FHIT and attention deficit-hyperactivity disorder: Although we did not replicate the association in stage two for FHIT and KCNC1 and did not observe any association between other gene variants and ADHD,Neale et al and Stergiakouli et al. also did not show a clear effect for potassium channel genes [81, 82], which may be interpreted bythe inadequate power to detect effects, the differences of studied samples in geography, ethnicityand clinical phenotypes (persistence, comorbidity, etc.)and multiple genetic factors for complex disorders such as ADHD.