C9 and age-related macular degeneration: In addition, four variants in or near the complement factor B (CFB) and complement component 2 (C2) genes, three variants in or near the complement component 3 (C3) gene, two variants in or near the complement factor I (CFI) gene, one variant in the complement component 9 (C9) gene and one variant near the vitronectin (VTN) gene have been associated with AMD [6,14,15].