[Analysis of clinical presentation and genetic characteristics of malignant infantile osteopetrosis].

Objective: To investigate the clinical presentation and genetic characteristics of malignant infantile osteopetrosis. Methods: This was a retrospective case study. Thirty-seven children with malignant infantile osteopetrosis admitted into Beijing Children's Hospital from January 2013 to September 2022 were enrolled in this study. According to the gene mutations, the patients were divided into the CLCN7 group and the TCIRG1 group. Clinical characteristics, laboratory tests, and prognosis were compared between two groups. Wilcoxon test or Fisher exact test were used in inter-group comparison. The survival rate was estimated with the Kaplan-Meier method and the Log-Rank test was used to compare the difference in survival between groups. Results: Among the 37 cases, there were 22 males and 15 females. The age of diagnosis was 0.5 (0.2, 1.0) year. There were 13 patients (35%) and 24 patients (65%) with mutations in CLCN7 and TCIRGI gene respectively. Patients in the CLCN7 group had an older age of diagnosis than those in the TCIRGI group (1.2 (0.4, 3.6) vs. 0.4 (0.2, 0.6) years, Z=-2.60, P=0.008). The levels of serum phosphorus (1.7 (1.3, 1.8) vs. 1.1 (0.8, 1.6) mmol/L, Z=-2.59, P=0.010), creatine kinase isoenzyme (CK-MB) (457 (143, 610) vs. 56 (37, 82) U/L, Z=-3.38, P=0.001) and the level of neutrophils (14.0 (9.9, 18.1) vs. 9.2 (6.7, 11.1) ×109/L, Z=-2.07, P=0.039) at diagnosis were higher in the CLCN7 group than that in the TCIRG1 group. However, the level of D-dimer in the CLCN7 group was lower than that in the TCIRGI group (2.7 (1.0, 3.1) vs. 6.3 (2.5, 9.7) µg/L, Z=2.83, P=0.005). After hematopoietic stem cell transplantation, there was no significant difference in 5-year overall survival rate between the two groups (92.3%±7.4% vs. 83.3%±7.6%, χ²=0.56, P=0.456). Conclusions: TCIRGI gene mutations are more common in children with osteopetrosis. Children with TCIRGI gene mutations have younger age, lower levels of phosphorus, CK-MB, and neutrophils and higher level of D-dimer at the onset. After hematopoietic stem cell transplantation, patients with CLCN7 or TCIRGI gene mutations have similar prognosis.

Effects of hypothalamic leptin gene therapy on osteopetrosis in leptin-deficient mice.

Impaired resorption of cartilage matrix deposited during endochondral ossification is a defining feature of juvenile osteopetrosis. Growing, leptin-deficient ob/ob mice exhibit a mild form of osteopetrosis. However, the extent to which the disease is (1) self-limiting and (2) reversible by leptin treatment is unknown. We addressed the first question by performing histomorphometric analysis of femurs in rapidly growing (2-month-old), slowly growing (4-month-old) and skeletally mature (6-month-old) wild-type (WT) and ob/ob male mice. Absent by 6 months of age in WT mice, cartilage matrix persisted to varying extents in distal femur epiphysis, metaphysis and diaphysis in ob/ob mice, suggesting that the osteopetrotic phenotype is not entirely self-limiting. To address the second question, we employed hypothalamic recombinant adeno-associated virus (rAAV) gene therapy to restore leptin signaling in ob/ob mice. Two-month-old mice were randomized to one of the three groups: (1) untreated control, (2) rAAV-Leptin or (3) control vector rAAV-green fluorescent protein and vectors injected intracerebroventricularly. Seven months later, rAAV-leptin-treated mice exhibited no cartilage in the metaphysis and greatly reduced cartilage in the epiphysis and diaphysis. At the cellular level, the reduction in cartilage was associated with increased bone turnover. These findings (1) support the concept that leptin is important for normal replacement of cartilage by bone, and (2) demonstrate that osteopetrosis in ob/ob mice is bone-compartment-specific and reversible by leptin at skeletal sites capable of undergoing robust bone turnover.

[Malignant infantile osteopetrosis revealed by choanal atresia: A case report]. / Ostéopétrose maligne infantile révélée par une atrésie des choanes : à propos d'un cas.

Malignant infantile osteopetrosis is a rare genetic disease characterized by increased bone density due to osteoclastic dysfunction. We report on the case of a 3-month-old girl who was referred to our hospital by the ENT department for severe anemia in the context of bilateral choanal atresia. Clinical examination showed failure to thrive, anemia, respiratory distress, bilateral choanal atresia, and chest deformation. The abdomen was soft with large hepatosplenomegaly. We noted a lack of eye tracking, no optical-visual reflexes, and left nerve facial paralysis. The blood count showed normocytic normochromic anemia with severe thrombocytopenia. The infectious work-up and blood smears were negative. The skeleton X-ray showed diffuse bone densification of the skull, long bones, pelvis, vertebrae, and ribs. The facial bone CT confirmed membranous choanal atresia. The molecular biology search for the TCIRG1 gene mutation was not available. The patient had supportive treatment (transfusion, oral steroid, vitamin D, oxygen, nutrition). Bone marrow transplantation was indicated but not available. She died at 6 months in a context of severe anemia and bleeding. Malignant infantile osteopetrosis is rare and symptoms are nonspecific. Diagnosis should be considered in young infants presenting refractory anemia, particularly in the context of choanal atresia. Bone marrow transplantation remains the only curative treatment.

Osteopetrorickets: case report.

UNLABELLED: We report the case of a baby girl who presented with rickets at 3 months. At the age of 5 months she was readmitted because of nystagmus and a diagnosis of osteopetrosis was made on the basis of clinical and radiological findings. Rickets is a paradoxical feature of osteopetrosis resulting from inability to maintain a normal calcium-phosphorus balance. In our patient the onset of rickets before other symptoms of osteopetrosis suggests a primary defect. CONCLUSION: It is possible that patients with osteopetrosis and rickets (osteopetrorickets) represent a different mutation like the osteopetrosis mouse, which is the only animal mutation with rickets.

Dual-energy x-ray absorptiometry in osteopetrosis.

We have used dual-energy x-ray absorptiometry (DXA) in evaluation and follow-up of a patient with osteopetrosis, before and after cord blood transplantation. Other methods of follow-up in such cases have been described, but the use of DXA has not previously been reported. We have shown that DXA offers a safe means of assessing disease progression, the timing of treatment, and response after therapy for osteopetrosis.

Managing osteopetrosis in children: a nutrition challenge.

Osteopetrosis, a rare condition caused by a failure of osteoclasts to resorb bone, results in dense and deformed bones, growth failure, anemia, hypoplastic dentition, chronic infection, blindness, and massive splenomegaly. Children with infantile osteopetrosis have disease-related complications that affect nutritional status. Altered calcium and phosphorus intake has been reported in these patients, but previous studies did not include an assessment of dietary adequacy or nutrition-related complications. A prospective study of six children with severe infantile osteopetrosis was conducted to identify specific nutrition-related problems and effective nutrition intervention strategies. Patients were monitored by a registered dietitian while they participated in a clinical research protocol at St Jude Children's Research Hospital. Dietary records for each patient were obtained at set intervals during the 4-month study period. Because most patients lacked adequate dentition, they had difficulty obtaining adequate nutrition through normal oral intake. Three children required nutrition supplementation (enteral feedings for one and oral supplements for two). We conclude that oral and enteral nutrition support can provide nutrients needed for improved growth and response to treatment in patients with osteopetrosis.

Normalization of mineral homeostasis after reversal of osteopetrosis.

Whether a radiographic and histologic cure of osteopetrosis includes normalization of mineral homeostasis remains unknown. Thus, we explored the extent of defective mineral metabolism in the microphthalmic (mi/mi) mouse before and after cure. Under basal conditions mi mutants exhibit normocalcemia, hypophosphatemia, and elevated renal 25-hydroxyvitamin D-1-hydroxylase activity. However, administration of PTHrP (3 micrograms/h x 24 h) further stimulated enzyme activity in mi mutants with active disease, to a level no different than that in treated normals. Serum phosphorus levels also declined in mi/mi mice following PTHrP, suggesting a normal renal response to this hormone. In contrast, failure to suppress enzyme function in mi/mi mice following prolonged calcitriol infusion indicates that the observed enhancement of 1,25-dihydroxyvitamin D production occurred secondary to autonomous parathyroid function and/or nonparathyroid hormone-related stimuli. Although an increased fractional excretion and decreased tubular reabsorption of phosphate were demonstrated in mi/mi mice, serum PTH levels were no different in mi mutants compared with normal littermates. Following skeletal cure, the mi/mi mice surprisingly display normal serum phosphorus levels and renal enzyme activity. Moreover, treatment restored normal responsiveness to calcitriol suppression and maintained normal PTHrP responsiveness of enzyme activity. These data indicate that the cure of osteopetrosis in the mi mutant is universal and includes normalization of serum phosphorus and renal 25-hydroxyvitamin D-1-hydroxylase. Furthermore, these data suggest that phosphate depletion of unknown origin is the likely cause of elevated enzyme activity in this murine osteopetrotic mutant.

Experimental studies of osteopetrosis in laboratory animals.

Osteopetrosis is a metabolic bone disease characterized by a systemic increase in skeletal mass. It results from a defect in the production or function of osteoclasts and is inherited in nine genetically distinct osteopetrotic animal mutations and man. Studies of these mutations have revealed that osteopetrosis is a complex, heterogeneous disorder in its expression, etiology, and response to treatment by bone marrow transplantation or by hormone/growth factor therapy. These animal mutations have been valuable tools for probing the pathogenesis and treatment of osteopetrosis, and information obtained from these studies has been used clinically for the treatment of humans with osteopetrosis. In addition, studies of these mutations have contributed significantly to understanding normal bone cell biology, including the origin of the osteoclast and the significance of colony-stimulating factor-1 in osteoclast development. The resistance of some of these mutations to cure by stem cell transplantation and hormone therapy, coupled with similar observations and experiences in the human condition, indicates that these animal mutations will continue to serve important roles in the development of alternative therapies to treat resistant forms of the disease. These studies are bound to improve the understanding of normal bone biology by providing additional insights into the regulation of osteoclasts by osteoblasts and their products or by other elements of the skeletal microenvironment.