Approaching virtual osteoid volume estimation and in-depth tissue characterization in patients with tumor-induced osteomalacia.

Tumor-induced osteomalacia (TIO) poses a significant diagnostic challenge, leading to increased disease duration and patient burden also by missing clinical suspicion. Today, diagnosis of osteomalacia relies on invasive iliac crest biopsy, if needed. Therefore, a noninvasive method would be beneficial for patients with severe osteomalacia, such as TIO, to inform their clinical management and address specific needs, like estimating the regeneration capacity at high osteoid volumes (OVs) or the potential of a hungry bone syndrome after tumor removal. Furthermore, given the lack of comprehensive histological characterization of TIO, there is a need for additional tissue characterization. Therefore, our assessment encompassed iliac crest biopsies that were examined using quantitative electron backscattered microscopy, Raman spectroscopy, micro-computed tomography, and histology to analyze the biopsy tissue. Our clinical assessment encompassed DXA and high-resolution peripheral quantitative computed tomography (HR-pQCT) alongside with biochemical analyses and clinical evaluations. Combining imaging and clinical data, we established a model to predict the OV. We compared 9 TIO patients with 10 osteoporosis (OPO) patients and 10 healthy controls. Histological analyses confirmed a pronounced OV in TIO patients (OPO: 1.20% ± 1.23% vs TIO: 23.55% ± 12.23%, P < .0005), and spectroscopy revealed lower phosphate levels in TIO biopsies. By combining HR-pQCT and laboratory diagnostics, we developed a linear regression model to noninvasively predict the OV revealing significantly higher modeled OV/BVmodel values of 24.46% ± 14.22% for TIO compared to the control group (5.952% ± 3.44%, P ≤ .001). By combining laboratory diagnostics, namely, ALP and Tt.BMDRadius measured by HR-pQCT, we achieved the calculation of the virtual osteoid volume to bone volume ratio (OV/BVmodel) with a significant correlation to histology as well as reliable identification of TIO patients compared to OPO and control. This novel approach is potentially helpful for predicting OV by noninvasive techniques in diagnostic procedures and improving the clinical management of TIO.

Osteomalacia, a bone mineralization disease, results in soft bones due to a lack of calcium or phosphate. Tumor-induced osteomalacia (TIO) is an acquired and challenging form of osteomalacia due to low serum phosphate levels that often lead to prolonged patient suffering. Current diagnosis of osteomalacia involves surgical bone biopsies, but a noninvasive approach would be beneficial, improving clinical management and addressing specific needs like estimating the bone's quality and ability to recover. We used advanced techniques like electron microscopy, spectroscopy, and high-resolution CT to study bone samples from 9 TIO patients. Additionally, we assessed their bone health through sophisticated imaging and blood analyses. Microscopy confirmed huge amounts of soft bone tissue due to a severe mineralization defect. By combining imaging and blood analysis, we developed a noninvasive method to predict the amount of soft tissue (osteoid) to understand soft bones without the need for surgical interventions. In conclusion, our innovative approach, combining blood diagnostics (alkaline phosphatase) with total BMD from high-resolution 3D clinical imaging of the lower arm, allows us to predict the osteoid amount virtually. This method can also compare TIO patients with controls or those with osteoporosis and might be helpful in the future.

Epidemiology of Tumor-Induced Osteomalacia in Germany Based on Real World Data.

Tumor-induced osteomalacia (TIO) is an ultra-rare disease caused mostly by benign tumors that secrete fibroblast growth factor-23. Because of nonspecific symptoms, the diagnostic delay is long, and therapy can be challenging. Moreover, epidemiological data on TIO are scarce owing to its rarity. Therefore, this study aimed to quantify TIO's incidence rates and prevalence in Germany. Retrospective longitudinal and cross-sectional analyses were conducted using anonymized German claims data from the statutory health insurance (SHI) database. This database, which comprises the data of approximately 5 million insurants, is a representative sample of the German population and supports national projections. As there is no unique International Statistical Classification of Diseases and Related Health Problems (ICD) code for TIO, operational categories based on different surrogates were defined to determine the prevalence and incidence rates of TIO among probable patients. This study showed that TIO has a prevalence of (documented code, advanced imaging, medication, or tumor removal) 0.187 per 100,000 persons and an incidence rate of ≤ 0.094 per 100,000 person years. This analysis provides the first epidemiological insight into German patients with TIO. Despite the general limitations associated with the analysis of SHI claims data of ultra-rare diseases, we believe that this analysis provides a sound basis for further analysis, particularly with regard to the care situation of patients with TIO.

AXIN1 bi-allelic variants disrupting the C-terminal DIX domain cause craniometadiaphyseal osteosclerosis with hip dysplasia.

Sclerosing skeletal dysplasias result from an imbalance between bone formation and resorption. We identified three homozygous, C-terminally truncating AXIN1 variants in seven individuals from four families affected by macrocephaly, cranial hyperostosis, and vertebral endplate sclerosis. Other frequent findings included hip dysplasia, heart malformations, variable developmental delay, and hematological anomalies. In line with AXIN1 being a central component of the ß-catenin destruction complex, analyses of primary and genome-edited cells harboring the truncating variants revealed enhanced basal canonical Wnt pathway activity. All three AXIN1-truncating variants resulted in reduced protein levels and impaired AXIN1 polymerization mediated by its C-terminal DIX domain but partially retained Wnt-inhibitory function upon overexpression. Addition of a tankyrase inhibitor attenuated Wnt overactivity in the AXIN1-mutant model systems. Our data suggest that AXIN1 coordinates the action of osteoblasts and osteoclasts and that tankyrase inhibitors can attenuate the effects of AXIN1 hypomorphic variants.

Catalysis-Independent ENPP1 Protein Signaling Regulates Mammalian Bone Mass.

Biallelic ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) deficiency induces vascular/soft tissue calcifications in generalized arterial calcification of infancy (GACI), and low bone mass with phosphate-wasting rickets in GACI survivors (autosomal hypophosphatemic rickets type-2). ENPP1 haploinsufficiency induces early-onset osteoporosis and mild phosphate wasting in adults. Both conditions demonstrate the unusual combination of reduced accrual of skeletal mineral, yet excess and progressive heterotopic mineralization. ENPP1 is the only enzyme that generates extracellular pyrophosphate (PPi), a potent inhibitor of both bone and heterotopic mineralization. Life-threatening vascular calcification in ENPP1 deficiency is due to decreased plasma PPi; however, the mechanism by which osteopenia results is not apparent from an understanding of the enzyme's catalytic activity. To probe for catalysis-independent ENPP1 pathways regulating bone, we developed a murine model uncoupling ENPP1 protein signaling from ENPP1 catalysis, Enpp1T238A mice. In contrast to Enpp1asj mice, which lack ENPP1, Enpp1T238A mice have normal trabecular bone microarchitecture and favorable biomechanical properties. However, both models demonstrate low plasma Pi and PPi, increased fibroblast growth factor 23 (FGF23), and by 23 weeks, osteomalacia demonstrating equivalent phosphate wasting in both models. Reflecting findings in whole bone, calvarial cell cultures from Enpp1asj mice demonstrated markedly decreased calcification, elevated transcription of Sfrp1, and decreased nuclear ß-catenin signaling compared to wild-type (WT) and Enpp1T238A cultures. Finally, the decreased calcification and nuclear ß-catenin signaling observed in Enpp1asj cultures was restored to WT levels by knockout of Sfrp1. Collectively, our findings demonstrate that catalysis-independent ENPP1 signaling pathways regulate bone mass via the expression of soluble Wnt inhibitors such as secreted frizzled-related protein 1 (SFRP1), whereas catalysis dependent pathways regulate phosphate homeostasis through the regulation of plasma FGF23. © 2022 American Society for Bone and Mineral Research (ASBMR).

Clinical Spectrum of Hereditary Hypophosphatemic Rickets With Hypercalciuria (HHRH).

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) represents an FGF23-independent disease caused by biallelic variants in the solute carrier family 34-member 3 (SLC34A3) gene. HHRH is characterized by chronic hypophosphatemia and an increased risk for nephrocalcinosis and rickets/osteomalacia, muscular weakness, and secondary limb deformity. Biochemical changes, but no relevant skeletal changes, have been reported for heterozygous SLC34A3 carriers. Therefore, we assessed the characteristics of individuals with biallelic and monoallelic SLC34A3 variants. In 8 index patients and 5 family members, genetic analysis was performed using a custom gene panel. The skeletal assessment comprised biochemical parameters, areal bone mineral density (aBMD), and bone microarchitecture. Pathogenic SLC34A3 variants were revealed in 7 of 13 individuals (2 homozygous, 5 heterozygous), whereas 3 of 13 carried monoallelic variants of unknown significance. Whereas both homozygous individuals had nephrocalcinosis, only one displayed a skeletal phenotype consistent with HHRH. Reduced to low-normal phosphate levels, decreased tubular reabsorption of phosphate (TRP), and high-normal to elevated values of 1,25-OH2 -D3 accompanied by normal cFGF23 levels were revealed independently of mutational status. Interestingly, individuals with nephrocalcinosis showed significantly increased calcium excretion and 1,25-OH2 -D3 levels but normal phosphate reabsorption. Furthermore, aBMD Z-score <-2.0 was revealed in 4 of 8 heterozygous carriers, and HR-pQCT analysis showed a moderate decrease in structural parameters. Our findings highlight the clinical relevance also of monoallelic SLC34A3 variants, including their potential skeletal impairment. Calcium excretion and 1,25-OH2 -D3 levels, but not TRP, were associated with nephrocalcinosis. Future studies should investigate the effects of distinct SLC34A3 variants and optimize treatment and monitoring regimens to prevent nephrocalcinosis and skeletal deterioration. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

[Tumor localization and treatment of tumor-induced osteomalacia]. / Tumorlokalisation und Therapie der onkogenen Osteomalazie.

Tumor-induced osteomalacia (TIO) or oncogenic osteomalacia (OOM) is a rare paraneoplastic renal phosphate wasting syndrome. The disease is mostly triggered by small, benign mesenchymal tumors that express somatostatin receptors (SSTR) and produce excessive levels of fibroblast growth factor 23 (FGF 23) or other phosphatonins. These reduce the phosphate back resorption in the proximal tubules of the kidneys, thereby causing hypophosphatemia and lead to an absolute or relatively low calcitriol serum concentration. The main symptoms include muscle weakness, bone pain and recurrent insufficiency fractures secondary to sometimes pronounced osteomalacia. The suspected diagnosis can only be confirmed by determination of the phosphate level. It can often take years before the tumor is successfully localized. The necessary tumor localization is often the most difficult step in the treatment before the OOM can be curatively treated by open surgical resection of the tumor. In recent years new approaches for faster tumor localization and treatment of the tumor have been developed. Positron emission tomography (PET) in co-registration with computed tomography (68Ga-DOTA-TATE PET/CT) is currently the most sensitive imaging methodology for tumor detection. The application of the monoclonal FGF 23 antibody burosumab represents a promising new option in the treatment of inoperable adult OOM.

Challenges in the management of tumor-induced osteomalacia (TIO).

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare acquired paraneoplastic disease, which is challenging to diagnose and treat. TIO is characterized by hypophosphatemia resulting from excess levels of tumor-secreted fibroblast growth factor 23 (FGF23), one of the key physiological regulators of phosphate metabolism. Elevated FGF23 results in renal phosphate wasting and compromised vitamin D activation, ultimately resulting in osteomalacia. Patients typically present with progressive and non-specific symptoms, including bone pain, multiple pathological fractures, and progressive muscle weakness. Diagnosis is often delayed or missed due to the non-specific nature of complaints and lack of disease awareness. Additionally, the disease-causing tumour is often difficult to detect and localize because they are often small, lack localizing symptoms and signs, and dwell in widely variable anatomical locations. Measuring serum/urine phosphate should be an inherent diagnostic component when assessing otherwise unexplained osteomalacia, fractures and weakness. In cases of hypophosphatemia with inappropriate (sustained) phosphaturia and inappropriately normal or frankly low 1,25-dihydroxy vitamin D, differentiation of the potential causes of renal phosphate wasting should include measurement of FGF23, and TIO should be considered. While patients experience severe disability without treatment, complete excision of the tumour is typically curative and results in a dramatic reversal of symptoms. Two additional key current unmet needs in optimizing TIO management are: (1 and 2) the considerable delay in diagnosis and consequent delay between the onset of symptoms and surgical resection; and (2) alternative management. These may be addressed by raising awareness of TIO, and taking into consideration the accessibility and variability of different healthcare infrastructures. By recognizing the challenges associated with the diagnosis and treatment of TIO and by applying a stepwise approach with clear clinical practice guidelines, patient care and outcomes will be improved in the future.

Bilateral Looser zones or pseudofractures in the anteromedial tibia as a component of medial tibial stress syndrome in athletes.

PURPOSE: Medial tibial stress syndrome (MTSS) represents a common diagnosis in individuals exposed to repetitive high-stress loads affecting the lower limb, e.g., high-performance athletes. However, the diagnostic approach and therapeutic regimens are not well established. METHODS: Nine patients, diagnosed as MTSS, were analyzed by a comprehensive skeletal analysis including laboratory bone turnover parameters, dual-energy X-Ray absorptiometry (DXA), and high-resolution peripheral quantitative computed tomography (HR-pQCT). RESULTS: In 4/9 patients, bilateral pseudofractures were detected in the mid-shaft tibia. These patients had significantly lower levels of 25-hydroxycholecalciferol compared to patients with MTSS but similar levels of bone turnover parameters. Interestingly, the skeletal assessment revealed significantly higher bone mineral density (BMD) Z-scores at the hip (1.3 ± 0.6 vs. - 0.7 ± 0.5, p = 0.013) in patients with pseudofractures and a trend towards higher bone microarchitecture parameters measured by HR-pQCT at the distal tibia. Vitamin D supplementation restored the calcium-homeostasis in all patients. Combined with weight-bearing as tolerated, pseudofractures healed in all patients and return to competition was achieved. CONCLUSION: In conclusion, deficient vitamin D levels may lead to pseudofractures due to localized deterioration of mineralization, representing a pivotal component of MTSS in athletes with increased repetitive mechanical loading of the lower limbs. Moreover, the manifestation of pseudofractures is not a consequence of an altered BMD nor microarchitecture but appears in patients with exercise-induced BMD increase in combination with reduced 25-OH-D levels. The screening of MTSS patients for pseudofractures is crucial for the initiation of an appropriate treatment such as vitamin D supplementation to prevent a prolonged course of healing or recurrence. LEVEL OF EVIDENCE: III.

Mice Carrying a Ubiquitous R235W Mutation of Wnt1 Display a Bone-Specific Phenotype.

Since a key function of Wnt1 in brain development was established early on through the generation of non-viable Wnt1-deficient mice, it was initially surprising that WNT1 mutations were found to cause either early-onset osteoporosis (EOOP) or osteogenesis imperfecta type XV (OI-XV). The deduced function of Wnt1 as an osteoanabolic factor has been confirmed in various mouse models with bone-specific inactivation or overexpression, but mice carrying disease-causing Wnt1 mutations have not yet been described. Triggered by the clinical analysis of EOOP patients carrying a heterozygous WNT1 mutation (p.R235W), we introduced this mutation into the murine Wnt1 gene to address the question of whether this would cause a skeletal phenotype. We observed that Wnt1+/R235W and Wnt1R235W/R235W mice were born at the expected Mendelian ratio and that they did not display postnatal lethality or obvious nonskeletal phenotypes. At 12 weeks of age, the homozygous presence of the Wnt1 mutation was associated with reduced trabecular and cortical bone mass, explained by a lower bone formation rate compared with wild-type littermates. At 52 weeks of age, we also observed a moderate bone mass reduction in heterozygous Wnt1+/R235W mice, thereby underscoring their value as a model of WNT1-dependent EOOP. Importantly, when we treated wild-type and Wnt1+/R235W mice by daily injection of parathyroid hormone (PTH), we detected the same osteoanabolic influence in both groups, together with an increased cortical thickness in the mutant mice. Our data demonstrate the pathogenicity of the WNT1-R235W mutation, confirm that controlling skeletal integrity is the primary physiological function of Wnt1, and suggest that osteoanabolic treatment with teriparatide should be applicable for individuals with WNT1-dependent EOOP. © 2020 American Society for Bone and Mineral Research.

Gnathodiaphyseal dysplasia is not recapitulated in a respective mouse model carrying a mutation of the Ano5 gene.

Mutations in the gene ANO5, encoding for the transmembrane protein Anoctamin 5 (Ano5), have been identified to cause gnathodiaphyseal dysplasia (GDD) in humans, a skeletal disorder characterized by sclerosis of tubular bones, increased fracture risk and fibro-osseous lesions of the jawbones. To better understand the pathomechanism of GDD we have generated via Crispr/CAS9 gene editing a mouse model harboring the murine equivalent (Ano5 p.T491F) of a GDD-causing ANO5 mutation identified in a previously reported patient. Skeletal phenotyping by contact radiography, µCT and undecalcified histomorphometry was performed in male mice, heterozygous and homozygous for the mutation, at the ages of 12 and 24 weeks. These mice did not display alterations of skeletal microarchitecture or mandible morphology. The results were confirmed in female mice and animals derived from a second, independent clone. Finally, no skeletal phenotype was observed in mice lacking ~40% of their Ano5 gene due to a frameshift mutation. Therefore, our results indicate that Ano5 is dispensable for bone homeostasis in mice, at least under unchallenged conditions, and that these animals may not present the most adequate model to study the physiological role of Anoctamin 5.

Adult Osteosclerotic Metaphyseal Dysplasia With Progressive Osteonecrosis of the Jaws and Abnormal Bone Resorption Pattern Due to a LRRK1 Splice Site Mutation.

Osteosclerotic metaphyseal dysplasia (OSMD) is a rare autosomal recessive sclerosing skeletal dysplasia. We report on a 34-year-old patient with sandwich vertebrae, platyspondyly, osteosclerosis of the tubular bones, pathologic fractures, and anemia. In the third decade, he developed osteonecrosis of the jaws, which was progressive in spite of repeated surgical treatment over a period of 11 years. An iliac crest bone biopsy revealed the presence of hypermineralized cartilage remnants, large multinucleated osteoclasts with abnormal morphology, and inadequate bone resorption typical for osteoclast-rich osteopetrosis. After exclusion of mutations in TCIRG1 and CLCN7 we performed trio-based exome sequencing. The novel homozygous splice-site mutation c.261G>A in the gene LRRK1 was found and co-segregated with the phenotype in the family. cDNA sequencing showed nearly complete skipping of exon 3 leading to a frameshift (p.Ala34Profs*33). Osteoclasts differentiated from the patient's peripheral blood monocytes were extremely large. Instead of resorption pits these cells were only capable of superficial erosion. Phosphorylation of L-plastin at position Ser5 was strongly reduced in patient-derived osteoclasts showing a loss of function of the mutated LRRK1 kinase protein. Our analysis indicates a strong overlap of LRRK1-related OSMD with other forms of intermediate osteopetrosis, but an exceptional abnormality of osteoclast resorption. Like in other osteoclast pathologies an increased risk for progressive osteonecrosis of the jaws should be considered in OSMD, an intermediate form of osteopetrosis. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Human Heterozygous ENPP1 Deficiency Is Associated With Early Onset Osteoporosis, a Phenotype Recapitulated in a Mouse Model of Enpp1 Deficiency.

Biallelic ENPP1 deficiency in humans induces generalized arterial calcification of infancy (GACI) and/or autosomal recessive hypophosphatemic rickets type 2 (ARHR2). The latter is characterized by markedly increased circulating FGF23 levels and renal phosphate wasting, but aberrant skeletal manifestations associated with heterozygous ENPP1 deficiency are unknown. Here, we report three adult men with early onset osteoporosis who presented with fractures in the thoracic spine and/or left radius, mildly elevated circulating FGF23, and hypophosphatemia. Total hip bone mineral density scans demonstrated osteoporosis (Z-score < -2.5) and HRpQCT demonstrated microarchitectural defects in trabecular and cortical bone. Next-generation sequencing revealed heterozygous loss-of-function mutations in ENPP1 previously observed as biallelic mutations in infants with GACI. In addition, we present bone mass and structure data as well as plasma pyrophosphate (PPi) data of two siblings suffering from ARHR2 in comparison to their heterozygous and wild-type family members indicative of an ENPP1 gene dose effect. The skeletal phenotype in murine Enpp1 deficiency yielded nearly identical findings. Ten-week-old male Enpp1 asj/asj mice exhibited mild elevations in plasma FGF23 and hypophosphatemia, and micro-CT analysis revealed microarchitectural defects in trabecular and cortical bone of similar magnitude to HRpQCT defects observed in humans. Histomorphometry revealed mild osteomalacia and osteopenia at both 10 and 23 weeks. The biomechanical relevance of these findings was demonstrated by increased bone fragility and ductility in Enpp1 asj/asj mice. In summary, ENPP1 exerts a gene dose effect such that humans with heterozygous ENPP1 deficiency exhibit intermediate levels of plasma analytes associated with bone mineralization disturbance resulting in early onset osteoporosis. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Intra-articular osteoid osteoma accompanied by extensive bone marrow edema. A clinical and micro-morphological analysis.

Osteoid osteoma (OO) is a benign bone tumor producing non-mineralized bone matrix (i.e., osteoid). While peritumoral edema is commonly found in OO, extensive bone marrow edema has been reported less frequently. Furthermore, the micro-morphological characteristics of the nidus and its central calcification remain unclear. In this study, a consecutive series of four patients suffering from extensive bone marrow edema triggered by intra-articular osteoid osteoma underwent clinical examination, magnetic resonance imaging (MRI) and computed tomography (CT) as well as dual-energy X-ray absorptiometry (DXA) and laboratory bone turnover analyses. The obtained resection specimens were processed by undecalcified histology and were subsequently analyzed by light microscopy and quantitative backscattered electron imaging (qBEI). We report an entity of intra-articular osteoid osteoma in the knee and foot, in which an extensive and persistent bone marrow edema syndrome masked the correct diagnosis. While metabolic bone diseases were excluded in all cases, the reassessment of the patients' clinical history including pain characteristics (nocturnal, aspirin sensitivity) led us to perform additional CT, where the tumor was diagnosed. The micro-morphological analysis of the OO biopsies revealed that the nidus was surrounded by hyperosteoidosis, while central mineralization was detected in all cases. This mineralized area showed a significantly higher mineralization heterogeneity than the surrounding trabecular bone and more disorganized collagen fibers detected by qBEI and polarized light microscopy, respectively. Taken together, our results indicate that osteoid osteoma should be considered when persistent and extensive, peri-articular bone marrow edema is diagnosed. The central calcification that is found inside the nidus in conventional imaging was mirrored by bone matrix with a heterogeneous mineralization pattern.

Wnt1 is an Lrp5-independent bone-anabolic Wnt ligand.

WNT1 mutations in humans are associated with a new form of osteogenesis imperfecta and with early-onset osteoporosis, suggesting a key role of WNT1 in bone mass regulation. However, the general mode of action and the therapeutic potential of Wnt1 in clinically relevant situations such as aging remain to be established. Here, we report the high prevalence of heterozygous WNT1 mutations in patients with early-onset osteoporosis. We show that inactivation of Wnt1 in osteoblasts causes severe osteoporosis and spontaneous bone fractures in mice. In contrast, conditional Wnt1 expression in osteoblasts promoted rapid bone mass increase in developing young, adult, and aged mice by rapidly increasing osteoblast numbers and function. Contrary to current mechanistic models, loss of Lrp5, the co-receptor thought to transmit extracellular WNT signals during bone mass regulation, did not reduce the bone-anabolic effect of Wnt1, providing direct evidence that Wnt1 function does not require the LRP5 co-receptor. The identification of Wnt1 as a regulator of bone formation and remodeling provides the basis for development of Wnt1-targeting drugs for the treatment of osteoporosis.

Is centrally induced alveolar bone loss in a large animal model preventable by peripheral hormone substitution?

OBJECTIVES: Alveolar bone structures are mostly investigated in small animal models. The majority of these studies examined local influences on the alveolar bone, but only a few examined systemic influencing factors. The hypothalamic-pituitary axis is known to be essential for a vital bone balance. The aim of this study was to analyse the effects that selective hormone treatments have on alveolar bone structure and quality in a sheep model for alveolar bone loss, induced by hypothalamic-pituitary disconnection (HPD). METHODS: Thirty sheep were randomly selected into six groups of five each: control (C), ovariectomy-OVX (O), O + HPD (OH), OH with oestrogen treatment (OHE), OH with thyroxine (T4) treatment (OHT), and OH with a combined treatment of oestrogen and thyroxine (OHTE). After OVX and HPD procedures and an additional 9-month observation/treatment period, structural bone analyses of the mandible were performed by contact radiography, micro-CT, and static histomorphometry. RESULTS: The HPD procedure caused structural alveolar bone parameters to decrease significantly compared to controls (C). Treatment with oestrogen (OHE) was protective and bone structure was maintained at baseline levels. Thyroxine treatment (OHT) promoted significant bone loss, but the combined treatment (OHTE) improved bone structure and volume parameters even above baseline levels. CONCLUSIONS: Alveolar bone homeostasis significantly underlies systemic regulatory systems. Centrally induced (HPD) bone loss can be prevented by combined peripheral treatment with oestrogen and thyroxine. CLINICAL RELEVANCE: These results demonstrate the significance of a balanced hormonal regulatory system for steady bone remodelling and maintenance of healthy alveolar bone.

High Bone Turnover in Mice Carrying a Pathogenic Notch2 Mutation Causing Hajdu-Cheney Syndrome.

Hajdu-Cheney syndrome (HCS) is a rare autosomal-dominant disorder primarily characterized by acro-osteolysis and early-onset osteoporosis. Genetically, HCS is caused by nonsense or deletion mutations within exon 34 of the NOTCH2 gene, resulting in premature translational termination and production of C-terminally truncated NOTCH2 proteins that are predicted to activate NOTCH2-dependent signaling. To understand the role of Notch2 in bone remodeling, we developed a mouse model of HCS by introducing a pathogenic mutation (6272delT) into the murine Notch2 gene. By µCT and undecalcified histology, we observed generalized osteopenia in two independent mouse lines derived by injection of different targeted embryonic stem (ES) cell clones, yet acro-osteolysis did not occur until the age of 52 weeks. Cellular and dynamic histomorphometry revealed a high bone turnover situation in Notch2+/HCS mice, since osteoblast and osteoclast indices were significantly increased compared with wild-type littermates. Whereas ex vivo cultures failed to uncover cell-autonomous gain-of-functions within the osteoclast or osteoblast lineage, an unbiased RNA sequencing approach identified Tnfsf11 and Il6 as Notch-signaling target genes in bone marrow cells cultured under osteogenic conditions. Because we further observed that the high-turnover pathology of Notch2+/HCS mice was fully normalized by alendronate treatment, our results demonstrate that mutational activation of Notch2 does not directly control osteoblast activity but favors a pro-osteoclastic gene expression pattern, which in turn triggers high bone turnover. © 2017 American Society for Bone and Mineral Research.

Sheep model for osteoporosis: The effects of peripheral hormone therapy on centrally induced systemic bone loss in an osteoporotic sheep model.

Hypothalamic-pituitary disconnection (HPD) leads to low bone turnover followed by bone loss and reduced biomechanical properties in sheep. To investigate the role of peripheral hormones in this centrally induced systemic bone loss model, we planned a hormone replacement experiment. Therefore, estrogen (OHE), thyroxin (OHT) or a combination of both (OHTE) was substituted in ovariectomized HPD sheep, as both hormones are decreased in HPD sheep and are known to have a significant but yet not fully understood impact on bone metabolism. Bone turnover and structural parameters were analyzed in comparison to different control groups - untreated sheep (C), ovariectomized (O) and ovariectomized+HPD sheep (OH). We performed histomorphometric and HR-pQCT analyses nine months after the HPD procedure, as well as biomechanical testing of all ewes studied. In HPD sheep (OH) the low bone turnover led to a significant bone loss. Treatment with thyroxin alone (OHT) mainly increased bone resorption, leading to a further reduction in bone volume. In contrast, the treatment with estrogen alone (OHE) and the combined treatment with estrogen and thyroxin (OHTE) prevented HPD-induced bone loss completely. In conclusion, peripheral hormone substitution was able to prevent HPD-induced low-turnover osteoporosis in sheep. But only the treatment with estrogen alone or in combination with thyroxin was able to completely preserve bone mass and structure. These findings demonstrate the importance of peripheral hormones for a balanced bone remodeling and a physiological bone turnover.

A Novel ANO5 Mutation Causing Gnathodiaphyseal Dysplasia With High Bone Turnover Osteosclerosis.

Gnathodiaphyseal dysplasia (GDD) is a rare skeletal syndrome that involves an osteopetrosis-like sclerosis of the long bones and fibrous dysplasia-like cemento-osseous lesions of the jawbone. Although the genetic analysis of the respective patients has revealed mutations in the ANO5 gene as an underlying cause, there is still no established consensus regarding the bone status of GDD patients. We report a new case of GDD in a 13-year-old boy with recurrent diaphyseal fractures of the femur, in whom we identified a novel de novo missense mutation in the ANO5 gene, causing a p.Ser500Phe substitution at the protein level. After confirming the presence of GDD-characteristic abnormalities within the jaw bones, we focused on a full osteologic assessment using dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT), and serum analyses. We thereby identified increased trabecular bone mass accompanied by elevated serum markers of bone formation and bone resorption. The high turnover bone pathology was further confirmed through the analysis of an iliac crest biopsy, where osteoblast and osteoclast indices were remarkably increased. Taken together, our findings provide evidence for a critical and generalized role of anoctamin-5 (the protein encoded by the ANO5 gene) in skeletal biology. As it is reasonable to speculate that modifying the function of anoctamin-5 might be useful for therapeutically activating bone remodeling, it is now required to analyze its function at a molecular level, for instance in mouse models. © 2016 American Society for Bone and Mineral Research.

Intra-articular osteoid osteoma in the proximal tibia and its imaging characteristics.

Due to mostly non-specific clinical symptoms and variable appearance on magnetic resonance imaging (MRI), the diagnosis of an intra-articular osteoid osteoma (iaOO) is often delayed. We report the case of a 26-year-old male with an atypical clinical manifestation of an iaOO in the proximal tibia and its MRI specific characteristics of tumor progression. The patient presented to our clinic after receiving multiple unsuccessful conservative and surgical interventions due to anterior knee pain, which persisted for 12months. Prior to the correct diagnosis of iaOO manifestation, the patient was subjected to multiple steroid infiltrations and two arthroscopies including partial meniscal resection. Due to increasing complaints, meniscal transplantation, bone decompression and/or ACL reconstruction were recommended. Subsequent computer tomography (CT) scanning and successful test medication with salicylates (ASS) confirmed iaOO presentation. Only after arthroscopic tumor resection was the patient symptom free at three months of follow-up. The present description of MRI specific characteristics of iaOO progression has the potential to accelerate correct tumor detection in the future.

Functional outcome of septic arthritis after anterior cruciate ligament surgery.

PURPOSE: Septic arthritis is a rare complication after cruciate ligament surgery. The lack of conclusive evidence makes it difficult to obtain a consensus concerning the best treatment option. METHODS: From June 1993 to May 2010, 31 patients met the inclusion criteria for this prospective case series. The average age at ACL injury was 33.5 years. Treatment protocol was based on the grade of infection. Options included arthroscopic treatment for infections of Gaechter grades 1 and 2 or arthrotomy for infections of grades 3 and 4. Graft retention was decided based on the clinical findings. The setting was a specialized trauma hospital. Follow-up included International Knee Documentation Committee (IKDC) forms, Tegner score, and Lysholm scores at a mean of six years (71 months; range, 13-140) after treatment. RESULTS: In all cases, treatment of infection was successful; overall, a mean of 2.6 operations were required. In eight cases, it was possible to salvage the graft. The Tegner activity level before the knee injury was 6.5 points. At follow-up, the average score was 4.5 points. The postoperative subjective IKDC score averaged 63. The mean Lysholm score was 63.9. On clinical examination, a mean extension deficit of 2.5° and a mean maximum flexion of 121° were found. In the single-legged hop test, a mean capacity of 68% compared with the uninjured side was measured. CONCLUSION: The stage-adapted procedure gives reliable results for septic arthritis after ACL surgery. There were no recurrences of septic arthritis or bone infection. Early infection can be managed arthroscopically with satisfactory results. More advanced infections should be addressed with a more radical approach. In conclusion, functional outcome in most of the presented cases was only fair compared with results from ACL surgery not complicated by infection.