Controversial New Push to Tie Microbes to Alzheimer’s Disease

Melinda Wenner Moyer in Scientific American:

BrainScientists have long puzzled over the root causes of Alzheimer's disease, a devastating and typically fatal condition that currently denies more than five million Americans their cognition and memory. But in a provocative editorial soon to be published in the Journal of Alzheimer’s Disease, a cadre of scientists argue that the complex disease may have a surprisingly simple trigger: tiny brain-infecting microbes. This controversial view, which is not new, has long been dismissed as outlandish, but a growing body of work suggests it may be worth considering and further studying. If researchers can prove the theory and iron out the many argued-over details—both formidable tasks, as brain infections are difficult to study—Alzheimer's could become a preventable illness.

The editorial, signed by 31 scientists around the world, argues that in certain vulnerable individuals—such as those with the APOE ε4 gene variant, a known Alzheimer’s risk factor—common microbial infections can infect the aging brain and cause debilitating damage. These microbes may include herpes simplex virus 1 (HSV-1), the ubiquitous virus that causes cold sores as well as Chlamydophila pneumoniae and Borrelia burgdorferi, the bacteria that cause pneumonia and Lyme disease, respectively. The controversial idea butts heads with the long-standing theory that amyloid-beta proteins and tau tangles, both of which build up inside the brains of those with Alzheimer’s, are the main drivers of disease-induced cell death. Instead, supporters of the pathogen hypothesis, as it is called, posit that either pathogens induce brain cells to produce the amyloid proteins and tau tangles or that nerve cells that have been damaged by infection produce them as part of an immune response.

More here.