Changes in Gut Microbiota May Affect Etiology and Symptomology of Schizophrenia  

Patients with schizophrenia may possess different intestinal microbiota abundance and beta diversity compared with healthy control individuals, suggesting the microbiome may play a role in the pathology of this disease, according to a systematic review and meta-analysis published in the Schizophrenia Bulletin.   

Research suggests the microbiome may be directly linked to brain function via the gut-brain axis. These connections may have effects on psychiatric conditions, such as schizophrenia, though the specific pathways are not well understood. Thus, researchers examined compositional and functional variations in the gut microbiota of patients with psychosis or schizophrenia.

PsycINFO, EMBASE, Web of Science, PubMed, MEDLINE, and Cochrane databases were searched from 1990 to July 2021 for human and animal studies reporting on gut microbiota analysis and diversity measures, as well as their clinical implications. Human studies included adults diagnosed with psychosis or schizophrenia, while animal studies focused on fecal microbiota transplant between case and control groups.

Meta-analyses were performed to detect differences in microbiota diversity, while standardized mean differences (SMD) and confidence intervals (CI) were used to compare diversity indices between patients with schizophrenia and healthy control individuals.

A total of 16 studies comprising 1376 patients (748 cases of psychosis/schizophrenia and 628 healthy controls) met study criteria. Reported use of antipsychotics was varied among studies, but included olanzapine, risperidone, quetiapine, amisulpride, aripiprazole, and clozapine.

The Chao 1 index was used to assess alpha diversity in 7 studies (375 cases vs 364 controls). While a decrease in alpha diversity was seen among patients with psychosis/schizophrenia (SMD, -0.64; 95% CI, -1.32 to 0.03), this result was not statistically significant. No other indices revealed differences in alpha diversity.

Beta diversity analysis was performed across 12 studies, with all 12 reporting differences between the psychosis/schizophrenia group vs the control group.

Differences in abundance of microbial taxa were reported across 14 studies. At the genus level, abundance increases in Bifidobacterium, Lactobacillus, Megasphaera, and Veillonella were most frequently reported in the psychosis/schizophrenia group vs control individuals, while decreases were most frequently reported in Coprococcus and Streptococcus.  

Twelve studies reported alterations in biosynthesis and metabolism among the psychosis/schizophrenia group.

Study limitations include the potential for limited results due to heterogeneity in data reporting and study designs. Diet and use of certain medications are known to affect microbiota, but were unable to be accounted for in the analysis. Finally, sample sizes of included studies were relatively small.

The researchers found no evidence of variations in intestinal microbiota between patients with psychosis or schizophrenia and control individuals. However, beta diversity was significantly different between psychosis and schizophrenia groups, compared with control individuals.

“The existing evidence suggests that the microbiome may play a role in the etiology, pathology, and symptomatology in schizophrenia,” study authors wrote. “Understanding how predicted or functional alterations in microbial genes or metabolic pathways influence symptomatic expression and downstream clinical outcomes may contribute to the development of microbiome targeted interventions for psychosis.”

This article originally appeared on Gastroenterology Advisor