Since the discovery of histamine H3 receptor in 1983 and cloning of its cDNA in 1999, this histamine receptor has gained the interest of many pharmaceutical companies as a potential drug target for the treatment of various important disorders, including obesity, attention-deficit hyperactivity disorder, Alzheimer’s disease, schizophrenia, as well as for myocardial ischemia, migraine and inflammatory diseases (33). This evidence concerns the gene HRH3 and attention deficit-hyperactivity disorder.