Five cases serve to identify a possible route of transmission of Alzheimer's disease

Cristina G. Lucio Madrid

Madrid

Updated Monday, January 29, 2024-17:03

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A team of British researchers describes in the latest issue of the journal

'Nature Medicine'

the case of five people who developed dementia similar to

Alzheimer's

decades after undergoing treatment with growth hormone obtained from cadavers.

This evidence suggests a possible route of transmission of Alzheimer's through this procedure, although the authors clarify that, in any case, it would be an exceptional route of transmission and that it

could no longer occur today

, since obtaining growth hormone stopped being made in the early 80s of the last century.

Nor does it mean that Alzheimer's is a contagious disorder. There is no evidence that the disease can be acquired through contact in daily activities or by undergoing common surgical procedures or medical treatments such as a blood transfusion.

A procedure now prohibited

The five people whose case is detailed in the medical journal received treatment with growth hormone

extracted from the pituitary glands of cadavers

, a procedure that was stopped more than 40 years ago, after it was found that it allowed the transmission of prions that cause

Creutzfeldt-Jakob

disease ,

a neurodegenerative disorder that became famous in the 90s after the so-called 'mad cow' crisis. Nowadays, the growth hormone used in different therapies is obtained synthetically.

The same group of researchers, led by

John Collinge

, from the Institute of Prion Diseases at University College London, had described in previous studies the presence of deposits of amyloid beta particles, a key peptide in Alzheimer's disease, in the brain of some of these patients affected by Creutzfeldt-Jakob, which led them to further investigate the relationship between treatment with growth hormone from cadavers and Alzheimer's.

First, they showed that several old samples of growth hormone from cadavers were contaminated with amyloid beta. But, in addition, they also proved that even though they had been stored for years, they were capable of causing the accumulation of

amyloid beta deposits

in the brains of mice if they were injected.

In the research they are now publishing, scientists studied the case of eight people from the United Kingdom who underwent treatment with growth hormone from cadavers in their childhood and did not develop Creutzfeldt-Jakob disease. Five of these patients did suffer symptoms of

early dementia

(they developed them between the ages of 38 and 55) compatible with a diagnosis of Alzheimer's.

The analyzes of biomarkers associated with the disease supported the classification of the problems as Alzheimer's in two of the cases studied, and pointed it out as possible in another of the individuals.

On the other hand, the researchers performed an autopsy on two patients who died during the investigation and confirmed the pathology in one of them. None of the patients analyzed had in their DNA the mutations associated with the development of early Alzheimer's, which rules out that they had developed dementia for this reason.

In the conclusions of their work, the scientists suggest that their findings indicate that Alzheimer's is a potentially transmissible disease and point out that, like Creutzfeld-Jakob disease, Alzheimer's could also be acquired by a mechanism similar to that of prions.

In the text, the researchers recognize that

this route of transmission is exceptional

, that it could not occur today due to the abandonment of this type of approach, and that the cases studied developed symptoms of dementia after years of exposure to this treatment.

In any case, they point out that "the discovery of this transmission in rare circumstances should lead us to review the measures to prevent any accidental transmission through other surgical or medical procedures," as Collinge indicated in a statement.

Furthermore, he adds, "our results also suggest that Alzheimer's and other neurological problems share processes with Creutzfeldt-Jakob disease, which could have important implications for understanding and treating Alzheimer's disease in the future."

Caution about the results

For

David Pérez

, head of the Neurology service at Hospital 12 de Octubre in Madrid, it is necessary to "take the results of this study with caution."

"In addition to the fact that the cases analyzed are very few, it must be taken into account that they are patients who suffered cranial tumors or complex malformations, which is why they had to undergo different surgeries, some with subsequent radiotherapy. The authors themselves acknowledge that this also could have influenced the development of later

cognitive impairment

," says Pérez.

Furthermore, he continues, "we must not forget that the condition appears 20 or 30 years later and in some cases it does not clinically resemble conventional Alzheimer's. The authors point out that this may have generated a type of atypical Alzheimer's disease due to the way in which which has been transmitted, but

this is already a hypothesis that would need to be validated

," he emphasizes.

In any case, the specialist recalls that this route of transmission would be very exceptional, it would only occur under extraordinary circumstances and, in fact, it could not occur today, when growth hormone is no longer obtained from corpses. "Alzheimer's is not a contagious disease and no one should be afraid to undergo a medical procedure for this reason," he notes.

Tara Spiers-Jones

, group leader at the Dementia Research Institute of the United Kingdom and president of the British Society for Neuroscience,

speaks along the same lines in statements to the Science Media Center: "This study looked at whether people can develop

Alzheimer's disease as a consequence of treatment with growth hormone that is no longer used. As mentioned by the authors of this study, there is no evidence that Alzheimer's pathology can be transmitted between individuals in activities of daily living. There is also no evidence that raise fears that current surgical procedures carry some risk of transmitting Alzheimer's disease.

"There is no evidence that the mode of disease transmission presented here has ever occurred elsewhere.

We are already very careful about transmitting brain tissue between people

, due to the small but real risk of transmitting prions that could cause Creutzfeldt-Jakob disease. There is evidence that beta-amyloid aggregates can travel across synapses in the brain, spreading dementia. This work reinforces this idea. It remains to be seen if the work has implications for therapeutic strategies. The article speculates on the possibility that there are different strains of beta-amyloid, resulting from different aggregate structures, but does not present direct evidence of this,"

Andrew Doig

, professor of Biochemistry and Medicine, also told SMC and in the same vein.

director of the Biochemistry Program at the University of Manchester.