PSEN1 and Alzheimer disease: The most frequently identified neurodegeneration-associated parent proteins are abundantly expressed in B lymphocytes and comprise notably the proteins encoded by: (i) the AD-related genes APP and PSEN1, (ii) the ALS/FTD-related genes PFN1, SQSTM1, GRN, SOD1, and VCP and (iii) the PD-related proteins PARK7 and GBA (Figure 1).