A Mendelian randomization analysis of genome-wide association study (GWAS) data investigated the potential causal links between gut microbiota composition and symptoms of obsessive-compulsive disorder (OCD). The results suggest that Proteobacteria in the gut may serve as a protective factor against the disorder, while Bacillales microorganisms may increase risk. Other families of microorganisms were also identified as contributing to OCD. The paper was published in the Journal of Affective Disorders.
Obsessive-compulsive disorder, or OCD, is a mental health condition in which a person experiences unwanted, intrusive thoughts called obsessions. These obsessions cause intense anxiety or discomfort. To reduce this distress, the person feels compelled to perform repetitive behaviors or mental rituals, known as compulsions.
Common obsessions include fears of contamination, harm, or making mistakes, while common compulsions include excessive cleaning, checking, or counting. People with OCD are usually aware that their thoughts and actions are irrational but feel unable to stop them. The disorder can consume significant time and interfere with daily life, relationships, and work. OCD often begins in childhood or adolescence and can become chronic if left untreated.
Study author Mingjie He and her colleagues aimed to explore whether gut microbiota composition might play a causal role in OCD symptoms. Gut microbiota refers to the vast community of trillions of microorganisms living in the human gut. These microbes help with digestion by breaking down molecules into nutrients the body can absorb.
More recently, scientists have discovered a bidirectional pathway known as the microbiota-gut-brain axis, through which these microorganisms can influence brain processes—and be influenced by them. Studies of this axis have shown that gut microbiota composition is linked to various psychological characteristics. In some cases, symptoms of psychological disorders have even been transferred from humans to healthy rodents through fecal microbiota transplantation.
To examine this potential relationship, the researchers used Mendelian randomization, a method that leverages genetic variation to infer causal relationships between an exposure (gut microbiota) and an outcome (OCD). The approach mimics a randomized controlled trial by relying on the random assortment of genes at conception, which helps reduce confounding and reverse causality that can affect observational studies.
The researchers drew on genetic and microbiome data from 18,340 individuals of primarily European ancestry. Their analysis revealed that, at the phylum level, Proteobacteria appeared to be a protective factor against OCD. At the order level, Bacillales were identified as a risk factor. At the family level, Ruminococcaceae also appeared to offer protection. At the genus level, Bilophila was associated with reduced risk, while the Eubacterium ruminantium group and Lachnospiraceae UCG001 were linked to increased risk. A reverse analysis found no evidence that OCD influences gut microbiota composition.
“Our analysis suggested that specific gut microbiota might have a causal relationship with OCD, revealing potential intervention strategies for the prevention and treatment of this disorder,” the study authors concluded.
The study sheds light on how gut microbiota composition may influence OCD symptoms. However, it is important to note that gut microbiota is shaped by many factors, including diet, lifestyle, and environment. Moreover, since the data used in this study came exclusively from individuals of European ancestry, the findings may not generalize to other ethnic or cultural groups.
The paper, “Causal link between gut microbiota and obsessive-compulsive disorder: A two-sample Mendelian randomization analysis,” was authored by Mingjie He, Hongyang Zhang, Zheng Luo, Xinhao Duan, Feng Zhao, Peng Su, Zhijun Zeng, Lixiao Zhou, Chengzhi Chen, and Jingfu Qiu.