Clinical and cognitive profile of nigral iron content in children with ADHD

BACKGROUND: ADHD has been associated with impaired central nervous dopaminergic pathways. Brain iron is an essential cofactor for the synthesis of dopamine and the substantia nigra (SN) is a significant pool of dopaminergic neurons playing a central role in the activity of the nigrostriatal pathway. The present study investigated SN iron content in children with ADHD, its relationship with ADHD symptom severity and cognitive performance.

METHODS: Neuroimaging and phenotypical data were extracted from the Healthy Brain Network dataset. After initial screening, 54 medication-naïve children with ADHD and 44 neurotypical (NT) children (8-12 year) were included. ADHD symptom severity was extracted from the Child Behavior Checklist (CBCL) Parent report and working memory (WM) and inhibitory control scores from the National Institute of Health toolbox.

RESULTS: A mixed between-within subjects ANOVA revealed no significant difference in SN iron content between medication-naïve children with ADHD and NT (partial eta squared = 0.001, p = .79). In the ADHD group, Spearman's correlation revealed a significant inverse relationship between left (r = -0.38; p < .01) and right (r = -0.33; p = .01) SN iron content and CBCL Attention Problems T score, while in the NT group left SN iron content significantly correlated with inhibitory control (r = 0.36; p = .02).

CONCLUSIONS: Although there was no difference in nigral iron content between both groups, higher SN iron content was associated with lower attention problems in children with ADHD and higher SN iron content was associated with better inhibitory control in NT children.