Osteopetrosis and its relevance for the discovery of new functions associated with the skeleton

Birefringence-induced phase delay enables Brillouin mechanical imaging in turbid media

Acoustic vibrations of matter convey fundamental viscoelastic information that can be optically retrieved by hyperfine spectral analysis of the inelastic Brillouin scattered light. Increasing evidence of the central role of the viscoelastic properties in biological processes has stimulated the rise of non-contact Brillouin microscopy, yet this method faces challenges in turbid samples due to overwhelming elastic background light. Here, we introduce a common-path Birefringence-Induced Phase Delay (BIPD) filter to disentangle the polarization states of the Brillouin and Rayleigh signals, enabling the rejection of the background light using a polarizer. We demonstrate a 65 dB extinction ratio in a single optical pass collecting Brillouin spectra in extremely scattering environments and across highly reflective interfaces. We further employ the BIPD filter to image bone tissues from a mouse model of osteopetrosis, highlighting altered biomechanical properties compared to the healthy control. Results herald new opportunities in mechanobiology where turbid biological samples remain poorly characterized.

Small nucleolar RNA host gene 5 plays a role in orthodontic tooth movement by inhibiting osteoclast differentiation

BACKGROUND AND OBJECTIVES

The alveolar bone remodelling promoted by reasonable mechanical force triggers orthodontic tooth movement (OTM). The generation of osteoclasts is essential in this process. However, the mechanism of mechanical force mediating osteoclast differentiation remains elusive. Small nucleolar RNA host gene 5 (SNHG5), which was reported to mediate the osteogenic differentiation of bone marrow mesenchymal stem cells in our previous study, was downregulated in human periodontal ligament cells (hPDLCs) under mechanical force. At the same time, the RANKL/OPG ratio increased. Based on this, we probed into the role of SNHG5 in osteoclast formation during OTM and the relevant mechanism.

MATERIALS AND METHODS

SNHG5 and the RANKL/OPG ratio under different compressive forces were detected by western blotting (WB) and qRT-PCR. Impact of overexpression or knockdown of SNHG5 on osteoclast differentiation was detected by qRT-PCR, WB and transwell experiments. The combination of SNHG5 and C/EBPβ was verified by RNA immunoprecipitation and RNA pull-down assays. The expression of SNHG5 and osteoclast markers in gingiva were analysed by qRT-PCR and the paraffin sections of periodontal tissues were used for histological analysis.

RESULTS

Compressive force downregulated SNHG5 and upregulated the RANKL/OPG ratio in hPDLCs. Overexpression of SNHG5 inhibited RANKL's expression and osteoclast differentiation. SNHG5 combined with C/EBPβ, a regulator of osteoclast. The expression of SNHG5 in periodontal tissue decreased during OTM.

CONCLUSION

SNHG5 inhibited osteoclast differentiation during OTM, achieved by affecting RANKL secretion, which may provide a new idea to interfere with bone resorption during orthodontic treatment.

Allogenic hematopoietic stem cell transplantation in an Iranian patient with osteopetrosis caused by carbonic anhydrase II deficiency: A case report

BACKGROUND

Osteopetrosis is a group of geneticall heterogeneous disorders resulting from impaired osteoclast function and bone resorption. The identification of specific genetic mutations can yield important prognostic and therapeutic implications. Herein, we present the diagnosis and successful application of hematopoietic stem cell transplantation (HSCT) in a patient with osteopetrosis caused by carbonic anhydrase II deficiency (Intermediate osteopetrosis).

CASE PRESENTATION

Herein, we describe a 2.5-year-old male patient born to consanguineous parents who presented at 8-month-old with hydrocephaly, brain shunt, and developmental delay. Later at 9 months old, he was found to have eye disorder such as nystagmus, fracture of the elbow, abnormal skeletal survey, normal cell blood count (CBC), and severe hypocellularity in the bone marrow. Further evaluation showed renal tubular acidosis type 2. Whole-exome sequencing revealed a pathogenic homozygous variant in intron 2 of the carbonic anhydrase 2 gene (CA2) gene (c.232 + 1 G>T). The diagnosis of intermediate autosomal recessive osteopetrosis was established, and allogenic HSCT from his mother, a full-matched related donor (MRD), was planned. The conditioning regimen included Busulfan, Fludarabine, and Rabbit anti-thymocyte globulin. Cyclosporine and Mycophenolate Mofetil were used for graft-versus-host-disease prophylaxis. He Engrafted on day +13, and 95% chimerism was achieved. He is currently doing well without immunosuppressive therapy, now 12 months post HSCT, with normal calcium level and improving visual quality and FISH analysis revealed complete donor chimerism.

DISCUSSION

HSCT could be a promising curative treatment for intermediate osteopetrosis and can provide long-term survival. Ongoing challenges in various aspects of HSCT remain to be addressed.

Osteopetrosis complicated by multilevel spondylolysis

Osteopetrosis is a heterogenous group of inheritable disorders which manifests as increased bone density and brittleness. The most common and mildest variant typically presents in adulthood with bone pain and pathologic fractures, including spondylolysis. We present the case of an otherwise healthy, active 17-year-old male with a history of osteopetrosis and 1 year of chronic back pain, found to have multilevel (L1-L4) spondylolysis in the setting of severe diffuse bony sclerosis consistent with osteopetrosis. While single-level spondylolysis is an uncommon complication of osteopetrosis, multilevel spondylolysis in the pediatric population is extremely rare and the genetics of prior cases studies have not been reported. Spondylolysis should be considered as one of the types of fractures that may occur in patients with osteopetrosis.

Fracture Patterns and Mortality in Osteopetrosis: A 7-year Retrospective Analysis from Türkiye's National Registry

BACKGROUND

The aim of this study is to determine the demographic data, fracture treatment methods, and medical treatments of patients diagnosed with osteopetrosis in the national registry.

METHODS

Patients with International Classification of Diseases (ICD)-10 code Q78.2 for osteopetrosis between January 1, 2016 and April 11, 2023 were retrospectively reviewed. Data on sex, age at time of diagnosis, fracture history, mortality, and use of medications were evaluated for all patients. In addition, open reduction and internal fixation, closed reduction and internal fixation, closed reduction and casting, and conservative treatment methods were noted. The number of patients requiring deformity surgery was determined. The incidence and prevalence of osteopetrosis were also calculated in this cross-sectional study.

RESULTS

A total of 476 patients diagnosed with osteopetrosis were identified. The mean age at time of diagnosis of these patients was 5.79 ± 5.43 years. A total of 101 patients died. As the age at diagnosis decreased, the mortality rate of the patients increased with statistical significance ( P <0.001). A total of 192 fractures were seen in 121 osteopetrosis patients in this study. Femur fractures were most common among these patients with osteopetrosis. A history of fracture was statistically significantly less common in patients using a combination of vitamin D + calcium compared with patients not using such medication ( P <0.001). In this 7-year cross-sectional study, the incidence was found to be 1 in 416,000 and the prevalence was 0.00199% in the population under 18 years of age.

CONCLUSION

Younger age at diagnosis is associated with higher mortality in patients with osteopetrosis. In addition, the combination of vitamin D and calcium were associated with lower fracture incidence.

LEVEL OF EVIDENCE

Prognostic Level II.

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Clinical, genetic aspects and molecular pathogenesis of osteopetrosis

Osteopetrosis ("marble bone", ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity. The name "osteopetrosis" comes from the Greek language: 'osteo' means 'bone' and 'petrosis' means 'stone', which characterizes the main feature of the disease: increased bone density caused by imbalances in bone formation and remodeling, leading to structural changes in bone tissue, predisposition to fractures, skeletal deformities. These defects, in turn, affect other important organs and tissues, especially bone marrow and the nervous system. The disease can be autosomal recessive, autosomal dominant, X-linked or sporadic. Autosomal dominant osteopetrosis has an incidence of 1 in 20,000 newborns and autosomal recessive one has 1 in 250,000. To date, 23 genes have been described, structural changes in which lead to the development of osteopetrosis. Clinical symptoms in osteopetrosis vary greatly in their presentation and severity. The mildest skeletal abnormalities are observed in adulthood and occur in the autosomal dominant form of osteopetrosis. Severe forms, being autosomal recessive and manifesting in early childhood, are characterized by fractures, mental retardation, skin lesions, immune system disorders, renal tubular acidosis. Clinical examination and review of radiographs, bone biopsy and genetic testing provide the bases for clinical diagnosis. The early and accurate detection and treatment of the disease are important to prevent hematologic abnormalities and disease progression to irreversible neurologic consequences. Most patients die within the first decade due to secondary infections, bone marrow suppression and/or bleeding. This article summarizes the current state of the art in this field, including clinical and genetic aspects, and the molecular pathogenesis of the osteopetrosis.

Nano-formulations for bone-specific delivery of siRNA for CrkII silencing-induced regulation of bone formation and resorption to maximize therapeutic potential for bone-related diseases

CrkII, a member of the adaptor protein family, is known to participate in bone homeostasis via the regulation of osteoclasts and osteoblasts. Therefore, silencing CrkII would beneficially impact the bone microenvironment. In this study, CrkII siRNA encapsulated by a bone-targeting peptide (AspSerSer)₆-liposome was evaluated for its therapeutic applications using a receptor activator of nuclear factor kappa-B ligand (RANKL)-induced bone loss model. (AspSerSer)₆-liposome-siCrkII maintained its gene-silencing ability in both osteoclasts and osteoblasts in vitro and significantly reduced osteoclast formation while increasing osteoblast differentiation in vitro. Fluorescence image analyses showed that the (AspSerSer)₆-liposome-siCrkII was present largely in bone, where it remained present for up to 24 hours and was cleared by 48 hours, even when systemically administrated. Importantly, microcomputed-tomography revealed that bone loss induced by RANKL administration was recovered by systemic administration of (AspSerSer)₆-liposome-siCrkII. Collectively, the findings of this study suggest that (AspSerSer)₆-liposome-siCrkII is a promising therapeutic strategy for the development of treatments for bone diseases, as it overcomes the adverse effects derived from ubiquitous expression via bone-specific delivery of siRNA.

Carbonic Anhydrase II Activators in Osteopetrosis Treatment: A Review

Osteopetrosis is a rare hereditary illness generated by failure in osteoclasts resulting in elevated bone densities. Patients with osteopetrosis possess several complications, like dental caries, earlier teeth loss, delayed eruption, malformed crowns and roots, and lamina dura thickening. Since deficiency of carbonic anhydrase II is a major cause behind osteopetrosis, carbonic anhydrase II activators have a large number of applications in osteopetrosis treatment. There is a lack of a comprehensive review on osteopetrosis, pathogenesis of dental abnormalities, and the role of carbonic anhydrase II activators in osteopetrosis treatment. To address this research gap, the authros perfomed a comprehensive review on osteopetrosis and its types, pathogenesis of dental abnormalities, and the role of carbonic anhydrase II activators in osteopetrosis treatment. A brief introduction to the pathogenesis of dental abnormalities and regeneration is provided in this survey. A discussion of types of osteopetrosis depending on genetic inheritance, such as autosomal dominant, autosomal recessive, and X-linked inheritance osteopetrosis, is presented in this survey. The paper also focuses on the importance of carbonic anhydrase II activators as a potential drug therapy for dental osteopetrosis. In addition, a brief note on the role of azole and fluconazole in treating osteopetrosis is given. Finally, future directions involving gene therapy for dental osteopetrosis are described.

SLC4A2, another gene involved in acid-base balancing machinery of osteoclasts, causes osteopetrosis

SLC4A2 belongs to the Na⁺-independent solute carrier family 4 (SLC4) of anion exchangers, which regulate electroneutral exchange of Cl^- for HCO₃^- and mediate intra- and extra-cellular pH, chloride concentration and cell volume. Slc4a2 also participates in gastric acid secretion, spermatogenesis and osteoclastogenesis. During osteoclast differentiation, Slc4a2 is exclusively expressed at the contra-lacunar membrane and is up-regulated with osteoclast maturation. Bi-allelic Slc4a2 loss-of-function mutations have been known to cause osteopetrosis in mice and cattle, but not in human. Recently, we have identified bi-allelic pathogenic variants in SLC4A2 in a patient affected by osteopetrosis with severe renal insufficiency, suggesting SLC4A2 deficiency causes a new type of autosomal recessive osteopetrosis (osteopetrosis, Ikegawa type). In this article, we review the advances in exploring the multiple functions of SLC4A2 with emphasis on its roles in osteoclast. Our review would contribute to understanding of the phenotypic spectrum and the pathomechanism of SLC4A2-associated osteopetrosis.

Spectrum of Skeletal Imaging Features in Osteopetrosis: Inheritance Pattern and Radiological Associations

Osteopetrosis (from the Greek "osteo": bone; "petrosis": stone) is a clinically and genetically heterogeneous group of rare diseases of the skeleton, sharing the same main characteristic of an abnormally increased bone density. Dense bones in radiological studies are considered the hallmark of these diseases, and the reason for the common term used: "Marble bone disease". Interestingly, a radiologist, Dr. Albers-Schonberg, described this disease for the first time in Germany in 1904. Indeed, radiology has a key role in the clinical diagnosis of osteopetrosis and is fundamental in assessing the disease severity and complications, as well as in follow-up controls and the evaluation of the response to treatment. Osteopetrosis includes a broad spectrum of genetic mutations with very different clinical symptoms, age onset, and prognosis (from mild to severe). This diversity translates into different imaging patterns related to specific mutations, and different disease severity. The main recognized types of osteopetrosis are the infantile malignant forms with autosomal recessive transmission (ARO-including the rarer X-linked recessive form); the intermediate autosomal recessive form (IAO); and the autosomal dominant ones ADO, type I, and type II, the latter being called 'Albers-Schonberg' disease. Imaging features may change among those distinct types with different patterns, severities, skeletal segment involvement, and speeds of progression. There are several classical and well-recognized radiological features related to osteopetrosis: increased bone density (all types with different degrees of severity assuming a 'Marble Bone Appearance' especially in the ARO type), different metaphyseal alterations/enlargement including the so-called 'Erlenmeyer flask deformity' (particularly of femoral bones, more frequent in ADO type 2, and less frequent in ARO and IAO), 'bone in bone' appearance (more frequent in ADO type 2, less frequent in ARO and IAO), and 'rugger-jersey spine' appearance (typical of ADO type 2). After conducting an overview of the epidemiological and clinical characteristic of the disease, this review article aims at summarizing the main radiological features found in different forms of osteopetrosis together with their inheritance pattern.

A library of Rhodamine6G-based pH-sensitive fluorescent probes with versatile in vivo and in vitro applications

Acidic pH is critical to the function of the gastrointestinal system, bone-resorbing osteoclasts, and the endolysosomal compartment of nearly every cell in the body. Non-invasive, real-time fluorescence imaging of acidic microenvironments represents a powerful tool for understanding normal cellular biology, defining mechanisms of disease, and monitoring for therapeutic response. While commercially available pH-sensitive fluorescent probes exist, several limitations hinder their widespread use and potential for biologic application. To address this need, we developed a novel library of pH-sensitive probes based on the highly photostable and water-soluble fluorescent molecule, Rhodamine 6G. We demonstrate versatility in terms of both pH sensitivity (i.e., pK a) and chemical functionality, allowing conjugation to small molecules, proteins, nanoparticles, and regenerative biomaterial scaffold matrices. Furthermore, we show preserved pH-sensitive fluorescence following a variety of forms of covalent functionalization and demonstrate three potential applications, both in vitro and in vivo, for intracellular and extracellular pH sensing. Finally, we develop a computation approach for predicting the pH sensitivity of R6G derivatives, which could be used to expand our library and generate probes with novel properties.

Utility of next-generation sequencing in genetic testing and counseling of disorders involving the musculoskeletal system—trends observed from a single genetic unit

Background

Disorders involving the musculoskeletal system are often identified with short stature and a range of orthopedic problems. The clinical and genetic heterogeneity of these diseases along with several characteristic overlaps makes definitive diagnosis difficult for clinicians. Hence, using molecular testing in addition to conventional tests becomes essential for appropriate diagnosis and management.

Methods

Comprehensive clinical examination, detailed pretest and posttest counseling, molecular diagnosis with next-generation sequencing (NGS), genotype–phenotype correlation and Sanger sequencing for targeted variant analysis.

Results

This manuscript reports a molecular spectrum of variants in 34 orthopedic cases referred to a single genetic unit attached to a tertiary care hospital. The diagnostic yield of NGS-based tests coupled with genetic counseling and segregation analysis was 79% which included 7 novel variants. In about 53% (i.e. 18/34 cases), molecular testing outcome was actionable since 8 of the 18 underwent prenatal diagnosis, as they were either in their early gestation or had planned a pregnancy subsequent to molecular testing, while ten cases were premaritally/prenatally counseled for the families to take informed decisions as they were in the reproductive age.

Conclusions

The report highlights the importance of NGS-based tests even in a low resource setting as it helps patients, families and healthcare providers in reducing the economic, social and emotional burden of these disorders.

Overlapping Phenotypes in Osteopetrosis and Pycnodysostosis in Asian-Indians

Osteopetrosis is a disorder characterized by high bone density, hepatosplenomegaly, visual and hearing loss, and anemia. Pycnodysostosis presents with short stature, acroosteolysis, and dense bones. We, hereby, present here a family with autosomal dominant osteopetrosis and also children with recessive osteopetrosis and pycnodysostosis. The molecular confirmation was done in 3 cases. Genetic heterogeneity in clinical presentation is discussed here. Further studies will help in identifying epigenetic alterations and population-specific variants and also developing targeted therapies.

Surgical management of chronic osteomyelitis with benign osteopetrosis: A case report

Introduction

Osteopetrosis is a rare genetic bone disease caused by a functional abnormality of the osteoclasts. Until now there is no codified management for the complications of this pathology and few cases cited in the literature.

Presentation of case

a 19-year-old adult followed in our maxillofacial surgery department in the IBN ROCHD University Hospital for chronic osteomyelitis complicating mandibular osteopetrosis with skin fistulas. Patient operated several times. The persistence of osteomyelitis prevents the installation of a dental prosthesis and the appearance of new fistulas with continuous flow of pus alters the patient's quality of life.

Discussion

Osteopetrosis is a group of rare genetic diseases characterized by osteoclastic insufficiency, poor bone remodeling and increased bone density. the benign form of osteopetrosis called Albers-Schönberg disease. It is a genetically inherited autosomal dominant disease.

The large number of surgical interventions and the use of antibiotics for long periods of time (risk of development of resistance) significantly reduces the quality of life of patients. We must seek other measures to improve the prognosis and codify management.

Conclusion

In osteopetrosis, the maxillofacial surgeons should be aware about the early diagnosis and the appropriate management of the signs and prevent complications.

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Osteopetrosis is a rare genetic bone disease.

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No codified management for the complications of this pathology.

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The maxillofacial surgeon must always choose between surgery and its risks and medical treatment.

A Homozygous Mutation in 5' Untranslated Region of TNFRSF11A Leading to Molecular Diagnosis of Osteopetrosis Coinheritance With Wiskott-Aldrich Syndrome

Wiskott-Aldrich syndrome (WAS) and osteopetrosis are 2 different, rare hereditary diseases. Here we report clinical and molecular genetics investigations on an infant patient with persistent thrombocytopenia and prolonged fever. He was clinical diagnosed as osteopetrosis according to clinical presentation, radiologic skeletal features, and bone biopsy results. Gene sequencing demonstrated a de novo homozygous mutation in 5'-untranslated region of TNFRSF11A, c.-45A>G, which is relating to osteopetrosis. Meanwhile, a hemizygous transition mutation in WAS gene, c.400G>A diagnosed the infant with WAS. This is the first clinical report for the diagnosis of osteopetrosis coinheritance with WAS in a single patient.

Bone Microvasculature: Stimulus for Tissue Function and Regeneration

Bone is a highly vascularized organ, providing structural support to the body, and its development, regeneration, and remodeling depend on the microvascular homeostasis. Loss or impairment of vascular function can develop diseases, such as large bone defects, avascular necrosis, osteoporosis, osteoarthritis, and osteopetrosis. In this review, we summarize how vasculature controls bone development and homeostasis in normal and disease cases. A better understanding of this process will facilitate the development of novel disease treatments that promote bone regeneration and remodeling. Specifically, approaches based on tissue engineering components, such as stem cells and growth factors, have demonstrated the capacity to induce bone microvasculature regeneration and mineralization. This knowledge will have relevant clinical implications for the treatment of bone disorders by developing novel pharmaceutical approaches and bone grafts. Finally, the tissue engineering approaches incorporating vascular components may widely be applied to treat other organ diseases by enhancing their regeneration capacity. Impact statement Bone vasculature is imperative in the process of bone development, regeneration, and remodeling. Alterations or disruption of the bone vasculature leads to loss of bone homeostasis and the development of bone diseases. In this study, we review the role of vasculature on bone diseases and how vascular tissue engineering strategies, with a detailed emphasis on the role of stem cells and growth factors, will contribute to bone therapeutics.

The Role of Autophagy in Osteoclast Differentiation and Bone Resorption Function

Autophagy is an evolutionary conserved and highly regulated recycling process of cellular wastes. Having a housekeeping role, autophagy through the digestion of domestic cytosolic organelles, proteins, macromolecules, and pathogens, eliminates unnecessary materials and provides nutrients and energy for cell survival and maintenance. The critical role of autophagy and autophagy-related proteins in osteoclast differentiation, bone resorption, and maintenance of bone homeostasis has previously been reported. Increasing evidence reveals that autophagy dysregulation leads to alteration of osteoclast function and enhanced bone loss, which is associated with the onset and progression of osteoporosis. In this review, we briefly consolidate the current state-of-the-art technology regarding the role of autophagy in osteoclast function in both physiologic and pathologic conditions to have a more general view on this issue.

Molecular insights into the human CLC-7/Ostm1 transporter

CLC family proteins translocate chloride ions across cell membranes to maintain the membrane potential, regulate the transepithelial Cl^- transport, and control the intravesicular pH among different organelles. CLC-7/Ostm1 is an electrogenic Cl^-/H⁺ antiporter that mainly resides in lysosomes and osteoclast ruffled membranes. Mutations in human CLC-7/Ostm1 lead to lysosomal storage disorders and severe osteopetrosis. Here, we present the cryo-electron microscopy (cryo-EM) structure of the human CLC-7/Ostm1 complex and reveal that the highly glycosylated Ostm1 functions like a lid positioned above CLC-7 and interacts extensively with CLC-7 within the membrane. Our complex structure reveals a functionally crucial domain interface between the amino terminus, TMD, and CBS domains of CLC-7. Structural analyses and electrophysiology studies suggest that the domain interaction interfaces affect the slow gating kinetics of CLC-7/Ostm1. Thus, our study deepens understanding of CLC-7/Ostm1 transporter and provides insights into the molecular basis of the disease-related mutations.

Bilateral Girdlestone Procedure as a Treatment Modality in a Case of Complicated Adult-Onset Osteopetrosis: A Case Report

CASE

We describe a nonambulatory 39-year-old man who presented with a diagnosis of osteopetrosis and ankyloses, having experienced bilateral fractures of his proximal femora, undergone unsuccessful conventional surgical interventions, and having developed chronic osteomyelitis of his right proximal femur. Bilateral Girdlestone procedures were performed. Postoperative range of hip motion and Harris hip scores improved, and he became ambulatory, achieving optimal function considering the circumstances at 12 months postoperatively.

CONCLUSIONS

Although the indications of the bilateral Girdlestone procedure remain undefined, these procedures may constitute acceptable treatment in patients with osteopetrosis with ankylosis and chronic osteomyelitis of the proximal femur.

Transcriptome sequencing identifies a noncoding, deep intronic variant in CLCN7 causing autosomal recessive osteopetrosis

Background

Over half of children with rare genetic diseases remain undiagnosed despite maximal clinical evaluation and DNA‐based genetic testing. As part of an Undiagnosed Diseases Program applying transcriptome (RNA) sequencing to identify the causes of these unsolved cases, we studied a child with severe infantile osteopetrosis leading to cranial nerve palsies, bone deformities, and bone marrow failure, for whom whole‐genome sequencing was nondiagnostic.

Methods

We performed transcriptome (RNA) sequencing of whole blood followed by analysis of aberrant transcript isoforms and osteoclast functional studies.

Results

We identified a pathogenic deep intronic variant in CLCN7 creating an unexpected, frameshifting pseudoexon causing complete loss of function. Functional studies, including osteoclastogenesis and bone resorption assays, confirmed normal osteoclast differentiation but loss of osteoclast function.

Conclusion

This is the first report of a pathogenic deep intronic variant in CLCN7, and our approach provides a model for systematic identification of noncoding variants causing osteopetrosis—a disease for which molecular‐genetic diagnosis can be pivotal for potentially curative hematopoietic stem cell transplantation. Our work illustrates that cryptic splice variants may elude DNA‐only sequencing and supports broad first‐line use of transcriptome sequencing for children with undiagnosed diseases.

RANKL biology: bone metabolism, the immune system, and beyond

Receptor activator of NF-κB (RANK) ligand (RANKL) induces the differentiation of monocyte/macrophage-lineage cells into the bone-resorbing cells called osteoclasts. Because abnormalities in RANKL, its signaling receptor RANK, or decoy receptor osteoprotegerin (OPG) lead to bone diseases such as osteopetrosis, the RANKL/RANK/OPG system is essential for bone resorption. RANKL was first discovered as a T cell-derived activator of dendritic cells (DCs) and has many functions in the immune system, including organogenesis, cellular development. The essentiality of RANKL in the bone and the immune systems lies at the root of the field of "osteoimmunology." Furthermore, this cytokine functions beyond the domains of bone metabolism and the immune system, e.g., mammary gland and hair follicle formation, body temperature regulation, muscle metabolism, and tumor development. In this review, we will summarize the current understanding of the functions of the RANKL/RANK/OPG system in biological processes.

Hematopoietic stem cell transplantation-induced bone remodeling in autosomal recessive osteopetrosis: Interaction between skeleton and hematopoietic and sensory nervous systems

OBJECTIVE

Autosomal recessive osteopetrosis (ARO) is a rare congenital disorder of defective bone resorption. The inability of osteoclasts to resorb bone compromises the development of bone marrow cavity, and ultimately, leads to defective hematopoiesis and death within the first decade. The only curative treatment currently available for certain forms of ARO is hematopoietic stem cell transplantation (HSCT). Infants over ten months of age suffering from ARO are defined as patients with advanced disease; HSCT to these patients is associated with high risk of transplant-related mortality (TRM). Because of the extreme variability of ARO clinical phenotypes, the most reliable predictive factor of TRM and graft failure risk is the residual bone marrow space volume.

CASE REPORT

We report clinical and radiological outcomes of one patient affected by ARO and treated with HSCT at advance stage of the disease. We describe the anomalies in various tissues, including bone marrow and bones at the moment of the diagnosis and document their gradual disappearance after HSCT until their complete resolution based on magnetic resonance imaging (MRI) observations. We provided radiological images of the cranial vault bone structure modifications, correlating the radiological appearance of the optical canals and nerves and of the cerebellum with the neurological manifestations of the disease.

CONCLUSIONS

Our results demonstrate that MRI is a highly sensitive technique that provides excellent images of bone marrow space before and after HSCT without exposing children to ionizing radiation. MRI also permits us to evaluate post-transplant skeletal remodeling and the deriving changes in the hematopoietic and sensory system.

Novel CLCN7 mutations cause autosomal dominant osteopetrosis type II and intermediate autosomal recessive osteopetrosis

Osteopetrosis refers to a group of rare genetic bone diseases that are clinically characterized by increased bone mass and fragility. The principal pathogenic defect in patients with chloride channel 7 (CLCN7) gene‑dependent osteopetrosis is reduced osteoclast activity, which leads to decreased bone resorption. Mutations in the CLCN7 gene result in autosomal dominant osteopetrosis type II (ADO‑II), autosomal recessive osteopetrosis (ARO) and intermediate ARO (IARO). In the present study, eight mutations in the CLCN7 gene were identified in six patients with familial osteopetrosis and one patient with sporadic osteopetrosis. Heterozygous mutations c.856C>T (R286W), c.2236T>G (Y746D), c.296A>G (Y99C) and c.937G>A (E313K), and a splice mutation (c.2232‑2A>G) in the CLCN7 gene were detected in patients with ADO‑II. A homozygous mutation c.2377G>C (G793R), and a compound heterozygous mutation c.1409C>T (P470L) and c.647_648dupTG (K217X) were detected in two Chinese families with IARO. Among these mutations, two heterozygous mutations (c.2236T>G and c.2232‑2A>G), one homozygous mutation (c.2377G>C) and the compound heterozygous mutation (c.1409C>T and c.647_648dupTG) are novel, to the best of our knowledge. The present findings not only broaden the allelic spectrum of CLCN7 mutations, but also provide increased knowledge of the clinical phenotypes observed in Chinese patients with osteopetrosis.

CLCN7 and TCIRG1 mutations in a single family: Evidence for digenic inheritance of osteopetrosis

Osteopetrosis is a monogenic condition with various inheritance patterns, including autosomal dominant, autosomal recessive and X‑linked. Several disease‑causing genes have been identified and three distinguished types of osteopetrosis have been reported. In the present study, a family with osteopetrosis was investigated. Two novel mutations in chloride voltage‑gated channel 7 (CLCN7) and T cell immune regulator 1 (TCIRG1) were identified by exome sequencing, Sanger sequencing and microsatellite marker analysis. The CLCN7 mutation occurred in amino acid R286, the same position as previously reported. The TCIRG1 mutation occurred on a splicing site of exon 15, thereby leading to a truncated transcript. These two mutations were undetected in 496 ethnic‑matched controls. To the best of our knowledge, this is the first report of human osteopetrosis involving digenic inheritance in a single family, which has important implications for decisions on clinical therapeutic regimen, prognosis evaluation and antenatal diagnosis.

Like a hole in the head: Development, evolutionary implications and diseases of the cranial foramina

Cranial foramina are holes in the skull through which nerves and blood vessels pass to reach both deep and superficial tissues. They are often overlooked in the literature; however they are complex structures that form within the developing cranial bones during embryogenesis and then remain open throughout life, despite the bone surrounding them undergoing constant remodelling. They are invaluable in assigning phylogeny in the fossil record and their size has been used, by some, to imply function of the nerve and/or blood vessel that they contained. Despite this, there are very few studies investigating the development or normal function of the cranial foramina. In this review, we will discuss the development of the cranial foramina and their subsequent maintenance, highlighting key gaps in the knowledge. We consider whether functional interpretations can be made from fossil material given a lack of knowledge regarding their contents and maintenance. Finally, we examine the significant role of malformation of foramina in congenital diseases such as craniosynostosis.

Bone Remodeling and the Role of TRAF3 in Osteoclastic Bone Resorption

Skeletal health is maintained by bone remodeling, a process in which microscopic sites of effete or damaged bone are degraded on bone surfaces by osteoclasts and subsequently replaced by new bone, which is laid down by osteoblasts. This normal process can be disturbed in a variety of pathologic processes, including localized or generalized inflammation, metabolic and endocrine disorders, primary and metastatic cancers, and during aging as a result of low-grade chronic inflammation. Osteoclast formation and activity are promoted by factors, including cytokines, hormones, growth factors, and free radicals, and require expression of macrophage-colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) by accessory cells in the bone marrow, including osteoblastic and immune cells. Expression of TNF receptor-associated factor 6 (TRAF6) is required in osteoclast precursors to mediate RANKL-induced activation of NF-κB, which is also necessary for osteoclast formation and activity. TRAF3, in contrast is not required for osteoclast formation, but it limits RANKL-induced osteoclast formation by promoting proteasomal degradation of NF-κB-inducing kinase in a complex with TRAF2 and cellular inhibitor of apoptosis proteins (cIAP). TRAF3 also limits osteoclast formation induced by TNF, which mediates inflammation and joint destruction in inflammatory diseases, including rheumatoid arthritis. Chloroquine and hydroxychloroquine, anti-inflammatory drugs used to treat rheumatoid arthritis, prevent TRAF3 degradation in osteoclast precursors and inhibit osteoclast formation in vitro. Chloroquine also inhibits bone destruction induced by ovariectomy and parathyroid hormone in mice in vivo. Mice genetically engineered to have TRAF3 deleted in osteoclast precursors and macrophages develop early onset osteoporosis, inflammation in multiple tissues, infections, and tumors, indicating that TRAF3 suppresses inflammation and tumors in myeloid cells. Mice with TRAF3 conditionally deleted in mesenchymal cells also develop early onset osteoporosis due to a combination of increased osteoclast formation and reduced osteoblast formation. TRAF3 protein levels decrease in bone and bone marrow during aging in mice and humans. Development of drugs to prevent TRAF3 degradation in immune and bone cells could be a novel therapeutic approach to prevent or reduce bone loss and the incidence of several common diseases associated with aging.

Genetic Analysis of CLCN7 in an Old Female Patient with Type II Autosomal Dominant Osteopetrosis

BACKGROUND

Type II autosomal dominant osteopetrosis (ADO II) is a rare genetically heterogeneous disorder characterized by osteosclerosis and increased bone mass, predominantly involving spine, pelvis, and skull. It is closely related to functional defect of osteoclasts caused by chloride voltage-gated channel 7 (CLCN7) gene mutations. In this study, we aimed to identify the pathogenic mutation in a Korean patient with ADO II using whole exome sequencing.

METHODS

We evaluated the clinical, biochemical, and radiographic analysis of a 68-year-old woman with ADO II. We also performed whole exome sequencing to identify pathogenic mutation of a rare genetic disorder of the skeleton. Moreover, a polymorphism phenotyping program, Polymorphism Phenotyping v2 (PolyPhen-2), was used to assess the effect of the identified mutation on protein function.

RESULTS

Whole exome sequencing using peripheral leukocytes revealed a heterozygous c.296A>G missense mutation in the CLCN7 gene. The mutation was also confirmed using Sanger sequencing. The mutation c.296A>G was regarded to have a pathogenic effect by PolyPhen-2 software.

CONCLUSION

We detect a heterozygous mutation in CLCN7 gene of a patient with ADO II, which is the first report in Korea. Our present findings suggest that symptoms and signs of ADO II patient having a c.296A>G mutation in CLCN7 may appear at a very late age. The present study would also enrich the database of CLCN7 mutations and improve our understanding of ADO II.

Cervical spine fractures in osteopetrosis: a case report and review of the literature

While management of appendicular fractures has been well described in the setting of osteopetrosis, there is limited information on managing fractures of the axial spine. Here we present an osteopetrotic patient with multiple traumatic multiple, comminuted, unstable cervical spinal fractures managed with non-operative stabilization, and provide a review of the pathophysiology, genetic characteristics, and special considerations that must be explored when determining operative versus non-operative management of spinal injury in osteopetrosis. A PubMed query was performed for English articles in the literature published up to June 2016, and used the following search terms alone and in combination: "osteopetrosis", "spine", "fractures", "osteoclasts", and "operative management". Within four months after initial injury, treatment with halo vest allowed for adequate healing. The patient was asymptomatic with cervical spine dynamic radiographs confirming stability at four months. On four-year follow up examination, the patient remained without neck pain, and CT scan demonstrated partially sclerotic fracture lines with appropriate anatomical alignment. In conclusion, external halo stabilization may be an effective option for treatment of multiple unstable acute traumatic cervical spine fractures in patients with osteopetrosis. Given the challenge of surgical stabilization in osteopetrosis, further research is necessary to elucidate the optimal form of treatment in this select patient population.

Loss of p53 compensates osteopenia in murine Mysm1 deficiency

Histone modifications critically contribute to the epigenetic orchestration of bone homeostasis-in part, by modifying the access of transcription factors to specific genes involved in the osteogenic differentiation process of bone marrow mesenchymal stem cells (MSCs) and osteoblasts. Based on our previous finding that histone H2A deubiquitinase 2A-DUB/Mysm1 interacts with the p53 axis in hematopoiesis and tissue development, we analyzed the molecular basis of the skeletal phenotype of Mysm1-deficient mice and dissected the underlying p53-dependent and -independent mechanisms. Visible morphologic, skeletal deformations of young Mysm1-deficient mice-including a kinked and truncated tail and shortened long bones-were associated with osteopenia of long bones. On the cellular level, Mysm1-deficient primary osteoblasts displayed reduced potential to differentiate into mature osteoblasts, as indicated by decreased expression of osteogenic markers. Reduced osteogenic differentiation capacity of Mysm1-deficient osteoblasts was accompanied by an impaired induction of osteogenic transcription factor Runx2. Osteogenic differentiation of Mysm1^-/- MSCs, however, was not compromised in vitro. In line with defective hematopoietic development of Mysm1-deficient mice, Mysm1^-/- osteoclasts had reduced resorption activity and were more prone to apoptosis in TUNEL assays. Skeletal alterations and osteopenia of Mysm1-deficient mice were phenotypically completely rescued by simultaneous ablation of p53 in p53^-/-Mysm1^-/- double-deficient mice-although p53 deficiency did not restore Runx2 expression in Mysm1^-/- osteoblasts on the molecular level but, instead, enhanced proliferation and osteogenic differentiation of MSCs. In summary, our results demonstrate novel roles for Mysm1 in osteoblast differentiation and osteoclast formation, resulting in osteopenia in Mysm1-deficient mice that could be abrogated by the loss of p53 from increased osteogenic differentiation of Mysm1^-/-p53^-/- MSCs.-Haffner-Luntzer, M., Kovtun, A., Fischer, V., Prystaz, K., Hainzl, A., Kroeger, C. M., Krikki, I., Brinker, T. J., Ignatius, A., Gatzka, M. Loss of p53 compensates osteopenia in murine Mysm1 deficiency.

Genetic Risk Factors for Atypical Femoral Fractures (AFFs): A Systematic Review

Atypical femoral fractures (AFFs) are uncommon and have been associated particularly with long‐term antiresorptive therapy, including bisphosphonates. Although the pathogenesis of AFFs is unknown, their identification in bisphosphonate‐naïve individuals and in monogenetic bone disorders has led to the hypothesis that genetic factors predispose to AFF. Our aim was to review and summarize the evidence for genetic factors in individuals with AFF. We conducted structured literature searches and hand‐searching of conference abstracts/reference lists for key words relating to AFF and identified 2566 citations. Two individuals independently reviewed citations for (i) cases of AFF in monogenetic bone diseases and (ii) genetic studies in individuals with AFF. AFFs were reported in 23 individuals with the following 7 monogenetic bone disorders (gene): osteogenesis imperfecta (COL1A1/COL1A2), pycnodysostosis (CTSK), hypophosphatasia (ALPL), X‐linked osteoporosis (PLS3), osteopetrosis, X‐linked hypophosphatemia (PHEX), and osteoporosis pseudoglioma syndrome (LRP5). In 8 cases (35%), the monogenetic bone disorder was uncovered after the AFF occurred. Cases of bisphosphonate‐naïve AFF were reported in pycnodysostosis, hypophosphatasia, osteopetrosis, X‐linked hypophosphatemia, and osteoporosis pseudoglioma syndrome. A pilot study in 13 AFF patients and 268 controls identified a greater number of rare variants in AFF cases using exon array analysis. A whole‐exome sequencing study in 3 sisters with AFFs showed, among 37 shared genetic variants, a p.Asp188Tyr mutation in the GGPS1 gene in the mevalonate pathway, critical to osteoclast function, which is also inhibited by bisphosphonates. Two studies completed targeted ALPL gene sequencing, an ALPL heterozygous mutation was found in 1 case of a cohort of 11 AFFs, whereas the second study comprising 10 AFF cases did not find mutations in ALPL. Targeted sequencing of ALPL, COL1A1, COL1A2, and SOX9 genes in 5 cases of AFF identified a variant in COL1A2 in 1 case. These findings suggest a genetic susceptibility for AFFs. A large multicenter collaborative study of well‐phenotyped AFF cases and controls is needed to understand the role of genetics in this uncommon condition. © 2017 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

[Morphological characteristics of osteopetrosis]

Osteopetrosis is a rare inherited bone disorder characterized by increased bone density owing to failure in bone resorption by the osteoclasts. The disease is genetically and histologically heterogeneous with a wide spectrum of microscopic findings. The histology varies from cases with a total absence of osteoclasts to bone biopsies characterized by high numbers of enlarged multinucleated osteoclasts on a background of sclerotic cancellous bone with or without additional defect of mineralization of the bone matrix. Here we present typical cases of human osteopetrosis on the basis of bone biopsies with four distinct genotypes (mutations of TNFRSF11A, TCIRG1, CNCL7, KINDLIN-3 genes) and discuss genotype-phenotype relationships. Analyzing human bone biopsies of rare skeletal disorders might improve our understanding of bone metabolism with possible implications for the clinical management of other bone diseases.

Decompressive Cranioplasty in a Patient with Osteopetrosis

BACKGROUND

Osteopetrosis is a heterogeneous group of uncommon congenital disorders that causes bony sclerosis and remodeling. Patients who are symptomatic can show significant neurologic consequences with the involvement of cranial nerves and symptoms of increased intracranial pressure (ICP).

CASE DESCRIPTION

We report an unusual case of a 26-year-old woman with an autosomal-dominant type of osteopetrosis who presented with headache and severe visual deterioration, both attributed to increased ICP. A hemicranioplasty was preformed, resulting in the resolution of her symptoms of ICP and stabilization of her vision. Postoperative imaging showed expansion of the ventricles and the subarachnoid spaces with an improvement of the associated cerebellar herniation.

CONCLUSIONS

In conclusion, in patients with symptomatic osteopetrosis, cranioplasty can be considered as an option to treat high ICP-related symptoms.

Guided growth for valgus deformity correction of knees in a girl with osteopetrosis: a case report

Autosomal dominant osteopetrosis (Albers-Schönberg disease) classically displays the radiographic signs of osteosclerosis. The main ADO complications involve the skeleton: low-impact bone fractures, scoliosis and hip osteoarthritis. Management of osteopetrosis-related orthopedic problems is a surgical challenge due to increased bone density. The healing process is very slow in these patients because of bone remodeling defects related to osteoblast function failure. In case of bone deformities, a realignment method should be appropriated to osteopetrosis conditions. This article presents a case report of operative treatment of an 11-year-old girl affected with ADO, who underwent a simultaneous valgus knee deformity correction of both limbs with medial eight-plate epiphysiodesis. Simultaneous correction of valgus deformity on both limbs using an extraperiosteal tension plate technique for medial tibial hemiepiphysiodesis was performed in a girl of 11.5 years old with autosomal dominant osteopetrosis. The treatment duration from surgery to complete deformity correction and removal of plates was 18 months. The final aMPTA was 86° on the right side and 85° on the left side. The correction rate was 0.61°/month (right tibia) and 0.67°/month (left tibia). The MAD correction rate was evaluated as 1.5 mm/month for the right limb and 1.6 mm/month for the left limb. At the moment of plate removal, one screw was broken because of tight fixation in osteopetrotic bone. But it did not compromise the final result. The latest follow-up visit at the age of 14 years 6 months revealed excellent realignment without any deformity relapse. There was no any functional impairment. We consider the guided growth by tension band technique as very interesting and promising solution for treatment of pediatric angular deformity in patients with OP. This method allows to avoid osteotomy and related important risk of delayed union or nonunion frequently observed in osteopetrosis.

Level of evidence: Level IV.

Rapid phenotyping of knockout mice to identify genetic determinants of bone strength

The genetic determinants of osteoporosis remain poorly understood, and there is a large unmet need for new treatments in our ageing society. Thus, new approaches for gene discovery in skeletal disease are required to complement the current genome-wide association studies in human populations. The International Knockout Mouse Consortium (IKMC) and the International Mouse Phenotyping Consortium (IMPC) provide such an opportunity. The IKMC generates knockout mice representing each of the known protein-coding genes in C57BL/6 mice and, as part of the IMPC initiative, the Origins of Bone and Cartilage Disease project identifies mutants with significant outlier skeletal phenotypes. This initiative will add value to data from large human cohorts and provide a new understanding of bone and cartilage pathophysiology, ultimately leading to the identification of novel drug targets for the treatment of skeletal disease.

Debridement in chronic osteomyelitis with benign osteopetrosis: A case report

Osteopetrosis is a rare bone disease caused by metabolic imbalances as a result of genetic mutations. For instance, autosomal dominant osteopetrosis is caused by a missense mutation of the C1CN7 gene. This was first reported in 1904 and is thought to be caused by osteoclastic dysfunction and an impaired bone resorption ability. An accumulation of cortical bone mass during the remodeling of the medullary bone may increase the bone density and give rise to a hard marble consistency. Osteopetrosis can be divided into benign and malignant forms; however, no curative treatment exists for benign osteopetrosis. The management of complications, such as chronic osteomyelitis and fractures, serves a key role in influencing the patient survival rates. Previous studies have demonstrated that a combined treatment of hyperbaric oxygen (HBO) lavage for debridement of the necrotic region and high-dose systemic antibiotics may be effective in the management of osteopetrosis. The present study reported a case of chronic mandible osteomyelitis and fistula occurring in association with maxillary sinusitis, who was successfully treated by through nasal endoscopy, using repeated flushing and cleaning every 2 weeks as a form of debridement, in the absence of high-dose antibiotics and HBO.

Novel CLCN7 mutation identified in a Han Chinese family with autosomal dominant osteopetrosis-2

Osteopetrosis is a heritable bone condition featuring increased bone density due to defective osteoclastic bone resorption. Exome sequencing and Sanger sequencing were conducted in Han Chinese family members, some of whom had typical osteopetrosis, and a novel missense variant c.2350A>T (p.R784W) in the chloride channel 7 gene (CLCN7) was identified. This variant cosegregated with the disorder in the family but was not observed in 800 controls. The data indicate that exome sequencing is a powerful and effective molecular diagnostic tool for detecting mutations in osteopetrosis, which is a genetically and clinically heterogeneous disorder. This discovery broadens the CLCN7 gene mutation spectrum and has important implications for clinical therapeutic regimen decisions, prognosis evaluations, and antenatal diagnoses.

Osteopetrosis in two siblings: two case reports

BACKGROUND

Osteopetrosis is a rare inherited metabolic bone disorder characterized by extensive sclerosis of skeletons, visual and hearing impairment, hepatosplenomegaly and anemia. It has two major clinical forms: the autosomal dominant adult (benign) form is associated with milder symptoms often appearing in later childhood and adulthood whereas the autosomal recessive infantile (malignant) form has severe presentations appearing in very early childhood, if untreated, is typically fatal during infancy or early childhood. A rare autosomal recessive (intermediate) form is present during childhood with some signs and symptoms of malignant osteopetrosis. Diagnosis is mainly based on clinical and typical generalized increase in bone density.

CASE PRESENTATION

The two siblings of Indo-Aryan ethnicity, aged five and 8 years, were admitted with irregular low grade fever and gradually increasing abdominal mass for last 3 years. They also had history of hearing loss. On examination, the patients were found pale with poor nutritional status, short stature, frontal bossing and splenomegaly. We made a clinical diagnosis of hemolytic anemia and investigated accordingly. Peripheral Blood Smear was suggestive of leucoerythroblastic picture in both the siblings. We extended our investigations and radiological survey revealed generalized increase in bone density which was consistent with osteopetrosis.

CONCLUSION

Osteopetrosis is a rare disease transmitted by autosomal dominant or recessive inheritance having variable penetrance. We report here milder form of disease in the two siblings having typical clinical features in the form of anemia, hepatosplenomegaly and hearing loss. Diagnosis was confirmed by typical generalized increase in bone density in both the patients.

Impaired differentiation of macrophage lineage cells attenuates bone remodeling and inflammatory angiogenesis in Ndrg1 deficient mice

N-myc downstream regulated gene 1 (NDRG1) is a responsible gene for a hereditary motor and sensory neuropathy-Lom (Charcot–Marie–Tooth disease type 4D). This is the first study aiming to assess the contribution of NDRG1 to differentiation of macrophage lineage cells, which has important implications for bone remodeling and inflammatory angiogenesis. Ndrg1 knockout (KO) mice exhibited abnormal curvature of the spine, high trabecular bone mass, and reduced number of osteoclasts. We observed that serum levels of macrophage colony-stimulating factor (M-CSF) and macrophage-related cytokines were markedly decreased in KO mice. Differentiation of bone marrow (BM) cells into osteoclasts, M1/M2-type macrophages and dendritic cells was all impaired. Furthermore, KO mice also showed reduced tumor growth and angiogenesis by cancer cells, accompanied by decreased infiltration of tumor-associated macrophages. The transfer of BM-derived macrophages from KO mice into BM-eradicated wild type (WT) mice induced much less tumor angiogenesis than observed in WT mice. Angiogenesis in corneas in response to inflammatory stimuli was also suppressed with decreased infiltration of macrophages. Taken together, these results indicate that NDRG1 deficiency attenuates the differentiation of macrophage lineage cells, suppressing bone remodeling and inflammatory angiogenesis. This study strongly suggests the crucial role of NDRG1 in differentiation process for macrophages.