Linkage disequilibrium mapping and positional cloning for gene identification in osteoporotic families

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Osteoporosis is a common chronic disease with associated pain, loss of function and death. Patients with the disease commonly experience spine, hip or wrist fracture. Fracture of vertebrae may result in chronic back pain and deformity. Respiratory and digestive health are then also compromised. In comparison, hip fracture may lead to a need for surgery, reduced mobility and institutionalization. In view of improved general community health and increased longevity, the incidence of this disease and the drain on public health funding will continue to increase substantially in coming years. Presently the cost in Australia is $7.5 billion per annum. Instituting effective prevention strategies is essential. This project aims to contribute to this goal by identifying a major gene(s) involved in disease susceptibility. The term osteoporosis covers a number of heterogeneous syndromes including juvenile osteoporosis, secondary osteoporosis (e.g. corticosteroid induced) and postmenopausal osteoporosis. In this later broad grouping there is evidence of a strong familial association. Previous work has shown that a family history of fracture increases your risk of fracture more than four fold. Furthermore, studies in twins have persistently shown that bone mineral density, the largest risk factor for osteoporotic fracture, is strongly inherited. This data confirms a genetic basis for the disease in some individuals. We have completed two whole genome screen projects and genetic linkage analysis in the families studied has highlighted four regions of the genome, which may harbour genes involved in the disease process. In this project we will fine map these regions and identify the genes that are responsible for the observed linkage. We will use a technique called positional cloning to discover the identity of the gene(s) and will characterise how genetic variation (polymorphism) in the gene leads to reduced bone mass and osteoporotic fracture.