Genetics of Paget's disease of bone
In Chapter 4, I investigated the roles of the RANK signalling partners RANK ligand (RANKL) and osteoprotegerin (OPG) in the pathogenesis of sporadic and familial PDB. One polymorphism in the RANK gene and five polymorphisms in the OPG gene were examined in sporadic PDB cases and in sex- and age-matched controls. No allele-disease or genotype-disease association was observed for the RANKL polymorphism, suggesting RANKL is not directly involved in susceptibility to sporadic PDB. Genotypes at two OPG polymorphisms did significantly predict disease status in individuals affected with sporadic PDB, suggesting a role for OPG in the pathogenesis of sporadic PDB. The five OPG polymorphisms were also examined in families affected with PDB. No evidence was found to either suggest or exclude the involvement of any of the OPG polymorphisms in familial PDB. In Chapter 5, I performed a genome-wide search for PDB susceptibility loci in families with inherited PDB. Three regions of potential linkage were identified at 2q36, 5q35 and 10p11. Fine mapping was performed for the candidate region on chromosome 5q35, and eight families with a high probability of linkage to 5q35 were identified. In seven of the families, a shared haplotype transmitted only with affected family members was present. The shared haplotype varied between families and no common allele existed in the seven families for any of the nine markers studied. However, one area of shared haplotype occurred in all seven families across three of the markers, supporting evidence for a susceptibility gene for PDB on 5q35 in these families and narrowing the candidate region. In summary, this study has further highlighted the importance of genetic heterogeneity in the pathogenesis of PDB, excluding the previously identified PDB2 susceptibility locus and identifying three novel regions potentially harbouring susceptibility loci in the families studied. This study has also further defined the role of members of the RANK signalling pathway in the pathogenesis of familial and sporadic PDB.