A large-scale microarray study of young, healthy old and AD brains identified marked changes in complement expression with ageing, and elevated expression of C4A, C4B, C3aR1, C5aR1, CFHR1, and CLU in AD compared to age-matched controls; C1q binding protein (C1qBP) expression decreased in AD (123). Here, C5AR1 is linked to Alzheimer disease.