Brain Science

Could Alzheimer’s Be Contagious?

Could Alzheimer’s Be Contagious? about undefined

For decades now scientists have been exploring why some people get Alzheimer’s disease and some don’t. They’ve pointed to amyloid-beta proteins, tau proteins, viruses, oxidative stress or free radicals, chronic inflammation, and genetics, but not once has anyone proposed that Alzheimer’s disease could be contagious. That is until now…

A first-of-its-kind study has revealed that Alzheimer’s disease can be “transmitted” to living people.

While it’s terrifying to consider that you could “catch” Alzheimer’s disease, we don’t want to be alarmist. As you’re about to see, this transmission happened under very specific circumstances. Still, scientists say the discovery will help them to better understand and treat neurodegenerative diseases like Alzheimer’s.

Contaminated Medical Therapy

Starting more than 60 years ago, from 1959 up until 1985, doctors in Britain treated 1,848 children with short stature using a type of human growth hormone (HGH) extracted from the pituitary glands of deceased adults.

Tragically, some batches of the HGH were contaminated with prions, an infectious protein that can cause normal proteins to misfold and then trigger cellular death. Prions cause prion diseases that are rare neurodegenerative diseases that are transmissible and fatal. These include Creutzfeldt-Jakob disease, among others.

Sadly, some of these young children went on to develop Creutzfeldt-Jakob disease. Professor John Collinge, director of the Institute of Prion Diseases at University College London (UCL), became increasingly concerned that Alzheimer’s could be triggered in a similar way. He began looking at the science and made a first-ever discovery…

Young Creutzfeldt-Jakob Victims Have Alzheimer's Plaques

Professor Collinge and his colleagues began studying the brains and bodies of eight deceased patients aged 36 to 51 with iatrogenic (doctor caused) Creutzfeldt-Jakob disease.

They discovered that six of these patients exhibited some degree of pathology from amyloid-beta proteins. Remember, these proteins can form the main components of the plaques that clog the brains of patients with Alzheimer’s disease. What’s more, amyloid-beta is rarely seen in patients within this age range.

To investigate if transmission could have occurred, they tracked down some of the pre-1985 vials of HGH the children had been treated with. Some of the samples did in fact have significant levels of amyloid-beta proteins, as well as tau proteins which are also implicated in the development of Alzheimer's.

Professor Collinge and his team took samples from the hormone vials and injected them into laboratory mice. They confirmed that the proteins can seed amyloid pathology even after decades of storage. Professor Collinge and his team published their first findings demonstrating this human transmission in 2015.

Then, in 2024, they published a paper in the journal Nature Medicine reporting on the development of Alzheimer’s pathology in eight people following repeated treatment with human pituitary-derived HGH in childhood.

Five of the eight were either already diagnosed with Alzheimer’s, had symptoms of the disease, or met the diagnostic criteria for mild cognitive impairment (MCI). They were all between ages 38 and 55 when neurological symptoms began and a genetic reason for contracting the disease at such a young age was ruled out.

Their conclusion? Contagious? No… Transmissible? Yes…

“Importantly, our findings also suggest that Alzheimer's and some other neurological conditions share similar disease processes to CJD, and this may have important implications for understanding and treating Alzheimer’s disease in the future,” explained Professor Collinge.

He went on to say, “the recognition of transmission of amyloid-beta pathology in these rare situations should lead us to review measures to prevent accidental transmission via other medical or surgical procedures, in order to prevent such cases occurring in future.”

His colleague Professor Jonathan Schott added: “These findings…provide potentially valuable insights into disease mechanisms and pave the way for further research which we hope will further our understanding of the causes of more typical, late onset Alzheimer’s disease.”

British neuroscientist and author Dr. Joseph Jebelli, who was not involved in the study, said: “It’s pretty clear that Alzheimer’s proteins spread through the brain in a prion-like fashion. The disease is not contagious, but the fact that it can be seeded into the brain by certain procedures forces us to rethink the underlying biology of the disease.”

“Investing more in this area of research is crucial. Without a deep grasp of the peculiar behavior of Alzheimer’s proteins, our attempts at drug development will remain somewhat in the dark.”

Scientists agree that Alzheimer’s is not contagious, however some are concerned because, at least theoretically, the disease could be transmitted through blood transfusion, surgical instruments, or dental treatments, even though no case has ever been reported. They call for increased vigilance and long-term monitoring, especially following procedures carried out in children that involve human fluids or tissues.

Their concerns are valid. Science has already proven that...

Amyloid-Beta Can Travel From Blood to Brain

Amyloid-beta is found in small amounts in the blood, and in animal research it can move into the brain if it’s injected into the bloodstream.

To find out if there’s enough amyloid-beta to form plaques in the brain, scientists carried out an experiment on mice, finding for the first time that the protein can indeed move from the blood to the brain and accumulate there.

Professor Collinge was not involved with this 2018 Canadian study but said, “The bottom line is that this study is thought-provoking but shouldn’t cause alarm. There really isn’t any evidence that you can transmit Alzheimer’s disease by blood transfusion.”

Another UCL study in 2018 found amyloid-beta pathology might have been transmitted through contaminated neurosurgical instruments. The study's first author, Zane Jaunmuktane, explained, saying, "Neurosurgery is becoming increasingly common in older individuals. As amyloid-beta pathology increases in brains with age, this raises the potential for onward transmission of protein pathology to other individuals in the same hospital."

It was theoretically possible for amyloid to stick to surgical instruments and be transferred to other patients if the instruments were improperly cleaned.

A study in the United Kingdom published in 2022 found that teeth pulled from patients with gum disease contained an abundance of amyloid. The researchers think they were formed in response to the infection and could, in theory, move into the blood circulation and into the brain. They wrote: “Like prions, insoluble Aβ (amyloid-beta) will remain a risk for being cross seeded to the brain and for the plausible development of AD (Alzheimer’s Disease) later in life.”

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