APP and Alzheimer disease: Yet, while our TSPAN15 experiment served to demonstrate that certain TSPANs can indeed alter ADAM10 cleavage of some substrates versus others, it is unlikely that the acitretin‐stimulated, selective increase in sAPPα in the AD patients is directly related to altered TSPAN15 expression, because acitretin (increased sAPPα, no effect on sNrCAM) and TSPAN15 expression (reduced sAPPα and increased sNrCAM) had opposite effects on cleavage of APP and NrCAM.