Relationship between interleukin 6 promoter polymorphism at position -174, IL-6 serum levels, and the risk of relapse/recurrence in polymyalgia rheumatica.

OBJECTIVE

To assess the role of -174 G/C promoter polymorphism of interleukin 6 (IL-6) in the susceptibility to polymyalgia rheumatica (PMR). We also investigated whether this polymorphism modulates the circulating level of IL-6 and the risk of relapse/recurrence in a series of patients with PMR followed up prospectively.

METHODS

A prospective study of 112 consecutive, untreated patients with isolated PMR (i.e., without evidence of giant cell arteritis) who were followed up for at least 24 months. This cohort represented all patients diagnosed over a 5-year period in one Italian rheumatological secondary referral center. Patients were monitored for clinical signs/symptoms and acute-phase reactants. All PMR patients and 112 population-based controls from the same geographic area were genotyped for IL-6 polymorphism at position -174 by molecular methods. IL-6 serum levels were measured in 67 PMR patients and 43 population-based controls.

RESULTS

The distribution of the G/C 174 genotype was similar in PMR patients and controls. No significant associations with IL-6 promoter polymorphism at position -174 were found when PMR patients with and without relapse/recurrence were compared. Controls homozygous for the C allele had higher serum IL-6 levels than the carriers of the G allele (4.5 +/- 3.7 pg/ml vs 1.8 +/- 2.1 pg/ml, p = 0.01). Patients homozygous for the allele C had significantly higher values of IL-6 during followup than patients carrying GC or GG genotypes. CC homozygosity was significantly more frequent in patients with persistently elevated levels of IL-6 than in those without. The presence of persistently elevated IL-6 levels, but not the CC genotype, was associated with an increased frequency of relapse/recurrence.

CONCLUSION

Our findings show that the 174 G/C promoter IL-6 polymorphism is not implicated in susceptibility to PMR. However, CC genotype characterized PMR patients with persistently elevated levels of IL-6 who are at higher risk of developing relapse/recurrence. A genetically modulated pattern of IL-6 production could affect the longterm outcome of patients with PMR.