CX3CR1 I249M280 Haplotype Is Associated With Retinal Vasculitis in UK Patients.

Abstract

Abstract: : Purpose:The CX3CR1 I249M280 haplotype is associated with reduced binding activity to the ligand CX3CL1. The purpose of this study was to investigate whether polymorphisms in the gene encoding the chemokine receptor CX3CR1, which has been linked to ligand binding activity, are associated with retinal vasculitis (RV) in a cohort of UK patients. Methods:Blood samples were collected by venepuncture from 126 patients with uveoretinitis attending the Medical Eye Unit at St. Thomas’ Hospital, London. Healthy individuals (n=95) provided blood as normal controls. In all cases full clinical information regarding severity relapse and outcome were available from our database. DNA was prepared by proteinase K digestion, and high salt extraction and stored at –70C until use. Polymorphisms in the coding region of the CX3CR1 gene at positions 249 and 280 were detected by a multiplex SSP–PCR assay. Associations with disease were calculated by both allelic frequency and haplotype analysis. Results:The 280T allele is significantly raised in patients with uveoretinitis compared to healthy controls (19.4% vs 10.5% c2 6.5 p=0.01). This increase was due to the increased number of heterozygotes in the RV patient population (28% vs 13%) and the concordant decrease in wild–type homozygotes (67% vs 83%). There was no significant difference in the genotype frequencies of 249G and 249A. Further analysis showed an increase in genotype 6 (GA/AT) in patients with RV compared to all other haplotypes (26% vs 11%; Χ²=8.15, p=0.004; OR 3, CI .1.3–6.8), and a consequent decrease in the wild type genotype 1 (GG/CC; 57% vs 66%). Linkage disequilibrium has shown that only three amino acid combinations are formed by CX3CR1 genes polymorphisms (V249/T280, I249/M240, I249/T280) and analysis of showed an increase in the mutant genotype I249/M280, 19% vs 10% Χ² 7.5 p=0.005, in patients compared to controls. Conclusions:It has recently been shown that iris and retinal explants constitutively expressed CX3CL1 protein in microvascular EC and several stromal cell types. We have shown an association between a functional polymorphism in CX3CR1 in patients with uveoretinitis.

Keywords: clinical (human) or epidemiologic studies: risk factor assessment • uveitis–clinical/animal model • cytokines/chemokines