Other genes in the complement system are strongly related to dementia, including CR1, C1S, CD33, and TREM2; interestingly, CR1, a well-established genetic risk factor for dementia, is a receptor for complement C3b and C4b proteins, and CD46 mediates inactivation of C3b and C4b, pointing to potential mechanistic pathways [50]. This evidence concerns the gene C3 and dementia.