(A) Schematic of APP processing. (B–E) Levels of intracellular APP (B), extracellular sAPPα (C), and sAPPβ (D) in FAD or UND fibroblasts by ELISA, as well as the sAPPβ/sAPPα ratio (E). (F–I) The levels of extracellular Aβ38 (F), Aβ40 (G), and Aβ42 (H) by multiplex-ELISA. The Aβ42/Aβ40 ratio was significantly increased in FAD fibroblasts (I). (J–K) γ-secretase activities in fibroblasts. The endopeptidase product line preference was increased in FAD fibroblasts (J). The carboxypeptidase activity did not differ between UND and FAD fibroblasts (K).