RESEARCH ARTICLE Conditional testing of mu y

Full list of author information is available at the end of the articleBackground Postmenopausal osteoporosis is a systemic bone disease that is characterised by low bone mass and disturbed micro architecture of bone tissue, resulting in decreased bone strength and a corresponding increase in the risk of fracture [1]. Bone mass peaks in early adult life, but declines in postmenopausal women due to a reduction in oestrogen production which has direct effects on bone as well as calcium handling by the intestine and renal system [2]. In addition to these effects and environmental factors, there is a strong genetic effect on peak bone mass, bone loss and fracture rates in postmenopausal women [3]. Twin and family studies suggest that 50-85 % of the variance in peak bone mass [4-7] and 25-68 % of the variance in osteoporotic fracture is heritable [8-10]. The whole genome linkage scanning approach has identified multiple quantitative trait loci (QTL) fo