Summary: The gut bacterial community in people at the earliest, pre-symptomatic stage of Alzheimer’s disease differs substantially from that of cognitively healthy individuals.
These differences suggest the gut microbiome could serve as a noninvasive marker to identify individuals at higher risk for dementia and might point toward microbiome-based strategies to prevent or slow cognitive decline. The direction of causality—whether gut changes drive brain pathology or vice versa—remains to be established.
Key Facts:
- Researchers observed distinct gut bacterial communities in healthy people compared with individuals showing biological signs of early, preclinical Alzheimer’s disease, despite similar dietary patterns.
- Microbiome differences correlated with levels of amyloid-beta and tau—proteins that accumulate in the brain long before cognitive symptoms appear—but these differences did not correlate with markers of neurodegeneration.
- The team has initiated a five-year follow-up study to determine whether microbiome changes precede and possibly contribute to Alzheimer’s pathology, or whether they are a consequence of early brain changes.
Source: WUSTL
People in the earliest stage of Alzheimer’s disease—after brain pathology has started but before memory or thinking problems emerge—harbor a gut bacterial profile distinct from that of healthy peers, according to research from Washington University School of Medicine in St. Louis.
Published June 14 in Science Translational Medicine, the study analyzed stool, blood and cerebrospinal fluid samples, food diaries, and brain imaging from volunteers at the Charles F. and Joanne Knight Alzheimer Disease Research Center. The findings point to the gut microbiome as a potential tool for early detection and as a possible target for preventive interventions.
“We don’t yet know whether the gut is influencing the brain or the brain is influencing the gut, but this association is important either way,” said co-corresponding author Gautam Dantas, Ph.D., the Conan Professor of Laboratory and Genomic Medicine. He emphasized that gut microbes produce metabolites that can affect inflammation locally in the gut and systemically through the bloodstream, potentially influencing immune responses linked to brain health.
The collaboration began informally, the authors note, when Dantas and Beau M. Ances, MD, Ph.D., the Daniel J. Brennan Professor of Neurology, discussed the intersection of microbiome science and neurology. Ances, who treats and studies people with Alzheimer’s disease, pointed out that earlier studies had already shown microbiome differences in symptomatic patients but had not examined people in the critical preclinical window.
“By the time people develop cognitive symptoms, significant and often irreversible changes have occurred,” Ances said. “Identifying disease in the preclinical stage would be the ideal moment to intervene with therapies that might prevent or delay symptomatic decline.”
In this cross-sectional study of 164 cognitively normal volunteers, 49 showed biomarker evidence of early Alzheimer’s—elevated amyloid-beta or tau—based on PET imaging and cerebrospinal fluid analysis. Despite similar diets recorded in food diaries, the gut bacterial species and their functional profiles differed between the preclinical group and those without Alzheimer’s biomarkers.
Notably, the microbiome differences tracked with amyloid and tau pathology, which accumulate years before cognitive symptoms, but not with indicators of neurodegeneration that typically appear closer to symptom onset. The authors suggest that a stool-based microbiome screen could become a simpler, more accessible option for population-level risk assessment compared with PET scans or lumbar punctures, potentially improving outreach to underrepresented groups.
To clarify causality, the researchers have begun a longitudinal five-year study to monitor how gut microbiome composition evolves relative to Alzheimer’s biomarkers over time. If a causal connection is established, it would likely involve inflammatory pathways modulated by microbial metabolites. In that case, interventions such as targeted probiotics, dietary modification, or fecal microbiota transplantation might be explored as ways to promote protective bacteria or reduce harmful taxa and their metabolites.
The study also used machine learning to test whether microbiome features could improve prediction of preclinical Alzheimer’s. Incorporating specific bacterial taxa associated with early pathology increased the accuracy, sensitivity and specificity of classifiers tested on a subset of participants, suggesting added value for risk stratification.
Overall, these results link gut microbiome composition to early Alzheimer’s neuropathology and highlight the potential for gut-derived biomarkers to inform research into disease mechanisms, early detection, and preventive strategies.
About this Alzheimer’s disease research news
Author: Tamara Bhandari
Source: WUSTL
Contact: Tamara Bhandari – WUSTL
Image: The image is credited to Neuroscience News
Original Research: Closed access. “Gut microbiome composition may be an indicator of preclinical Alzheimer’s disease” by Aura Ferreiro et al., Science Translational Medicine
Abstract
Gut microbiome composition may be an indicator of preclinical Alzheimer’s disease
Alzheimer’s disease (AD) progresses from normal cognition through a lengthy preclinical phase and finally to symptomatic AD with cognitive impairment. Prior studies have reported altered gut microbial taxa in symptomatic AD patients compared with healthy, age-matched controls, but understanding of microbiome changes before symptom onset has been limited.
In this cross-sectional analysis that controlled for clinical covariates and dietary intake, researchers compared gut microbial taxonomy and function in 164 cognitively normal individuals, 49 of whom had biomarker evidence of early preclinical AD. Gut microbial taxonomic profiles in individuals with preclinical AD differed from those without biomarkers of preclinical disease.
These microbiome changes correlated with β-amyloid (Aβ) and tau pathological biomarkers but not with neurodegeneration markers, implying that the gut microbiome may change early in the AD process. The study identified specific bacterial taxa associated with preclinical AD, and adding these microbiome features improved machine learning classifiers used to predict preclinical AD status in a validation subset.
Gut microbiome correlates of preclinical AD neuropathology may deepen understanding of disease etiology and help identify gut-derived markers of AD risk.