In the ADHD cultures incubated with NE, a positive correlation between chronotype and Clock (ADHD with 0.1 μM NE at ZT4, rs = 0.574, p = 0.031), Cry1 (ADHD with 0.1 μM NE at ZT4, rs = 0.547, p = 0.043), Per1 (ADHD with 1 μM NE at ZT20, rs = 0.554, p = 0.040) and Per2 (ADHD with 1 μM NE at ZT24, rs = 0.628, p = 0.039) was observed. This evidence concerns the gene PER2 and attention deficit-hyperactivity disorder.