KL and attention deficit-hyperactivity disorder: Concerning α-Klotho, although there is no direct link between this protein and ADHD in the literature, α-Klotho is highly expressed in the brain and plays an important neuroprotective role [54], which could in part be mediated by the suppression of proinflammatory cytokines in the central nervous system [55], thus establishing a hypothetical link with the proinflammatory theory of ADHD.