BACE1 and Alzheimer disease: The level of serum miR-27a-3p in AD patients was positively correlated with the level of cerebrospinal fluid miR-27a-3p (r = 0.695, P < 0.05), negatively correlated with the level of SUVR and cerebrospinal fluid BACE1 (r = − 0.521, − 0.447, P < 0.05), There was no correlation between level Aβ 42、Aβ40, MMSE score and MOCA score (P > 0.05), as shown in Table 5.