Toxoplasma gondii IgG Serointensity and Cognitive Function in Bipolar Disorder

Abstract Background Alongside affective episodes, cognitive dysfunction is a core symptom of bipolar disorder. The intracellular parasite Toxoplasma gondii has been positively associated with both a diagnosis of bipolar disorder as well as poorer cognitive performance, across diagnostic boundaries. Methods A total of 76 participants with bipolar disorder were tested for Toxoplasma gondii -specific IgG and IgM antibodies and for cognitive performance with a neuropsychological test battery. Cognitive parameters were categorized into three cognitive domains (attention and processing speed, verbal memory, executive function). Statistical analysis of associations between continuous indicators of cognitive status as dependent variables in relationship to Toxoplasma gondii, included multivariate analyses of co-variance for seropositivity, and partial correlations with IgG serointensity in IgG seropositives. All analyses were controlled for age and premorbid IQ. Results In seropositives (n = 27), individual parameters in the verbal memory domain showed significant inverse partial correlations with IgG antibody levels. Cognitive functioning did not differ between IgG seropositive and seronegative individuals in any of the cognitive domains (n = 76). IgM positives (n = 7) were too few to be analyzed. Conclusions This investigation is the first to show an association between Toxoplasma gondii IgG serointensity and memory function in a well-diagnosed bipolar disorder sample. While further research is necessary, latent Toxoplasma gondii infections could represent a risk factor for functional decline for patients with bipolar disorder and Toxoplasma gondii serointensity in seropositives may emerge as a biomarker for personalized treatment.