Background and aims C4 complement gene has been observed to be a susceptibility gene for SLE. Lower C4 gene (C4A and C4B) copy number (CN) is a risk factor for SLE, where as higher C4 CN is a protective factor. We investigated the association of C4 gene copy number variation in a north Indian cohort of SLE patients

Methods We recruited 112 aSLE and 52 pSLE patients with 115 healthy adult (CA) and 60 healthy paediatric (CP) controls and compared for C4A and C4B CN by RT-PCR, serum C3, C4 by nephelometry and ANA autoantibodies by line blot assay

Results C4A low copy number was higher in pSLE (OR=1.82, p=0.67) and aSLE (OR=1.51, p=0.41) as compared to their respective controls, pSLE had higher C4A low copy number than the aSLE (OR=1.33, p=0.58), though they were not statistically significant. C4A and C4B CN negatively correlated with several ANA autoantibodies. The total C4 (C4A +C4B) CN negatively correlated with Ro52 (r=−0.29, p=0.03), dsDNA (r=−0.32, p=0.02), SSB (r=−0.33, p=0.01), nucleosome (r=−0.28, p=0.04) and histone (r=−0.34, p=0.01) in pSLE and with nucleosome (r=−0.20, p=0.03) in aSLE. The total C4 CN positively correlated with serum C4 level (r=0.26, p=0.007) in both groups of patients

Conclusions We demonstrate that low copy numbers of complement genes correlate with the propensity for increased antibody secretion in both aSLE and pSLE. Thus, more productions of autoantibodies cause large number of immune complex formation with defective clearance process, due to low serum C4 level and low gene copy number