APP and Alzheimer disease: Many studies reported that miRNAs in blood, CSF and brain are affected through upregulation or downregulation of their expression in AD patients and also influence some signaling pathways involved in AD progression by targeting APP or BACE 1 expression as well as their roles in neuronal function and synaptic transmission making them ideal candidates to be used as biomarkers for the diagnosis of AD at early stages and a new approach for AD treatment16,17.