CX3CL1 and amyotrophic lateral sclerosis: Chemokines are classified into four families: CXC, CC, CX3C, and C. One of the many crucial glial cell communication axes that maintain microglia homeostasis is CX3CR1 and its neuronal ligand CX3CL1 signaling, and loss-of-function variants of CX3CR1 have been associated with worsening Braak staging, neurodegeneration, as well as decreased survival in patients with AD and ALS (47).