DLG4 and Alzheimer disease: Since APOER2 isoforms have been shown to modify synapse number and function [14,15], we performed immunofluorescence labeling using antibodies against the presynaptic protein synapsin and the postsynaptic marker PSD95 on Apoer2 knockout mouse neurons rescued with lentiviral human APOER2-FL, APOER2 variants found in human control (APOER2 Δex4-5, +ex6B, Δex18, APOER2 +ex6B, Δex8, Δex18) or AD brains (APOER2 Δex4-5, +ex6B, Δex15, APOER2 +ex6B, Δex14, Δex18 isoforms).