Association of two functional polymorphisms in the CCR5 gene with juvenile rheumatoid arthritis

Abstract

Juvenile rheumatoid arthritis (JRA) is mediated by Th1-immune responses. In children with JRA, synovial T cells express high levels of the Th1-chemokine receptor CC chemokine receptor 5 (CCR5), which has been implicated in susceptibility to rheumatoid arthritis. To test the hypothesis that genetic variation in CCR5 is associated with susceptibility to JRA, we analyzed patterns of variation in the 5'cis-regulatory region of CCR5 in 124 multiplex families from a JRA-affected sibpair registry. After sequencing the upstream region of CCR5, variants were tested for association with JRA by transmission disequilibrium testing. A single nucleotide polymorphism, C-1835T, was significantly undertransmitted to children with early-onset JRA (P<0.01). C-1835T was genotyped in 424 additional simplex and multiplex families. CCR5-1835T allele was undertransmitted in the cohort of all probands with JRA (P<0.02), as well as in those with early-onset (P<0.01) or pauciarticular JRA (P<0.05). Another variant, a 32-bp deletion in the open reading frame of CCR5 (CCR5-Delta32) was also tested in approximately 700 simplex and multiplex families. CCR5-Delta32 was also significantly undertransmitted to probands with early-onset JRA (P<0.05). Both variants are in regions under natural selection, and result in functional consequences. Our results suggest these CCR5 variants are protective against early-onset JRA.

Figure 1. Linkage disequilibrium and haplotypes at the CCR5 locus

An LD plot is depicted in the bottom part of the figure based on the measured r². Each square represents the magnitude of LD for a single pair of markers, with black color indicating high r². A key is provided below the LD plot. Analysis of this LD plot suggests the presence of a single haplotype block. Haplotypes spanning this block are shown above the LD plot, along with their frequency among unrelated, unaffected parents. Only haplotypes with a frequency >5 % are shown. The haplotypes were formed by SNPs at positions −2852, −2753, −2554, −2459, −2135, - 2086, and −1835 relative to the translational start site, and the CCR5-Δ32 polymorphism in the open reading frame on exon 3 of the CCR5 gene. Unrelated, unaffected parents of the multiplex families were used for the haplotype and LD analysis of all pairwise comparisons, with the exception of the comparison between the CCR5 C-1835T and CCR5-Δ32 polymorphisms, for which the unrelated, unaffected parents of all the simplex and multiplex families were used. CCR5 C-1835T and CCR5-Δ32 were 2.3 kb apart, and had a D′ of 1, but r² of only 0.012. The frequencies of the CCR5-1835C-CCR5 WT, CCR5-1835T-CCR5 WT, CCR5-1835C-CCR5 Δ32, and CCR5-1835T-CCR5 Δ32, two-locus haplotypes were 9.9 %, 80.4 %, 9.7 % and 0 % respectively.