PER3 and attention deficit-hyperactivity disorder: When comparing the two study groups, significant different Clock (F = 4.145, p = 0.010), Bmal1 (F = 4.815, p = 0.005) and Per3 (F = 4.042, p = 0.011) expressions were observed in HDFs exposed to ATO collected from ADHD participants exhibiting neutral and moderate evening preference, as well as from healthy participants with morning preference.