For example, complement 3 (C3) levels are increased, whereas the levels of signal regulatory protein (SIRP) α, a protein negatively regulating phagocytosis, and its corresponding receptor on microglia, cluster of differentiation (CD) 47, are reduced in the frontal cortex of FTLD patients compared to healthy controls or ALS and FTLD/ALS patients (Gitik et al., 2011; Umoh et al., 2018). Here, C3 is linked to amyotrophic lateral sclerosis.