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Latent Toxoplasma gondii infection associated with symptom severity in adult ADHD

Natalia Reoutova
07 Sep 2020

A sex- and age-matched case-control study of 140 adults with attention-deficit/hyperactivity disorder (ADHD) finds that Toxoplasma gondii seropositivity is associated with a 2.8-fold increase in the odds of ADHD and reveals its significant association with ADHD symptom severity.

Seropositivity for anti-T. gondii immunoglobulin G (IgG) was detected in 27.1 percent of individuals (n=19) in the ADHD group vs only 12.9 percent (n=9) in the control group. ADHD showed a significant association with anti-T. gondii seropositivity in univariable analysis (odds ratio [OR], 2.53; 95 percent confidence interval [CI], 1.05 to 6.06; p=0.038), which was further confirmed in confounder-adjusted multivariable analysis (OR, 2.77; 95 percent CI, 1.01 to 7.56; p=0.047). [Sci Rep 2020;10:2707]

Recent population-based registry studies in children and adults suggest that infections are associated with an increased risk of mental disorders by directly influencing the nervous system, immune activation, or inflammatory mediators. [JAMA Psychiatry 2018, doi: 10.1001/jamapsychiatry.2018.3428; Pharmacol Biochem Behav 2019, doi: 10.1016/j.pbb.2019.05.005] However, studies focusing on the general relationship of infectious agents and ADHD are scarce. [Afr Health Sci 2014;14:439-445; Acta Trop 2016;154:155-159] “This case-control study is the first to show that seropositive individuals had more than 2.5 times greater risk of adult ADHD than seronegative individuals,” pointed out the researchers.

Seropositivity showed a significant association with ADHD-related symptoms (p=0.012). “Patients with adult ADHD and T. gondii antibodies showed significantly higher ADHD index scores than seronegative ADHD patients,” reported the researchers. “Furthermore, specific influences of T. gondii serointensity and IgG avidity on ADHD-related symptoms were found in individuals with ADHD and controls, which hints at the fact that a latent infection may be able to trigger ADHD-related symptoms in individuals without ADHD.”

A regression analysis of risk factors for seropositivity in the ADHD group yielded a model in which male sex (odds ratio [OR], 3.00; 95 percent CI, 0.86 to 10.45; p=0.085), age (OR, 1.11; 95 percent CI, 1.02 to 1.20; p=0.015), having never been married (OR, 3.75; 95 percent CI, 0.71 to 19.69, p=0.118), and consumption of  raw/undercooked meat (OR, 4.26; 95 percent CI, 11.13 to 16.06; p=0.032) were predictive for seropositivity of T. gondii. “Consumption of undercooked meat, which may carry parasite’s cysts, is one of the main risk factors for infection in humans,” explained the researchers.

When linking T. gondii with psychiatric diseases, prior research demonstrated the importance of serointensity (defined as the concentration of the IgG antibodies) over the measurement of seroprevalence. [Biol Psychiatry 2012;72:290-295] In the current study, serointensity had significant influences on the ADHD index and the ADHD total score according to the Diagnostic and Statistical Manual of Mental Disorders Fourth Edition, as well as on both hyperactivity subscales. “Furthermore, we found a positive association of hyperactivity and serointensity in males,” wrote the researchers. “However, our data did not reveal an influence of T. gondii seropositivity or serointensity on depressive symptoms.”

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