The concurrence of the SLC6A4 rs6354 GG/GT and ADRA2A rs553668GG/GA genotypes is associated with a 6.15-fold increased risk of ADHD in comparison to cases carrying the combination of ADRA2A rs553668 AA and ANKK1 rs1800497 AA genotypes highlighting the role of the gene-gene interactions and polygenic effects in the occurrence of the ADHD as shown in a case-control study (Wang et al., 2021). This evidence concerns the gene SLC6A4 and attention deficit-hyperactivity disorder.