Toronto, Long assumed to originate in the brain, Alzheimer's disease -- the leading cause of dementia -- might be the result of a breakdown elsewhere in the body, new research has claimed.
In people with Alzheimer's disease, a protein called amyloid-beta forms clumps or "plaques" that smother brain cells.
Besides the brain, the protein is also produced in blood platelets, blood vessels and muscles, and its precursor protein is found in several other organs.
According to researchers, these amyloid-beta has cancer-like properties and can travel to brain from other parts of the body where it accumulates and begins to inflict damage.
"The blood-brain barrier weakens as we age, " said Weihong Song, Professor at the University of British Columbia in Canada.
"That might allow more amyloid-beta to infiltrate the brain, supplementing what is produced by the brain itself and accelerating the deterioration."
For the study, published in the journal Molecular Psychiatry, the team attached normal mice, which do not naturally develop Alzheimer's disease, to mice modified to carry a mutant human gene that produces high levels of amyloid-beta protein.
Normal mice that had been joined to genetically modified partners for a year "contracted" Alzheimer's disease.
Moreover, the normal mice also developed a pathology similar to "tangles" -- twisted protein strands that form inside brain cells --, disrupting brain function.
In addition, the ability to transmit electrical signals involved in learning and memory was impaired even in mice that had been joined for just four months.
The findings offer hope that future drug therapies might be able to stop or slow the disease without acting directly on the brain.
Instead, it could target the kidney or liver and thus get rid of the toxic protein before it ever reaches the brain.
"Alzheimer's disease is clearly a disease of the brain, but we need to pay attention to the whole body to understand where it comes from, and how to stop it, " Song noted.