One of the five studies included investigated the association between intestinal barrier function, immune response, and ADHD [5]; three investigated the association between impaired IP, immune responses, and serum zonulin/plasma haptoglobin levels and ASD [6,7,8]; and one investigated serum zonulin and claudin-5 levels in OCD [9]. The gene discussed is CLDN5; the disease is attention deficit-hyperactivity disorder.