Association analysis of polymorphisms at the interleukin-1 locus in essential hypertension.

Abstract

Infection with microorganisms such as Helicobacter pylori and Chlamydia pneumoniae has been associated with coronary heart disease (CAD) and hypertension (HT). Infection increases the release of pro-inflammatory cytokines, thus facilitating interactions that lead to vascular damage and other effects. We hypothesized that genetically determined differences in activity or responsiveness of cytokine(s) might contribute to HT. The interleukin-1 gene (IL1) cluster on chromosome 2q14 contains three related genes (IL1A, IL1B, and IL1RN) located within a 430-kb region. These encode IL-1alpha and IL-1beta, as well as their endogenous receptor antagonist, IL-1ra. The IL1RN gene has a penta-allelic 86-bp tandem repeat in intron 2. Allele IL1RN* 2 is associated with a wide range of chronic inflammatory and autoimmune conditions, and its combination with the -31T variant of an IL1B C(-31)T polymorphism constitutes a pro-inflammatory haplotype that leads to vigorous IL-1beta production. We therefore tested each of these polymorphisms for association with HT. Subjects were white Anglo-Celtic residents of Sydney, Australia. Frequencies of IL1B C(-31)T genotypes CC, CT, and TT were 0.50, 0.40, and 0.10 in normotensive (NT) and 0.46, 0.46, and 0.08 in HT, respectively (chi(2) = 1.2, P = 0.55). T allele frequency in NT (0.30) was similar to that in HT (0.31). For the IL1RN variant, frequencies of alleles IL1RN* 1 and * 2 and combined minor alleles * 3, * 4, and * 5 were 0.61, 0.36, and 0.03 in NT and 0.54, 0.36, and 0.10 in HT, respectively (chi(2) = 11, P = 0.004). In conclusion, no association of the IL1B C(- 31)T with HT was found, whereas combined frequency of the minor alleles of the IL1RN polymorphism was increased in the HT cohort studied.