Analysis of IL6 and IL1A gene polymorphisms in UK and Dutch patients with sarcoidosis

Background: Proinflammatory cytokines are a major determinant in the inflammatory events leading to sarcoidosis. Genetic variations in the genes encoding these cytokines might contribute to sarcoidosis susceptibility, disease severity and outcome. Methods: In the present study we genotyped two clinically well-defined cohorts of Caucasian sarcoidosis patients from different European countries (each with their own controls) for the following polymorphisms using SSP-PCR: IL6-174(G/C), IL6 intron 4(A/G) and IL1A-889(C/T). In total, 516 individuals were studied (147 UK + 102 Dutch patients, 101 UK + 166 Dutch controls). Disease severity data at presentation included chest radiographic stage, FVC, DL_CO, and extrapulmonary manifestations. Disease progression was evaluated on follow-up chest radiographs and sequential lung function measurements (2, 4 years). Results: No differences in genotype, carriage and allele frequencies of the investigated polymorphisms were found in either of the populations. Analysis of genotype data in relation to disease severity data, however, showed a slightly increased carrier frequency of the rarer -174C allele in patients with Stage IV sarcoidosis (p = 0.03, p_c = 0.09). Pulmonary function progression analysis did not reveal significant associations. Conclusions: Although the investigated polymorphisms are unlikely to contribute to sarcoidosis susceptibility, the IL6-174C allele might have a role in the genetics underlying sarcoidosis severity or the progression towards pulmonary fibrosis in a particular subgroup.