[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.

Human Genetics of Sclerosing Bone Disorders.

PURPOSE OF REVIEW: The group of sclerosing bone disorders encompasses a variety of disorders all marked by increased bone mass. In this review, we give an overview of the genetic causes of this heterogeneous group of disorders and briefly touch upon the value of these findings for the development of novel therapeutic agents. RECENT FINDINGS: Advances in the next-generation sequencing technologies are accelerating the molecular dissection of the pathogenic mechanisms underlying skeletal dysplasias. Throughout the years, the genetic cause of these disorders has been extensively studied which resulted in the identification of a variety of disease-causing genes and pathways that are involved in bone formation by osteoblasts, bone resorption by osteoclasts, or both processes. Due to this rapidly increasing knowledge, the insights into the regulatory mechanisms of bone metabolism are continuously improving resulting in the identification of novel therapeutic targets for disorders with reduced bone mass and increased bone fragility.

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 due to Snx10 deficiency in mice results from both failed osteoclast activity and loss of gastric acid-dependent calcium absorption.

Mutations in sorting nexin 10 (Snx10) have recently been found to account for roughly 4% of all human malignant osteopetrosis, some of them fatal. To study the disease pathogenesis, we investigated the expression of Snx10 and created mouse models in which Snx10 was knocked down globally or knocked out in osteoclasts. Endocytosis is severely defective in Snx10-deficient osteoclasts, as is extracellular acidification, ruffled border formation, and bone resorption. We also discovered that Snx10 is highly expressed in stomach epithelium, with mutations leading to high stomach pH and low calcium solubilization. Global Snx10-deficiency in mice results in a combined phenotype: osteopetrosis (due to osteoclast defect) and rickets (due to high stomach pH and low calcium availability, resulting in impaired bone mineralization). Osteopetrorickets, the paradoxical association of insufficient mineralization in the context of a positive total body calcium balance, is thought to occur due to the inability of the osteoclasts to maintain normal calcium-phosphorus homeostasis. However, osteoclast-specific Snx10 knockout had no effect on calcium balance, and therefore led to severe osteopetrosis without rickets. Moreover, supplementation with calcium gluconate rescued mice from the rachitic phenotype and dramatically extended life span in global Snx10-deficient mice, suggesting that this may be a life-saving component of the clinical approach to Snx10-dependent human osteopetrosis that has previously gone unrecognized. We conclude that tissue-specific effects of Snx10 mutation need to be considered in clinical approaches to this disease entity. Reliance solely on hematopoietic stem cell transplantation can leave hypocalcemia uncorrected with sometimes fatal consequences. These studies established an essential role for Snx10 in bone homeostasis and underscore the importance of gastric acidification in calcium uptake.

Dynein light chain LC8 inhibits osteoclast differentiation and prevents bone loss in mice.

NF-κB is one of the key transcription factors activated by receptor activator of NF-κB ligand (RANKL) during osteoclast differentiation. The 8-kDa dynein L chain (LC8) was previously identified as a novel NF-κB regulator. However, its physiological role as an NF-κB inhibitor remains elusive. In this study, we showed the inhibitory role of LC8 in RANKL-induced osteoclastogenesis and signaling pathways and its protective role in osteolytic animal models. LC8 suppressed RANKL-induced osteoclast differentiation, actin ring formation, and osteoclastic bone resorption. LC8 inhibited RANKL-induced phosphorylation and subsequent degradation of IκBα, the expression of c-Fos, and the consequent activation of NFATc1, which is a pivotal determinant of osteoclastogenesis. LC8 also inhibited RANKL-induced activation of JNK and ERK. LC8-transgenic mice exhibited a mild osteopetrotic phenotype. Moreover, LC8 inhibited inflammation-induced bone erosion and protected against ovariectomy-induced bone loss in mice. Thus, our results suggest that LC8 inhibits osteoclast differentiation by regulating NF-κB and MAPK pathways and provide the molecular basis of a new strategy for treating osteoporosis and other bone diseases.

Rickets in osteopetrosis--a paradoxical association.

Osteopetrosis is a hereditary bone disease with intense positive balance of body calcium. Infantile variety is often associated with rickets--a paradoxical association. Two siblings with osteopetro rickets are reported in the article. The pathophysiologic mechanism of the paradoxical association has been explained and various management options have been discussed. Both cases were treated with high dose calcitriol and calcium supplements.

Osteopetrosis and thalamic hypomyelinosis with synaptic degeneration in DAP12-deficient mice.

Deletions in the DAP12 gene in humans result in Nasu-Hakola disease, characterized by a combination of bone fractures and psychotic symptoms similar to schizophrenia, rapidly progressing to presenile dementia. However, it is not known why these disorders develop upon deficiency in DAP12, an immunoreceptor signal activator protein initially identified in the immune system. Here we show that DAP12-deficient (DAP12(-/-)) mice develop an increased bone mass (osteopetrosis) and a reduction of myelin (hypomyelinosis) accentuated in the thalamus. In vitro osteoclast induction from DAP12(-/-) bone marrow cells yielded immature cells with attenuated bone resorption activity. Moreover, immature oligodendrocytes were arrested in the vicinity of the thalamus, suggesting that the primary defects in DAP12(-/-) mice are the developmental arrest of osteoclasts and oligodendrocytes. In addition, the mutant mice also showed synaptic degeneration, impaired prepulse inhibition, which is commonly observed in several neuropsychiatric diseases in humans including schizophrenia, and aberrant electrophysiological profiles in the thalami. These results provide a molecular basis for a unique combination of skeletal and psychotic characteristics of Nasu-Hakola disease as well as for schizophrenia and presenile dementia.

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.

Skeletal resistance to 1,25-dihydroxyvitamin D3 in osteopetrotic rats.

The osteopetrotic (op/op) rat mutation is a lethal mutation in which decreased osteoclast function (bone resorption) coexists with markedly elevated serum levels of 1 ,25-dihydroxyvitamin D3[1,25(OH)2D3]. Increased circulating levels of 1,25(OH)2D3 have been reported in other osteopetrotic animal mutations and in some osteopetrotic children. This study examined the effects of 1,25(OH)2D3 infusions on serum and skeletal parameters in normal and mutant rats of op stock. We also examined vitamin D receptor expression and binding in bone cells from op normal and mutant animals. Four-week-old normal and mutant rats were infused either with propylene glycol (used as controls) or with 12.5-125 ng of 1,25(OH)2D3/d using osmotic minipumps implanted subcutaneously for 1 wk. Sera were analyzed for calcium, phosphorus, and 1,25(OH)2D3 levels. Histomorphometric analyses of proximal tibiae from treated normal (50 ng/d) and op mutant (125 ng/d) rats and their vehicle-infused controls were performed. Normal animals infused with 1,25(OH)2D3 exhibited a dose-dependent increase in serum calcium levels. Histomorphometric analyses of metaphyseal bone within the primary spongiosae region showed that 1,25(OH)2D3 increased osteoclast number with a reduction in osteoblast surface associated with a decrease in growth plate cartilage thickness. However, similar analyses on secondary spongiosae showed a decrease in osteoclast number and surface associated with an anabolic response. Op mutants infused with 1,25(OH)2D3 did not exhibit any change in serum calcium levels or histomorphometric parameters related to growth plate cartilage and metaphyseal bone compared with mutant controls. Vitamin D mRNA and protein levels were increased twoto threefold in op mutants compared to age-matched normal rats. However, binding affinity of 1,25(OH)2D3 to its receptor was similar between op mutant and normal animals. High dose calcitriol therapy, under the conditions and period of treatment used in this study, failed to stimulate bone turnover in op rats, suggesting that they are resistant to the skeletal effects of 1,25(OH)2D3. The failure of osteoclast activation in response to 1,25(OH)2D3 treatment may be associated with osteoblast incompetence in this mutation.

The protein tyrosine kinase p60c-Src is not implicated in the pathogenesis of the human autosomal recessive form of osteopetrosis: a study of 13 children.

Osteopetrosis has been described in mice generated by homozygous gene disruption of c-src gene encoding for the p60c-Src protein tyrosine kinase (Src-/- mice). The similarities of bone histologic findings in this murine model to those observed in some patients first seen with autosomal recessive osteopetrosis, "malignant" osteopetrosis, led us to investigate the potential role of p60c-Src in the pathogenesis of malignant osteopetrosis in 13 children. In 4 patients a c-src mutation was ruled out by an intragenic microsatellite segregation study. In the other 9 we analyzed p60c-Src expression and function, as well as c-src sequence. The expression was normal in all of the patients tested. In addition, the tyrosine phosphorylation and kinase activity of p60c-Src were also normal in all of the patients. Moreover, in these patients, sequences of the coding region of c-src were identical to the published sequence of the human c-src complementary DNA. These results exclude a role for c-src in the pathogenesis of human malignant osteopetrosis in the 13 patients analyzed.

Ultrastructure of the ankylotic area in the osteopetrotic op/op mouse.

The op/op mouse, which carries an osteopetrotic mutation, suffers from complete failure of tooth eruption. Commonly the teeth are ankylosed to the bone. Previous reports of ankylosis in the op/op mouse have been based on light microscopy. The aim of this study was to clarify the ultrastructural features of the ankylotic area using the oolong tea extract (OTE) staining technique. The ultrastructural features of ankylosis did not parallel the findings of light microscopy. OTE staining clearly stained the collagen fibers of bone and tooth, and the space dividing the tooth and bone was revealed by transmission electron microscopy. In comparison, light microscopy failed to reveal this space and the ankylosis was unclear. The true ankylotic area was smooth and the tooth was tightly ankylosed to the bone.

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.

Regulation of mineral homeostasis in osteopetrotic (op) rats.

The osteopetrotic (op) rat is a lethal mutation characterized by severe skeletal sclerosis resulting from reduced bone resorption. Although the skeletal manifestations have been studied extensively, little is known about mineral homeostasis in this mutation. This paucity of data prompted us to undertake this study quantitating circulating levels of calcium, phosphorus, 1,25-dihydroxyvitamin D [1,25(OH)2D] and parathyroid hormone (PTH) in op mutants and normal rats between 2 and 8 wk of age. Calcium and phosphorus levels were significantly lower in op mutants at younger ages; both parameters normalized by 6 wk. Serum levels of 1,25(OH)2D were markedly elevated in op rats at all ages and showed no signs of normalization. Serum PTH levels were also elevated at most ages, with the greatest increase occurring when op mutants were severely hypocalcemic. These results demonstrate that, in op mutants, changes in circulating PTH and calcium levels were interdependent; however, levels of 1,25(OH)2D did not change despite normalization of serum calcium and phosphorus. The latter deserves further investigation and supports the hypothesis of a localized (skeletal) resistance to 1,25(OH)2D.

Neonatal reductions in osteoclast number and function account for the transient nature of osteopetrosis in the rat mutation microphthalmia blanc (mib).

We have examined the general and skeletal manifestations of osteopetrosis in a new, mild osteopetrotic mutation in the rat, microphalmia blanc (mib). Newborn mutant (mib) rats exhibit the typical skeletal deformities and sclerosis of osteopetrosis at birth, which are reduced significantly during the first postnatal month but don't disappear entirely up to 8 months later. Osteoclast numbers, staining for TRAP and TraATPase, and bone resorption are reduced in mutants during the first 2 postnatal weeks but improve by 1 month. In mutants, serum concentrations of calcium and phosphorus are normal, but 1,25(OH)2 D levels are higher at 1 week than those in normal littermates. Neonatally, mutants exhibit extramedullary hemopoiesis in the spleen. These results are interpreted to mean that the transient perinatal skeletal sclerosis in mib rats is caused by reduced production and function of osteoclasts in this period. The recent description of transient, perinatal osteopetrosis in a child suggests that analyses of the early differences between mild and severe animal mutations might distinguish those children with osteopetrosis who need treatment from those who do not.

Cranial imaging in autosomal recessive osteopetrosis. Part II. Skull base and brain.

The authors reviewed cranial imaging studies (radiographs, computed tomographic scans, and magnetic resonance [MR] images) in 13 infants and children with the autosomal recessive form of osteopetrosis to characterize patterns of skull base, brain, and cranial nerve involvement at presentation and with progression of disease. Marked sclerosis and deposition of osteopetrotic bone was noted along the anterior (but not posterior) occipitomastoid suture (n = 8), at the basioccipital-exoccipital synchondrosis (n = 9), and along the sphenooccipital synchondrosis (n = 8). Endobones, presumably representing unresorbed primitive ossification centers, were seen in the sphenoidal body and basioccipital bone in 11 of the 13 patients. Marked cupping at the basioccipital-exoccipital synchondrosis was observed in three. Neurologic deficits included blindness (n = 11), conductive hearing loss (n = 11), and facial nerve palsies (n = 4). Delayed myelination was seen with MR imaging in two of five retarded infants, including one with a documented coexisting neuronal storage defect. Prominent extracerebral cerebrospinal fluid spaces were present over the frontal lobes in five of the eight developmentally normal patients, representing either subclinical parenchymal disease or a phenomenon related to discordant growth rates between skull and brain.

The osteopetrotic rabbit: general and skeletal features of a new outbred stock.

Stock of the lethal osteopetrotic mutation in the rabbit has been outbred to robust New Zealand White stock. Features of this new stock include skeletal sclerosis and failure of tooth eruption characteristic of osteopetrosis, together with hypocalcemia, hypophosphatemia, and osteoclasts of reduced numbers and abnormal cytology. No abnormalities of carbonic anhydrase II were detectable by electrophoresis. The commercial availability of mutants of this new stock makes them a potentially important source of information about both osteopetrosis and osteoclast biology.

"Osteopetrosis" in the Fairbank Collection.

The "osteopetrosis" section of the Fairbank Collection in the Radiology Museum of the Royal National Orthopaedic Hospital contains radiographs and case notes of twenty-two patients. This material has been reviewed in terms of modern concepts in an attempt to obtain a long-term follow-up and a firm diagnosis in each individual. Nine patients proved to have the classical autosomal dominant form of osteopetrosis, four had the malignant autosomal recessive type, craniometaphyseal dysplasia was present in two kindreds and isolated individuals had pyknodysostosis, atypical craniodiaphyseal dysplasia and craniosclerosis with osteopathia striata. As these conditions differ greatly in their clinical and genetic prognoses, diagnostic categorisation is of practical importance.