PER3 and attention deficit-hyperactivity disorder: In the ADHD group, statistical significant differences were observed at ZT24 and ZT28 between cultures incubated with dopamine and negative controls, particularly, for period genes Per1 (ZT28, F = 5.103, p = 0.012) and Per3 (ZT24, F = 7.703, p = 0.002; ZT28, F = 3.800, p = 0.033).