Interleukin 6 and the prognosis of abdominal aortic aneurysms

Background: Abdominal aortic aneurysm (AAA) is a familial disorder, inflammation being an important pathophysiological feature. Increased plasma concentrations of the inflammatory cytokine interleukin (IL) 6 have been associated with AAA and early aortic dilatation. This study was designed to test the hypothesis that high concentrations of plasma IL‐6 and/or IL‐6 genotype predict rapid AAA growth. Methods: Genomic DNA from 466 patients, kept under ultrasonographic surveillance for small AAAs, was analysed for a G to C polymorphism at position −174 of the IL‐6 promoter. Baseline plasma IL‐6 concentration was measured by enzyme‐linked immunosorbent assay and AAA growth rates were calculated by linear regression. Results: The median concentration of plasma IL‐6 was 4·9 (range 0–604) pg ml −1 . IL‐6 concentration was not associated with aneurysm growth rate. The frequency of the C allele was 0·40, similar to that in the healthy population. Patients of GG genotype had a lower plasma concentration of IL‐6 than patients of either GC or CC genotype (median 1·9, 4·8 and 15·6 pg ml −1 respectively; P = 0·047, Kruskal–Wallis test). The AAA growth rate for patients of GG, GC and CC genotypes was 0·38, 0·36 and 0·36 cm per year respectively ( P = 0·37). Mortality was lower for patients of GG genotype than for those with GC or CC genotype: hazard ratio 0·51 (95 per cent confidence interval (c.i.) 0·25–1·00), P = 0·05; and 0·32 (95 per cent c.i. 0·12–0·93), P = 0·036, for all‐cause and cardiovascular mortality respectively. Conclusion: Genetic polymorphism is associated with clinical events in patients with an AAA. The G to C IL‐6 polymorphism at position −174 predicts future cardiovascular mortality. Neither plasma IL‐6 concentration nor IL‐6 genotype predicts AAA growth. © 2001 British Journal of Surgery Society Ltd