The colocalization of HTRA1 with parenchymal Aβ plaques in patient brain tissue sections further strengthened this link (Grau et al., 2005), but additional data from humans did not emerge until recently, when elevated HTRA1 levels were reported in two proteomic studies investigating AD brain samples (Bai et al., 2020; Drummond et al., 2022). Here, HTRA1 is linked to Alzheimer disease.