VCP and frontotemporal dementia: Dysfunction of the endolysosome pathway is emerging as an important pathogenic process in FTD and ALS.29 VCP has previously been found to localize to the early endosome membrane, where it binds early endosomal autoantigen 1 (EEA1) to regulate the size of early endosomes.30 To investigate how VCP mutations impact the endolysosomal pathway, we used high resolution iSIM to measure the size of endogenous EEA1 (a well established early endosome protein31) (Fig. 1A).