The gut microbiome and inflammation in obsessive-compulsive disorder patients compared to age-and sex-matched controls: a pilot study. Objective: To compare the gut microbiome profile (by way of taxon analysis and indices of band a-diversity) and inflammatory markers (C-reactive protein [CRP], interleukin-6[IL-6] and tumour necrosis factor-a [TNF-a]) of obsessive-compulsive disorder (OCD) outpatients and non-psychiatric community controls. Methods: We collected morning stool and blood samples from 21 nondepressed, medication-free OCD patients and 22 age-and sex-matched non-psychiatric community controls. Microbiota analysis was performed using Illumina sequencing of the V3 region of 16S rRNA; serum CRP samples were analysed using immunoturbidimetry and plasma IL-6/TNF-a were examined by high-sensitivity ELISA. Multiple comparisons were corrected for using the false discovery rate (a = 0.05). Results: Compared to controls, the OCD group presented lower species richness/evenness (a-diversity, Inverse Simpson) and lower relative abundance of three butyrate producing genera (Oscillospira, Odoribacter and Anaerostipes). Compared to controls, mean CRP, but not IL-6 and TNF-a, was elevated OCD patients. CRP revealed moderate to strong associations with psychiatric symptomatology. Conclusion: To our knowledge, this is the first investigation of the gut microbiome in OCD. In addition, our findings lend further support for the potential association of inflammation and OCD. These results suggest the gut microbiome may be a potential pathway of interest for future OCD research.

The gut microbiome has become a topic of major interest as of late, with a new focus specifically on psychiatric disorders. Recent studies have revealed that variations in the composition of the gut microbiota may influence anxiety and mood and vice versa. Keeping the concept of this bidirectional "microbiota-gut-brain" axis in mind, this review aims to shed light on how these findings may also be implicated in obsessive-compulsive disorder (OCD); potentially outlining a novel etiological pathway of interest for future research in the field.

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