Those mutant C4B genes are present in a bimodular short-short (SS) haplotype linked to HLA A30, B18 and DR7. Intriguingly, such HLA-A30 B18 DR7 haplotype with two identical C4B mutations at the splice junction of exon-intron 28 were found earlier in two other families with multiplex SLE nephritis. Here, C4B is linked to lupus nephritis.