Canadian Study Offers New Insight Into ‘Transmissible’ Alzheimer’s Disease

New laboratory-based research in mice, published in the scientific journal Stem Cell Reports, has suggested that a form of Alzheimer’s disease can be transferred via bone marrow transplants.

However, experts cautioned that phenomenon had only been observed in mice, and the study’s conclusions couldn’t be extended to people undergoing bone marrow transplants.

The researchers, from University of British Columbia in Canada, took bone marrow cells from mice that carried a faulty version of a gene linked to Alzheimer’s, called the amyloid precursor protein gene (or APP), and transplanted them into healthy mice who lacked this genetic fault. Some of these recipient mice carried ‘normal’ versions of the APP gene; others had been engineered to lack the gene entirely (so-called ‘APP-knockout’ mice).

After the transplant, both groups of mice developed Alzheimer’s – identified through symptoms of cognitive decline and increased levels of amyloid, a hallmark protein of Alzheimer’s, in the brain. Both groups developed symptoms a few months earlier than did the donor mice, who already carried the faulty APP gene.

“The fact that we could see significant behavioural differences and cognitive decline in the APP-knockouts at 6 months was surprising, but also intriguing because it just showed the appearance of the disease that was being accelerated after being transferred,” said first author, Chaahat Singh.

Dr Sheona Scales, Director of Research at Alzheimer’s Research UK, emphasised that these experiments were conducted in mice specially bred with a rare genetic mutation, which only represents “an extremely small number of Alzheimer’s cases in people.”

While noting that animal research provides valuable insights into the origins and progression of dementia-related diseases, Dr Scales stressed the need for further research to determine if similar processes occur in humans. “It’s far from clear that this mechanism is relevant outside of a laboratory experiment” she said.

The transplanted cells used in the study were stem cells that have the potential to develop into blood and immune cells, but not into nerve cells. As a result, the researchers speculated that this suggests that amyloid build-up in the brain in Alzheimer’s disease can be triggered by the presence of amyloid outside of the brain.

The researchers now plan to test whether other types of transplants have the same result.

Earlier this year, a UK-based research team identified five very rare cases of transmissible Alzheimer’s disease in humans, believed to have arisen because of a medical treatment decades earlier. Reflecting on both studies, Dr Scales stressed that there is “no evidence” that Alzheimer’s can be caught from contact with someone with the disease, or from regular medical treatments.