INTRODUCTION

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that can affect substantially any organ in the body. One of its most severe manifestations is lupus nephritis. Hereditary C1q deficiency is strongly related to SLE but there are very few and inconsistent studies exploring the single nucleotide polymorphisms (SNPs) of the C1q gene cluster in relation to the pathogenesis of SLE. In the present study we evaluated the possible association of gene variants in complement C1q gene cluster with susceptibility to lupus nephritis in a Bulgarian population, focusing on five previously associated with SLE SNPs in other populations.

MATERIALS AND METHODS

Thirty-eight patients with lupus nephritis and 185 healthy controls, all from Bulgaria, were genotyped for the five C1q SNPs, rs587585, rs292001, rs172378, rs294179 and rs631090, by quantitive real-time PCR methods. We also determined C1q serum levels of C1q and haemolytic activity of C1q in relation to C1q genotypes.

RESULTS

Lupus nephritis patients and healthy controls had statistically similar frequencies of genotypes and alleles of rs587585, rs292001, rs294179 and rs631090 SNPs. Nevertheless, minor G allele in rs172378 was significantly overrepresented in lupus nephritis patients when compared with healthy controls (36% vs. 23%, odds ratio = 1.80, 95% confidence interval = 1.06-3.06, p = 0.029). The SNP rs292001 showed a trend towards lower serum C1q levels in healthy controls. Two SNPs - rs294179 and rs292001 - were in a linkage disequilibrium in patients and healthy controls with different power (healthy controls: r (2 )= 0.6526, D' = 0.842; lupus nephritis patients: r (2 )= 0.491, D' = 0.686). The haplotype C-A-A-T-T in the patient group was associated with lupus nephritis: 7.7% vs. 0.8%, odds ratio = 10.81, 95% confidence interval = 1.45-80.57, p = 0.002.

CONCLUSIONS

These results support the implication of the G allele in rs172378 as a risk factor for lupus nephritis in a homozygous status, at least for a Bulgarian population.