In the latest AD meta‐analysis, 19 loci in addition to the well‐established APOE locus were pinpointed.1 The latest ALS meta‐analysis identified three ALS‐associated loci2 and the latest PD meta‐analysis brought the total number of established PD loci to 26.3 Despite progress in identifying genetic hits in these neurodegenerative diseases, the underlying processes or cell types mediating the pathology remain uncertain. This evidence concerns the gene APOE and Alzheimer disease.