It has been demonstrated that miR-9, which is encoded by 3 different genes (MIR9-1, MIR9-2, and MIR9-3), may be relevant in AD pathogenesis since it targets two of the most important proteins involved in the disease pathology: amyloid-β precursor protein (AβPP), which carries the amyloid-β peptide (Aβ) that precipitates in the amyloid plaques, and BACE1 that cleaves APP to originate Aβ [24]. The gene discussed is BACE1; the disease is Alzheimer disease.