gms | German Medical Science

Introduction: GPA is a systemic autoimmune disease defined by a necrotizing granulomatous inflammation involving the respiratory tract and an anti-neutrophil cytoplasmic autoantibody (c-ANCA)-associated vasculitis (AAV). c-ANCA are directed primarily against proteinase 3 (PR3), a neutral serine protease expressed in neutrophils and monocytes. As the immune response against the autoantigen PR3 is a central aetiological feature of PR3-ANCA-associated vasculitis, we focused on the question, whether amino acid polymorphisms of PR3 are associated with the development of systemic autoimmune vasculitis or not.

Methods: In order to identify enzyme polymorphisms of PR3, we screened the entire coding region of the PRTN3 gene of a cohort of 41 GPA patients and 44 healthy controls by means of PCR and direct sequencing of the resulting amplicons. Subsequently, allele frequencies were compared between the GPA patients and the control group.

Results: By direct sequencing analyses, two rare (RS139778046 and RS150802678) polymorphisms and a common one (RS351111) were detected in the exon sequences of the PR3 gene. The rare mutations lead to amino acid changes from histidine to leucine (H185L) and arginine to histidine (R249H), respectively. The common SNP (RS351111) changes the first base of the codon 119 from guanine to adenine leading to an amino acid change from valine to isoleucine. We analyzed whether there is a correlation between the major or minor allele of these SNPs and GPA. However, no statistically significant under- or over-representation was obvious in our patient cohort (p>0.05). For RS351111 we also analyzed the allele frequencies and calculated the expected genotype. However, we could not found significant differences between the control group and the GPA cohort. In addition, we verified that both groups are in Hardy-Weinberg equilibrium (for GPA: p=0.50, for control: p=0.90).

Conclusion: Although PR3 is the main autoantigen in GPA, the contribution of PR3 polymorphisms to GPA has not yet sufficiently characterized. Our study revealed that PR3 protein polymorphisms are not predictive for a GPA diagnosis and can be excluded as (auto-)antigenic stimuli in GPA. Nevertheless, genetic variations in the noncoding area of the PRTN3 gene might have an impact on autoimmune vasculitis and could generate a better understanding of the AAV pathogenesis.