Functional variants within the secreted frizzled-related protein 3 gene are associated with hip osteoarthritis in females

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Abstract
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 alpha-induced protein 6 gene in all probands and the integrin alpha 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 alpha-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.