The high asthma rate in children with ADHD could potentially be linked to the recent discovery of genetic association, in which several studies suggested that a gene polymorphism of dopamine receptor D5 (DRD5), a form of the dopamine D1-like receptor, is associated with a ADHD behavior subtype and that the expression of DRD5 is found in both the mammalian brain and peripheral blood leukocytes [38–40]. Here, DRD5 is linked to asthma.