Long-term outcome of haematopoietic stem cell transplantation in autosomal recessive osteopetrosis: an EBMT report

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.

Advances in hematopoietic stem cells ex vivo expansion associated with bone marrow niche

Hematopoietic stem cells (HSCs) are an ideal source for the treatment of many hematological diseases and malignancies, as well as diseases of other systems, because of their two important features, self-renewal and multipotential differentiation, which have the ability to rebuild the blood system and immune system of the body. However, so far, the insufficient number of available HSCs, whether from bone marrow (BM), mobilized peripheral blood or umbilical cord blood, is still the main restricting factor for the clinical application. Therefore, strategies to expand HSCs numbers and maintain HSCs functions through ex vivo culture are urgently required. In this review, we outline the basic biology characteristics of HSCs, and focus on the regulatory factors in BM niche affecting the functions of HSCs. Then, we introduce several representative strategies used for HSCs from these three sources ex vivo expansion associated with BM niche. These findings have deepened our understanding of the mechanisms by which HSCs balance self-renewal and differentiation and provided a theoretical basis for the efficient clinical HSCs expansion.

Hematopoietic stem cell transplantation, a curative approach in infantile osteopetrosis

Most patients with osteopetrosis (OPT) can be causally and curatively treated with allogeneic hematopoietic stem cell transplantation (HSCT) because osteoclasts are derived from the HSC. However, HSCT is contraindicated in some forms of OPT, namely OPT with neurodegeneration (in all patients with OSTM1 and about half of patients with CLCN7 mutations) and OPT caused by an osteoblast defect (patients with RANKL mutations). HSCT for OPT risks serious side effects, such as transplant failure, venous occlusive disease, pulmonary hypertension, and hypercalcemic crises. Nevertheless, the success rate of HSCT has improved significantly in recent decades. This applies, in particular, to HSCT from non-HLA compatible (haploidentical) donors. Therefore, nowadays an HSCT can be discussed for intermediate OPT forms. After a successful HSCT, most patients have very good quality of life, but about two-thirds are visually impaired, and in rarer cases show motor and neurological disabilities. Early diagnosis, further improvements in transplantation procedures, and advances to improve quality-of-life after transplantation are challenges for the future.

Imaging in osteopetrosis

Imaging investigations are critical in the management of children with suspected and confirmed osteopetrosis. In severe cases, imaging can provide rapid confirmation of the diagnosis, whilst in milder cases, imaging findings may be the first or only indicators of the disease. Imaging can also identify major complications, including fractures and neurological compromise. We review the pathophysiological basis for the imaging findings in osteopetrosis, focusing on the impact of loss of various osteoclast functions leading to elevated bone density, hyperostosis, modelling abnormalities and bone fragility. We give an overview of the specific imaging findings, both skeletal and neuroradiological, in the spectrum of osteopetrotic disorders, including in the related entities of pyknodysostosis and dysosteosclerosis. We also explore potential radiological differential diagnoses.

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.

Haploidentical haematopoietic stem cell transplantation for malignant infantile osteopetrosis and intermediate osteopetrosis: a retrospective analysis of a single centre

OBJECTIVE

To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.

METHODS

Children with MIOP and IOP who underwent haplo-HSCT in Beijing Children's Hospital, Capital Medical University, from January 2010 to May 2018 were retrospectively analysed. Data relating to the clinical manifestations, engraftment, and prognosis of the children were extracted from medical records.

RESULTS

Twenty-seven patients, including 18 males and 9 females, with an onset age of 12 (0.04-72) months were enrolled in this study. The median time from diagnosis to transplantation was 4 (1-23) months. All patients received haplo-HSCT with a myeloablative conditioning regimen (including fludarabine, busulfan, and cyclophosphamide). Graft versus host disease (GVHD) prophylaxis was based on anti-human T lymphocyte porcine immunoglobulin/anti-human thymus globulin, methotrexate, and mycophenolate mofetil. The median observation time was 55.2 (0.3-126.2) months. By the end of follow-up, twenty patients survived and seven patients died. The 5 year overall survival rate was 73.9%. Stage I-II acute GVHD was observed in 20 patients, stage III GVHD in 1 patient and no patients had stage IV disease. Chronic GVHD was observed in 11 patients (40.7%) and was controlled by anti-GVHD therapy.

CONCLUSIONS

Haplo-HSCT was an effective treatment for MIOP and IOP, with a high survival rate and significantly improved clinical symptoms. For patients with a vision impairment before HSCT, the improvement was slow after transplantation. The incidence of GVHD was high but mild and was effectively controlled by appropriate treatment. These data indicated that haplo-HSCT was a feasible treatment for MIOP and IOP.

Autosomal recessive osteopetrosis: mechanisms and treatments

Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation. Clinical manifestations include dense and brittle bones, anemia and progressive nerve compression, which hamper the quality of patients' lives and cause death in the first 10 years of age. This Review describes the pathogenesis of ARO and highlights the strengths and weaknesses of the current standard of care, namely hematopoietic stem cell transplantation (HSCT). Despite an improvement in the overall survival and outcomes of HSCT, transplant-related morbidity and the pre-existence of neurological symptoms significantly limit the success of HSCT, while the availability of human leukocyte antigen (HLA)-matched donors still remains an open issue. Novel therapeutic approaches are needed for ARO patients, especially for those that cannot benefit from HSCT. Here, we review preclinical and proof-of-concept studies, such as gene therapy, systematic administration of deficient protein, in utero HSCT and gene editing.

Summary: Autosomal recessive osteopetrosis is a heterogeneous and rare bone disease for which effective treatments are still lacking for many patients. Here, we review the literature on clinical, preclinical and proof-of-concept studies.

Gene therapy for infantile malignant osteopetrosis: review of pre-clinical research and proof-of-concept for phenotypic reversal

Infantile malignant osteopetrosis is a devastating disorder of early childhood that is frequently fatal and for which there are only limited therapeutic options. Gene therapy utilizing autologous hematopoietic stem and progenitor cells represents a potentially advantageous therapeutic alternative for this multisystemic disease. Gene therapy can be performed relatively rapidly following diagnosis, will not result in graft versus host disease, and may also have potential for reduced incidences of other transplant-related complications. In this review, we have summarized the past sixteen years of research aimed at developing a gene therapy for infantile malignant osteopetrosis; these efforts have culminated in the first clinical trial employing lentiviral-mediated delivery of TCIRG1 in autologous hematopoietic stem and progenitor cells.

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.

Emerging insights on the role of V-ATPase in human diseases: Therapeutic challenges and opportunities

The control of the intracellular pH is vital for the survival of all organisms. Membrane transporters, both at the plasma and intracellular membranes, are key players in maintaining a finely tuned pH balance between intra- and extracellular spaces, and therefore in cellular homeostasis. V-ATPase is a housekeeping ATP-driven proton pump highly conserved among prokaryotes and eukaryotes. This proton pump, which exhibits a complex multisubunit structure based on cell type-specific isoforms, is essential for pH regulation and for a multitude of ubiquitous and specialized functions. Thus, it is not surprising that V-ATPase aberrant overexpression, mislocalization, and mutations in V-ATPase subunit-encoding genes have been associated with several human diseases. However, the ubiquitous expression of this transporter and the high toxicity driven by its off-target inhibition, renders V-ATPase-directed therapies very challenging and increases the need for selective strategies. Here we review emerging evidence linking V-ATPase and both inherited and acquired human diseases, explore the therapeutic challenges and opportunities envisaged from recent data, and advance future research avenues. We highlight the importance of V-ATPases with unique subunit isoform molecular signatures and disease-associated isoforms to design selective V-ATPase-directed therapies. We also discuss the rational design of drug development pipelines and cutting-edge methodological approaches toward V-ATPase-centered drug discovery. Diseases like cancer, osteoporosis, and even fungal infections can benefit from V-ATPase-directed therapies.

Challenges in long-term control of hypercalcaemia with denosumab after haematopoietic stem cell transplantation for TNFRSF11A osteoclast-poor autosomal recessive osteopetrosis

Autosomal recessive osteopetrosis (ARO) is rare, involving increased bone density due to defective osteoclast differentiation or function, with several genetic subtypes.

Case

This child with compound heterozygous novel loss-of-function TNFRSF11A pathogenic variants causing osteoclast-poor ARO underwent haematopoietic stem cell transplantation (HSCT) aged 3.1 years and experienced episodic severe hypercalcaemia over 2.5 years. She initially presented aged 8 months with craniosynostosis and visual impairment and underwent surgery; no increased bone density evident on skull imaging nor variants in genes associated with craniosynostosis identified. She was subsequently referred for investigation of poor linear growth and low alkaline phosphatase. Clinical abnormalities included asymmetric pectus carinatum, thickened anterior tibia and wrists, and markedly delayed dentition. Skeletal survey revealed generalised osteosclerosis with undertubulation.

Management

She received haploidentical HSCT aged 3.1 years and developed hypercalcaemia (adjusted calcium 4.09mmol/L = 16.4mg/dL) Day 18 post-HSCT, unresponsive to hyperhydration and diuretics. Denosumab achieved normocalcaemia, which required 0.6mg/kg every 6 weeks long-term. The ensuing 2.75 years feature full donor engraftment, good HSCT graft function, skeletal remodelling with 2.5 years recurrent severe hypercalcaemia and nine fragility long bone fractures.

Conclusion

This case illustrates challenges of bone and calcium management in ultrarare TNFRSF11A-related OP-ARO. Craniosynostosis was an early feature, evident pre-sclerosis in osteopetrosis. Following HSCT, restoration of osteoclast activity in the context of elevated bone mass produced severe and prolonged (2.5 years) hypercalcaemia. Denosumab was effective medium-term, but required concurrent long duration (11 months) zoledronic acid to manage recurrent hypercalcaemia. Fragility fractures brought appreciable additional morbidity in the post-HSCT phase.

Malignant Infantile Osteopetrosis: A Case Report

Osteopetrosis is a rare genetic disease of bone resorption. It includes a variety of hereditary skeletal disorders that have the main radiographic feature of increased bone density and thickness due to differentiation or functional defects in osteoclast. The clinical presentation varies widely based on the type of osteopetrosis and ranges in severity from asymptomatic to a fatal course. Our case is of the infantile malignant osteopetrosis (IMOP) form. It is inherited as an autosomal recessive pattern that generally starts in intrauterine life and manifests at birth or early childhood. It is the most severe form and has an incidence of 1 in 250,000 births. The patient presented at the age of two months with a history of recurrent fever, recurrent pneumonia, developmental delay, and infantile spasms. Upon examination, she was found to have hepatosplenomegaly, axial hypotonia, limb spasticity, and visual impairment. Genetic testing revealed a homozygous variant of OSTM1 gene, which is a known Saudi mutation of autosomal recessive osteopetrosis (ARO). IMOP should be considered as a rare differential of hepatosplenomegaly. Early diagnosis by clinical picture, imaging, and genetic testing is important to direct the appropriate management in order to prevent disease progression before the irreversible neurological sequelae occur. Patients should be managed by a comprehensive approach, and currently, hematopoietic stem cell transplantation (HSCT) provides a better outcome for IMOP patients.

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

OBJECTIVE

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

CASE REPORT

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

CONCLUSIONS

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

A Rare Case of Osteoclast-poor Osteopetrosis (RANKL Mutation) with Recurrent Osteomyelitis of Mandible: A Case Report

Osteopetrosis (OP) is a group of rare genetic bone disorders. Osteoclast-poor form of osteopetrosis is much rarer in humans and represents a small percentage of the total cases of autosomal recessive osteopetrosis presenting with impaired bone remodeling due to defective osteoclastic activity and is characterized by distinctive increase in bone density and high bone fragility. Reduction in marrow spaces with decreased vasculature to the bone owing to increased bone mass makes the bones vulnerable for varied infections resulting in osteomyelitis. This case report discusses challenges in management of recalcitrant osteomyelitis of mandible developed as a complication in an 8-year-old girl child identified with rare, dual heterozygous mutations in RANKL (TNFSF11) gene and COL5A1 gene with uncertain significance responsible for osteoclast-poor osteopetrosis and Classic Ehlers-Danlos, respectively.

Genotyping, generation and proteomic profiling of the first human autosomal dominant osteopetrosis type II-specific induced pluripotent stem cells

Background

Autosomal dominant osteopetrosis type II (ADO2) is a rare human genetic disease that has been broadly studied as an important osteopetrosis model; however, there are no disease-specific induced pluripotent stem cells (ADO2-iPSCs) that may be valuable for understanding the pathogenesis and may be a potential source of cells for autologous cell-based therapies.

Methods

To generate the first human ADO2-iPSCs from a Chinese family with ADO2 and to identify their characteristics, blood samples were collected from the proband and his parents and were used for genotyping by whole-exome sequencing (WES); the urine-derived cells of the proband were reprogrammed with episomal plasmids that contained transcription factors, such as KLF4, OCT4, c-MYC, and SOX2. The proteome-wide protein quantification and lysine 2-hydroxyisobutyrylation detection of the ADO2-iPSCs and normal control iPSCs (NC-iPSCs) were performed by high-resolution LC-MS/MS and bioinformatics analysis.

Results

WES with filtering strategies identified a mutation in CLCN7 (R286W) in the proband and his father, which was absent in the proband’s mother and the healthy controls; this was confirmed by Sanger sequencing. The ADO2-iPSCs were successfully generated, which carried a normal male karyotype (46, XY) and the mutation of CLCN7 (R286W); the ADO2-iPSCs positively expressed alkaline phosphatase and other surface markers; and no vector and transgene were detected. The ADO2-iPSCs could differentiate into all three germ cell layers, both in vitro and in vivo. The proteomic profiling revealed similar expression of pluripotency markers in the two cell lines and identified 7405 proteins and 3664 2-hydroxyisobutyrylated peptides in 1036 proteins in the ADO2-iPSCs.

Conclusions

Our data indicated that the mutation CLCN7 (R286W) may be a cause of the osteopetrosis family. The generated vector-free and transgene-free ADO2-iPSCs with known proteomic characteristics may be valuable for personalized and cell-based regenerative medicine in the future.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1369-8) contains supplementary material, which is available to authorized users.

Hematopoietic Stem Cell-Targeted Neonatal Gene Therapy with a Clinically Applicable Lentiviral Vector Corrects Osteopetrosis in oc/oc Mice

Infantile malignant osteopetrosis (IMO) is an autosomal recessive disorder characterized by nonfunctional osteoclasts. Approximately 50% of the patients have mutations in the TCIRG1 gene, encoding for a subunit of the osteoclast proton pump. Gene therapy represents a potential alternative treatment to allogeneic stem cell transplantation for IMO. The oc/oc mouse is a model of IMO characterized by a 1,500 bp deletion in the TCIRG1 gene, severe osteopetrosis, and a life span of only 3 weeks. Here we show that the osteopetrotic phenotype in oc/oc mice can be reversed by hematopoietic stem cell-targeted gene therapy with a clinically applicable lentiviral vector expressing a wild-type form of human TCIRG1 under the mammalian promoter elongation factor 1α short (EFS-hT). oc/oc c-kit⁺ fetal liver cells transduced with EFS-hT were transplanted into sublethally irradiated oc/oc mice by temporal vein injection 1 day after birth. A total of 9 of 12 mice survived long term (19-25 weeks) with evidence of tooth eruption, uncharacteristic of oc/oc mice. Splenocytes were harvested 19-25 weeks after transplantation and differentiated into osteoclasts on bone slices to assess resorption and on plastic to assess TCIRG1 protein expression. Vector-corrected osteoclasts showed human TCIRG1 expression by Western blot. CTX-I release relative to that mediated by oc/oc-derived osteoclasts increased 8-239-fold. Resorption pits on bone slices were observed for osteoclasts derived from 7/9 surviving transplanted oc/oc mice. Histopathology of the bones of surviving animals showed varying degrees of rescued phenotype, the majority with almost full correction. The average vector copy number per cell in the bone marrow was 1.8 ± 0.5. Overall, 75% of transplanted mice exhibited long-term survival and marked reversal of the osteopetrotic bone phenotype. These findings represent a significant step toward the clinical application of gene therapy for IMO.

Hematopoietic Stem Cell Transplantation: A Neonatal Perspective

Allogeneic hematopoietic stem cell transplantation (HSCT) is indicated in various nonmalignant disorders that arise from genetic, hematopoietic, and immune system defects. Many of the disorders described here have life-threatening consequences in the absence of HSCT, a curative intervention. However, timing and approach to HSCT vary by disorder and optimum results are achieved by performing transplantation before irreversible disease-related morbidity or infectious complications. This article details the principles of HSCT in the very young, lists indications, and explores the factors that contribute to successful outcomes based on transplantation and disease-related nuances. It provides an overview into the HSCT realm from a neonatologist's perspective, describes the current status of transplantation for relevant disorders of infancy, and provides a glimpse into future efforts at improving on current success.

Biochemical and clinical response after umbilical cord blood transplant in a boy with early childhood-onset beta-mannosidosis

BACKGROUND

Deficiency in the enzyme β-mannosidase was described over three decades ago. Although rare in occurrence, the presentation of childhood-onset β-mannosidase deficiency consists of hypotonia in the newborn period followed by global development delay, behavior problems, and intellectual disability. No effective pharmacologic treatments have been available.

METHODS

We report 2-year outcomes following the first umbilical cord blood transplant in a 4-year-old boy with early childhood-onset disease.

RESULTS

We show restoration of leukocyte β-mannosidase activity which remained normal at 2 years posttransplant, and a simultaneous increase in plasma β-mannosidase activity and dramatic decrease in urine-free oligosaccharides were also observed. MRI of the brain remained stable. Neurocognitive evaluation revealed test point gains, although the magnitude of improvement was less than expected for age, causing lower IQ scores that represent a wider developmental gap between the patient and unaffected peers.

CONCLUSION

Our findings suggest that hematopoietic cell transplant can correct the biochemical defect in β-mannosidosis, although preservation of the neurocognitive trajectory may be a challenge.

Comparison of Optic Canal Diameter in Children With Malignant Infantile Osteopetrosis and Normal Children and the Effects of Hematopoietic Stem Cell Transplantation on the Optic Canal Diameter

PURPOSE

To investigate the difference in the optic canal diameter between children with autosomal recessive malignant infantile osteopetrosis and normal children, and to assess the influence of hematopoietic stem cell transplantation on the optic canal diameter.

METHODS

Twenty pediatric patients with malignant infantile osteopetrosis and 22 normal control children were included in this study. Eleven patients with malignant infantile osteopetrosis underwent hematopoietic stem cell transplantation. The measurements included optical canal diameter and flash visual evoked potential. Comparisons of these measurements between patients with malignant infantile osteopetrosis and normal controls as well as before and after hematopoietic stem cell transplantation were performed. The correlation between age and optic canal diameter was analyzed using Pearson correlation analysis.

RESULTS

The mean optic canal diameter before hematopoietic stem cell transplantation was 1.65 ± 0.54 mm in patients with malignant infantile osteopetrosis and 3.38 ± 0.60 mm in the control group (P < .001). The mean optic canal diameter after hematopoietic stem cell transplantation was 2.72 ± 0.66 mm, which was significantly different from the pre-transplantation measurement (P < .001). The P2 latency for the flash visual evoked potential after hematopoietic stem cell transplantation (152.3 ± 36.4 ms) was significantly less than that before transplantation (165.5 ± 27.7 ms; P = .051). Pearson correlation analysis revealed a significant correlation between age and optic canal diameter (r = 0.722, P < .001).

CONCLUSIONS

The optic canal was narrower in pediatric patients with malignant infantile osteopetrosis than in age-matched normal controls. This condition can be relieved through hematopoietic stem cell transplantation and the impaired conductibility of the optic nerve can be improved in some cases. [J Pediatr Ophthalmol Strabismus. 2019;56(1):35-42.].

Impact of hematopoietic stem cell transplant on VEP and ABR values of the patients with malignant infantile osteopetrosis

OBJECTIVES

Malignant Infantile Osteopetrosis (MIOP) is a rare inherited disorder with neurological complications, notably visual impairment and decrease of hearing level. Although Hematopoietic Stem Cell Transplantation (HSCT) has been approved as the only curative treatment for these patients, the exact impact of it on visual and hearing level is still unclear.

STUDY DESIGN

We analyzed the P2 latency and amplitude from Visual Evoked Potentials (VEP) of 10 patients (20 eyes) and the threshold of wave V from Auditory Brainstem Response (ABR) of 15 patients (30 ears) with MIOP before, 6 and 12 months after HSCT.

RESULTS

Before the HSCT, 10/30 ears demonstrated some degree of hearing loss; while only 3/20 eyes had P2 wave latencies in normal range for age. Using GEE models, it was shown that 12 months after HSCT, wave V threshold of ABR of the patients was significantly lower compared to its value from before the transplant (p value: 0.04). The analysis of latency and amplitude of P2 wave of VEPs showed no significant difference between before and after the transplant.

CONCLUSION

This study clearly showed that HSCT can improve the hearing level of the patients in terms of ABR threshold. Although HSCT made no significant improvement in latency of P2 in VEP of the patients, it can be concluded that transplant can halt visual regression in these patients. Early diagnosis of MIOP with this objective tools and subsequently early HSCT in these patients can decrease the rate of neurological complications of MIOP and improve the quality of life in them.

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.

Case update on cranial osteopetrosis: which is the role of the neurosurgeon?

PURPOSE

Osteopetrosis (OP) is a rare skeletal disease, which can affect the skull base and calvaria. A multidisciplinary approach is mandatory and patient may need neurosurgical care. Few observations have been published, and optimal management of OP is not established yet.

METHOD

We report a case of an infant with OP diagnosed at 5 months, who presented signs of intracranial hypertension associated with unilateral blindness. Bone marrow allograft was performed at 6 months of age. At neurosurgical first examination at 11 months, the child was hypotonic, with severe amblyopia; features of bicoronal synostosis were appreciated, with tense anterior fontanel bulging indicating synostotic oxycephaly. Head circumference had decreased from +3 SD to +1SD. Cerebral CT scan showed reduction of intracranial volume, inward thickening of the calvaria, bilateral stenosis of optic canal, ventricular dilatation, enlarged arachnoid spaces, and tonsillar herniation. We performed cranial vault expansion with frontal advancement and bi parietal decompression, thinning of the inner table, unroofing of the left orbit and optic canal in order to obtain optic nerve decompression.

RESULTS

Postoperative course was uneventful, and the patient was discharged on day 8. Vision was unchanged but rapid improvement of axial tonus was noted. The CT scan showed satisfactory calvarial expansion with regression of tonsillar herniation.

CONCLUSIONS

Neurosurgical evaluation and care are necessary in the context of a multidisciplinary approach to the patient affected by osteopetrosis. Cranial vault remodeling and expansion should be considered in patients with sign of intracranial hypertension. Timing of optic canal decompression is to be defined.

Osteopetroses, emphasizing potential approaches to treatment

Osteopetroses are a heterogeneous group of rare genetic bone diseases sharing the common hallmarks of reduced osteoclast activity, increased bone mass and high bone fragility. Osteoclasts are bone resorbing cells that contribute to bone growth and renewal through the erosion of the mineralized matrix. Alongside the bone forming activity by osteoblasts, osteoclasts allow the skeleton to grow harmonically and maintain a healthy balance between bone resorption and formation. Osteoclast impairment in osteopetroses prevents bone renewal and deteriorates bone quality, causing atraumatic fractures. Osteopetroses vary in severity and are caused by mutations in a variety of genes involved in bone resorption or in osteoclastogenesis. Frequent signs and symptoms include osteosclerosis, deformity, dwarfism and narrowing of the bony canals, including the nerve foramina, leading to hematological and neural failures. The disease is autosomal, with only one extremely rare form associated so far to the X-chromosome, and can have either recessive or dominant inheritance. Recessive ostepetroses are generally lethal in infancy or childhood, with a few milder forms clinically denominated intermediate osteopetroses. Dominant osteopetrosis is so far associated only with mutations in the CLCN7 gene and, although described as a benign form, it can be severely debilitating, although not at the same level as recessive forms, and can rarely result in reduced life expectancy. Severe osteopetroses due to osteoclast autonomous defects can be treated by Hematopoietic Stem Cell Transplant (HSCT), but those due to deficiency of the pro-osteoclastogenic cytokine, RANKL, are not suitable for this procedure. Likewise, it is unclear as to whether HSCT, which has high intrinsic risks, results in clinical improvement in autosomal dominant osteopetrosis. Therefore, there is an unmet medical need to identify new therapies and studies are currently in progress to test gene and cell therapies, small interfering RNA approach and novel pharmacologic treatments.

The Holy Grail of Orthopedic Surgery: Mesenchymal Stem Cells-Their Current Uses and Potential Applications

Only select tissues and organs are able to spontaneously regenerate after disease or trauma, and this regenerative capacity diminishes over time. Human stem cell research explores therapeutic regenerative approaches to treat various conditions. Mesenchymal stem cells (MSCs) are derived from adult stem cells; they are multipotent and exert anti-inflammatory and immunomodulatory effects. They can differentiate into multiple cell types of the mesenchyme, for example, endothelial cells, osteoblasts, chondrocytes, fibroblasts, tenocytes, vascular smooth muscle cells, and sarcomere muscular cells. MSCs are easily obtained and can be cultivated and expanded in vitro; thus, they represent a promising and encouraging treatment approach in orthopedic surgery. Here, we review the application of MSCs to various orthopedic conditions, namely, orthopedic trauma; muscle injury; articular cartilage defects and osteoarthritis; meniscal injuries; bone disease; nerve, tendon, and ligament injuries; spinal cord injuries; intervertebral disc problems; pediatrics; and rotator cuff repair. The use of MSCs in orthopedics may transition the practice in the field from predominately surgical replacement and reconstruction to bioregeneration and prevention. However, additional research is necessary to explore the safety and effectiveness of MSC treatment in orthopedics, as well as applications in other medical specialties.

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

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

Level of evidence: Level IV.

Transplantation of Haploidentical TcRaß-Depleted Hematopoietic Cells Allows for Optimal Timing and Sustained Correction of the Metabolic Defect in Children With Infantile Osteopetrosis

In osteopetrosis, osteoclast dysfunction can lead to deafness, blindness, bone marrow failure, and death. Hematopoietic cell transplantation (HCT) is currently the only curative treatment, but outcome remains disappointing. Although a rapid progression toward HCT is detrimental to prevent further progress of disease manifestations, 70% of cases lack an HLA-matched sibling and require alternative stem cell sources. We present two cases of osteopetrosis that successfully received an HCT with haploidentical TcRαβ-depleted cells from one of the parents. These cases showed no further disease progression, had restoration of functional osteoclasts, and illustrate this approach to enable prompt HCT with ready available parental donors and rapid and sustained hematological, including osteoclast, recovery. © 2016 American Society for Bone and Mineral Research.

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.

Osteopetrosis in two siblings: two case reports

BACKGROUND

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

CASE PRESENTATION

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

CONCLUSION

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

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.

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.

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.

HLA-haploidentical stem cell transplantation after removal of αβ+ T and B cells in children with nonmalignant disorders

Removal of αβ+ T and CD19+ B cells is an effective strategy for successful HLA-haploidentical hematopoietic stem cell transplantation. The high probability of disease-free survival renders this transplant option attractive for any child with a nonmalignant disorder.

Lentiviral gene transfer of TCIRG1 into peripheral blood CD34(+) cells restores osteoclast function in infantile malignant osteopetrosis

Infantile malignant osteopetrosis (IMO) is a rare, lethal, autosomal recessive disorder characterized by non-functional osteoclasts. More than 50% of the patients have mutations in the TCIRG1 gene, encoding for a subunit of the osteoclast proton pump. The aim of this study was to restore the resorptive function of IMO osteoclasts by lentiviral mediated gene transfer of the TCIRG1 cDNA. CD34(+) cells from peripheral blood of five IMO patients and from normal cord blood were transduced with lentiviral vectors expressing TCIRG1 and GFP under a SFFV promoter, expanded in culture and differentiated on bone slices to mature osteoclasts. qPCR analysis and western blot revealed increased mRNA and protein levels of TCIRG1, comparable to controls. Vector corrected IMO osteoclasts generated increased release of Ca(2+) and bone degradation product CTX-I into the media as well as increased formation of resorption pits in the bone slices, while non-corrected IMO osteoclasts failed to resorb bone. Resorption was approximately 70-80% of that of osteoclasts generated from cord blood. Furthermore, transduced CD34(+) cells successfully engrafted in NSG-mice. In conclusion we provide the first evidence of lentiviral-mediated correction of a human genetic disease affecting the osteoclastic lineage.

Osteopetrosis: genetics, treatment and new insights into osteoclast function

Osteopetrosis is a genetic condition of increased bone mass, which is caused by defects in osteoclast formation and function. Both autosomal recessive and autosomal dominant forms exist, but this Review focuses on autosomal recessive osteopetrosis (ARO), also known as malignant infantile osteopetrosis. The genetic basis of this disease is now largely uncovered: mutations in TCIRG1, CLCN7, OSTM1, SNX10 and PLEKHM1 lead to osteoclast-rich ARO (in which osteoclasts are abundant but have severely impaired resorptive function), whereas mutations in TNFSF11 and TNFRSF11A lead to osteoclast-poor ARO. In osteoclast-rich ARO, impaired endosomal and lysosomal vesicle trafficking results in defective osteoclast ruffled-border formation and, hence, the inability to resorb bone and mineralized cartilage. ARO presents soon after birth and can be fatal if left untreated. However, the disease is heterogeneous in clinical presentation and often misdiagnosed. This article describes the genetics of ARO and discusses the diagnostic role of next-generation sequencing methods. The management of affected patients, including guidelines for the indication of haematopoietic stem cell transplantation (which can provide a cure for many types of ARO), are outlined. Finally, novel treatments, including preclinical data on in utero stem cell treatment, RANKL replacement therapy and denosumab therapy for hypercalcaemia are also discussed.

RANKL cytokine: from pioneer of the osteoimmunology era to cure for a rare disease

Since its identification, the RANKL cytokine has been demonstrated to play a crucial role in bone homeostasis and lymphoid tissue organization. Genetic defects impairing its function lead to a peculiar form of autosomal recessive osteopetrosis (ARO), a rare genetic bone disease presenting early in life and characterized by increased bone density due to failure in bone resorption by the osteoclasts. Hematopoietic stem cell transplantation (HSCT) is the only option for the majority of patients affected by this life-threatening disease. However, the RANKL-dependent ARO does not gain any benefit from this approach, because the genetic defect is not intrinsic to the hematopoietic osteoclast lineage but rather to the mesenchymal one. Of note, we recently provided proof of concept of the efficacy of a pharmacological RANKL-based therapy to cure this form of the disease. Here we provide an overview of the diverse roles of RANKL in the bone and immune systems and review the clinical features of RANKL-deficient ARO patients and the results of our preclinical studies. We emphasize that these patients present a continuous worsening of the disease in the absence of a cure and strongly wish that the therapy we propose will be further developed.

Osteomyelitis of the mandible in a patient with osteopetrosis. Case report and review of the literature

Osteopetrosis is a rare hereditary bone disorder presenting with variable clinical features and is characterized by an increase in bone density and reduction of marrow spaces that result from a defect in the function of osteoclasts and, consequently, a decrease in bone turnover. This disease is generally divided into three types: severe infantile malignant autosomal recessive, intermediate mild autosomal recessive, and benign autosomal dominant. The prognosis of the first two types is very poor and is characterized by an early onset, usually within the first decade of life, and early death. The benign-type is characterized by a later onset and a longer life span. Ten percent of osteopetrosis cases develop osteomyelitis that usually involves the mandible. The osteomyelitis is generally caused by tooth extraction or pulpal necrosis. The leading cause of the increased rate of infection is thought to be a lack of adequate bone vasculature. Treatment of osteomyelitis secondary to osteopetrosis is controversial. Treatment regimens include high-dose systemic antibiotics coupled with thorough debridement of necrotic bone and primary closure of soft tissues, if possible. Hyperbaric oxygen has been used for the treatment of chronic osteomyelitis.

A novel missense mutation in the CLCN7 gene linked to benign autosomal dominant osteopetrosis: a case series

Introduction

Osteopetrosis is a rare inherited genetic disease characterized by sclerosis of the skeleton. The absence or malfunction of osteoclasts is found to be strongly associated with the disease evolution. Currently, four clinically distinct forms of the disease have been recognized: the infantile autosomal recessive osteopetrosis, the malignant and the intermediate forms, and autosomal dominant osteopetrosis, type I and type II forms. The autosomal recessive types are the most severe forms with symptoms in very early childhood, whereas the autosomal dominant classes exhibit a heterogeneous trait with milder symptoms, often at later childhood or adulthood.

Case presentation

Case 1 is the 12-year-old daughter (index patient) of an Iraqi-Kurdish family who, at the age of eight years, was diagnosed clinically to have mild autosomal dominant osteopetrosis. Presently, at 12-years old, she has severe complications due to the disease progression. In addition, the same family previously experienced the death of a female child in her late childhood. The deceased child had been misdiagnosed, at that time, with thalassemia major. In this report, we extended our investigation to identify the type of the inheritance patterns of osteopetrosis using molecular techniques, because consanguineous marriages exist within the family history. We have detected one heterozygous mutation in exon 15 of the Chloride Channel 7 gene in the index patient (Case 1), whereas other mutations were not detected in the associated genes TCIRG1, OSTM1, RANK, and RANKL. The missense mutation (CGG>TGG) located in exon 15 (c.1225C>T) of the Chloride Channel 7 gene changed the amino acid position 409 from arginine to tryptophan (p.R409W, c.1225C>T).

Case 2 is the 16-year-old son (brother of the index patient) of the same family who was diagnosed clinically with mild autosomal dominant osteopetrosis. We have identified the same heterozygous mutation in exon 15 of the Chloride channel 7 gene in this patient (Case 2). The missense mutation (CGG>TGG) located in exon 15 (c.1225C>T) of the Chloride channel 7 gene changed the amino acid position 409 from arginine to tryptophan (p.R409W, c.1225C>T).

In addition to the clinical diagnosis of both cases, the missense mutation we identified in one allele of the Chloride channel 7 gene could be linked to autosomal dominant osteopetrosis-II because the symptoms appear in late childhood or adolescence.

Conclusion

In this family, the molecular diagnosis was confirmed after identification of the same mutation in the older son (sibling). Furthermore, we detected that the father and his brother (the uncle) are carriers of the same mutation, whereas the mother and her sister (the aunt) do not carry any mutation of the Chloride channel 7 gene. Thus, the disease penetrance is at least 60% in the family. The mother and father are cousins and a further consanguineous marriage between the aunt and the uncle is not recommended because the dominant allele of the Chloride channel 7 gene will be transferred to the progeny. However, a similar risk is also expected following a marriage between the uncle and an unrelated woman. The p.R409W mutation in the Chloride channel 7 gene has not yet been described in the literature and it possibly has a dominant-negative impact on the protein.

Rapid gene identification in a Chinese osteopetrosis family by whole exome sequencing

Osteopetrosis is a rare genetically heterogeneous disorder of bone metabolism characterized by increased skeleton density. In the past, standard methods for genetic diagnosis of osteopetrosis have primarily been performed by candidate gene screening and positional cloning. However, these methods are time and labor consumptive; and the genetic basis of approximately 30% of the cases is yet to be elucidated. Here, we employed whole exome sequencing of two affected individuals from an osteopetrosis family to identify a candidate mutation in CLCN7 (Y99C). It was identified from a total of 1757 and 1728 genetic variations found in either patient, which were then distilled using filtering strategies and confirmed using Sanger sequencing. We identified this mutation in six family members, while not in population matched controls. This mutation was previously found in osteopetrosis patients by other researchers. Our evolutionary analysis also indicated that it is under extremely high selective pressure, and is likely to be critical for the correct function of ClC-7, and thus is likely to be the responsible cause of disease. Collectively, our data further indicated that mutation (Y99C) may be a cause of osteopetrosis, and highlights the use of whole exome sequencing as a valuable approach to identifying disease mutations in a cost and time efficient manner.

Osteopetrosis rescue upon RANKL administration to Rankl(-/-) mice: a new therapy for human RANKL-dependent ARO

In the last decades the molecular basis of monogenic diseases has been largely unraveled, although their treatment has often remained unsatisfactory. Autosomal recessive osteopetrosis (ARO) belongs to the small group of genetic diseases that are usually treated with hematopoietic stem cell transplantation (HSCT). However, this approach is not effective in the recently identified form carrying mutations in the receptor activator of NF-κB ligand (RANKL) gene. In this subset, therapy replacement approach based on RANKL delivery has a strong rationale. Here we demonstrate that the systematic administration of RANKL for 1 month to Rankl(-/-) mice, which closely resemble the human disease, significantly improves the bone phenotype and has beneficial effects on bone marrow, spleen and thymus; major adverse effects arise only when mice are clearly overtreated. Overall, we provide evidence that the pharmacological administration of RANKL represents the appropriate treatment option for RANKL-deficient ARO patients, to be validated in a pilot clinical trial.