DNAAF4 and attention deficit-hyperactivity disorder: The composite genotype of DCDC2-DYX1C1 SNPs presented significant association with ADHD (ADHD-vs-Ctr_ADHD), with lower p-values when comorbid samples were considered jointly (ADHD+Com-vs-Ctr_ADHD), and also in the Com-vs-Ctr_ADHD test.