MAPT and early-onset autosomal dominant Alzheimer disease: In Alzheimer’s disease (AD) and Parkinson’s disease (PD) animal models, CX3CR1 deficiency shows paradoxical outcomes, attenuating or exacerbating amyloid-β (Aβ) and tau pathologies in AD, while consistently worsening α-synuclein-induced neurodegeneration in PD.