Objectives. To ascertain whether a relationship exists between the PiZ alpha₁‐antitrypsin (α₁AT) variant and antineutrophil cytoplasm antibodies (ANCA)‐positive vasculitis in a large group of Swedish patients, and whether analysis for the presence of the PiZ variant might be useful for diagnostic or prognostic purposes.

Design. Retrospective cross‐sectional study.

Setting. The Department of Internal Medicine, Malmö General Hospital, and the Department of Nephrology, University of Lund, Sweden.

Subjects and main outcome measures. Serum samples from 105 proteinase 3‐ANCA‐positive patients were analysed using an elisa with a monoclonal antibody specific for the PiZ‐gene product. Complete clinical data were retrieved for 84% (88/105) of the patients, for diagnosis and survival analysis.

Results. We identified 17 heterozygotes and one homozygote (P < 0.0001). All 88 patients with available clinical data were considered to have some form of microscopic vasculitis including 66 (75%) diagnosed as having Wegener's granulomatosis (WG), of whom 15 (23%) were PiZ heterozygotes (odds ratio 6.0, 95% confidence interval 3–10). There were no significant differences between PiZ carriers and noncarriers in sex distribution, mean age at onset of disease, interval between onset and inclusion in the study, or in median duration of follow‐up (P > 0.2 for all comparisons). During follow‐up, 38% (6/16) of the PiZ heterozygotes died, compared with 17% (11/66) of noncarriers of the variant (P = 0.02), which suggests that PiZ heterozygosity may be a marker of poor prognosis. PiZ heterozygotes with systemic vasculitis would not appear to be identifiable by their pretreatment plasma α₁AT concentrations, as all such patients in the present study had concentrations within or above the normal range.

Conclusion. We conclude that heterozygotes for the PiZ variant of the α₁AT gene are at greater risk of than the general population of developing WG. Knowledge of such a genetic factor may not only aid our understanding of the mechanism involved in this illness but may also serve as significant prognostic factor in following the course of the disease.