Interleukin-6 (IL6) has come to be regarded as a potential osteoporotic factor 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 microsatellite with bone mineral density (BMD), as well as genetic linkage of the IL6 locus to human osteoporosis, by means of sib-pair analysis. However, the molecular mechanism by which this locus regulates BMD remains unknown. Accordingly, we searched for polymorphisms in the 5Ј and 3Ј 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) Ϫ634 in the promoter region, a G/A substitution at nt 4391 in the 3Ј noncoding region, and a variation in the AnTn tract around nt Ϫ447. The last of these had already been observed in Caucasians, as well as in Japanese. The single-nucleotide polymorphism at Ϫ634 created a restriction site for the BsrBI endonuclease, and the frequency of the minor (G) allele was 0.184. Five haplotypes were constructed among three variations examined in the population. Linkage disequilibrium was observed between the variation at Ϫ634 and the variation at 4391, as well as between the variation at Ϫ634 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 genotypic groups (G/G, G/C, C/C) at nt Ϫ634, BMD was lowest among the G/G homozygotes (mean Ϯ SD; 0.284 Ϯ 0.062 g/cm 2 ), highest among the C/C homozygotes (0.314 Ϯ 0.059 g/cm 2 ), and intermediate among the heterozygotes (0.303 Ϯ 0.066 g/cm 2 ; P Ͻ 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.

Interleukin 11 (IL11) is a member of the interleukin 6 (IL6)-related cytokine subfamily, which stimulates T cell-dependent development of immunoglobulinproducing B cells. IL11 is also an important paracrine regulator of bone metabolism that induces formation of osteoclasts. In the work reported here, we sequenced the entire IL11 structural gene of 48 alleles in a Japanese test population. These experiments identified ten singlenucleotide polymorphisms (SNPs) and determined their allelic frequencies. One polymorphism was identified upstream of exon 1, one in exon 3, four in intron 4 and four in the 3Ј untranslated region (3ЈUTR) of exon 5. Based on the genotype data, we constructed six haplotypes in the tested population. Two-way comparisons of SNPs revealed two combinations in complete linkage disequilibrium, one with SNPs at nucleotide positions 2753, 3644, 5154, and 5568, and another with SNPs at positions 3686, 5141, and 5734. These results will be useful in disease-association studies where a contribution of the human IL11 gene has been suspected, especially in disorders affecting immune response and bone metabolism.

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The polymorphisms and allele frequencies obtained in this study will be useful for genetic studies of common diseases such as osteoporosis and rheumatoid arthritis in the Japanese population.

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