Gut–brain Axis Dysregulation and Microbial Dysbiosis as Emerging Diagnostic Markers in Psychiatric Disorders: A Systematic Review
Paula Espinosa Villagomez1, Mario Hinojosa-Figueroa1, Gabriela Burneo1, Paula Vallejo1, Felipe Pérez1, Coralía Villarreal1, Jose Rodas2, Jose E Leon-Rojas3
1NeurAll Research Group, 2University College Dublin, 3Cerebro, Emoción, Conducta (CEC) Research Group, Escuela de Medicina, Universidad de las Américas (UDLA)
Objective:
Psychiatric disorders impose a major global health burden. Increasing evidence implicates the gut–brain axis in psychiatric pathophysiology, with intestinal microbiome (IM) alterations as a key factor.
Background:
This review summarizes microbial composition changes across psychiatric disorders—schizophrenia, autism spectrum disorder (ASD), mood, eating, and attention disorders—highlighting diagnostic and translational implications.
Design/Methods:
A systematic review was conducted following PRISMA 2020 guidelines across PubMed, Scopus, CENTRAL, and PsycINFO. Studies were eligible if psychiatric diagnoses were DSM-V–based and IM composition was characterized at phylum, family, or genus level. Observational and interventional studies were included. Risk of bias was assessed using NIH Quality Assessment Tools.
Results:
Eighty studies involving 2,691 participants met criteria. Consistent alterations were observed in Firmicutes, Bacteroidetes, and Actinobacteria, with both disorder-specific and overlapping patterns. ASD showed reduced Firmicutes (↓4.8%) and Bacteroidetes (↓3.3%), but elevated Bifidobacteriaceae (↑5.9%) and Eggerthellaceae (↑5.5%). Mood disorders, including depression and bipolar disorder, were associated with increased Christensenellaceae (↑18.1%) and decreased Ruminococcaceae (↓2.0%). Schizophrenia displayed enrichment of Lachnospiraceae, Christensenellaceae, and Enterobacteriaceae (↑11–28%) alongside reductions in Akkermansia and Turicibacteraceae (↓9–28%). Eating disorders showed profound dysbiosis, with complete loss of Akkermansia (100%) and reductions in Lactobacillus (↓48.5%). ADHD was marked by Firmicutes/Bacteroidetes imbalance (↑49.8%, ↓56.6%).
Conclusions:
Psychiatric disorders are consistently linked to distinct patterns of gut microbial dysbiosis. While some changes are disorder-specific, others overlap, suggesting shared mechanisms within the gut–brain axis. These microbial signatures may represent candidate biomarkers and potential therapeutic targets. Standardized, longitudinal, and mechanistic studies are needed to establish causality and to validate microbiome-based strategies for psychiatric diagnosis and treatment.
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