C4A and systemic lupus erythematosus: On a recent case/control study of British SLE (cases, N = 501; controls, N = 719), total C4 GCNs were determined by a paralog ratio test, which employed a set of primers (16-mer) that hybridized to and PCR-amplified the duplicated regions of complement C4 in the MHC plus a unique and non-variable region in chromosome 19 as reference control (for two copies).