The pathophysiology of schizophrenia spectrum disorders and associated mood disorders
is complex and highly heterogeneous, suggesting that different molecular pathways are involved
in it. Among those, the microbiome and its connection to the brain (“gut-brain axis”) has emerged
as a highly promising research avenue. To evaluate the role of the human microbiome in the gutbrain axis, we evaluated the relationship between gut and oral bacterial and fungal loads using
qPCR, quantification of serum cytokine and chemokine concentrations, and brain imaging data in
a cohort of schizophrenia spectrum and mood disorder patients. We found that gut bacterial and
fungal load was significantly different between cases and controls, that load was positively
correlated with several pro-inflammatory cytokines, and that the relation between stool fungal load,
percentage of grey matter, and cytokine and chemokine measures was mediated by sex of the
patient. Our findings have important implications for future studies and highlight the relevance of
studying the gut and oral microbiome in schizophrenia spectrum and associated mood disorders
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