A nucleotide variant in the promoter region of the interleukin-6 gene associated with decreased bone mineral density

Interleukin-6 (IL6) has come to be regarded as a potential osteoporotic fac tor because it has stimulatory effects on cells of the osteoclast lineage, and, thus. may play a role in the pathogenesis of bone loss associated with estrogen deficiency. We previously described association of the IL6 micros atellite with bone mineral density (BMD), as well as genetic linkage of the IL6 locus to human osteoporosis, by means of sib-pair analysis. However, t he molecular mechanism by which this locus regulates BMD remains unknown. A ccordingly, we searched for polymorphisms in the 5' and 3' flanking regions and in all five exons of the IL6 gene in a Japanese population sample. We identified three single-nucleotide sequence variations: a C/G substitution at nucleotide (nt) --634 in the promoter region, a G/A substitution at nt 4 391 in the 3' noncoding region, and a variation in the AnTn tract around nt -447. The last of these had already been observed in Caucasians, as well a s in Japanese. The single-nucleotide polymorphism at --634 created a restri ction site for the BsrBI endonuclease, and the frequency of the minor (G) a llele was 0.184. Five haplotypes were constructed among three variations ex amined in the population. Linkage disequilibrium was observed between the v ariation at --634 and the variation at 4391, as well as between the variati on at -634 and the AnTn tract variation. We found a significant correlation , in 470 subjects, between the presence of the G allele and decreased BMD. by analysis of variance. When BMD values were compared among the three geno typic groups (GIG, GIC, CIC) at nt -634, BMD was lowest among the GIG homoz ygotes (mean +/- SD: 0.284 +/- 0.062g/cm(2)), highest among the C/C homozy gotes (0.314 +/- 0.059g/cm(2)), and intermediate among the heterozygotes (0 .303 +/- 0.066g/cm(2); P < 0.05). Given the several lines of evidence from different genetic studies, we suggest that IL6 is, indeed, one of the genes affecting bone metabolism, in which variations can lead to osteoporosis.