Genetic determinants in hepatitis C virus–associated mixed cryoglobulinemia: Role of polymorphic variants of BAFF promoter and Fcγ receptors

Objective Mixed cryoglobulinemia (MC) is a hepatitis C virus (HCV)–related immune complex disorder. Only some HCV‐infected patients develop MC, which suggests that the genetic background of the host plays a key role. This study was undertaken to evaluate the contribution of host genetic factors in the pathogenesis of HCV‐associated MC (HCV‐MC) by analyzing allelic variants of low‐affinity Fcγ receptor (FcγR) genes and BAFF promoter. Methods FcγR polymorphisms (FCGR2A 131 R/H, FCGR2B 232 I/T, FCGR3A 176 V/F, and FCGR3B NA1/NA2) and BAFF promoter polymorphism −871 C/T were analyzed in 102 patients with HCV‐MC and 108 patients with HCV without MC, using polymerase chain reaction–based techniques. Results A higher prevalence of −871 T/T homozygosity (31% versus 16%; P = 0.001) and a greater frequency of T alleles of the BAFF promoter (80% versus 57%; P = 0.004) were found in the HCV‐MC group than in the HCV group. A significant increase in serum BAFF concentration was significantly associated with the higher frequency of the T allele in HCV‐MC (mean ± SD 4.12 ± 1.29 versus 2.09 ± 0.81 ng/ml; P < 0.0005). The distribution of the FcγR genotypes was not significantly different. In the 21 HCV‐MC patients treated with rituximab, the response was strictly related to F allele homozygosity (significantly reduced in 5 of 5 patients with the FCGR3A F/F genotype versus 4 of 16 with V/V or V/F; P < 0.0005). Conclusion These results indicate the importance of host genetic background in the development of HCV‐MC, suggesting that mechanisms enhancing Ig production and B cell survival may play a relevant role. Genetic FcγR variants seem to be crucial to the effectiveness of rituximab therapy.