Altered Gut Microbiota in Adults with Subjective Cognitive Decline: The SILCODE Study.

Area of Science:

• Microbiome research
• Neuroscience
• Gastroenterology

Background:

• Subjective cognitive decline (SCD) is the earliest indicator of preclinical Alzheimer's disease (AD).
• Gut microbiota alterations are implicated in mild cognitive impairment (MCI) and AD dementia.
• The specific changes in gut microbial composition in individuals with SCD are not well understood.

Purpose of the Study:

• To characterize the gut microbiota in individuals experiencing subjective cognitive decline.
• To investigate the relationship between gut microbial composition and cognitive performance in early AD stages.

Main Methods:

• 16S rRNA Illumina Miseq sequencing of fecal samples from 105 participants (38 normal controls, 53 SCD, 14 cognitive impairment).
• Comparative analysis of gut microbial compositions across the three groups.
• Association analysis between altered gut microbiota and cognitive performance, with amyloid PET validation in selected SCD individuals.

Main Results:

• A progressive decline in the abundance of Firmicutes, Clostridia, Clostridiales, Ruminococcaceae, and Faecalibacterium was observed from normal controls to SCD and cognitive impairment groups.
• The anti-inflammatory genus Faecalibacterium was significantly reduced in individuals with SCD compared to normal controls.
• Altered bacterial taxa were associated with cognitive performance, and findings were consistent in SCD participants with positive amyloid evidence.

Conclusions:

• Gut microbiota composition is altered in individuals with subjective cognitive decline.
• These alterations may offer novel insights into the pathophysiological mechanisms of Alzheimer's disease.
• This study highlights the potential role of the gut microbiome in the early stages of AD.