According to research, Alzheimer's could be transmissible

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Care (symbolic image): Not transferable from person to person

Photo: Martin Wagner / imago images/Martin Wagner

Alzheimer's is by far the most common form of dementia worldwide - it is estimated that around a million people are affected in Germany alone. Until now, two forms of the disease were known, in which nerve cells in the brain die: The age-related, so-called sporadic variant is common, and the genetic form is much less common. British doctors are now writing in the journal Nature Medicine about an extremely rare third type, transmitted through a very special medical procedure that has not been used for almost 40 years.

The group led by John Collinge from the London National Prion Clinic (NPC) bases the claim on case reports from eight people who were injected with growth hormone taken from the brain tissue of deceased people in their childhood - before 1985. They therefore developed Alzheimer's symptoms a few decades later, at a noticeably young age. “Alzheimer’s disease should now be recognized as a potentially transmissible disorder,” writes the team in the journal “Nature Medicine.”

German experts who were not involved in the study were somewhat more cautious: the connection has not yet been clearly proven, says Mathias Jucker from the Hertie Institute for Clinical Brain Research at the University of Tübingen and the German Center for Neurodegenerative Diseases (DZNE). If confirmed, the discovery would be “a incredibly significant result.” Among other things, it would be proof of the long-discussed assumption that misfolded forms of the protein amyloid beta can cause the disease - and are not just a byproduct of the death of brain cells.

Inga Zerr from the University Hospital of Göttingen is also initially cautious: “The data is still incomplete,” says the neurologist, “but it fits into the picture. The matter needs to be investigated further.”

No transmission from sick people

One thing is clear: all experts emphasize that there is no risk whatsoever in daily interaction with Alzheimer's patients or in their medical care. Collinge's group looked at cases of people who had been subjected to very special therapy in their childhood because of growth disorders: They were each injected intramuscularly several times with human growth hormone (hGH), which at that time was still obtained from the pituitary gland of dead people .

From 1959 to 1985, at least 1,848 people were treated with it in Great Britain alone - the therapy was also used in France, the USA, Australia and Germany. The practice was stopped after more than 200 recipients worldwide, 80 of them in the UK, became infected with Creutzfeldt-Jakob disease (CJD), a rare, always fatal brain disease. In their case, the injected preparation contained misfolded proteins – so-called prions – which can spread throughout the body and cause this disease.

However, such transmissions were very rare, emphasizes Collinge's group. In Germany, there has been no CJD transmission through this procedure, says Göttingen expert Zerr, who studies prion diseases. “We would have seen that.” The hormone is now produced differently.

It has long been known that prion diseases can be transmitted - for example through the consumption of prion-infected beef. But when investigating CJD deaths in which those affected had been treated with growth hormone, doctors also discovered pronounced deposits of the misfolded protein amyloid beta (Aß) in the brains of some of the deceased. These deposits are a pathological feature of Alzheimer's disease and are probably the main cause. However, it was unclear whether these people would have developed Alzheimer's symptoms if they had not died of CJD and lived longer.

Subsequent analyzes of such preparations showed that some of the hormone medications administered at the time actually contained misfolded amyloid beta. The cases now presented concern people who were treated with such hormone preparations and did not develop Creutzfeldt-Jakob disease. Five of them developed Alzheimer's symptoms about three to four decades after the hormone injections - noticeably early, between the ages of 38 and 55.

The research team did not find any other reasons for this development, in particular a genetic predisposition, in the current study. There is also no evidence that the lack of growth hormone itself or other administered therapies could have triggered the dementia.

Instead, the researchers assume that in addition to the two known variants, there must be a third form of Alzheimer's disease that is caused by medical measures - so-called iatrogenic. This is extremely rare, it goes on to say. On the one hand, this is because hormone therapy has no longer been used since 1985. In addition, the cases only concern recipients of the growth hormone preparation, which not only came from the pituitary gland of dead people, but was also prepared using a very special method: This so-called Wilhelmi process cannot render prions and amyloid beta contained in it harmless it in a “Nature” commentary.

"The people we describe had been subjected to a specific medical treatment that had long been abandoned," emphasizes Collinge in a statement from University College London. “They were injected with material that we now know was contaminated with disease-related proteins. There is no evidence that Alzheimer's disease can be transmitted between people during everyday activities or during normal medical care."

“After this publication, there will certainly be a lot of follow-up work that examines the results,” says Jucker. "If the result is confirmed, it would be mechanistically extremely interesting." For example, research into Alzheimer's therapies that target amyloid beta could experience a boost. It would also suggest that Alzheimer's syndrome is a prion disease - that is, it is based on misfolded proteins that spread throughout the body.

dpa/ani