Variants of the interleukin-1 receptor antagonist gene are associated with fat mass in men.

Context:Immune functions seem to have connections to variations in body fat mass. Studies of knockout mice indicate that endogenous interleukin (IL)-1 can suppress mature-onset obesity.Objective:To systematically investigate our hypotheses that single-nucleotide polymorphisms (SNPs) and/or haplotypes variants in the IL-1 gene system are associated with fat mass.Subjects:The Gothenburg osteoporosis and obesity determinants (GOOD) study is a population-based cross-sectional study of 18-20 year-old men (n=1068), from Gothenburg, Sweden. Major findings were confirmed in elderly men (n=3014) from the Swedish part of the osteoporotic fractures in men (MrOS) multicenter population-based study.Main Outcome Measure:The genotype distributions and their association with body fat mass in different compartments, measured with dual-energy X-ray absorptiometry (DXA).Results:Out of 15 investigated SNPs in the IL-1 receptor antagonist (IL1RN) gene, a recently identified 3\u27 untranslated region C>T (rs4252041, minor allele frequency=4%) SNP was associated with the primary outcome total fat mass (P=0.003) and regional fat masses, but not with lean body mass or serum IL-1 receptor 1 (IL1RN) levels. This SNP was also associated with body fat when correcting the earlier reported IL1RN+2018 T>C (rs419598) SNP (in linkage disequilibrium with a well-studied variable number tandem repeat of 86 bp). The association between rs4252041 SNP and body fat was confirmed in the older MrOS population (P=0.03). The rs4252041 SNP was part of three haplotypes consisting of five adjacent SNPs that were identified by a sliding window approach. These haplotypes had a highly significant global association with total body fat (