TRAPPC9 and attention deficit-hyperactivity disorder: Most importantly, studies have shown that knockdown or knockout of target homologous genes (e.g., GARNL3, SLC6A3, LPHN3, NF1, MEF2C, and TRAPPC9) in Drosophila results in ADHD-like behaviors (attention deficit or hyperactivity) that can be rescued by MPH treatment [25–28].