Does Toxoplasma gondii infection have a causal impact on human psychopathology? A Mendelian randomization analysis

05/08/2026

AI Summary

Mendelian randomization analyses found no significant causal association between genetic liability to T. gondii infection and studied psychiatric disorders or risk-taking behaviour.
Instrumental variables comprised 25 SNPs for anti-T. gondii IgG seropositivity and 76 SNPs for IgG levels, analysed across 18 European GWAS datasets.
If causal, effect sizes are likely small: OR <1.18 for schizophrenia and <1.29 for bipolar disorder; smaller than observational seroepidemiological estimates.

AI Summary

Using genome-wide association study (GWAS) data, we selected 25 and 76 single-nucleotide polymorphisms as instrumental variables for anti-T. gondii IgG seropositivity and anti-T. gondii IgG levels, respectively, and conducted two-sample Mendelian randomization (MR) analyses across 18 GWAS datasets to investigate potential causal effects on addiction, bipolar disorder, obsessive-compulsive disorder, schizophrenia, and risk-taking behavior in European populations.

Contrary to previous epidemiological evidence, our MR analyses do not support a significant causal association between T. gondii infection and any of the studied psychiatric disorders or risk-taking behavior.

Collectively, these results establish that any true causal effect of genetic liability to T. gondii infection is likely to be small (OR < 1.18 for schizophrenia, < 1.29 for bipolar disorder) and below the effect sizes typically reported in observational seroepidemiological studies, although small or infection-phase-specific effects cannot be excluded.

Basic summary

PLoS Pathog. 2026 Aug 4;22(8):e1014312. doi: 10.1371/journal.ppat.1014312. Online ahead of print.

ABSTRACT

Toxoplasma gondii (T. gondii) is a prevalent zoonotic parasite that has been implicated in influencing human psychiatric disorders and risk-taking behaviors. Using genome-wide association study (GWAS) data, we selected 25 and 76 single-nucleotide polymorphisms as instrumental variables for anti-T. gondii IgG seropositivity and anti-T. gondii IgG levels, respectively, and conducted two-sample Mendelian randomization (MR) analyses across 18 GWAS datasets to investigate potential causal effects on addiction, bipolar disorder, obsessive-compulsive disorder, schizophrenia, and risk-taking behavior in European populations. Contrary to previous epidemiological evidence, our MR analyses do not support a significant causal association between T. gondii infection and any of the studied psychiatric disorders or risk-taking behavior. Collectively, these results establish that any true causal effect of genetic liability to T. gondii infection is likely to be small (OR < 1.18 for schizophrenia, < 1.29 for bipolar disorder) and below the effect sizes typically reported in observational seroepidemiological studies, although small or infection-phase-specific effects cannot be excluded.

PMID:42550877 | DOI:10.1371/journal.ppat.1014312

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