Osteocytes are the most abundant cells in bone and are ideally located to influence bone turnover through their syncytial relationship with surface bone cells. Osteocyte-derived signals have remained largely enigmatic, but it was recently reported that human osteocytes secrete sclerostin, an inhibitor of bone formation. Absent sclerostin protein results in the high bone mass clinical disorder sclerosteosis. Here we report that within adult iliac bone, newly embedded osteocytes were negative for sclerostin staining but became positive at or after primary mineralization. The majority of mature osteocytes in mineralized cortical and cancellous bone was positive for sclerostin with diffuse staining along dendrites in the osteocyte canaliculi. These findings provide for the first time in vivo evidence to support the concept that osteocytes secrete sclerostin after they become embedded in a mineralized matrix to limit further bone formation by osteoblasts. Sclerostin did not appear to influence the formation of osteocytes. We propose that sclerostin production by osteocytes may regulate the linear extent of formation and the induction or maintenance of a lining cell phenotype on bone surfaces. In doing so, sclerostin may act as a key inhibitory signal governing skeletal microarchitecture.

The distribution of cortical bone in the proximal femur is believed to be a critical component in determining fracture resistance. Current CT technology is limited in its ability to measure cortical thickness, especially in the sub-millimetre range which lies within the point spread function of today’s clinical scanners. In this paper, we present a novel technique that is capable of producing unbiased thickness estimates down to 0.3 mm. The technique relies on a mathematical model of the anatomy and the imaging system, which is fitted to the data at a large number of sites around the proximal femur, producing around 17,000 independent thickness estimates per specimen. In a series of experiments on 16 cadaveric femurs, estimation errors were measured as −0.01 ± 0.58 mm (mean ± 1 std.dev.) for cortical thicknesses in the range 0.3–4 mm. This compares with 0.25 ± 0.69 mm for simple thresholding and 0.90 ± 0.92 mm for a variant of the 50% relative threshold method. In the clinically relevant sub-millimetre range, thresholding increasingly fails to detect the cortex at all, whereas the new technique continues to perform well. The many cortical thickness estimates can be displayed as a colour map painted onto the femoral surface. Computation of the surfaces and colour maps is largely automatic, requiring around 15 min on a modest laptop computer.

Background The UK 100,000 Genomes Project is in the process of investigating the role of genome sequencing of patients with undiagnosed rare disease following usual care, and the alignment of research with healthcare implementation in the UK’s national health service. (Other parts of this Project focus on patients with cancer and infection.) Methods We enrolled participants, collected clinical features with human phenotype ontology terms, undertook genome sequencing and applied automated variant prioritization based on virtual gene panels (PanelApp) and phenotypes (Exomiser), alongside identification of novel pathogenic variants through research analysis. We report results on a pilot study of 4660 participants from 2183 families with 161 disorders covering a broad spectrum of rare disease. Results Diagnostic yields varied by family structure and were highest in trios and larger pedigrees. Likely monogenic disorders had much higher diagnostic yields (35%) with intellectual disability, hearing and vision disorders, achieving yields between 40 and 55%. Those with more complex etiologies had an overall 25% yield. Combining research and automated approaches was critical to 14% of diagnoses in which we found etiologic non-coding, structural and mitochondrial genome variants and coding variants poorly covered by exome sequencing. Cohort-wide burden testing across 57,000 genomes enabled discovery of 3 new disease genes and 19 novel associations. Of the genetic diagnoses that we made, 24% had immediate ramifications for the clinical decision-making for the patient or their relatives. Conclusion Our pilot study of genome sequencing in a national health care system demonstrates diagnostic uplift across a range of rare diseases. (Funded by National Institute for Health Research and others)

Highlights► Focal thinning of cortical bone in the proximal femur predisposes a hip to fracture. ► Thinning is difficult to detect in CT since the cortex may be narrower than the PSF. ► We present a model-fitting technique to estimate cortical thickness, density and mass. ► Evaluation on cadaveric femurs confirms accurate measurement of mass and peak density. ► Thickness errors do not exceed 20% and are confined to regions of thin cortex.

The anatomic distribution of cortical and cancellous bone in the femoral neck may be critical in determining resistance to fracture. We investigated the effects of aging on femoral neck bone in women. In this cross-sectional study, we used clinical multidetector computed tomography (MDCT) of the hips to investigate aging effects in 100 female volunteers aged 20 to 90 years. We developed a clinically efficient protocol to measure cortical thickness (C.Th) and cortical, trabecular, and integral bone mineral density (CtBMD, TrBMD, and iBMD in mg/cm 3 ) in anatomic quadrants of the femoral neck. We used a nested ANOVA to evaluate their associations with height, weight, location in the femoral neck, and age of the subject. Age was the principal determinant of both cortical thickness and BMD. Age had significantly different effects within the anatomic quadrants; compared with young women, elderly subjects had relative preservation of the inferoanterior (IA) quadrant but strikingly reduced C.Th and BMD superiorly. A model including height, weight, and region of interest (and their interactions) explained 83% of the measurement variance ( p < .0001). There were marked C.Th and BMD differences between age 25 and age 85 in the already thin superior quadrants. At 25 years the predicted C.Th of the superoposterior quadrant was 1.63 mm, whereas at 85 years it was 0.33 mm [À1.33 mm, 95% confidence interval (CI) of difference over 60 years À1.69 to À0.95]. By contrast, at 25 years mean C.Th of the IA quadrant was 3.9 mm, whereas at 85 years it was 3.3 mm (À0.6 mm, 95% CI À0.83 to À0.10). CtBMD of the IA region was equivalent at 25 and 85 years. In conclusion, elderly women had relative preservation of IA femoral neck bone over seven decades compared with young women but markedly lower C.Th and BMD in the other three quadrants. The IA quadrant transmits mechanical load from walking. Mechanical theory and laboratory tests on cadaveric femurs suggest that localized bone loss may increase the risk of fracture in elderly fallers. It remains to be determined whether this MDCT technique can provide better prediction of hip fracture than conventional clinical dual X-ray absorptiometry (DXA). ß

SummaryHigh bone mineral density on routine dual energy X-ray absorptiometry (DXA) may indicate an underlying skeletal dysplasia. Two hundred fifty-eight individuals with unexplained high bone mass (HBM), 236 relatives (41% with HBM) and 58 spouses were studied. Cases could not float, had mandible enlargement, extra bone, broad frames, larger shoe sizes and increased body mass index (BMI). HBM cases may harbour an underlying genetic disorder.IntroductionHigh bone mineral density is a sporadic incidental finding on routine DXA scanning of apparently asymptomatic individuals. Such individuals may have an underlying skeletal dysplasia, as seen in LRP5 mutations. We aimed to characterize unexplained HBM and determine the potential for an underlying skeletal dysplasia.MethodsTwo hundred fifty-eight individuals with unexplained HBM (defined as L1 Z-score ≥ +3.2 plus total hip Z-score ≥ +1.2, or total hip Z-score ≥ +3.2) were recruited from 15 UK centres, by screening 335,115 DXA scans. Unexplained HBM affected 0.181% of DXA scans. Next 236 relatives were recruited of whom 94 (41%) had HBM (defined as L1 Z-score + total hip Z-score ≥ +3.2). Fifty-eight spouses were also recruited together with the unaffected relatives as controls. Phenotypes of cases and controls, obtained from clinical assessment, were compared using random-effects linear and logistic regression models, clustered by family, adjusted for confounders, including age and sex.ResultsIndividuals with unexplained HBM had an excess of sinking when swimming (7.11 [3.65, 13.84], p < 0.001; adjusted odds ratio with 95% confidence interval shown), mandible enlargement (4.16 [2.34, 7.39], p < 0.001), extra bone at tendon/ligament insertions (2.07 [1.13, 3.78], p = 0.018) and broad frame (3.55 [2.12, 5.95], p < 0.001). HBM cases also had a larger shoe size (mean difference 0.4 [0.1, 0.7] UK sizes, p = 0.009) and increased BMI (mean difference 2.2 [1.3, 3.1] kg/m2, p < 0.001).ConclusionIndividuals with unexplained HBM have an excess of clinical characteristics associated with skeletal dysplasia and their relatives are commonly affected, suggesting many may harbour an underlying genetic disorder affecting bone mass.Electronic supplementary materialThe online version of this article (doi:10.1007/s00198-011-1603-4) contains supplementary material, which is available to authorized users.

In this prospective nested case-control study we analyzed the circumferential differences in estimated cortical thickness (Est CTh) of the mid femoral neck as a risk factor for osteoporotic hip fractures in elderly women and men. Segmental QCT analysis of the mid femoral neck was applied to assess cortical thickness in anatomical quadrants. The superior region of the femoral neck was a stronger predictor for hip fracture than the inferior region, particularly in men. There were significant gender differences in Est CTh measurements in the control group but not in the case group. In multivariable analysis for risk of femoral neck (FN) fracture, Est CTh in the supero-anterior (SA) quadrant was significant in both women and men, and remained a significant predictor after adjustment for FN areal BMD (aBMD, dimensions g/cm2, DXA-like), (p=0.05 and p<0.0001, respectively). In conclusion, Est CTh in the SA quadrant best discriminated cases (n=143) from controls (n=298), especially in men. Cortical thinning superiorly in the hip might be of importance in determining resistance to fracture.

Regular exercisers have lower fracture risk, despite modest effects of exercise on bone mineral content (BMC). Exercise may produce localized cortical and trabecular bone changes that affect bone strength independently of BMC. We previously demonstrated that brief, daily unilateral hopping exercises increased femoral neck BMC in the exercise leg versus the control leg of older men. This study evaluated the effects of these exercises on cortical and trabecular bone and its 3D distribution across the proximal femur, using clinical CT. Fifty healthy men had pelvic CT scans before and after the exercise intervention. We used hip QCT analysis to quantify BMC in traditional regions of interest and estimate biomechanical variables. Cortical bone mapping localized cortical mass surface density and endocortical trabecular density changes across each proximal femur, which involved registration to a canonical proximal femur model. Following statistical parametric mapping, we visualized and quantified statistically significant changes of variables over time in both legs, and significant differences between legs. Thirty-four men aged mean (SD) 70 (4) years exercised for 12-months, attending 92% of prescribed sessions. In traditional regions of interest, cortical and trabecular BMC increased over time in both legs. Cortical BMC at the trochanter increased more in the exercise than control leg, whereas femoral neck buckling ratio declined more in the exercise than control leg. Across the entire proximal femur, cortical mass surface density increased significantly with exercise (2.7%; p < 0.001), with larger changes (> 6%) at anterior and posterior aspects of the femoral neck and anterior shaft. Endocortical trabecular density also increased (6.4%; p < 0.001), with localized changes of > 12% at the anterior femoral neck, trochanter, and inferior femoral head. Odd impact exercise increased cortical mass surface density and endocortical trabecular density, at regions that may be important to structural integrity. These exercise-induced changes were localized rather than being evenly distributed across the proximal femur.