No, Alzheimer's is not contagious
A false sensation in the wake of one discovery
News from CNN: No, Alzheimer's is not contagiousThe headlines of many British (and Russian) publications on Thursday sounded very impressive:
"Alzheimer's disease can be infected", "Alzheimer's disease can be infectious", "Alzheimer's connection with blood transfusions", "Cases of infection with Alzheimer's disease have been identified", "Scientists have proved that Alzheimer's disease can be contagious".
Shock newsHowever, they are all completely wrong and resemble the famous comic book about the cycle of scientific discoveries, in which a correlative study of a scientist with a number of reservations, having made the way from a scientific article to television news and popular programs, turns into a recommendation from his grandmother to wear a foil cap for self-defense.
The author of the study, which was published in Nature and referred to by journalists, Simon Mead from the Institute of Neurology at University College London (Institute of Neurology at the University College London) told CNN that "the headlines this morning were a little shocking."
In fact, the study has no basis for conclusions about the contagiousness of Alzheimer's, and in the article itself, the authors conclude that "there is no reason to believe that Alzheimer's disease is contagious, and in epidemiological studies there is no evidence that it can be transmitted, including through blood transfusions."
PhenomenonThe work "Evidence of transmission of beta-amyloid pathology and cerebral amyloid angiopathy from person to person" (Evidence for human transmission of amyloid-β pathology and cerebral amyloid angiopathy) describes a phenomenon found in a small group of patients with Creutzfeldt-Jakob disease who were once injected with human growth hormone.
Upon autopsy of the bodies of eight deceased patients, four of them showed signs of the presence of an abnormal protein – amyloid-β – characteristic of Alzheimer's disease. This means that in one particular case, an element of Alzheimer's disease (but not the disease itself) could be transmitted from person to person.
In the article, scientists warn that their discovery does not apply to the general population. Patients whose brains were examined after death were part of a group of 30 thousand people who were injected with growth hormone obtained from the pituitary glands of the deceased at a young age due to stunting. This practice was discontinued in 1985, when it became clear that the prevalence of Creutzfeldt-Jakob disease (extremely rare in the general population of prion neurodegenerative disease) was too high among these patients. It was assumed that the prions were introduced along with the hormone. None of these patients were diagnosed with Alzheimer's disease during their lifetime.
The authors of the study in Nature suggested that beta-amyloid was introduced to some patients along with prions. Previously, proteins characteristic of Alzheimer's disease could be transmitted and spread only by direct injection into the brain (such an experiment was conducted on a mouse model), but this does not mean that amyloid can be transmitted by blood transfusion. Moreover, the work of the Ministry of Foreign Affairs and colleagues does not prove that amyloid was really introduced: plaques could form within the natural course of CDJ. Indirectly, the latter version is disputed only by the fact that the authors reviewed the autopsy results of another 120 patients with prion diseases and found no clusters of abnormal proteins associated with Alzheimer's disease.
"Complete nonsense"Another limitation of the study is the fact that amyloid accumulations do not yet mean either the presence or the prospect of developing Alzheimer's disease.
Amyloid plaques are found in many people during pathologic and anatomical examination, but there was no disease itself. Actually, it is still not known whether amyloid-β in brain tissues is the cause or consequence of the development of Alzheimer's.
In total, Alzheimer's has three characteristic signs: amyloid-β, another abnormal protein (tau) and loss of neural connections, which causes the death of neurons and atrophy of brain tissues. The second and third elements of the four victims were not found.
Perhaps the patients whose material was studied in the work of the Ministry of Foreign Affairs simply did not live to see the full clinical picture of Alzheimer's disease unfold: they died of CDJ at the age of 36-51. However, the only practical consideration that the authors consider possible to extract from the work is that 30 thousand patients who were injected with growth hormone may be at risk for complications such as stroke and cerebral hemorrhage. "The idea that Alzheimer's disease is contagious is complete nonsense. What we would not want in any way is panic or avoidance of surgical operations and blood transfusions," the Foreign Ministry concluded.
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14.09.2015