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.

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.

CSF1R-dependent macrophages control postnatal somatic growth and organ maturation.

Homozygous mutation of the Csf1r locus (Csf1rko) in mice, rats and humans leads to multiple postnatal developmental abnormalities. To enable analysis of the mechanisms underlying the phenotypic impacts of Csf1r mutation, we bred a rat Csf1rko allele to the inbred dark agouti (DA) genetic background and to a Csf1r-mApple reporter transgene. The Csf1rko led to almost complete loss of embryonic macrophages and ablation of most adult tissue macrophage populations. We extended previous analysis of the Csf1rko phenotype to early postnatal development to reveal impacts on musculoskeletal development and proliferation and morphogenesis in multiple organs. Expression profiling of 3-week old wild-type (WT) and Csf1rko livers identified 2760 differentially expressed genes associated with the loss of macrophages, severe hypoplasia, delayed hepatocyte maturation, disrupted lipid metabolism and the IGF1/IGF binding protein system. Older Csf1rko rats developed severe hepatic steatosis. Consistent with the developmental delay in the liver Csf1rko rats had greatly-reduced circulating IGF1. Transfer of WT bone marrow (BM) cells at weaning without conditioning repopulated resident macrophages in all organs, including microglia in the brain, and reversed the mutant phenotypes enabling long term survival and fertility. WT BM transfer restored osteoclasts, eliminated osteopetrosis, restored bone marrow cellularity and architecture and reversed granulocytosis and B cell deficiency. Csf1rko rats had an elevated circulating CSF1 concentration which was rapidly reduced to WT levels following BM transfer. However, CD43hi non-classical monocytes, absent in the Csf1rko, were not rescued and bone marrow progenitors remained unresponsive to CSF1. The results demonstrate that the Csf1rko phenotype is autonomous to BM-derived cells and indicate that BM contains a progenitor of tissue macrophages distinct from hematopoietic stem cells. The model provides a unique system in which to define the pathways of development of resident tissue macrophages and their local and systemic roles in growth and organ maturation.

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.

Bone marrow transplantation as a therapy for autosomal dominant osteopetrosis type 2 in mice.

Autosomal dominant osteopetrosis type II (ADO2) is a heritable bone disease of impaired osteoclastic bone resorption caused by missense mutations in the chloride channel 7 (CLCN7) gene. Clinical features of ADO2 include fractures, osteomyelitis of jaw, vision loss, and in severe cases, bone marrow failure. Currently, there is no effective therapy for ADO2, and patients usually receive symptomatic treatments. Theoretically, bone marrow transplantation (BMT), which is commonly used in recessive osteopetrosis, could be used to treat ADO2, although the frequency of complications related to BMT is quite high. We created an ADO2 knock-in (p.G213R mutation) mouse model on the 129 genetic background, and their phenotypes mimic the human disease of ADO2. To test whether BMT could restore osteoclast function and rescue the bone phenotypes in ADO2 mice, we transplanted bone marrow cells from 6-8 weeks old male WT donor mice into recipient female ADO2 mice. Also, to determine whether age at the time of transplant may play a role in transplant success, we performed BMT in young (12-week-old) and old (9-month-old) ADO2 mice. Our data indicate that ADO2 mice transplanted with WT marrow achieved more than 90% engraftment up to 6 months post-transplantation at both young and old ages. The in-vivo DXA data revealed that young ADO2 mice transplanted with WT marrow had significantly lower whole body and spine areal bone mineral density (aBMD) at month 6 post-transplantation compared to the ADO2 control mice. The old ADO2 mice also displayed significantly lower whole body, femur, and spine aBMD at months 4 and 5 post-transplantation compared to the age-matched control mice. The in-vivo micro-CT data showed that ADO2 experimental mice transplanted with WT marrow had significantly lower BV/TV at months 2 and 4 post-transplantation compared to the ADO2 control mice at a young age. In contrast, ADO2 control and experimental mice displayed similar BV/TV values for all post-transplantation time points at old age. In addition, serum CTX was significantly higher at month 2 post-transplantation in both young and old ADO2 experimental mice compared to the ADO2 control mice. Serum P1NP levels in young ADO2 experimental mice were significantly higher at baseline and month 2 post-transplantation compared to the ADO2 control mice. These data suggest that BMT may provide, at least, some beneficial effect at both young and adult ages.

A cross-sectional nationwide survey of osteosclerotic skeletal dysplasias in Japan.

BACKGROUND: The osteosclerotic skeletal dysplasias (OSSDs) are a heterogeneous group of disorders characterized by systemic bone sclerosis. Little is known about OSSDs because of their rarity. We conducted a cross-sectional nationwide survey of OSSDs and examined the incidence, epidemiology, and therapeutic interventions on these disorders. METHODS: This study consisted of a two-step survey. The number of patients with OSSDs who had visited medical institutions between April 2017 and March 2018 was reported from a total of 341 facilities (1364 departments from pediatrics, orthopaedic surgery, neurosurgery, and otolaryngology in each facility) by the first questionnaire. In the secondary survey, their clinical features were assessed by collecting demographic data, diagnostic details, current status, family histories, therapeutic interventions, histories of bone fracture and osteomyelitis, severity assessed by the modified Rankin Scale (mRS) and recent lifestyle conditions of the patient by the EQ-5D. RESULTS: In the first survey, 51 facilities (56 departments) reported one or more OSSDs patients, including 50 patients with osteopetrosis and 57 patients of other OSSDs. Among 87 patients eligible for inclusion in the analysis in the secondary survey, we investigated detailed information on the 42 patients with osteopetrosis. The number of initial visits of osteopetrosis patients during the surveillance period was five per year, indicating that the estimated incidence of osteopetrosis seemed to be 0.6 per 100,000 live births. Eighty-six bone fractures were reported in 22 patients (52%), and interventions of pseudarthrosis were conducted in five patients. Nine patients (23%) showed significant disabilities with the mRS of grade 3 or higher. Neurological complications and severe anemia were the factors that deteriorate patients' quality of life. CONCLUSIONS: This is the first study to examine the detailed epidemiology of OSSDs in Japan. We demonstrated that the incidence of OSSDs is extremely rare. Bone fragility and delayed fracture healing seem to be important orthopaedic problems for patients with osteopetrosis.

Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis.

Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene. Despite recent progress in conditioning, a relevant number of patients are not eligible for allogeneic stem cell transplantation because of the severity of the disease and significant transplant-related morbidity. We exploited peripheral CD34+ cells, known to circulate at high frequency in the peripheral blood of TCIRG1-deficient patients, as a novel cell source for autologous transplantation of gene corrected cells. Detailed phenotypical analysis showed that circulating CD34+ cells have a cellular composition that resembles bone marrow, supporting their use in gene therapy protocols. Transcriptomic profile revealed enrichment in genes expressed by hematopoietic stem and progenitor cells (HSPCs). To overcome the limit of bone marrow harvest/ HSPC mobilization and serial blood drawings in TCIRG1 patients, we applied UM171-based ex-vivo expansion of HSPCs coupled with lentiviral gene transfer. Circulating CD34+ cells from TCIRG1-defective patients were transduced with a clinically-optimized lentiviral vector (LV) expressing TCIRG1 under the control of phosphoglycerate promoter and expanded ex vivo. Expanded cells maintained long-term engraftment capacity and multi-lineage repopulating potential when transplanted in vivo both in primary and secondary NSG recipients. Moreover, when CD34+ cells were differentiated in vitro, genetically corrected osteoclasts resorbed the bone efficiently. Overall, we provide evidence that expansion of circulating HSPCs coupled to gene therapy can overcome the limit of stem cell harvest in osteopetrotic patients, thus opening the way to future gene-based treatment of skeletal diseases caused by bone marrow fibrosis.

How we approach malignant infantile osteopetrosis.

Malignant infantile osteopetrosis (MIOP) is a rare hereditary disorder characterized by excessive bone overgrowth due to a defect in bone marrow resorption by osteoclasts. In most cases, hematopoietic stem cell transplantation (HSCT) may correct bone metabolism but the rapidly progressing nature of this condition necessitates early diagnosis and prompt treatment to minimize irreversible cranial nerve damage. The management of patients with MIOP presents many unique challenges. In this review, the clinical management of patients with MIOP is discussed, including diagnosis, preparation for HSCT and special transplant considerations, management of unique HSCT complications, and long-term follow-up.

Successful hematopoietic stem cell transplantation for osteopetrosis using reduced intensity conditioning.

BACKGROUND: Infantile malignant osteopetrosis (IMO) is an autosomal recessive condition characterized by defective osteoclast activity, with hematopoietic bone marrow transplant being the only available cure. Over the past several years, new conditioning regimes and donor options have emerged, thus extending the possibility of cure to a greater number of patients and improving the outcomes of bone marrow transplant. Here we detail the outcomes of bone marrow transplant in a cohort of 31 patients treated with a combination of fludarabine, treosulphan, thiotepa, and antithymocyte globulin. PROCEDURES: Thirty-one patients with IMO who underwent hematopoietic stem cell transplantation with fludarabine, treosulphan, thiotepa, and antithymocyte globulin at our center from 2012 to 2017 are retrospectively reviewed in this study. Twenty-six patients were transplanted from 10/10 matched donors (13 from siblings, 11 from unrelated, and two from extended family donors), four from 9/10 matched unrelated donors, and one from a 9/10 matched family donor. RESULTS: Overall survival was 100% with a median follow-up of 363 days (range 74-1891). There were 12 cases of acute graft versus host disease (GvHD) (38.7%), no cases of veno-occlusive disease, and eight cases of hypercalcemia (25.8%). Almost 80% of patients suffered viral reactivations with two cases of Epstein-Barr-virus-driven post-transplant lymphoproliferative disease. All cases of GvHD and viral reactivation were successfully treated. CONCLUSIONS: We conclude that transplantation in children with IMO using fludarabine, treosulphan, thiotepa, and antithymocyte globulin is safe and effective and should be performed as early as possible following diagnosis, prior to the development of severe disease sequelae.

Hematopoietic stem cell transplantation for infantile osteopetrosis.

We report the international experience in outcomes after related and unrelated hematopoietic transplantation for infantile osteopetrosis in 193 patients. Thirty-four percent of transplants used grafts from HLA-matched siblings, 13% from HLA-mismatched relatives, 12% from HLA-matched, and 41% from HLA-mismatched unrelated donors. The median age at transplantation was 12 months. Busulfan and cyclophosphamide was the most common conditioning regimen. Long-term survival was higher after HLA-matched sibling compared to alternative donor transplantation. There were no differences in survival after HLA-mismatched related, HLA-matched unrelated, or mismatched unrelated donor transplantation. The 5- and 10-year probabilities of survival were 62% and 62% after HLA-matched sibling and 42% and 39% after alternative donor transplantation (P = .01 and P = .002, respectively). Graft failure was the most common cause of death, accounting for 50% of deaths after HLA-matched sibling and 43% of deaths after alternative donor transplantation. The day-28 incidence of neutrophil recovery was 66% after HLA-matched sibling and 61% after alternative donor transplantation (P = .49). The median age of surviving patients is 7 years. Of evaluable surviving patients, 70% are visually impaired; 10% have impaired hearing and gross motor delay. Nevertheless, 65% reported performance scores of 90 or 100, and in 17%, a score of 80 at last contact. Most survivors >5 years are attending mainstream or specialized schools. Rates of veno-occlusive disease and interstitial pneumonitis were high at 20%. Though allogeneic transplantation results in long-term survival with acceptable social function, strategies to lower graft failure and hepatic and pulmonary toxicity are urgently needed.

Outcomes after Unrelated Umbilical Cord Blood Transplantation for Children with Osteopetrosis.

Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for most children with osteopetrosis (OP). Timing of HSCT is critical; therefore, umbilical cord blood transplantation (UCBT) is an attractive option. We analyzed outcomes after UCBT in 51 OP children. Median age at UCBT was 6 months. Seventy-seven percent of the cord blood grafts had 0 or 1 HLA disparity with the recipient. Conditioning regimen was myeloablative (mostly busulfan-based in 84% and treosulfan-based in 10%). Antithymocyte globulin was given to 90% of patients. Median number of total nucleated and CD34+ cells infused was 14 × 107/kg and 3.4 × 105/kg, respectively. Median follow-up for survivors was 74 months. Cumulative incidence (CI) of neutrophil recovery was 67% with a median time to recovery of 23 days; 33% of patients had graft failure, 81% of engrafted patients had full donor engraftment, and 19% had mixed donor chimerism. Day 100 CI of acute graft-versus-host disease (grades II to IV) was 31% and 6-year CI of chronic graft-versus-host disease was 21%. Mechanical ventilation was required in 28%, and veno-occlusive disease was diagnosed in 16% of cases. Six-year overall survival rate was 46%. Comparative studies with other alternative donors should be performed to evaluate whether UCBT remains a valid alternative for children with OP without an HLA-matched donor.

Improved Outcomes of Hematopoietic Stem Cell Transplantation in Patients With Infantile Malignant Osteopetrosis Using Fludarabine-Based Conditioning.

BACKGROUND: Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for infantile malignant osteopetrosis (IMO), but is associated with a high incidence of adverse outcomes. In this study, we present our experience with HSCT for IMO patients comparing different types of conditioning regimens. METHODS: Thirty-eight patients with IMO (aged from 1 month to 6 years, median 0.66 years) who underwent allogeneic HSCT from 1983 in our hospital were included in this retrospective study. Fludarabine-based conditioning regimens were used in 26 patients and 12 patients were transplanted using other conditioning regimens. RESULTS: The overall survival after conditioning with fludarabine was 96% (25/26) versus 58% (7/12) for the alternative regimens (P = 0.004), with significantly fewer adverse effects including hypercalcemia and veno-occlusive disease of liver. All patients who survive are clinically well. CONCLUSIONS: We conclude that fludarabine-based conditioning regimens are safe and effective in patients with IMO, improving morbidity and mortality related to HSCT.

Unmistakable Morphology? Infantile Malignant Osteopetrosis Resembling Juvenile Myelomonocytic Leukemia in Infants.

The initial clinical and hematologic presentation of infantile malignant osteopetrosis may be indistinguishable from that of juvenile myelomonocytic leukemia in infants. Timely radiographic imaging, however, allows straightforward delineation of these 2 severe diseases and facilitates immediate initiation of appropriate therapy.

Radiologic resolution of malignant infantile osteopetrosis skeletal changes following hematopoietic stem cell transplantation.

INTRODUCTION: Hematopoietic stem cell transplantation (HSCT) is the only known curative treatment of malignant infantile osteopetrosis (MIOP). In this study, short-term serial bone surveys were used to assess radiologic evolution of skeletal changes after HSCT in MIOP. MATERIALS AND METHODS: Baseline whole-body bone survey was performed in all patients. HSCT was successful in 14 patients (11 with full chimerism, three with mixed chimerism) in whom follow-up bone surveys were carried out at 6 and 12 months after HSCT. RESULTS: Normal corticomedullary differentiation was evident in five (P = 0.06) and 12 (P < 0.005) patients at 6 and 12 months, respectively. Abnormal endobone appearance in long bones, present in 11 participants at baseline exam, disappeared in eight (P = 0.008) and all (P = 0.001) patients at 6 and 12 months, respectively. In 6-month follow-up, rachitic changes significantly disappeared (P < 0.01) in long bones; however, they were evident in ribs of 12 patients (P = 0.50). No patient had rickets in ribs or long bones after 12 months. CONCLUSION: We observed considerable resolution of MIOP skeletal changes after HSCT in all patients with either full or mixed chimerism. Rachitic changes in long bones, attenuated corticomedullary differentiation, and endobone appearance were the first to resolve. We propose using single long bone plain x-ray to demonstrate short-term skeletal response to HSCT.

A new mutation in the KINDLIN-3 gene ablates integrin-dependent leukocyte, platelet, and osteoclast function in a patient with leukocyte adhesion deficiency-III.

Disabling mutations in integrin-mediated cell signaling have been a major focus of interest over the last decade for patients affected with leukocyte adhesion deficiency-III (LAD-III). In this study, we identified a new C>T point mutation in exon 13 in the FERMT3 gene in an infant diagnosed with LAD-III and showed that KINDLIN-3 expression is required for platelet aggregation and leukocyte function, but also osteoclast-mediated bone resorption. After allogeneic bone marrow transplant, all overt symptoms disappeared. This newly identified mutation along with its novel role in dysregulation of bone homeostasis extends our understanding of KINDLIN-3 in humans.

Non-total body irradiation myeloablative conditioning with intravenous busulfan and cyclophosphamide in hematopoietic stem cell transplantation for malignant infantile osteopetrosis.

HSCT is the only curative treatment for MIOP. We prospectively investigated the outcome of HSCT using intravenous busulfan-based conditioning regimen from 2008 to 2013. Nineteen patients (median age = 17 months) underwent transplantation from HLA-matched related donors (n = 14), HLA-haploidentical related donors (n = 2), partially matched cord blood donors (n = 2), and HLA-matched unrelated donor (n = 1). Bone marrow (n = 9), peripheral blood (n = 8), and cord blood (n = 2) were used as stem cell sources. All but one patient demonstrated primary engraftment. Two patients experienced secondary graft failure. During the follow-up period, three patients showed mixed chimerism (45%, 45%, and 70% of donor cells were engrafted in each one of these patients) but are disease free. Two-yr OS and DFS were 84.2% and 73.7%, respectively. Improvement of visual acuity and partial reversal of mild conductive hearing loss occurred in two and four patients, respectively. The causes of death among three patients were infection, GvHD, and disease progression. In conclusion, due to major side effects of MIOP such as visual and hearing loss, early treatment using myeloablative conditioning without irradiation HSCT is suggested. The use of an HLA-matched related donor seems to be highly successful in this regard. Also, according to results of our study, mixed chimerism may be sufficient to resolve symptoms of disease.

Hypohidrotic ectodermal dysplasia, osteopetrosis, lymphedema, and immunodeficiency in an infant with multiple opportunistic infections.

Osteopetrosis, lymphedema, hypohidrotic ectodermal dysplasia, and immunodeficiency (OL-HED-ID) is a rare X-linked disorder with only three reported prior cases in the English-language literature. We describe a case of OL-HED-ID in a male infant who initially presented with congenital lymphedema, leukocytosis, and thrombocytopenia of unknown etiology at 7 days of age. He subsequently developed gram-negative sepsis and multiple opportunistic infections including high-level cytomegalovirus viremia and Pneumocystis jiroveci pneumonia. The infant was noted to have mildly xerotic skin, fine sparse hair, and periorbital wrinkling, all features suggestive of ectodermal dysplasia. Skeletal imaging showed findings consistent with osteopetrosis, and immunologic investigation revealed hypogammaglobulinemia and mixed T- and B-cell dysfunction. Genetic testing revealed a novel mutation in the nuclear factor kappa beta (NF-KB) essential modulator (NEMO) gene, confirming the diagnosis of OL-HED-ID. Mutations in the NEMO gene have been reported in association with hypohidrotic ectodermal dysplasia with immunodeficiency (HED-ID), OL-HED-ID, and incontinentia pigmenti. In this case, we report a novel mutation in the NEMO gene associated with OL-HED-ID. This article highlights the dermatologic manifestations of a rare disorder, OL-HED-ID, and underscores the importance of early recognition and prompt intervention to prevent life-threatening infections.