Infantile malignant osteopetrosis (IMOP) is a rare bone resorptive disorder with an autosomal recessive inheritance pattern. It is characterized by increased bone density due to osteoclastic failure in differentiation or function. The clinical manifestations of IMOP start at birth or infancy with varied rings according to the type and degree of osteopetrosis. We presented a 3-year-old female patient referred to us due to chronic anaemia six months ago. The physical examination revealed hepatosplenomegaly, axial hypotonia, and visual impairment. Blood investigation revealed pancytopenia and hypocalcemia. Radiologic studies revealed a generalized increase in bone density, abnormal metaphyseal remodelling, and rain atrophy. The bone marrow aspiration (BMA) shows dry tap and hypocellularity of all cell lines. IMOP was diagnosed depending on clinical, radiologic, and BMA results. In conclusion, IMOP is relatively uncommon. Accurate diagnosis should be made through clinical, BMA, and radiologic investigations, especially in a resource-limited setting, as performed in our case.

Infantile malignant osteopetrosis (IMO) is a rare autosomal recessive disease characterized by a higher bone density in bone marrow caused by the dysfunction of bone resorption. Clinically, IMO can be diagnosed with medical examination, bone mineral density test and whole genome sequencing.
We present the case of a 4-month-old male infant with abnormal skull development, hypocalcemia and premature closure of the cranial sutures. Due to the hyper bone density showed by his radiographic examination, which are characteristic patterns of IMO, we speculated that he might be an IMO patient. In order to confirm this diagnosis, a high-precision whole exome sequencing of the infant and his parents was performed. The analysis of high-precision whole exome sequencing results lead to the identification of two novel heterozygous mutations c.504-1G > C (a splicing site mutation) and c.1371delC (p.G458Afs*70, a frameshift mutation) in gene TCIRG1 derived from his parents. Therefore, we propose that there is a close association between these two mutations and the onset of IMO.
To date, these two novel mutations in gene TCIRG1 have not been reported in the reference gene database of Chinese population. These variants have likewise not been reported outside of China in the Genome Aggregation Database (gnomAD). Our case suggests that the use of whole exome sequencing to detect these two mutations will improve the identification and early diagnosis of IMO, and more specifically, the identification of homozygous individuals with TCIRG1 gene mutation. We propose that these mutations in gene TCIRG1 could be a novel therapeutic target for the IMO in the future.

A case of SNX10 gene mutation in a patient with infantile malignant osteopetrosis (IMO) was admitted to Department of Pediatrics, Third Xiangya Hospital, Central South University. The patient had the symptom of anemia, hepatosplenomegaly and growth retardation. The X-ray examination suggested extensive increase of bone density throughout the body, which was clinically diagnosed as IMO. The homozygous mutation of SNX10 gene c.61C>T was found via gene sequencing. We reviewed the relevant literatures and found that anemia, visual and hearing impairment, hepatosplenomegaly are the main clinical symptoms of IMO, SNX10 gene mutation is a rare cause of IMO, and hematopoietic stem cell transplantation is an effective treatment.
中南大学湘雅三医院儿科收治1例SNX10基因突变致婴儿恶性石骨症(infantile malignant osteopetrosis，IMO)患儿。该患儿临床表现为贫血、肝脾肿大、生长发育迟缓，X线检查提示全身骨密度广泛增高，临床诊断为IMO。基因测序为SNX10基因c.61C>T纯合突变。通过对国内外相关文献进行复习，发现贫血、视听力障碍、肝脾肿大是IMO的主要临床症状，SNX10基因突变是导致IMO的罕见原因，造血干细胞移植是其有效的治疗手段。.

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.

Infantile malignant osteopetrosis (IMO) is an autosomal recessive disorder characterized by non-functional osteoclasts and a fatal outcome early in childhood. About 50% of patients have mutations in the TCIRG1 gene.
IMO iPSCs were generated from a patient carrying a homozygous c.11279G>A (IVS18+1) mutation in TCIRG1 and transduced with a lentiviral vector expressing human TCIRG1. Embryoid bodies were generated and differentiated into monocytes. Non-adherent cells were harvested and further differentiated into osteoclasts on bovine bone slices.
Release of the bone resorption biomarker CTX-I into the media of gene-corrected osteoclasts was 5-fold higher than that of the uncorrected osteoclasts and 35% of that of control osteoclasts. Bone resorption potential was confirmed by the presence of pits on the bones cultured with gene-corrected osteoclasts, absent in the uncorrected IMO osteoclasts.
The disease phenotype was partially corrected in vitro, providing a valuable resource for therapy development for this form of severe osteopetrosis.

Osteopetrosis is a heterogeneous group of diseases that are characterized by increased bone density due to abnormalities in osteoclast differentiation or function, which result in a lack of bone resorption.
Two patients with osteopetrosis onset since the first months of life, with facial dysmorphia, blindness, deafness, hepatosplenomegaly, hypotonia, neurodevelopmental retardation and bicytopenia. Bone radiographs showed osteosclerosis. They were assessed by different specialists prior to definitive diagnosis. Genetic analysis determined mutations in the TCIRG1 gene. Patient 1 had a homozygous mutation for p.Ile720Alafs*14 identified, which hasn\'t been previously reported. Patient 2 had a compound heterozygous mutation: the first one, p.Phe459Leufs*79, and the second one, p.Gly159Argfs*68, none of which has been previously reported as far as we know.
The only therapeutic option for patients with osteopetrosis is hematopoietic stem cell transplantation (HSCT), which should be carried out in the course of the first 3 months of life, before neurological damage occurs. Although osteopetrosis diagnosis is relatively simple, it is delayed owing to the lack of clinical suspicion.
Antecedentes: La osteopetrosis es un grupo heterogéneo de enfermedades que se caracterizan por aumento de la densidad ósea debido a anomalías en la diferenciación o función de los osteoclastos, lo que se traduce en falta de reabsorción ósea. Reporte de casos: Dos pacientes con osteopetrosis quienes iniciaron su padecimiento desde los primeros meses de vida, con dismorfia facial, ceguera, sordera, hepatoesplenomegalia, hipotonía, retraso del neurodesarrollo y bicitopenia. Las radiografías óseas mostraron osteoesclerosis. Fueron valorados por diversos especialistas antes del diagnóstico definitivo. El análisis genético determinó mutaciones en el gen TCIRG1. En el paciente 1 se identificó una mutación homocigota para p.Ile720Alafs*14, la cual no ha sido reportada. En el paciente 2 se registró una mutación heterocigota compuesta: la primera p.Phe459Leufs*79 y la segunda p.Gly159Argfs*68, ninguna de las cuales han sido descritas hasta donde tenemos conocimiento. Conclusión: La única opción terapéutica de los pacientes con osteopetrosis es el trasplante de células progenitoras hematopoyéticas (TCPH), que se debe realizar en el transcurso de los primeros tres meses de vida, antes de que se origine daño neurológico. Si bien el diagnóstico de osteopetrosis es relativamente sencillo, se retrasa debido a la falta de sospecha clínica.

Tfifha M, Gaha M, Gamaoun W, Chemli J, Mabrouk S, Hassayoun S, Zouari N, Jemni H, Abroug S. Clinical and imaging features of malignant infantile osteopetrosis. Turk J Pediatr 2017; 59: 452-457. Human osteopetrosis is a rare genetic disorder caused by osteoclast failure. It encompasses a group of highly heterogeneous forms, ranged widely in severity. Patients with autosomal recessive osteopetrosis are the most severely affected osteopetrotic patients. Here we describe Tunisian children with severe phenotype. They are native from the same geographic region, born to consanguineous parents. Clinical features were cranio-facial dysmorphy, macrocephaly, hepatosplenomegaly, severe anemia and thrombocytopenia with precocious onset of neuronopathic complications, blindness and deafness. Retinal atrophy, reported in a minority of forms is highlighted. Skeletal radiographs revealed generalized increase in bone density and abnormal metaphyseal remodeling, and superimposed rickets resulting from the defect in osteoclasts to provide a normal Ca/P balance. We report an exceptional association with congenital hypothyroidism. Multi-organ failure due to sepsis is one the most severe complications observed. The issue was fatal without hematopoietic stem cell transplantation.

Osteopetrosis is a rare inherited bone disorder mainly described as an increased bone density caused by defective osteoclastic bone resorption. To date, genetic variants of eleven genes have been reported so far to be associated with different types of osteopetrosis. However, malignant infantile osteopetrosis, a lethal form of the disease, is mostly (50%) caused by mutation(s) in TCIRG1 gene. In this study, we investigated a consanguineous Pakistani family clinically and genetically to elucidate underlying molecular basis of the infantile osteopetrosis.
DNA samples from five family members were subjected to SNP-array based whole genome homozygosity mapping. Data was analyzed and potentially pathogenic mutation was identified by Sanger sequencing of two affected as well as three phenotypically healthy individuals in the family. The significance of identified pathogenic variation and its impact on protein structure and function was studied using various bioinformatics tools.
DNA samples from five family members were subjected to genome-wide SNP array genotyping and homozygosity mapping which identified ~4 Mb region on chr11 harboring the TCIRG1 gene. Sanger sequencing unveiled a novel homozygous deletion c. 624delC in exon 6 of the TCIRG1 gene encodes a3 subunit of V-ATPase complex. The identified deletion resulted in a frame shift producing a truncated protein of 208 aa. In silico analysis of premature termination of the a3 subunit of V-ATPase complex revealed deleterious effects on the protein structure, predicting impaired or complete loss of V-ATPase function causing infantile osteopetrosis.
Since a3 subunit of V-ATPase complex plays a crucial role in bone resorption process, structurally abnormal a3 subunit might have adversely affected bone resorption process, leading to infantile osteopetrosis in Pakistani family. Therefore, the present study not only expands the genotypic spectrum of osteopetrosis but also improve understandings of the role of V-ATPase a3 subunit in bone resorption process. Moreover, our findings should help in genetic counseling and provide further insight into the disease pathogenesis and potential targeted therapy.

OBJECTIVE: To evaluate radiological findings in a cohort of 22 patients with infantile malignant osteopetrosis in order to establish the correlation between radiological findings and different genetic backgrounds.
METHODS: Clinical files, genetic analysis results, and radiological examinations of children treated for osteopetrosis with bone marrow transplantation in a referral center in the last 5 years were retrospectively evaluated. The study received institutional review board (IRB) approval.
RESULTS: Twenty-two patients were included in the study: 18 males, four females, ages 1 month-9 years 10 months, and the median age was 11 months (mean 23 months). There were 12 patients with different mutations in the TCIRG1 gene, five with mutations in the SNX10 gene, four children harbored RANK mutations, and one patient had a CLCN7 mutation. We noted more severe radiological findings in patients with TCIRG1 and RANK mutations, including fractures, osteopetrorickets, hydrocephalus, and hepatomegaly. Varus deformity of the femoral neck was seen exclusively in patients with a TCIRG1 mutation.
CONCLUSIONS: The variable genetic spectrum of osteopetrosis is associated with a variable radiological presentation. These correlations may be helpful for priorities in genetic analysis.

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.