Additionally, reduced levels of brain-derived neurotrophic factor (BDNF) have been associated with sleep disturbances [40], and Klil-Drori and Hechtman [41] reported that aerobic exercise improved ADHD symptoms by increasing BDNF concentrations, suggesting a role for this protein in enhancing sleep in individuals with ADHD. The gene discussed is BDNF; the disease is attention deficit-hyperactivity disorder.