This work extends the study of 50% BACE1 inhibition as a therapeutic approach, demonstrating that 50% BACE1 reduction in 5XFAD transgenic mice, which display aggressive, early onset amyloid pathology [27], decreases Aβ42, plaques, and BACE1-cleaved APP fragments (C99 and sAPPβ) at 4, 6 and 9 months of age, but unexpectedly only in females, which have higher levels of Aβ42 and amyloid plaques than males. This evidence concerns the gene BACE1 and amyloidosis.