Several lines of evidence suggest an involvement of the gut microbiota in the pathophysiology of psychiatric disorders, albeit with contradictory results. A review and meta-analysis of studies examining alpha and beta diversity and relative abundance of gut microbes in adult psychiatric populations (major depressive disorder [MDD], bipolar disorder [BD], psychosis and schizophrenia, anorexia nervosa, anxiety, obsessive compulsive disorder, posttraumatic stress disorder, or attention-deficit hyperactivity disorder) versus controls was recently completed to characterize contradictory findings. Data from 59 studies (64 case-controlled comparisons of 2,643 patients and 2,336 controls) were included in various analyses. A significant decrease in alpha diversity richness in patients compared with controls was found (observed species standardized mean difference [SMD] = -0.26, p = 0.01; Chao1 SMD = -0.5, p = 0.001). When examined by individual diagnosis, only BD showed consistently decreased richness (observed species SMD = -0.61, p = 0.04; Chao1 SMD = -0.53, p = 0.03). Across measures of alpha diversity, Shannon index and Simpson index showed non-significant differences between patients and controls; however, there was a significant decrease in phylogenetic diversity of patients versus controls (SMD = -0.24, p = 0.049). Differences in beta diversity were consistently observed only for MDD and psychosis and schizophrenia. There was little evidence of disorder specificity in relative abundance of microbial taxa; however, there was a transdiagnostic pattern of microbiota signatures. Depleted levels of Faecalibacterium and Coprococcus and enriched levels of Eggerthella were shared between MDD, BD, psychosis and schizophrenia, and anxiety. Overall, these findings did not find evidence of disorder-specific microbial alterations. Rather, transdiagnostic microbial alterations were observed that are characterized by depleted anti-inflammatory butyrate-producing bacteria and enriched proinflammatory bacteria. Future studies should consider investigating microbial alterations as a function of transdiagnostic clinical features and underlying pathophysiology rather than distinct diagnostic categories.
Nikolova VL et al. JAMA Psychiatry 2021; Epub ahead of print. Abstract