BACE1 and Alzheimer disease: For example, miR‐31 expression level was found to be reduced in AD patients.[220] A study led by Barros‐Viegas et al. intracranially injected miR‐31‐carrying lentivirus into the hippocampus of AD triple‐transgenic (3xTg‐AD) mice, which resulted in a simultaneous reduction of BACE1 mRNA levels as well as APP production.