C3 and age-related macular degeneration: On the other hand, the independent effect of rs433594 in the C3 gene appears to arise due to the strong association between AMD and a haplotype spanning exon 19 of C3. The genetic risk in the exon 19 region appears to be independent of the established genetic risks of non-synonymous SNPs in exons 3 and 9 of C3. Thus, it is possible that the genomic region spanning exon 19 contains a variant on a specific haplotype (see Independent genetic effects within the ARMS2 and C3 loci in Results section) that increases the risk of AMD.