Association of a common complement receptor 2 haplotype with increased risk of systemic lupus erythematosus

Abstract

A genomic region on distal mouse chromosome 1 and its syntenic human counterpart 1q23-42 show strong evidence of harboring lupus susceptibility genes. We found evidence of linkage at 1q32.2 in a targeted genome scan of 1q21-43 in 126 lupus multiplex families containing 151 affected sibpairs (nonparametric linkage score 2.52, P = 0.006). A positional candidate gene at 1q32.2, complement receptor 2 (CR2), is also a candidate in the murine Sle1c lupus susceptibility locus. To explore its role in human disease, we analyzed 1,416 individuals from 258 Caucasian and 142 Chinese lupus simplex families and demonstrated that a common three-single-nucleotide polymorphism CR2 haplotype (rs3813946, rs1048971, rs17615) was associated with lupus susceptibility (P = 0.00001) with a 1.54-fold increased risk for the development of disease. Single-nucleotide polymorphism 1 (rs3813946), located in the 5' untranslated region of the CR2 gene, altered transcriptional activity, suggesting a potential mechanism by which CR2 could contribute to the development of lupus. Our findings reveal that CR2 is a likely susceptibility gene for human lupus at 1q32.2, extending previous studies suggesting that CR2 participates in the pathogenesis of systemic lupus erythematosus.

Fig. 1.

Linkage to SLE within 1q21–43. The vertical axis represents the NPL score for linkage analysis, and the horizontal axis corresponds to genetic distance in centimorgans. Microsatellite markers tested are shown.

Fig. 2.

CR2 SNP locations and haplotype blocks. (A) The CR2 gene is composed of 19 exons (37). Ten SNPs in exon 1 (5′ UTR), intron 1, intron 6, exon 10 (SCR9 and SCR10), the alternatively spliced exon 10a (SCR11), intron 16, exon 17 (transmembrane domain), and intron 17 were genotyped. (B) Two haplotype blocks were constructed. D′ (the top number in each box) and r² (the bottom number) of each SNP pair are depicted. Based on the strength of LD among SNP pairs, the first 6 SNPs formed the 19-kb block 1 and the next 3 SNPs formed the 7-kb block 2, which excluded the 10th SNP. (C) SNPs 1, 2, and 3 located in block 1 were assessed in extended Caucasian and Chinese SLE simplex families. (D) Pairwise LD of 374 SNPs from the 321-kb genomic region containing CR2 and its nearest known genes DAF and CR1. (Upper) Relative positions and sizes of CR2, the 5′ flanking hypothetical transcript AK023372 and DAF, and the 3′ flanking CR1. (Lower) Evidence of LD in D′ from 30 Caucasian trios and 45 Chinese individuals (HapMap Phase II, July 2006). ∗, Position of a single SNP (rs2135924) located within AK023372.

Fig. 3.

Transcriptional effects of SNP1. (A) Transcription factor binding sites within the proximal CR2 promoter critical for regulation of basal transcription (17). Shown are nucleotide positions and functional role of localized elements (−ve, repressor motif; +ve, activator motif; C.S, cell type-specific), TATA box, transcriptional initiation site (arrow), and position of SNP1. (B) Transcriptional activity of CR2 constructs expressing the major (CR2^+21T/Luc, n = 6) or minor (CR2^+21C/Luc, n = 10) SNP1 allele. Results shown represent mean promoter activity ± SEM and are expressed as normalized transcriptional activity of the minor allele construct relative to the major allele construct. (C) Correlation of peripheral blood CR2 mRNA levels with SNP1 genotype. T, major allele of SNP1; C, minor allele of SNP1. The fold expression of CR2 mRNA normalized to CD19 mRNA for each subject relative to the lowest normalized CR2 mRNA level is shown. The bar marks mean fold expression for each genotype.