Disease Phenotypes and Gender Association of FCRL3 Single-Nucleotide Polymorphism −169T/C in Taiwanese Patients with Systemic Lupus Erythematosus and Rheumatoid Arthritis

Objective. To investigate the association of the functional FCRL3 single-nucleotide polymorphism (SNP) −169T/C with disease phenotypes and susceptibility to systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) in Taiwanese. Methods. FCRL3 SNP −169T/C was genotyped in 573 patients with SLE, 670 patients with RA, and 758 controls. Genotype distributions and allele frequencies were compared among the 3 groups as aggregates or as stratified by clinical characteristics, autoantibody profile, and sex within patient groups. Results. Overall, FCRL3 SNP −169T/C was not associated with susceptibility to either SLE or RA. However, −169CC genotype was significantly reduced in leukopenia-positive SLE patients as compared to the leukopenia-negative SLE patients (CC vs CT+TT, p = 6 × 10 −4 , OR 0.444, 95% CI 0.279–0.708) and controls (p = 6.1 × 10 −3 , OR 0.583, 95% CI 0.396–0.857). On the other hand, −169TT genotypes were significantly more numerous in RA patients with non-destructive disease as compared with patients with destructive disease (CC+CT vs TT: p = 0.007, OR 1.672, 95% CI 1.149–2.432). The −169T allele frequency was also significantly increased in non-destructive RA compared with patients with destructive disease (C vs T: p = 0.010, OR 1.423, 95% CI 1.089–1.859). FCRL3 SNP −169TT homozygous donors were significantly more numerous among female cyclic citrullinated peptide (CCP)-negative RA patients versus female CCP-positive RA patients (CC+CT vs TT: p = 0.019, OR 1.64, 95% CI 1.085–2.479). Conclusion. The functional FCRL3 SNP −169T/C appears to play important roles in the development of certain phenotypes such as SLE leukopenia and RA disease severity in Taiwanese patients with SLE and RA.