Osteoarthritis (OA) is a leading cause of disability in Western society with multiple risk factors, including a complex genetic pattern. Identifying loci involved in the heredity of OA might lead to insights into the molecular pathogenesis of this common disorder. A previous genome scan mapped a primary hip OA susceptibility locus to chromosome 2q with a maximum multipoint logarithm of odds score of 1.6 in 378 affected sibling pair families. Here, microsatellite targeting of eight candidate genes in this region from 2q23-2q32 demonstrated significant associations with the tumor necrosis factor ␣-induced protein 6 gene in all probands and the integrin ␣6 and frizzled motif associated with bone development (FRZB) genes in female probands. However, genotyping showed lack of association for a nonsynonymous single-nucleotide polymorphism in tumor necrosis factor ␣-induced protein 6, whereas a single-nucleotide polymorphism in FRZB resulting in an Arg324Gly substitution at the carboxyl terminus was associated with hip OA in the female probands (P ‫؍‬ 0.04). This association was confirmed in an independent cohort of female hip cases (n ‫؍‬ 338; P ‫؍‬ 0.04). In addition, a haplotype coding for substitutions of two highly conserved arginine residues (Arg200Trp and Arg324Gly) in FRZB was a strong risk factor for primary hip OA, with an odds ratio of 4.1 (P ‫؍‬ 0.004). FRZB encodes secreted frizzled-related protein 3, which is a soluble antagonist of wingless (wnt) signaling. Variant secreted frizzled-related protein 3 with the Arg324Gly substitution had diminished ability to antagonize wnt signaling in vitro. Hence, functional polymorphisms within FRZB confer susceptibility for hip OA in females and implicate the wnt signaling pathway in the pathogenesis of this disease.

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Objective. To test a high density of microsatellite markers from within a primary osteoarthritis (OA) locus on chromosome 6 for association with OA as a means of narrowing and focusing our search for the susceptibility gene.Methods. One hundred forty-six families, each with 2 or more women concordant for primary OA (ascertained by total hip replacement), were genotyped for 36 microsatellite markers from within a narrow interval at 6p12.3-q13 which we had previously shown to be linked to OA. Each marker was tested for linkage and for association, the latter by means of the transmission disequilibrium test and by a case-control analysis.Results. The highest 2-point logarithm of odds (LOD) score was 4.8, with 11 markers having LOD scores >2.0. Several markers demonstrated evidence of association, in particular, a cluster of markers positioned within or near the functional candidate gene BMP5.Conclusion. Our linkage data reinforce the evidence of a major susceptibility locus on chromosome 6. We had previously failed to detect an association with BMP5 using gene-based single-nucleotide polymorphisms. The association data reported here prompt us to speculate that the chromosome 6 susceptibility may be coded for by cis-acting polymorphism in the regulatory elements of this gene, rather than by variation in its protein coding sequence.

Objective. To more finely linkage-map primary osteoarthritis (OA) susceptibility loci on chromosomes 4 and 16.Methods. Two hundred eighteen families, each with 2 or more women concordant for primary OA (ascertained by total hip replacement [THR] or total knee replacement), were genotyped using highly polymorphic microsatellite markers from chromosomes 4 and 16, at an average density of 1 marker every 4 cM. Two-point and multipoint linkage analyses were performed for all 218 families and for the 146 families from the 218 that included women concordant for THR (female-THR families).Results. A single region of linkage was identified on chromosome 4q, with a maximum multipoint logarithm of odds (LOD) score (MLS) of 3.1 in the 146 female-THR families. This locus was centered 79 cM from the 4p telomere and had a 1-LOD support interval of 4 cM. Two regions of linkage were identified on chromosome 16, the first on 16p with an MLS of 1.7 in the female-THR families and the second on 16q with an MLS of 1.9 in all 218 families. The first locus was centered 46 cM and the second 89 cM from the p-telomere. The 1-LOD support intervals were 12 cM and 10 cM, respectively. Conclusion.Finer linkage mapping using a high density of microsatellite markers has narrowed female OA susceptibility loci on chromosomes 4 and 16. The regions have been narrowed sufficiently for association analysis.