A new study published in Nature may have just uncovered evidence that Alzheimer’s disease can be transmitted between humans in a way other than genetics—which, if true, could radicalize how the disease is understood.
A contaminated sample
Between 1958 and 1985, around 1800 UK children received therapy in the form of growth hormones taken from cadaver brains. What no one knew at the time, however, was that the sample was contaminated with disease-causing prions.
Prions are malformed versions of proteins that can be transmitted through infected meat or contaminated surgical instruments. While they contain no genetic material, they can reproduce on their own and become infectious. And, they cannot be killed—they aren’t alive. Which means that they have no treatment or cure. So while prions can have an incubation period of decades, once they are activated they cause diseases that fill the brain with holes and eventually kill the host.
According to the authors, scientists have long wondered if diseases involving misfolded proteins or if amyloids could be transmitted like prions, and now they may have proof.
The team examined the brains of eight of those given the growth hormone—all of whom had died from a prion disease known as Creutzfeldt-Jakob Disease (CJD). Of the eight, six had significant amounts of amyloid plaques, which is a hallmark of Alzheimer’s. However, they all died between the ages of 36 and 51.
“This is a highly unusual finding. We wouldn’t have expected to see this Alzheimer’s amyloid deposition in this age group,” author Dr. John Collinge told reporters at a media briefing assembled by Nature. “It’s normally only seen in elderly individuals, unless you have a genetic predisposition to it, and none of these patients did.”
Further examination of 116 other cases of prion-caused deaths (which were not related to the contaminated hormone) showed that there was no evidence of Alzheimer’s. This seems to suggest that the source of the amyloid was not genetic vulnerability or a consequence of Creutzfeldt-Jakob Disease, but instead came from the hormone itself.
Amyloid was also found inside the pituitary glands of Alzheimer’s patients. The pituitary gland is the part of the brain that naturally produces growth hormone—which suggests that amyloid seeds could very well have come from the growth hormone, because it congregates there naturally during the course of the disease.
Moreover, past experiments have shown that amyloid seeds can induce Alzheimer’s in mice and primates—so it could very well be possible for humans as well.
The big “but”
The study had several limitations, especially in the size of the group studied—eight people is hardly conclusive. Further, all of the six patients who showed amyloid plaques might never have developed Alzheimer’s—they died before it could have developed, and they lacked the other hallmark known as tau tangles.
Most importantly, correlation is not causation. There is no definitive proof that the hormone conveyed the Alzheimer’s, because the team couldn’t analyze samples of the growth hormone to confirm it.
According to Collinge, samples of the hormone does still exist, and his team is aiming to study them. “But the experiments take one or two years,” he told New Scientist.
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Feature Image: Thinkstock
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