Linkage and association genetic studies could, in parallel, help to establish TP and RT-based endophenotypes as neurobiological markers in ADHD that could contribute to better understand its etiology [21] and support the contribution of the ADGRL3, SNAP-25, FGF1 and DRD4 genes, which were previously reported to be associated with ADHD [4,5,147,148,149,150,151,152]. The gene discussed is DRD4; the disease is attention deficit-hyperactivity disorder.