HTR1A and attention deficit-hyperactivity disorder: By contrast, differences in methylation percentage between ADHD and control mothers were not significant for these two genes (ADHD vs. control: LSD = 0.34, p = 0.460 for HTR1A, ADHD vs. control: LSD = 0.29, p = 0.750 for RELN) and also for BDNF and MTHFR genes.