BACE1 and Alzheimer disease: Notably, the depression groups LLD AD and LLD NoAD showed significant differences in Ng, BACE1 and Ng/BACE1 ratio with higher levels for Ng (pADJ < 0.001), BACE1 (pADJ < 0.05) and the Ng/BACE1 ratio (pADJ < 0.01) in the LLD AD group.