‘Potentially Transmissible’
The cases offered diverse presentations. Some were not symptomatic and some failed to meet current diagnostic criteria for sporadic Alzheimer’s disease. Treatment duration and frequency differed among those in the study, as did their age at treatment onset and completion. That and other factors could contribute to the diverse phenotype recorded in individuals, investigators note.
Investigators examined and ruled out other factors that might explain the individuals’ cognitive symptoms, including childhood intellectual disability, which has been linked to dementia risk, the underlying condition that prompted their treatment with c-hGH, growth hormone deficiency, and cranial radiotherapy, which four of the individuals had received. They also ruled out inherited disease in all five of the cases with samples available for testing.
“Taken together, the only factor common to all of the patients whom we describe is treatment with the HWP subtype of c-hGH,” the authors write. “Given the strong experimental evidence for A-beta transmission from relevant archived HWP c-hGH batches, we conclude that this is the most plausible explanation for the findings observed.”
Investigators say the findings show that, like other prion diseases, AD has three etiologies: sporadic, inherited, and rare acquired forms, or iatrogenic AD.
“The clinical syndrome developed by these individuals can, therefore, be termed iatrogenic Alzheimer’s disease, and Alzheimer’s disease should now be recognized as a potentially transmissible disorder,” the authors write.
“Our cases suggest that, similarly to what is observed in human prion diseases, iatrogenic forms of Alzheimer’s disease differ phenotypically from sporadic and inherited forms, with some individuals remaining asymptomatic despite exposure to A-beta seeds due to protective factors that, at present, are unknown,” they continue
‘Measure of Skepticism’
In an accompanying editorial, Mathias Jucker, PhD, of the Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany, and Lary C. Walker, PhD, in the Department of Neurology at Emory University, Atlanta, write that the findings should be considered “with a measure of skepticism.”
“The cases presented are diverse and complicated; the individuals had undergone a variety of medical interventions for various disorders earlier in life, and it is difficult to exclude a contribution of these circumstances to the complex disease phenotypes that appeared many years later,” they write.
However, they continue, “there is good reason to take the findings seriously.”
“From a practical standpoint, this report reinforces the potential of amyloid-beta seeds as targets for early prevention, and it underscores the importance of informed caution in the preparation of surgical instruments, handling of tissues, and implementation of therapeutic biologics, particularly those derived from human sources,” Dr. Jucker and Dr. Walker write.
Commenting on the findings for this news organization, Christopher Weber, PhD, director of global science initiatives for the Alzheimer’s Association, says the idea that amyloid-beta is transmissible between individuals has been shown before.
“We’ve known for a long time that it is possible to create abnormal amyloid buildup — similar to that seen in Alzheimer’s – in the brain of an animal by injecting it with amyloid-beta. We also transfer human Alzheimer’s genes into animals to initiate abnormal, Alzheimer’s-like processes in their brains,” he said. “Thus, the idea that amyloid is transferable between individuals is not so novel as implied in the new paper.”
However, the study does highlight the importance of safety measures to prevent the accidental transmission of amyloid-beta, Weber added.
“It is a reasonable and actionable caution that the scientific and clinical communities must understand the possible risks and ensure that all methods of transmission are eliminated — for example, with complete and conscientious sterilization of surgical instruments,” he said. “Bottom line: We shouldn’t put amyloid-beta into people’s brains, either accidentally or on purpose, and appropriate measures should be in place to ensure that doesn’t happen.”
The study was supported by the Medical Research Council, the National Institute for Health and Care Research (NIHR), the NIHR University College of London Hospital Biomedical Research Centre, Alzheimer’s Research UK, and the Stroke Association. Dr. Collinge is a shareholder and director of D-Gen, Ltd., an academic spin-out company working in the field of prion disease diagnosis, decontamination and therapeutics. Dr. Jucker and Dr. Walker report no conflicts of interest.
A version of this article appeared on Medscape.com.