Changes in serum miRNA-let-7 level in children with attention deficit hyperactivity disorder treated by repetitive transcranial magnetic stimulation or atomoxetine: An exploratory trial

•We investigated whether miRNA-let-7d or miRNA-107 serve as biomarkers of ADHD in diagnosis and therapy.•There were significant differences of miRNA-let-7d between ADHD and healthy children after rTMS or ATX treatment.•MiRNA-107 had no obvious changes ADHD patients and healthy children after rTMS or ATX treatment.•Our results suggest serum miRNA-let-7d may serve as a potential biomarker for children with ADHD. We aimed to investigate whether microRNA-let-7d (miRNA-let-7d) and miRNA-107 may serve as diagnostic and therapeutic biomarkers of attention deficit hyperactivity disorder (ADHD). The relative expression level of miRNA-let-7d and miRNA-107 in patients with ADHD and in a healthy control group was detected by real-time polymerase chain reaction. The blood samples were collected at 6 weeks after repetitive transcranial magnetic stimulation (rTMS) or atomoxetine (ATX) in ADHD patients, and the relative expression levels of the two miRNAs before and after treatments were compared. There were significant differences in the expression level of miRNA-let-7d between ADHD patients and healthy children, as well as before and after rTMS or ATX treatment in ADHD patients. However, the expression of miRNA-107 showed no significant difference between ADHD patients and healthy children or before and after rTMS (or ATX treatment). These results suggest that serum miRNA-let-7d may serve as a potential diagnostic and therapeutic biomarker for children with ADHD.