C9 and age-related macular degeneration: In addition to genetic variation at the CFH locus, variants in or near the complement factor B (CFB), complement component C3 (C3), complement component C9 (C9), complement factor I (CFI) and vitronectin (VTN) genes have been associated with AMD (Gold et al., 2006; Yates et al., 2007; Fritsche et al., 2016).