Figure 6.

Structural forms of the C4 locus and their associations with blood C4 levels. (A) The effects of common structural C4 haplotypes on blood C4 protein levels (β; 95% CIs), haplotype frequencies, and association P values. C4A and C4B differ only by four amino acids, and the human endogenous retroviral (HERV) element is integrated in intron 9 of the C4A and C4B genes, contributing to interlocus and interallelic length heterogeneity of C4 genes. (B) Heat map of blood C4 levels as a function of ten common combinations of C4A and C4B gene copy numbers; the path from left to right on the plot corresponds to the increasing C4A gene copy, and the path from bottom to top corresponds to the increasing C4B gene copy numbers. Mutually adjusted per-copy effects on blood C4 levels and the corresponding P values are also depicted.