Objective: To examine whether single-nucleotide polymorphisms (SNPs) of the interleukin-4 receptor gene IL4R influence susceptibility to, or radiographic progression in, rheumatoid arthritis (RA).
Methods: The contribution of 2 SNPs (I50V and Q551R) in the coding region of IL4R to RA susceptibility was analyzed by allele-specific polymerase chain reaction in a case-control study of 471 RA patients and 371 healthy controls. Patients with available radiographs of the hands and feet obtained 2 years after disease onset (n = 302) were stratified retrospectively according to radiologic outcome into an erosive and a nonerosive group to evaluate the association between IL4R SNPs and disease progression.
Results: No differences in the genotype and allele frequencies of the I50V or Q551R SNPs were identified between the RA patients and healthy controls. In contrast, significant differences in the distribution of I50V IL4R SNP genotypes between patients with erosive and nonerosive disease were observed (chi2 = 15.68, P = 0.0004). Bone erosions at 2 years after disease onset were present in 68.1% of patients homozygous for the V50 allele compared with 37.0% of patients homozygous for the I50 allele (odds ratio 3.86, P < 0.0001). This association was independent of individual factors previously associated with severe disease, such as rheumatoid factor or the HLA-DR shared epitope. On a cellular level, the V50 allele conferred significantly reduced responsiveness to interleukin-4, providing a possible mechanism for the association of the I50V IL4R polymorphism with early erosions in RA.
Conclusion: Our data identify the I50V IL4R SNP as a novel genetic marker in RA, showing high predictive value for early joint destruction.