Barr et al. (2000) were the first to detect the Mnll polymorphism (rs3746544), a relatively often researched SNP found in the 3′-untranslated region (3′-UTR), which is linked to ADHD. Early in Chen et al. (2008) indicated that SNPs in the 3′-UTR constitute a crucial microRNA-binding site and may alter binding sites while demolishing the operating site or generating another illegitimate site (Chen et al., 2008), which could impact the expression of the SNAP-25 gene and may ultimately increase the susceptibility for the progression of ADHD (Németh et al., 2013; Ye et al., 2016). This evidence concerns the gene SNAP25 and attention deficit-hyperactivity disorder.