HRH3 and early-onset autosomal dominant Alzheimer disease: The histamine H3 receptor (H3R) is associated with various neurological disorders such as Alzheimer’s disease, Parkinson’s disease, narcolepsy, and sleeping and learning disorders due to its important role in the central nervous system (CNS) by pre-synaptically controlling the release of histamine and other neurotransmitters including acetylcholine, dopamine, noradrenaline, serotonin, γ-aminobutyric acid, and glutamate [23].