Diagnosis and Management of Osteopetrosis: Consensus Guidelines From the Osteopetrosis Working Group

Successful completion of orthodontic therapy in a patient with osteopetrosis: Case Report

INTRODUCTION

Orthodontic therapy in patients with osteopetrosis (OP) of the jaws has typically been contraindicated owing to the presence of poorly perfused and extremely compact bone, and the potential risk for infection and osteomyelitis. As such, completed orthodontic cases in association with OP, have rarely been published.

PATIENT CONCERNS

A patient aged 14 years 6 months, with no known diagnosis of OP, sought orthodontic assessment for anterior crowding.

CLINICAL FINDINGS

The patient exhibited a straight facial profile and increased mandibular facial height, competent lips, shallow mentolabial sulcus with mild mentalis strain, flat/reverse smile arc and wide buccal corridors on smiling.Primary diagnosis:The patient had a Class I incisor relationship on Class 1 skeletal bases with bilateral Class I molars and Class II canine relationships. This was complicated by a crossbite involving the lateral incisors and a Bolton discrepancy due to small maxillary lateral incisors. A radiologic assessment revealed polyostotic OP of the oromaxillofacial complex.

INTERVENTIONS

Treatment consisted of maxillary and mandibular fixed orthodontic therapy, bite turbos and elastics to level and align the dentition. Extractions of permanent teeth were not needed.

OUTCOMES

At the conclusion of treatment, there was a slight left Class II malocclusion, with incomplete intercuspation on the left side due to tooth size discrepancy, possibly attributed to inadequate elastics compliance and the presence of osteopetrotic bone. The treatment was completed in 3 years, 1 year longer than anticipated.

CONCLUSION

This report represents the second published account of a patient with OP successfully managed with comprehensive orthodontic care and without osseous complications. Obtaining cephalometric measurements on OP-affected patients may be imprecise owing to the presence of extremely dense bone and difficulty to identify bony landmarks. To reduce osteopetrotic sequelae, attending clinicians should consider reduced exertional orthodontic forces and closely monitor patients for adverse alveolar events.

Adoptive Transfer of Lepr+ Bone Marrow Cells Attenuates the Osteopetrotic Phenotype of db/db Mice

Leptin-deficient (ob/ob) and leptin receptor (Lepr)-deficient db/db mice develop a mild form of osteoclast-rich osteopetrosis, most evident in long bone epiphyses, implying leptin is important for normal replacement of cartilage during skeletal maturation. However, it is unclear whether leptin acts as a permissive or regulatory factor and whether its actions are mediated via peripheral pathways. Here we show the osteopetrotic phenotype is not evident in ob/+ or db/+ mice, suggesting that leptin acts as a critical but permissive factor for skeletal maturation. The importance of leptin is further supported by our results showing that interventions known to increase bone resorption (mild cold stress, simulated microgravity, or particle-induced inflammation) did not advance skeletal maturation in ob/ob mice whereas long-duration hypothalamic leptin gene therapy was effective. Additionally, administration of leptin by subcutaneously implanted osmotic pumps (400 ng/h) for 2 weeks accelerated skeletal maturation in ob/ob mice. Because leptin has the potential to act on the skeleton through peripheral pathways, we interrogated osteoclast-lineage cells for the presence of Lepr and evaluated skeletal response to the introduction of bone marrow Lepr+ cells into db/db mice. We identified Lepr on marrow MCSFR+CD11b+ osteoclast precursors and on osteoclasts generated in vitro. We then adoptively transferred Lepr+ marrow cells from GFP mice or wildtype (WT) mice into Lepr-db/db mice. Following engraftment, most MCSFR+ CD11b+ cells in marrow expressed GFP. Whereas db/db→db/db had minimal influence on epiphyseal cartilage, WT→db/db decreased cartilage. These findings suggest peripheral leptin signaling is required for normal osteoclast-dependent replacement of cartilage by bone during skeletal maturation.

Identification of a novel mutation in the CLCN7 gene in pediatric osteopetrosis: case report

Osteopetrosis, also known as osteosclerosis and marble-bone disease, is a rare genetic metabolic bone disorder caused by the dysplasia or dysfunction of osteoclasts, usually caused by variants of chloride voltage-gated channel 7 (CLCN7) gene. We retrospectively analyzed the clinical data of two children with osteopetrosis and their families. Whole-exome sequencing (WES) was used for genetic analysis, and Sanger sequencing confirmed possible pathogenic variants. In family 1, the proband harbored a novel mutation c.2351G>C (p.R784T) in CLCN7 gene. The initial symptom of proband 1 was a post-traumatic fracture, and imaging features was "sandwich cake" -like changes. In family 2, the proband harbored previously reported compound heterozygous variants in CLCN7 gene: c.899C>T (p.A300V) and c.1534G>A (p.G512R). Among them, c.1534G>A (p.G512R) was only recorded in clinvar and no reports of protein function prediction. The initial symptom of proband 2 was cough, and imaging features was "sandwich vertebrae". Our study expands the mutation spectrum of the CLCN7 gene and provides new insights into the pathogenesis of osteopetrosis.

Rare Cause of Bone Marrow Failure: Osteopetrosis, Case Series

Osteopetrosis is a rare metabolic bone disease that can lead to progressive bone marrow failure if left untreated. Resulting cytopenia and extramedullary hematopoiesis are frequently encountered in autosomal recessive form of the disease (ARO) and may result in death. Recurrent bone fractures and skeletal deformities are mostly seen in autosomal dominant form osteopetrosis (ADO) and cause significant morbidity. In this report, clinical, laboratory, and radiological findings of 5 patients with osteopetrosis were presented. Three had cytopenias, typical peripheral smear, and bone marrow aspiration findings regarding bone marrow failure as well as extensively increased bone density which was a classical radiological appearance. Two of them had TCIRG1 mutations associated with ARO, died because of severe infections. One with certain findings of ARO without genetic analysis is alive after hematopoietic stem cell transplantation. Two siblings had novel variants of CLCN7 (NM_001114331) p.Val755Serfs*4 (c.2263del) heterozygocity, associated with ADO and severe skeletal problems. One had been followed up also for nephrotic syndrome. Detection of genetic abnormalities is important as well as typical physical examination findings and, presence of hematological or radiological indicators in definitive diagnosis of the disease. Although osteopetrosis is rare, it is a potentially fatal disease that should be considered in the differential diagnosis.

Patient-Reported Outcomes in Autosomal Dominant Osteopetrosis: Findings From the Osteopetrosis Registry Study

CONTEXT

Autosomal dominant osteopetrosis (ADO) is a rare sclerotic bone disease characterized by impaired osteoclast activity, resulting in high bone mineral density and skeletal fragility. The full phenotype and disease burden on patients' daily lives has not been systematically measured.

OBJECTIVE

We developed an online registry to ascertain population-based data on the spectrum and rate of progression of disease and to identify relevant patient-centered outcomes that could be used to measure treatment effects and guide the design of future clinical trials.

METHODS

Cross-sectional data from participants with osteopetrosis were collected using an online REDCap-based database. Thirty-four participants with a confirmed diagnosis of ADO, aged 4-84 years were included. Participants aged 18 years and older completed the PROMIS 57, participants aged 8-17 years completed the PROMIS Pediatric 49, and parents of participants aged <18 years completed the PROMIS Parent Proxy 49.

RESULTS

Based on the PROMIS 57, relative to the general population, adults with ADO reported low physical function and low ability to participate in social roles and activities, and high levels of anxiety, fatigue, sleep problems, and pain interference. Daily pain medications were reported by 24% of the adult population. In contrast, neither pediatric participants nor their parent proxy reported a negative impact on health-related quality of life.

CONCLUSION

Data from this registry demonstrate the broad spectrum of ADO disease severity and high impact on health-related quality of life in adults with ADO.

Metabolomics study of osteopetrosis caused by CLCN7 mutation reveals novel pathway and potential biomarkers

Objective

CLCN7 mutation caused abnormal osteoclasts, resulting in osteopetrosis. Depending on the type of mutation, CLCN7 mutations can lead to severe or relatively benign forms of osteopetrosis. However, the serum metabolic alterations in osteopetrosis caused by CLCN7 mutation are still unknown. We aimed to investigate the differences in the metabolome of osteopetrosis patients caused by CLCN7 mutation versus healthy controls (HC), uncovering potential subtype diagnosis biomarkers.

Methods

19 osteopetrosis patients caused by CLCN7 mutation and 19 HC were recruited for liquid chromatography-tandem mass spectrometry analysis. The screened pathway was validated in the myeloid cell specific Clcn7G763R mutant mouse model by quantitative real-time PCR analysis.

Results

Three metabolic pathways were significantly enriched, including glycerophospholipid metabolism (P=0.036948), arachidonic acid metabolism (P=0.0058585) and linoleic acid metabolism (P=0.032035). Ten differential expressed metabolites were located in these three pathways and classified ability with areas under the curve over 0.7 in receiver operating characteristic analysis, suggesting a certain accuracy for being the potential biological markers. Especially, we found that the proteins in glycerophospholipid metabolism were predicted to interact with ClC-7 and further verified that the expression of coding genes were significantly up-regulated in myeloid cell specific Clcn7G763R mutant mouse.

Conclusion

This study provides data on serum metabolomics in osteopetrosis caused by CLCN7 mutation and provides new potential metabolic markers and pathways for diagnosis and pathogenesis of osteopetrosis.

Spontaneous Anterior Arch Fracture of the Atlas Following C1 Laminectomy in a Patient With Osteopetrosis: A Case With Five Years of Follow-Up

Osteopetrosis is a rare group of genetic disorders characterized by excessive bone density due to impaired osteoclast function and can lead to various complications, including fractures and immune dysfunction. We describe the case of a 63-year-old man with osteopetrosis who presented with cervical discomfort and was diagnosed with an anterior arch fracture of the atlas, a rare spontaneous fracture following C1 laminectomy. Initially, no neurological abnormalities were observed, and imaging confirmed the continuity of the transverse ligament. Thus, the decision was made to follow the natural course in the absence of instability. Conservative treatment with a cervical collar was initiated, and the fracture gap began to fill by three years postoperatively, though nonunion persisted at five years. The patient remained asymptomatic and did not require further surgical intervention. This case highlights that stress concentrated on the anterior arch of the atlas due to the unique bone quality in osteopetrosis, and the subsequent natural course of the fracture did not require additional surgical treatment. Careful follow-up is essential to monitor for any pathological changes.

A comprehensive report of the clinical and mutational profiles of 30 Iranian malignant infantile osteopetrosis patients

Osteopetrosis is a group of genetically and clinically diverse inherited disorders characterized by an increase in bone density. The main known cause is an abnormality in the development or function of osteoclasts. Hence, the process of bone resorption is impaired, resulting in: 1- a reduction in bone marrow volume and, subsequently, a decrement in the hematopoietic capacity of bone marrow, which leads to anemia and compromised immunological function; 2- improper bone development, which leads to pressure on peripheral nerves, causing auditory, visual, and movement impairments; and 3- disturbance in the formation of bone microstructure that leads to susceptibility to bone fracture. This study aimed to evaluate the clinical symptoms and genetic causes of 30 patients (probands) who suffered from malignant infantile osteopetrosis, a subtype of this disorder. The Sanger sequencing technique was used to sequence four common genes (TCIRG1, CLCN7, SNX10, and OSTM1) in osteopetrosis. Subsequently, the selected variants were subjected to segregation analysis between the probands and their parents. Consequently, the sequencing of these four genes in probands revealed 16 pathogenic and likely pathogenic mutations, five of which had never been reported before. The TCIRG1 gene has three novel splice site variations and one frameshift variant. The CLCN7 gene had a novel missense variant. Also, a total of five variants of uncertain significance (VUSs) were identified in the analyzed sequences, of which three haven't been reported to date, and two were observed in osteopetrosis patients. Therefore, by documenting these novel likely pathogenic variants and VUS in known genes associated with this disease in patients, specialists can conduct more accurate genetic analysis and counseling when encountering these variants. Additionally, this documentation will facilitate the reclassification of these variants.

The Use of Bone Biomarkers, Imaging Tools, and Genetic Tests in the Diagnosis of Rare Bone Disorders

Rare bone diseases are clinically and genetically heterogenous. Despite those differences, the underlying pathophysiology is not infrequently different. Several of these diseases are characterized by abnormal bone metabolism and turnover with subsequent abnormalities in markers of bone turnover, rendering them useful adjuncts in the diagnostic process. As most rare bone diseases are inherited, genetic testing for implicated pathogenic variants, where known, is another relevant tool that can aid in diagnosis. While some skeletal disorders can be localized or monostotic, others can involve multiple skeletal sites and warrant imaging tools to localize them and determine the severity of disease and/or presence of complications as well as to assess bone quality and the potential risk of fractures. Rare bone disorders pose a great challenge in their diagnosis, ultimately resulting in delayed diagnosis, higher risk of complications and a poor quality of life in affected individuals. In this review we discuss the biochemical and radiological tools that can be utilized to diagnose selected orphan bone disorders, the clinical utility and limitations of these diagnostic tools, and areas where future research is warranted.

A trend of osteocalcin in diabetes mellitus research: bibliometric and visualization analysis

Background

Osteocalcin has attracted attention for its potential role in diabetes management. However, there has been no bibliometric assessment of scientific progress in this field.

Methods

We analysed 1680 articles retrieved from the Web of Science Core Collection (WoSCC) between 1 January 1986 and 10 May 2024 using various online tools.

Result

These papers accumulated 42,714 citations,with an average of 25.43 citations per paper. Publication output increased sharply from 1991 onwards. The United States and China are at the forefront of this research area.

Discussion

The keywords were grouped into four clusters: 'Differential and functional osteocalcin genes', 'Differential expression of osteocalcin genes in relation to diabetes mellitus', 'Role of osteocalcin in the assessment of osteoporosis and diabetes mellitus', and 'Indirect involvement of osteocalcin in metabolic processes'. Analysis using the VoS viewer suggests a shift in research focus towards the correlation between osteocalcin levels and diabetic complications, the clinical efficacy of therapeutic agents or vitamins in the treatment of osteoporosis in diabetic patients, and the mechanisms by which osteocalcin modulates insulin action. The proposed focus areas are "osteocalcin genes", "insulin regulation and osteoporosis ", "different populations", "diabetes-related complications" and "type 2 diabetes mellitus","effect of osteocalcin expression on insulin sensitivity as well as secretion","osteocalcin expression in different populations of diabetic patients and treatment-related studies".

Extracellular derivatives for bone metabolism

BACKGROUND

Bone metabolism can maintain the normal homeostasis and function of bone tissue. Once the bone metabolism balance is broken, it will cause osteoporosis, osteoarthritis, bone defects, bone tumors, or other bone diseases. However, such orthopedic diseases still have many limitations in clinical treatment, such as drug restrictions, drug tolerance, drug side effects, and implant rejection.

AIM OF REVIEW

In complex bone therapy and bone regeneration, extracellular derivatives have become a promising research focus to solve the problems of bone metabolic diseases. These derivatives, which include components such as extracellular matrix, growth factors, and extracellular vesicles, have significant therapeutic potential. It has the advantages of good biocompatibility, low immune response, and dynamic demand for bone tissue. The purpose of this review is to provide a comprehensive perspective on extracellular derivatives for bone metabolism and elucidate the intrinsic properties and versatility of extracellular derivatives. Further discussion of them as innovative advanced orthopedic materials for improving the effectiveness of bone therapy and regeneration processes.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, we first listed the types and functions of three extracellular derivatives. Then, we discussed the effects of extracellular derivatives of different cell sources on bone metabolism. Subsequently, we collected applications of extracellular derivatives in the treatment of bone metabolic diseases and summarized the advantages and challenges of extracellular derivatives in clinical applications. Finally, we prospected the extracellular derivatives in novel orthopedic materials and clinical applications. We hope that the comprehensive understanding of extracellular derivatives in bone metabolism will provide new solutions to bone diseases.

Unusual presentation of chronic headaches revealing osteopetrosis: A case report

Osteopetrosis, also known as the disease of marbled bones, refers to a group of constitutional bone diseases resulting from a defect in bone metabolism. This condition is characterized by its manifestation, most often at a young age, and is typically revealed by its complications, primarily fractures. Diagnosis is currently confirmed through genetics but also relies on imaging such as standard radiography and computed tomography. We report the case of a child, aged 13 years, presenting with osteopetrosis revealed by atypical symptoms, confirmed by computed tomography imaging mainly in our country in Morocco where access to care is sometimes difficult for some patients.

Osteopetrosis-like disorders induced by osteoblast-specific retinoic acid signaling inhibition in mice

Osteopetrosis is an inherited metabolic disease, characterized by increased bone density and narrow marrow cavity. Patients with severe osteopetrosis exhibit abnormal bone brittleness, anemia, and infection complications, which commonly cause death within the first decade of life. Pathologically, osteopetrosis impairs not only the skeletal system, but also the hemopoietic and immune systems during development, while the underlying osteoimmunological mechanisms remain unclear. Osteoclastic mutations are regarded as the major causes of osteopetrosis, while osteoclast non-autonomous theories have been proposed in recent years with unclear underlying mechanisms. Retinoic acid (RA), the metabolite of Vitamin A, is an essential requirement for skeletal and hematopoietic development, through the activation of retinoic acid signaling. RA can relieve osteopetrosis symptoms in some animal models, while its effect on bone health is still controversial and the underlying mechanisms remain unclear. In this study, we constructed an osteoblast-specific inhibitory retinoic acid signaling mouse model and surprisingly found it mimicked the symptoms of osteopetrosis found in clinical cases: dwarfism, increased imperfectly-formed trabecular bone deposition with a reduced marrow cavity, thin cortical bone with a brittle skeleton, and hematopoietic and immune dysfunction. Micro-CT, the three-point bending test, and histological analysis drew a landscape of poor bone quality. Single-cell RNA sequencing (scRNA-seq) of the femur and RNA-seq of osteoblasts uncovered an atlas of pathological skeletal metabolism dysfunction in the mutant mice showing that osteogenesis was impaired in a cell-autonomous manner and osteoclastogenesis was impaired via osteoblast-osteoclast crosstalk. Moreover, scRNA-seq of bone marrow and flow cytometry of peripheral blood, spleen, and bone marrow uncovered pathology in the hematopoietic and immune systems in the mutant mice, mimicking human osteopetrosis. Results showed that hematopoietic progenitors and B lymphocyte differentiation were affected and the osteoblast-dominated cell crosstalk was impaired, which may result from transcriptional impairment of the ligands Pdgfd and Sema4d. In summary, we uncovered previously unreported pathogenesis of osteopetrosis-like disorder in mice with skeletal, hematopoietic, and immune system dysfunction, which was induced by the inhibition of retinoic acid signaling in osteoblasts, and sheds new insights into a potential treatment for osteopetrosis.

Beyond resorption: osteoclasts as drivers of bone formation

Emerging evidence illustrates that osteoclasts (OCs) play diverse roles beyond bone resorption, contributing significantly to bone formation and regeneration. Despite this, OCs remain mysterious cells, with aspects of their lifespan-from origin, fusion, alterations in cellular characteristics, to functions-remaining incompletely understood. Recent studies have identified that embryonic osteoclastogenesis is primarily driven by osteoclast precursors (OCPs) derived from erythromyeloid progenitors (EMPs). These precursor cells subsequently fuse into OCs essential for normal bone development and repair. Postnatally, hematopoietic stem cells (HSCs) become the primary source of OCs, gradually replacing EMP-derived OCs and assuming functional roles in adulthood. The absence of OCs during bone development results in bone structure malformation, including abnormal bone marrow cavity formation and shorter long bones. Additionally, OCs are reported to have intimate interactions with blood vessels, influencing bone formation and repair through angiogenesis regulation. Upon biomaterial implantation, activation of the innate immune system ensues immediately. OCs, originating from macrophages, closely interact with the immune system. Furthermore, evidence from material-induced bone formation events suggests that OCs are pivotal in these de novo bone formation processes. Nevertheless, achieving a pure OC culture remains challenging, and interpreting OC functions in vivo faces difficulties due to the presence of other multinucleated cells around bone-forming biomaterials. We here describe the fusion characteristics of OCPs and summarize reliable markers and morphological changes in OCs during their fusion process, providing guidance for researchers in identifying OCs both in vitro and in vivo. This review focuses on OC formation, characterization, and the roles of OCs beyond resorption in various bone pathophysiological processes. Finally, therapeutic strategies targeting OCs are discussed.

Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning

Introduction

Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function. Most of the cases are due to TCIRG1 gene mutation, leading to severe bone phenotype and death in the first years of life. The standard therapy is the hematopoietic stem cell transplantation (HSCT), but its success is limited by several constraints. Conversely, gene therapy (GT) could minimize the immune-mediated complications of allogeneic HSCT and offer a prompt treatment to these patients.

Methods

The Tcirg1-defective oc/oc mouse model displays a short lifespan and high bone density, closely mirroring the human condition. In this work, we exploited the oc/oc neonate mice to optimize the critical steps for a successful therapy.

Results

First, we showed that lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis. Then, we demonstrated that plerixafor-induced mobilization can further increase the high number of HSPCs circulating in peripheral blood, facilitating the collection of adequate numbers of cells for therapeutic purposes. Finally, pre-transplant non-genotoxic conditioning allowed the stable engraftment of HSPCs, albeit at lower level than conventional total body irradiation, and led to long-term survival and correction of bone phenotype, in the absence of acute toxicity.

Conclusion

These results will pave the way to the implementation of an effective GT protocol, reducing the transplant-related complication risks in the very young and severely affected ARO patients.

Infantile osteopetrosis with delayed development, organomegaly and wandering eyes: case report

Osteopetrosis encompasses rare inherited metabolic bone disorders with defect in the osteoclast activity. Severe forms of presentation such as malignant infantile osteopetrosis are seen in infants and milder forms in older children. The clinical presentation includes failure to thrive, severe pallor, optic atrophy and hepatosplenomegaly. The disorder is characterised by dense bone on radiography, hence the name marble bone disease. A 10-month-old boy who presented with developmental delay, failure to thrive, nystagmus (which the mother described as wandering eye movements), splenomegaly of 16 cm and hepatomegaly of 8 cm. Investigations demonstrated severe anaemia (5.7 g/dL) and thrombocytopenia (34 x 109/L). Radiological signs which help in the diagnosis include diffuse sclerosis, bone within bone appearance, sandwich vertebrae and Erlenmeyer flask deformity. Plain radiography is an easily available and cost effective tool which can aid in the diagnosis of osteopetrosis.

Effect of Allele-Specific Clcn7G213R siRNA Delivered Via a Novel Nanocarrier on Bone Phenotypes in ADO2 Mice on 129S Background

Autosomal dominant osteopetrosis type 2 (ADO2) is a rare inherited bone disorder characterised by dense but brittle bones. It displays striking phenotypic variability, with the most severe symptoms, including blindness and bone marrow failure. Disease management largely relies on symptomatic treatment since there is no safe and effective treatment. Most ADO2 cases are caused by heterozygous loss-of-function mutations in the CLCN7 gene, which encodes an essential Cl-/H+ antiporter for proper bone resorption by osteoclasts. Thus, siRNA-mediated silencing of the mutant allele is a promising therapeutic approach, but targeting bone for first-in-human translation remains challenging. Here, we demonstrate the utility of silicon-stabilised hybrid lipid nanoparticles (sshLNPs) as a next-generation nucleic acid nanocarrier capable of delivering allele-specific siRNA to bone. Using a Clcn7G213R knock-in mouse model recapitulating one of the most common human ADO2 mutations and based on the 129S genetic background (which produces the most severe disease phenotype amongst current models), we show substantial knockdown of the mutant allele in femur when siRNA targeting the pathogenic variant is delivered by sshLNPs. We observed lower areal bone mineral density in femur and reduced trabecular thickness in femur and tibia, when siRNA-loaded sshLNPs were administered subcutaneously (representing the most relevant administration route for clinical adoption and patient adherence). Importantly, sshLNPs have improved stability over conventional LNPs and enable 'post hoc loading' for point-of-care formulation. The treatment was well tolerated, suggesting that sshLNP-enabled gene therapy might allow successful clinical translation of essential new treatments for ADO2 and potentially other rare genetic bone diseases.

Molecular Heterogeneity of Osteopetrosis in India: Report of 17 Novel Variants

Osteopetrosis is a clinically and genetically heterogeneous group of inherited bone disorders that is caused by defects in osteoclast formation or function. Treatment options vary with the disease severity and an accurate molecular diagnosis helps in prognostication and treatment decisions. We investigated the genetic causes of osteopetrosis in 31 unrelated patients of Indian origin. Screening for the genetic variants was done by Sanger sequencing or next generation sequencing in 48 samples that included 31 samples from index patients, 16 from parents' and 1 chorionic villus sample. A total of 30 variants, including 29 unique variants, were identified in 26 of the 31 patients in the study. TCIRG1 was the most involved gene (n = 14) followed by TNFRSF11A (n = 4) and CLCN7 (n = 3). A total of 17 novel variants were identified. Prenatal diagnosis was done in one family and the foetus showed homozygous c.807 + 2T > G variant in TCIRG1. Molecular diagnosis of osteopetrosis aids in therapeutic decisions including the need for a stem cell transplantation and gives a possible option of performing prenatal diagnosis in affected families. Further studies would help in understanding the genetic etiology in patients where no variants were identified.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-023-01732-4.

Genetic testing confirmed osteopetrosis with initial presentation of nystagmus

Osteopetrosis (OS) is a rare heritable disorder characterized by osteoclast dysfunction and increased bone density on radiography. Optic nerve osseous compression is the most frequent ocular complication of OS, with nystagmus, strabismus, ptosis, proptosis, and lagophthalmos occurring less frequently. However, it is uncommon for patients to have neurological or ocular symptoms at initial presentation. Herein, we present the case of a 3-year-old girl with the initial presentation of ocular symptoms who was confirmed to have OS through genetic testing. She was born full-term and found to have nystagmus since the age of 1 year. Her best-corrected visual acuity was 1.2/60 for both eyes. Exotropia of the left eye and bilateral small-amplitude pendular nystagmus were also noted. Color fundoscopy revealed a tessellated fundus and pale discs with cup-to-disc ratios of 0.5-0.6. Magnetic resonance imaging revealed bilateral optic canal stenosis and optic nerve atrophy. Whole-exome sequencing revealed a biallelic chloride voltage-gated channel 7 mutation, c.2297T > C (p.Leu766Pro) and c.1577G > A (p.Arg526Gln), and autosomal recessive OS was diagnosed. The patient is currently being evaluated for possible hematopoietic stem cell transplantation. We suggest that OS should be considered a differential diagnosis for unexplained nystagmus and optic nerve atrophy.

Osteopetrosis in the pediatric patient: what the radiologist needs to know

Osteopetrosis describes several types of rare sclerosing bone dysplasias of varying clinical and radiographic severity. The classic autosomal dominant subtype emerges most often in adolescence but can present from infancy through adulthood. The autosomal recessive osteopetrosis, or "malignant infantile osteopetrosis," presents in infancy with a grimmer prognosis, though the autosomal dominant forms (often mislabeled as "benign") actually can have life-threatening consequences as well. Often osteopetrosis is detected due to skeletal findings on radiographs performed to evaluate injury or as an incidental finding during evaluation for illness. Given the varied phenotypic severity and presentations at different ages, radiologists play an integral role in the care of these patients both in diagnosis and in clinical evaluation and monitoring. A deeper understanding of the underlying genetic basis of the disease can aid in the radiologist in diagnosis and in anticipation of unique complications. An overview of current clinical management is also discussed.

Osteopetrosis and related osteoclast disorders in adults: A review and knowledge gaps On behalf of the European calcified tissue society and ERN BOND

Osteopetrosis refers to a group of related rare bone diseases characterized by a high bone mass due to impaired bone resorption by osteoclasts. Despite the high bone mass, skeletal strength is compromised and the risk of fracture is high, particularly in the long bones. Osteopetrosis was classically categorized by inheritance pattern into autosomal recessive forms (ARO), which are severe and diagnosed within the first years of life, an intermediate form and an autosomal dominant (ADO) form; the latter with variable clinical severity and typically diagnosed during adolescence or in young adulthood. Subsequently, the AD form was shown to be a result of mutations in the gene CLCN7 encoding for the ClC-7 chloride channel). Traditionally, the diagnosis of osteopetrosis was made on radiograph appearance alone, but recent molecular and genetic advances have enabled a greater fidelity in classification of osteopetrosis subtypes. In the more severe ARO forms (e.g., malignant infantile osteopetrosis MIOP) typical clinical features have severe consequences and often result in death in early childhood. Major complications of ADO are atypical fractures with delay or failure of repair and challenge in orthopedic management. Bone marrow failure, dental abscess, deafness and visual loss are often underestimated and neglected in relation with lack of awareness and expertise. Accordingly, the care of adult patients with osteopetrosis requires a multidisciplinary approach ideally in specialized centers. Apart from hematopoietic stem cell transplantation in certain infantile forms, the treatment of patients with osteopetrosis, has not been standardized and remains supportive. Further clinical studies are needed to improve our knowledge of the natural history, optimum management and impact of osteopetrosis on the lives of patients living with the disorder.

Management of Osteomyelitis in Autosomal Dominant Osteopetrosis: A Rare Case Report

Albers-Schönberg disease, also known as osteopetrosis or marble bone disease, is a rare genetic disorder characterised by increased cortical bone mass due to dysfunctional osteoclast cells. This case report presents a 34-year-old male with autosomal dominant osteopetrosis (ADO), who was referred for evaluation and treatment of a chronic mandibular abscess with associated osteomyelitis and fistula. The patient's medical history included multiple fractures necessitating open reduction and internal fixation. Radiological examinations revealed the presence of chronic osteomyelitis in the mandible, marked by an increase in bone density and obliteration of medullary spaces. The treatment approach included surgical debridement, extraction of adjacent teeth, sequestrectomy, and antibiotic therapy. Notably, Enterobacter cloacae bacteria were identified through culture, leading to a tailored antibiotic regimen. Follow-up assessments, including clinical photographs and postoperative CT scans, were conducted to monitor the patient's progress. Histopathological examination confirmed osteomyelitis showing both viable and non-viable bone, surrounded by significant inflammatory infiltrate. This case underscores the complexity of managing osteomyelitis in patients with osteopetrosis and highlights the importance of early diagnosis, particularly before dental extractions, to prevent disease exacerbation. The rarity of this condition emphasises the need for further research and awareness among healthcare providers for optimal patient care.

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.

Management of RANKL-mediated Disorders With Denosumab in Children and Adolescents: A Global Expert Guidance Document

CONTEXT

Denosumab is an effective treatment for many receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated disorders but there are potential safety considerations and limited data to guide its use in children and adolescents.

OBJECTIVE

This document seeks to summarize the evidence and provide expert opinion on safe and appropriate use of denosumab in pediatric RANKL-mediated disorders.

PARTICIPANTS

Ten experts in pediatric bone and mineral medicine from 6 countries with experience in the use of denosumab participated in the creation of this document.

EVIDENCE

Data were sourced from the published literature, primarily consisting of case reports/series and review articles because of the lack of higher level evidence. Expert opinion of the authors was used substantially when no published data were available.

CONCLUSION

Denosumab is an effective treatment for RANKL-mediated disorders in children and adolescents but is often not curative and, in some cases, is best used in conjunction with surgical or other medical treatments. Careful multidisciplinary planning is required to define the goals of treatment and expert oversight needed to manage the risk of mineral abnormalities. Substantive, collaborative research efforts are needed to determine optimal treatment regimens and minimize risks.

Osteopetrorickets: two contradictory patterns-one unifying diagnosis

A 5-month-old infant with bone findings on x-ray presented an apparent contradiction including findings of both diffusely dense bones and rickets in the context of a history and laboratory investigation that suggested leukemia. Next generation gene panel sequencing revealed a TCIRG1 mutation which is consistent with autosomal recessive osteopetrosis. The paradoxical x-ray findings underscore a recently elucidated mechanism for the pathogenesis of a TCIRG mutation. This case highlights the importance of recognizing this radiographic, seeming contradictory, association in the context of a confusing clinical presentation. Failure to recognize this pattern promptly may lead to a delay in diagnosis, thus potentially permanent organ failure.

Current knowledge of bone-derived factor osteocalcin: its role in the management and treatment of diabetes mellitus, osteoporosis, osteopetrosis and inflammatory joint diseases

Osteocalcin (OC) is the most abundant non-collagenous and osteoblast-secreted protein in bone. It consists of two forms such as carboxylated OC (cOC) and undercarboxylated OC (ucOC). While cOC promotes bone mineralization and increases bone strength, ucOC is regarded an endocrinologically active form that may have several functions in multiple end organs and tissues. Total OC (tOC) includes both of these forms (cOC and ucOC) and is considered a marker of bone turnover in clinical settings. Most of the data on OC is limited to preclinical studies and therefore may not accurately reflect the situation in clinical conditions. For the stated reason, the aim of this review was not only to summarize current knowledge of all forms of OC and characterize its role in diabetes mellitus, osteoporosis, osteopetrosis, inflammatory joint diseases, but also to provide new interpretations of its involvement in the management and treatment of aforementioned diseases. In this context, special emphasis was placed on available clinical trials. Significantly lower levels of tOC and ucOC could be associated with the risk of type 2 diabetes mellitus. On the contrary, tOC level does not seem to be a good indicator of high bone turnover status in postmenopausal osteoporosis, osteoarthritis and rheumatoid arthritis. The associations between several pharmacological drugs used to treat all disorders mentioned above and OC levels have also been provided. From this perspective, OC may serve as a medium through which certain medications can influence glucose metabolism, body weight, adiponectin secretion, and synovial inflammation.

[Research Progress in the Regulatory Role of circRNA-miRNA Network in Bone Remodeling]

The dynamic balance between bone formation and bone resorption is a critical process of bone remodeling. The imbalance of bone formation and bone resorption is closely associated with the occurrence and development of various bone-related diseases. Under both physiological and pathological conditions, non-coding RNAs (ncRNAs) play a crucial regulatory role in protein expression through either inhibiting mRNAs translation or promoting mRNAs degradation. Circular RNAs (circRNAs) are a type of non-linear ncRNAs that can resist the degradation of RNA exonucleases. There is accumulating evidence suggesting that circRNAs and microRNAs (miRNAs) serve as critical regulators of bone remodeling through their direct or indirect regulation of the expression of osteogenesis-related genes. Additionally, recent studies have revealed the involvement of the circRNAs-miRNAs regulatory network in the process by which mesenchymal stem cells (MSCs) differentiate towards the osteoblasts (OB) lineage and the process by which bone marrow-derived macrophages (BMDM) differentiate towards osteoclasts (OC). The circRNA-miRNA network plays an important regulatory role in the osteoblastic-osteoclastic balance of bone remodeling. Therefore, a thorough understanding of the circRNA-miRNA regulatory mechanisms will contribute to a better understanding of the regulatory mechanisms of the balance between osteoblastic and osteoclastic activities in the process of bone remodeling and the diagnosis and treatment of related diseases. Herein, we reviewed the functions of circRNA and microRNA. We also reviewed their roles in and the mechanisms of the circRNA-miRNA regulatory network in the process of bone remodeling. This review provides references and ideas for further research on the regulation of bone remodeling and the prevention and treatment of bone-related diseases.

Demystifying Skeletal Dysplasias: A Practical Approach for the Pediatric Endocrinologist

BACKGROUND

Skeletal dysplasias encompass a group of genetic conditions associated with cartilaginous and bone tissue abnormalities, exhibiting a variable phenotype depending on the involved genes and mechanisms. Differential diagnosis is challenging as there are many skeletal dysplasias with similar phenotypes.

SUMMARY

In this review, we describe the physiology of skeletal development and the classification of skeletal dysplasias, followed by a practical approach to the workup of a child with suspected skeletal dysplasia. Diagnosis requires clinical, laboratory, and radiological evaluation to differentiate potential conditions in the patient. Genotyping has emerged as a confirmatory tool in many cases, enabling personalized treatment through a multidisciplinary approach and assessment of associated comorbidities.

KEY MESSAGES

As skeletal dysplasias often present with short stature, proportionate or disproportionate, the pediatric endocrinologist plays a crucial role in initial investigative and diagnostic guidance. Identifying the critical clinical manifestations, conducting appropriate initial screening tests, and referring for multidisciplinary follow-up contribute to expeditious diagnosis and family support.

Early Recovery of Physical Function After Total Hip Arthroplasty in a Patient With Osteopetrosis: A Case Report

Osteopetrosis is an uncommon and inherited disorder. Some disease-specific characteristics, such as diffuse osteosclerosis and a high incidence of fractures, may potentially affect postoperative rehabilitation. This report presents a case of successful rehabilitation early after total hip arthroplasty for osteopetrosis. A 56-year-old Japanese man, who was diagnosed with osteopetrosis at the age of 11, underwent total hip arthroplasty in the right hip. Full weight-bearing was allowed on the day after the operation; the postoperative rehabilitation program was proceeded based on a standard program as done after total hip arthroplasty for osteoarthritis. A shoe lift in the left leg was used in supervised walking training to correct the imbalanced alignment due to leg length discrepancy. The patient could walk independently with a cane 17 days after the operation. Three weeks after the operation, the patient demonstrated comfortable and maximal walking speed of 1.11 and 1.34 m/s, respectively, and maximal hip abductor muscle strength of 3.96 kgf･m, both of which were better than those before the operation. There were no adverse events during the postoperative rehabilitation course. These findings suggest the safety and efficacy of standard rehabilitation programs after total hip arthroplasty even in individuals with osteopetrosis. In addition, it may be important to consider the whole-body condition in the rehabilitation of individuals 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.

Metabolic bone disorders and the promise of marine osteoactive compounds

Metabolic bone disorders and associated fragility fractures are major causes of disability and mortality worldwide and place an important financial burden on the global health systems. These disorders result from an unbalance between bone anabolic and resorptive processes and are characterized by different pathophysiological mechanisms. Drugs are available to treat bone metabolic pathologies, but they are either poorly effective or associated with undesired side effects that limit their use. The molecular mechanism underlying the most common metabolic bone disorders, and the availability, efficacy, and limitations of therapeutic options currently available are discussed here. A source for the unmet need of novel drugs to treat metabolic bone disorders is marine organisms, which produce natural osteoactive compounds of high pharmaceutical potential. In this review, we have inventoried the marine osteoactive compounds (MOCs) currently identified and spotted the groups of marine organisms with potential for MOC production. Finally, we briefly examine the availability of in vivo screening and validation tools for the study of MOCs.

Osteobiologies for Spinal Fusion from Biological Mechanisms to Clinical Applications: A Narrative Review

Degenerative lumbar spinal disease (DLSD), including spondylolisthesis and spinal stenosis, is increasing due to the aging population. Along with the disease severity, lumbar interbody fusion (LIF) is a mainstay of surgical treatment through decompression, the restoration of intervertebral heights, and the stabilization of motion segments. Currently, pseudoarthrosis after LIF is an important and unsolved issue, which is closely related to osteobiologies. Of the many signaling pathways, the bone morphogenetic protein (BMP) signaling pathway contributes to osteoblast differentiation, which is generally regulated by SMAD proteins as common in the TGF-β superfamily. BMP-2 and -4 are also inter-connected with Wnt/β-catenin, Notch, and FGF signaling pathways. With the potent potential for osteoinduction in BMP-2 and -4, the combination of allogenous bone and recombinant human BMPs (rhBMPs) is currently an ideal fusion material, which has equalized or improved fusion rates compared to traditional materials. However, safety issues in the dosage of BMP remain, so overcoming current limitations will provide significant advancement in spine surgery. In the future, translational research and the application of clinical study will be important to overcome the current limitations of spinal surgery.

Hypophosphatemic rickets: An unexplained early feature of craniometaphyseal dysplasia

Craniometaphyseal dysplasia (CMD) is an infrequently occurring skeletal dysplasia often caused by a mutation in ANKH. The most common features are early and progressive hyperostosis of craniofacial bones, which may cause obstruction of cranial nerves, and metaphyseal flaring of long bones. Rarely, rickets has been associated with CMD, occurring early in the course of the disease. We report an infant with CMD who presented with elevated serum alkaline phosphatase activity and low serum phosphorus at age 1 month and radiographic changes of rickets at 3 months of age. Further biochemical investigations revealed a high tubular reabsorption of phosphate and suppressed FGF23 level congruent with a deficit of phosphorus availability. Therapy with phosphorus was started at 4 months of age; calcitriol was subsequently added upon emergence of secondary hyperparathyroidism. A heterozygous pathogenic variant in ANKH c.1124_1126del (p.Ser375del) was identified. At 19 months of age therapy was discontinued in view of the corrected biochemical profile and radiographic improvement of rickets. ©The Authors. All rights reserved.

The molecular spectrum of Turkish osteopetrosis and related osteoclast disorders with natural history, including a candidate gene, CCDC120

BACKGROUND

Osteopetrosis and related osteoclastic disorders are a heterogeneous group of inherited diseases characterized by increased bone density. The aim of this study is to investigate the molecular spectrum and natural history of the clinical and radiological features of these disorders.

METHODS

28 patients from 20 families were enrolled in the study; 20 of them were followed for a period of 1-16 years. Targeted gene analysis and whole-exome sequencing (WES) were performed.

RESULTS

Biallelic mutations in CLCN7 and TCIRG1 were detected in three families each, in TNFRSF11A and CA2 in two families each, and in SNX10 in one family in the osteopetrosis group. A heterozygous variant in CLCN7 was also found in one family. In the osteopetrosis and related osteoclast disorders group, three different variants in CTSK were detected in five families with pycnodysostosis and a SLC29A3 variant causing dysosteosclerosis was detected in one family. In autosomal recessive osteopetrosis (ARO), a malignant infantile form, four patients died during follow-up, two of whom had undergone hematopoietic stem cell transplantation. Interestingly, all patients had osteopetrorickets of the long bone metaphyses in infancy, typical skeletal features such as Erlenmeyer flask deformity and bone-in-bone appearance that developed toward the end of early childhood. Two siblings with a biallelic missense mutation in CLCN7 and one patient with the compound heterozygous novel splicing variants in intron 15 and 17 in TCIRG1 corresponded to the intermediate form of ARO (IARO); there was intrafamilial clinical heterogeneity in the family with the CLCN7 variant. One of two patients with IARO and distal tubular acidosis was found to have a large deletion in CA2. In one family, two siblings with a heterozygous mutation in CLCN7 were affected, whereas the father with the same mutation was asymptomatic. In WES analysis of three brothers from a family without mutations in osteopetrosis genes, a hemizygous missense variant in CCDC120, a novel gene, was found to be associated with high bone mass.

CONCLUSION

This study extended the natural history of the different types of osteopetrosis and also introduced a candidate gene, CCDC120, potentially causing osteopetrosis.

Surgical outcome of distal tibia Salter Harris II fracture in osteopetrosis patient

INTRODUCTION

Osteopetrosis is a rare genetic disorder characterized by increased bone density. This condition is clinically manifested with a brittle intramedullary structure and reduced bone toughness, increasing the risk of fracture. A limited case has been reported on the management of physeal fracture in patients with osteopetrosis. The objective of this study is to report a rare osteopetrosis patient who sustains Salter-Harris II at the distal tibia with its long-term follow-up along with its literature review.

PRESENTATION OF CASE

We report a case of a four-year-old boy with an established a diagnosis of osteopetrosis brought by the parents to the emergency department after sustaining a fall while playing in the playground. Radiological examination revealed a Salter-Harris type II distal tibial fracture. The patient underwent closed reduction and fixation using the cannulated screw. 18-month postoperative patients have an uneventful healing.

DISCUSSION

Osteopetrosis is caused by impaired osteoclast function and differentiation, leading to impaired in remodelling. Salter-Harris type II distal tibial fracture can be treated by either closed reduction or open reduction. A closed reduction was performed successfully with cannulated screw in his patient.

CONCLUSION

There is a delayed union of fracture in osteopetrosis patient. This will increase the risk of displacement which will eventually resulted in growth disturbance. Delayed weight bearing and stable fixation is highly recommended.

Case Report: Osteosclerotic metaphyseal dysplasia with optic nerve involvement and progressive osteonecrosis of the jaw due to a novel LRRK1 mutation

Background

Osteosclerotic metaphyseal dysplasia (OSMD, OMIM 615198) is an extremely rare autosomal recessive osteopetrosis disorder resulting in a distinctive pattern of osteosclerosis of the metaphyseal margins of long tubular bones. To date, only thirteen cases have been reported (eight molecularly confirmed). Five homozygous sequence variants in the leucine-rich repeat kinase 1 (LRRK1) gene have been identified to cause OSMD. We present two male siblings with OSMD with a novel LRRK1 variant.

Cases

The index case, now aged 6 years, was referred aged 9 months when diffuse sclerosis of the ribs and vertebral bodies, suggestive of osteopetrosis, was incidentally identified on a chest radiograph for suspected lower respiratory tract infection. Parents were consanguineous and of Pakistani origin. Further evaluation revealed developmental delay, nystagmus with bilateral optic nerve hypoplasia and severe visual impairment. Skeletal survey confirmed typical changes of OSMD, with widespread diffuse sclerosis and Erlenmeyer flask deformity of long bones. His older sibling, now aged 12 years, was 7 years at the time of referral and had similar clinical course and skeletal findings. Additionally, he had a chronic progressive osteonecrosis of the left mandible that required debridement, debulking and long-term antibiotics. Skeletal survey revealed findings similar to his sibling. Neither sibling had significant skeletal fractures or seizures. Unlike most previous reports suggesting sparing of the skull and lack of visual impairment, our patients had evidence of osteosclerosis of the cranium. Genetic screening for the common autosomal recessive and dominant pathogenic variants of osteopetrosis was negative. Whole Exome Sequencing (WES) followed by Sanger sequencing, identified a novel homozygous LRRK1 c.2506C>T p. (Gln836Ter) nonsense variant predicted to result in premature truncation of LRRK1 transcript.

Conclusion

Our cases confirm the autosomal recessive inheritance and expand the spectrum of genotype and phenotype of OSMD reported in the literature. Increasing reports of LRRK1 variants in this phenotype raise the question of whether LRRK1 should be included in targeted osteopetrosis panels. Bone histology in previous cases has shown this to be an osteoclast rich form of osteopetrosis raising the possibility that haematopoietic stem cell transplantation may be an appropriate treatment modality.

Cranial distraction osteogenesis for craniosynostosis associated with osteopetrosis: A case report

Background

Osteopetrosis is a rare disease characterized by systemic osteosclerosis and hematopoietic disturbances. Childhood-onset cases are often accompanied by hydrocephalus and craniosynostosis; however, there have been no established treatments. We performed cranial distraction in a child with osteopetrosis who presented with craniosynostosis and intracranial hypertension.

Case Description

The patient was a 4-year-1-month-old boy. His pregnancy and birth were normal, but at 4 months of age, he was diagnosed with osteopetrosis based on generalized osteosclerosis and family history. A computed tomography scan of the head revealed early sagittal suture fusion and ventricular enlargement. A ventriculoperitoneal shunt was placed for intracranial hypertension; however, slit ventricle syndrome ensued and pansynostosis developed. To improve uncontrolled high intracranial pressure, cranial distraction was performed for intracranial volume expansion. No perioperative hemorrhagic or infectious complications were observed. After the start of distraction, the intracranial pressure gradually decreased, and clinical findings such as disturbance of consciousness and bradycardia disappeared. Bone regeneration in the defect site was good, and the extension device was removed 6 months after the operation.

Conclusion

For osteopetrosis with poorly controlled intracranial hypertension, cranial distraction was considered to be an effective treatment.

Defects in Bone and Bone Marrow in Inherited Anemias: the Chicken or the Egg

PURPOSE OF REVIEW

Recently, there has been an increasing number of studies on the crosstalk between the bone and the bone marrow and how it pertains to anemia. Here, we discuss four heritable clinical syndromes contrasting those in which anemia affects bone growth and development, with those in which abnormal bone development results in anemia, highlighting the multifaceted interactions between skeletal development and hematopoiesis.

RECENT FINDINGS

Anemia results from both inherited and acquired disorders caused by either impaired production or premature destruction of red blood cells or blood loss. The downstream effects on bone development and growth in patients with anemia often constitute an important part of their clinical condition. We will discuss the interdependence of abnormal bone development and growth and hematopoietic abnormalities, with a focus on the erythroid lineage. To illustrate those points, we selected four heritable anemias that arise from either defective hematopoiesis impacting the skeletal system (the hemoglobinopathies β-thalassemia and sickle cell disease) versus defective osteogenesis resulting in impaired hematopoiesis (osteopetrosis). Finally, we will discuss recent findings in Diamond Blackfan anemia, an intrinsic disorder of both the erythron and the bone. By focusing on four representative hereditary hematopoietic disorders, this complex relationship between bone and blood should lead to new areas of research in the field.

Novel hybrid silicon-lipid nanoparticles deliver a siRNA to cure autosomal dominant osteopetrosis in mice. Implications for gene therapy in humans

Rare skeletal diseases are still in need of proper clinically available transfection agents as the major challenge for first-in-human translation relates to intrinsic difficulty in targeting bone without exacerbating any inherent toxicity due to used vector. SiSaf's silicon stabilized hybrid lipid nanoparticles (sshLNPs) constitute next-generation non-viral vectors able to retain the integrity and stability of constructs and to accommodate considerable payloads of biologicals, without requiring cold-chain storage. sshLNP was complexed with a small interfering RNA (siRNA) specifically designed against the human CLCN7G215R mRNA. When tested via single intraperitoneal injection in pre-puberal autosomal dominant osteopetrosis type 2 (ADO2) mice, carrying a heterozygous mutation of the Clcn7 gene (Clcn7G213R), sshLNP, this significantly downregulated the Clcn7G213R related mRNA levels in femurs at 48 h. Confirmatory results were observed at 2 weeks and 4 weeks after treatments (3 intraperitoneal injections/week), with rescue of the bone phenotype and demonstrating safety. The pre-clinical results will enable advanced preclinical development of RNA-based therapy for orphan and genetic skeletal disorders by safely and effectively delivering biologicals of interest to cure human systemic conditions.

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.

Increased Bone Formation and Accelerated Bone Mass Accrual in a Man Presenting with Diffuse Osteosclerosis/High Bone Mass Phenotype and Adenocarcinoma of Unknown Primary

A 71-year-old man was referred for evaluation of incidental generalized osteosclerosis. He was found to have a high bone mass (HBM) with an elevated lumbar spine bone mineral density (BMD) Z-score of +5.3. Over an 18-month period, his lumbar spine BMD measured by dual energy X-ray absorptiometry (DXA) had increased by +64% from 1.09 to 1.79 g/cm2 and femoral neck by +21% from 0.83 to 1.01 g/cm2. Biochemical markers of bone turnover were markedly increased (serum propeptide of type 1 collagen and urine telopeptides greater than 10-times normal). The high bone formation and increased skeletal calcium acquisition resulted in profound hypocalcemia (low serum calcium 1.88 mmol/L) and hypocalciuria (low urinary calcium <0.2 mmol/day). Positron emission tomography (PET) with 2-deoxy-2-[fluorine-18] fluoro-D-glucose (FDG) confirmed diffuse osteosclerosis without focal areas of abnormal FDG uptake in the skeleton or elsewhere to suggest either an underlying primary malignancy or metastatic disease. Bone biopsy showed markedly sclerotic woven and lamellar bone. The marrow space was devoid of typical bone cells and adipocytes and instead was filled by fibromyxoid stroma, infiltrated by small clusters of tumor cells. Bone histomorphometry and micro-computed tomography demonstrated an elevated trabecular bone volume and trabecular plate thickness. The bone disorder in this case is unique and raises the possibility of a new yet undefined novel anabolic paracrine factor (or factors) secreted by an adenocarcinoma of unknown primary that resulted in dramatic increases in BMD, HBM, and radiological osteosclerosis. The differential diagnosis and potential mechanisms responsible for the HBM are discussed. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Severe hypophosphataemia can be an early sign of osteopetrorickets: a case report

Osteopetrorickets is a rare complication of autosomal recessive ("malignant") osteopetrosis. Its prompt diagnosis is essential, because early suspicion of infantile osteopetrosis enables treatment with human stem cell transplantation, depending on the gene involved. It is important to identify not only the characteristic radiological changes of rickets, but also the coexistence of increased bone density, so as not to miss this very rare entity. Herein, a brief case report is presented.

Integrated Osteoinductive Factors─Exosome@MicroRNA-26a Hydrogel Enhances Bone Regeneration

MicroRNAs (miRNAs) are a new therapeutic tool that can target multiple genes by inducing translation repression and target mRNA degradation. Although miRNAs have gained significant attention in oncology and in work on genetic disorders and autoimmune diseases, their application in tissue regeneration remains hindered by several challenges, such as miRNA degradation. Here, we reported Exosome@MicroRNA-26a (Exo@miR-26a), an osteoinductive factor that can be substituted for routinely used growth factors, which was constructed using bone marrow stem cell (BMSC)-derived exosomes and microRNA-26a (miR-26a). Exo@miR-26a-integrated hydrogels significantly promoted bone regeneration when implanted into defect sites; as the exosome stimulated angiogenesis, miR-26a promoted osteogenesis while the hydrogel enabled a site-directed release. Moreover, BMSC-derived exosomes further facilitated healthy bone regeneration by repressing osteoclast differentiation-related genes rather than damaging osteoclasts. Taken together, our findings demonstrate the promising potential of Exo@miR-26a for bone regeneration and provide a new strategy for the application of miRNA therapy in tissue engineering.

Autosomal dominant osteopetrosis

Autosomal dominant osteopetrosis (ADO) is the most common form of osteopetrosis. ADO is characterized by generalized osteosclerosis along with characteristic radiographic features such as a "bone-in-bone" appearance of long bones and sclerosis of the superior and inferior vertebral body endplates. Generalized osteosclerosis in ADO typically results from abnormalities in osteoclast function, due most commonly to mutations in the chloride channel 7 (CLCN7) gene. A variety of debilitating complications can occur over time due to bone fragility, impingement of cranial nerves, encroachment of osteopetrotic bone in the marrow space, and poor bone vascularity. There is a wide spectrum of disease phenotype, even within the same family. Currently, there is no disease specific treatment for ADO, so clinical care focuses on monitoring for disease complications and symptomatic treatment. This review describes the history of ADO, the wide disease phenotype, and potential new therapies.

Bone and Cytokine Markers Associated With Bone Disease in Systemic Mastocytosis

BACKGROUND

Mastocytosis encompasses a heterogeneous group of diseases characterized by tissue accumulation of clonal mast cells, which frequently includes bone involvement. Several cytokines have been shown to play a role in the pathogenesis of bone mass loss in systemic mastocytosis (SM), but their role in SM-associated osteosclerosis remains unknown.

OBJECTIVE

To investigate the potential association between cytokine and bone remodeling markers with bone disease in SM, aiming at identifying biomarker profiles associated with bone loss and/or osteosclerosis.

METHODS

A total of 120 adult patients with SM, divided into 3 age and sex-matched groups according to their bone status were studied: (1) healthy bone (n = 46), (2) significant bone loss (n = 47), and (3) diffuse bone sclerosis (n = 27). Plasma levels of cytokines and serum baseline tryptase and bone turnover marker levels were measured at diagnosis.

RESULTS

Bone loss was associated with significantly higher levels of serum baseline tryptase (P = .01), IFN-γ (P = .05), IL-1β (P = .05), and IL-6 (P = .05) versus those found in patients with healthy bone. In contrast, patients with diffuse bone sclerosis showed significantly higher levels of serum baseline tryptase (P < .001), C-terminal telopeptide (P < .001), amino-terminal propeptide of type I procollagen (P < .001), osteocalcin (P < .001), bone alkaline phosphatase (P < .001), osteopontin (P < .01), and the C-C Motif Chemokine Ligand 5/RANTES chemokine (P = .01), together with lower IFN-γ (P = .03) and RANK-ligand (P = .04) plasma levels versus healthy bone cases.

CONCLUSIONS

SM with bone mass loss is associated with a proinflammatory cytokine profile in plasma, whereas diffuse bone sclerosis shows increased serum/plasma levels of biomarkers related to bone formation and turnover, in association with an immunosuppressive cytokine secretion profile.

Origin of Osteoclasts: Osteoclast Precursor Cells

Osteoclasts are multinucleated bone-resorbing cells and a key player in bone remodeling for health and disease. Since the discovery of osteoclasts in 1873, the structure and function of osteoclasts and the molecular and cellular mechanisms of osteoclastogenesis have been extensively studied. Moreover, it has been well established that osteoclasts are differentiated in vitro from myeloid cells such as bone marrow macrophages or monocytes. The concept showing that osteoclasts are derived from a specific population (named osteoclast precursor cells [OCPs]) among myeloid cells has been long hypothesized. However, the specific precursor population of osteoclasts is not clearly defined yet. A growing body of work provides evidence of the developmental origin and lifespan of murine osteoclasts, particularly in vivo. Here, we review the emerging evidence that supports the existence of OCPs and discuss current insights into their identity.

Outlining the Clinical Profile of TCIRG1 14 Variants including 5 Novels with Overview of ARO Phenotype and Ethnic Impact in 20 Egyptian Families

TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density. The disorder is known to exhibit marked genetic heterogeneity, has no treatment, and is lethal in most instances. There are reports of ethnic variations affecting bone mineral density and variants' expression as diverse phenotypes even within individuals descending from the same pedigree. We herein focus on one of osteopetrosis's three types: the autosomal recessive malignant form (MIM 259700) (ARO) that is almost always associated with severe clinical symptoms. We reviewed the results of about 1800 Egyptian exomes and we did not detect similar variants within our Egyptian dataset and secondary neurological deficit. We studied twenty Egyptian families: sixteen ARO patients, ten carrier parents with at least one ARO affected sib, and two fetuses. They were all subjected to thorough evaluation and TCIRG1 gene sequencing. Our results of twenty-eight individuals descending from twenty Egyptian pedigrees with at least one ARO patient, expand the phenotype as well as genotype spectrum of recessive mutations in the TCIRG1 gene by five novel pathogenic variants. Identifying TCIRG1 gene mutations in Egyptian patients with ARO allowed the provision of proper genetic counseling, carrier detection, and prenatal diagnosis starting with two families included herein. It also could pave the way to modern genomic therapeutic approaches.