Decreased serum orexin A levels in drug-naive children with attention deficit and hyperactivity disorder.

Attention deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood and characterized by inattention, hyperactivity, and impulsivity. ADHD is a neurodevelopmental disorder, and its etiology has not yet been determined precisely. Orexin A is thought to play an important role in different forms of learning, memory, and attention. Despite its importance in attention and learning, no study has investigated serum orexin levels in patients with ADHD. In the present study, we aimed to compare serum orexigenic neuropeptides such as orexin A and orexin B, neuropeptide Y, and ghrelin between drug naive children with ADHD and healthy children. Fifty-six drug-naive children with ADHD and 40 healthy controls were enrolled in the study. After comparison of serum orexin A and orexin B, neuropeptide Y, and ghrelin, we found that serum orexin A levels were significantly lower in the ADHD group (p = 0.001). Furthermore, serum orexin A levels were compared between ADHD subgroups. Orexin A levels were significantly lower in the inattentive subtype compared with the hyperactive subtype and combined subtype (p = 0.009). Our results indicate that orexin A might be a neurobiological etiological factor in ADHD, particularly associated with attention symptoms. The present study is the first to demonstrate decreased serum orexin A levels in drug-naive children with ADHD. Further studies are needed to confirm our results and to show the effects of treatments involving orexin A in patients with ADHD.