APP and Alzheimer disease: The evidence that NGFR/p75NTR could represent a specific biomarker for AD emerged in 2015 from a study of Yao and colleagues [77], who reported a significant reduction of NGFR/p75NTR ECD levels in cerebrospinal fluid (CFS) and in the brains of AD patients and of APP/PSEN1 double-transgenic mice, due to the Aβ-induced reduction in the expression and activity of ADAM17 (Table 1).