Thus, our findings confirm the linkage between the gene loci of C4 and of HLA-DRB1*0301, an association which primarily appears to reflect a highly conserved ancestral haplotype in European lupus patients.32 Despite the reproducibility of these findings, the relative weight of either component appears to be less clear. The gene discussed is HLA-DRB1; the disease is systemic lupus erythematosus.