Thompson et al. identified the OX2 Pro11Thr variant in two DQB1*0602-negative excessive daytime sleepiness (EDS) patients and the OX2 Pro10Ser variant in a Tourette’s syndrome patient comorbid with attention deficit hyperactivity disorder (ADHD) and probable EDS (Figure 2) [5]. Here, CD200 is linked to attention deficit-hyperactivity disorder.