The role of Interleukin-6 as a biomarker in ADHD

Introduction: Attention-Deficit Hyperactivity Disorder (ADHD) is a common psychiatric syndrome with a strong genetic component. ADHD can have adverse effects on academic, professional, financial, and interpersonal achievement. Previous studies have indicated that inflammation and interleukin-6 (IL-6) may be involved in the pathophysiology of ADHD. However, conflicting results have been reported in previous meta-analyses, and errors in data extraction are common. Additionally, previous meta-analyses have not analysed IL-6 assuming it is an exponentially distributed biomarker. Aim: To investigate if IL-6 levels are elevated in patients with ADHD in peripheral blood. Materials and methods: This meta-analysis is a replication of the most recently published meta-analysis with an extended literature search. The studies included measured IL-6 in peripheral blood in patients with ADHD without severe neurological disease and a healthy control group. The values were analysed in their raw form and log-transformed to approximate a normal distribution. Results: Errors in data extraction and computational errors were detected in the replicated meta-analysis, which removed the significance of the result of a pooled analysis. After an extended literature search, no significant association between IL-6 and ADHD was found (estimate = 0.5861, 95%CI = -0.2539 – 1.4261, p = 0.17, I 2 = 96.6%). Conclusion: No significant association between IL-6 and ADHD was observed in this meta-analysis. This study confirms that errors in meta-analyses are common.