C9 and age-related macular degeneration: Interestingly, 15 AMD-associated risk genes such as C3 (Complement C3), APOE (Apolipoprotein E) and TGFBR1 (Transforming Growth Factor Beta Receptor 1), were predominantly expressed in retinal microglia, whereas only three and five risk genes were preferentially expressed in retinal (e.g. CFI (Complement Factor I)) or RPE/choroid tissue (e.g. C9 (Complement C9)), respectively (Figure 1F).