterilising surgical equipment.
If anyone with CJD needs brain surgery, hospitals take extreme steps to avoid contamination, including destroying the surgical instruments used, and they may close the operating theatres to other people that day. Hospitals don’t do that after brain surgery on those with Alzheimer’s disease. As Alzheimer’s is a much more common condition than CJD, the costs and impracticalities of such a policy change make it almost inconceivable.
The latest study isn’t yet sufficient evidence for hospitals to change their practice in this way, says Bart De Strooper at University College London. But we should set up rigorous monitoring systems to find out if people are more likely to develop Alzheimer’s if they have had previous neurosurgery, he says.
On a brighter note, the new insights about amyloid misfolding may also shed light on Alzheimer’s disease more generally. There is still lots to understand as we don’t know why amyloid builds up in some people and not others, or why some people have high amyloid levels but no dementia symptoms.
Anything that can help lead to new treatments for this devastating condition must be welcomed. For a long read on how lifestyle changes can reduce our risk, go here.
