Neurology Central

Ask the Experts: Is Alzheimer’s disease transmissible? (Part 1: Introduction to transmissible neurological disorders)

In this latest instalment of our ‘Ask the Experts’ column, we ask the question, ‘Is Alzheimer’s disease transmissible?’. This highly provocative topic has hit the headlines in recent months, so we have drawn together experts from the fields of Alzheimer’s and prion research to share their views on the subject. Our experts this month are Karl Frontzek (University of Zurich, Switzerland), Herbert Budka (University of Zurich, Switzerland), Marc Diamond (University of Texas Southwestern, TX, USA), Masahito Yamada (Kanazawa University, Japan) and Dennis Selkoe (Harvard Institutes of Medicine, MA, USA). Find out more about our experts at the bottom of this page.
Over the coming days, our experts will discuss what is really meant by ‘transmissible’ in a neurological sense, the evidence for and against the case for Alzheimer’s transmission, and how the future of Alzheimer’s research and treatment will be shaped by recent research advances.

What is the definition of ‘transmissible’ in a neurological sense?

KF: To me, a transmissible disease is defined by spread of the agent from one organism to another, be it directly (bodily fluids, aerosols) or via vectors (infusions, medical instruments). When it comes to research about transmissible diseases, in my opinion, it is only a ‘transmissible’ disease if the recipient would not have caught the disease on a natural course, meaning that if one infects an organism with a toxic agent that would develop naturally on its own (e.g., through genetic overexpression or pathological mutation) it is not per sé transmissible.

…transmission is the consistent elicitation of a disease by inoculation with material from another individual with this disease.
– Herbert Budka

HB: In a neurological sense, transmission is the consistent elicitation of a disease by inoculation with material from another individual with this disease.

However, the term transmission has been used, sometimes confusingly, for several distinct processes that, in my opinion, need to be distinguished:

  1. Molecular seeding or templating – a molecule seeds the replication of itself in template-like fashion
  2. Cell-to-cell spread – propagation of molecules or subcellular structures from one cell to another, e.g., by exosomes or tunneling nanotubes
  3. Interindividual transmission / infection – from one host to another by an infectious agent, e.g., by bacteria, fungi, viruses, prions. All of these run with a complete infectious cycle (with step-wise infection of, multiplication and propagation within intermediate cell populations, e.g., after oral inoculation). This process may or may not associate with manifest disease.
What neurological diseases are we currently aware of as being transmissible?
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