Dysosteosclerosis presents as an "osteoclast-poor" form of osteopetrosis: comprehensive investigation of a 3-year-old girl and literature review

Effects of anti-RANKL antibodies administered to pregnant mice on bone and tooth development in neonates

OBJECTIVES

This study examined how the anti-bone resorptive agent denosumab, which comprises anti-receptor activator of nuclear factor kappa B ligand (anti-RANKL) monoclonal antibodies, administered during pregnancy affected neonatal development. Anti-RANKL antibodies, which are known to bind to mouse RANKL and inhibit osteoclast formation, were administered to pregnant mice. Following this, the survival, growth, bone mineralization, and tooth development of their neonates were analyzed.

METHODS

Anti-RANKL antibodies (5 mg/kg) were injected into pregnant mice on day 17 of gestation. After parturition, their neonatal offspring underwent microcomputed tomography at 24 h and at 2, 4, and 6 weeks after birth. Three-dimensional bone and teeth images were subjected to histological analysis.

RESULTS

Approximately 70% of the neonatal mice born to mice who received anti-RANKL antibodies died within 6 weeks after birth. These mice had a significantly lower body weight and significantly higher bone mass compared with the control group. Furthermore, delayed tooth eruption and abnormal tooth morphology (eruption length, enamel surface, and cusps) were observed. Conversely, while the tooth germ shape and mothers against decapentaplegic homolog 1/5/8 expression remained unchanged at 24 h after birth in the neonatal mice born to mice that received anti-RANKL antibodies, osteoclasts were not formed.

CONCLUSIONS

These results suggest that anti-RANKL antibodies administered to mice in the late stage of pregnancy results in adverse events in their neonatal offspring. Thus, it is speculated that administering denosumab to pregnant humans will affect fetal development and growth after birth.

Osteopetrosis: Gene-based nosology and significance Dysosteosclerosis

Dysosteosclerosis (DSS) refers to skeletal dysplasias that radiographically feature focal appendicular osteosclerosis with variable platyspondyly. Genetic heterogeneity is increasingly reported for the DSS phenotype and now involves mutations of SLC29A3, TNFRSF11A, TCIRG1, LRRK1, and CSF1R. Typical radiological findings are widened radiolucent long bones with thin cortices yet dense irregular metaphyses, flattened vertebral bodies, dense ribs, and multiple fractures. However, the radiographic features of DSS evolve, and the metaphyseal and/or appendicular osteosclerosis variably fades with increasing patient age, likely due to some residual osteoclast function. Fractures are the principal presentation of DSS, and may even occur in infancy with SLC29A3-associated DSS. Cranial base sclerosis can lead to cranial nerve palsies such as optic atrophy, and may be the initial presentation, though not observed with SLC29A3-associated DSS. Gene-specific extra-skeletal features can be the main complication in some forms of DSS such as CSF1R- associated DSS. Further genetic heterogeneity is likely, especially for X-linked recessive DSS and cases currently with an unknown genetic defect. Distinguishing DSS can be challenging due to variable clinical and radiological features and an evolving phenotype. However, defining the DSS phenotype is important for predicting complications, prognosis, and instituting appropriate health surveillance and treatment.

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 remodeling: an operational process ensuring survival and bone mechanical competence

Bone remodeling replaces old and damaged bone with new bone through a sequence of cellular events occurring on the same surface without any change in bone shape. It was initially thought that the basic multicellular unit (BMU) responsible for bone remodeling consists of osteoclasts and osteoblasts functioning through a hierarchical sequence of events organized into distinct stages. However, recent discoveries have indicated that all bone cells participate in BMU formation by interacting both simultaneously and at different differentiation stages with their progenitors, other cells, and bone matrix constituents. Therefore, bone remodeling is currently considered a physiological outcome of continuous cellular operational processes optimized to confer a survival advantage. Bone remodeling defines the primary activities that BMUs need to perform to renew successfully bone structural units. Hence, this review summarizes the current understanding of bone remodeling and future research directions with the aim of providing a clinically relevant biological background with which to identify targets for therapeutic strategies in osteoporosis.

Precontouring Plates for MIS Bilateral Femur Osteosynthesis Using a Patient-Specific 3D Printed Model: A Case Report

CASE

A 27-year-old woman with increasing bilateral thigh pain and underlying diagnosis of dysosteosclerosis was diagnosed with bilateral impending pathological femur fractures. Both femurs exhibited abnormal morphology with bowing, thickened cortices, and narrow intramedullary canals. We planned minimally invasive prophylactic plate osteosynthesis. Computed tomography scans of both femora were obtained and used to generate 3-dimensional (3D) printed models. Osteosynthesis plates were precontoured to fit the 3D models and sterilized, and prophylactic fixation was performed using a minimally invasive submuscular technique.

CONCLUSION

3D printed models aided in precontouring fixation plates in a case with challenging bony anatomy, enabling minimally invasive surgery.

A Null Mutation of TNFRSF11A Causes Dysosteosclerosis, Not Osteopetrosis

Dysosteosclerosis (DOS) is a rare sclerosing bone dysplasia characterized by unique osteosclerosis of the long tubular bones and platyspondyly. DOS is inherited in an autosomal recessive manner and is genetically and clinically heterogeneous. To date, four individuals with DOS who have five different TNFRSF11A mutations have been reported. Based on their data, it is hypothesized that mutations producing aberrant mutant RANK proteins (missense or truncated or elongated) cause DOS, while null mutations lead to osteopetrosis, autosomal recessive 7 (OPTB7). Herein, we present the fifth case of TNFRSF11A-associated DOS with a novel homozygous frame-shift mutation (c.19_31del; p.[Arg7CysfsTer172]). The mutation is predicted to cause nonsense mutation-mediated mRNA decay (NMD) in all RANK isoform transcripts, resulting in totally null allele. Our findings suggest genotype-phenotype relationship in TNFRSF11A-associated OPTB7 and DOS remains unclear, and that the deficiency of TNFRSF11A functions might cause DOS, rather than osteopetrosis. More data are necessary to understand the phenotypic spectrum caused by TNFRSF11A mutations.

Osteosclerotic metaphyseal dysplasia, dysosteosclerosis or osteomyelitis? Paediatric case presentation with associated mandibular swelling and a review of the literature

Osteosclerotic metaphyseal dysplasia (OMD) is an extremely rare form of osteopetrosis, which bears significant clinical similarities to dysosteosclerosis (DSS). We aim to present a rare case of OMD with mandibular swelling and osteomyelitis infection including diagnosis journey as well as management in 7-year-old patient. Literature review completed for OMD cases. Case report investigative methods include genetic testing, CT facial bones and MRI scan, orthopantogram and bone biopsies. An initial suspected diagnosis of DSS with chronic osteomyelitis was made. However, following genetic testing, a diagnosis of OMD was confirmed. Our patient underwent a surgical debulking procedure and antibiotic treatment. Less than 10 patients with this condition have been reported within the international literature. There is a wide range of presentation. OMD, DSS and osteomyelitis are all within a similar spectrum of bone conditions. Our understanding, regarding OMD, remains limited and, hence, further research is required to elucidate a thorough clinical picture.

Brain Abscess in a Patient with Osteopetrosis: A Rare Complication

Brain abscess formation is extremely rare in patients with osteopetrosis. Herein, we report a case of viridans streptococci brain abscess in an immunocompromised child diagnosed with osteopetrosis. The patient presented with a sudden change in mental status and convulsions. Radiological evaluation revealed a temporal lobe brain abscess, and intravenous antibiotherapy was started immediately. The patient underwent abscess drainage, and laboratory investigation of pus material revealed viridans streptococci.

Spleen tyrosine kinase (SYK) inhibitor PRT062607 protects against ovariectomy-induced bone loss and breast cancer-induced bone destruction

Osteolytic diseases, including breast cancer-induced osteolysis and postmenopausal osteoporosis, are attributed to excessive bone resorption by osteoclasts. Spleen tyrosine kinase (SYK) is involved in osteoclastogenesis and bone resorption, whose role in breast cancer though remains controversial. Effects of PRT062607 (PRT), a highly specific inhibitor of SYK, on the osteoclast and breast cancer functionalities are yet to be clarified. This study demonstrated the in vitro inhibitory actions of PRT on the osteoclast-specific gene expression, bone resorption, and osteoclastogenesis caused by receptor activator of nuclear factor kappa B ligand (RANKL), as well as its in vitro suppressive effects on the growth, migration and invasion of breast carcinoma cell line MDA-MB-231, which were achieved through PLCγ2 and PI3K-AKT-mTOR pathways. Further, we proved that PRT could prevent post-ovariectomy (OVX) loss of bone and breast cancer-induced bone destruction in vivo, which agreed with the in vitro outcomes. In conclusion, our findings suggest the potential value of PRT in managing osteolytic diseases mediated by osteoclasts.

Resolution of sclerotic lesions of dysosteosclerosis due to biallelic SLC29A3 variant in a Turkish girl

Dysosteosclerosis is a group of sclerosing bone dysplasia characterized by short stature, increased bone fragility, osteosclerosis, and platyspondyly. It is a genetically heterogeneous disorder caused by biallelic mutations in the SLC29A3, TNFRSF11A, TCIRG1, and CSF1R genes. To date, four dysosteosclerosis patients with SLC29A3 mutations have been reported. Here, we report biallelic SLC29A3 (c.303_320dupCTACTTTGAGAGCTACCT) variant in a three-year-old girl. She had large anterior fontanelle, fracture history, short stature, camptodactyly, elbow contracture, and melanocytic nevus. Initial skeletal radiographs revealed platyspondyly, dense vertebral endplates (sandwich appearance of the vertebral bodies), diffuse sclerosis of the peripheral side of the pelvic bones, sclerosis of metaphysis and diaphysis of the long bones, metaphyseal widening, and diaphyseal cortical thickening. Mild sclerosis was also present in the skull base, maxilla, rib, scapula, and phalanges. Notably, we observed that sandwich vertebrae appearance significantly resolved and sclerosis of ribs, scapula, pelvis, and long bone metaphysis regressed over a 2.5-year period. However, platyspondyly, metaphyseal widening, and diaphyseal cortical thickening persisted. In conclusion, this study demonstrates spontaneous resolution of osteosclerosis, which was not described previously in patients with dysosteosclerosis.

Further expanding the mutational spectrum of brain abnormalities, neurodegeneration, and dysosteosclerosis: A rare disorder with neurologic regression and skeletal features

Colony stimulating factor 1 receptor (CSF1R, MIM# 164770) encodes a tyrosine-kinase receptor playing an important role in development of osteoclasts and microglia. Heterozygous CSF1R variants have been known to cause hereditary diffuse leukoencephalopathy with spheroids (HDLS, MIM# 221820), an adult-onset leukoencephalopathy characterized by loss of motor functions and cognitive decline. Recently, a new phenotype characterized by brain abnormalities, neurodegeneration, and dysosteosclerosis (BANDDOS) with biallelic CSF1R pathogenic variants in the etiology has been described. BANDDOS differs from HDLS by early-onset neurodegenerative changes with additional structural brain abnormalities and skeletal findings resembling dysosteosclerosis (DOS). Described skeletal findings of the disease are highly variable ranging from absence of a skeletal phenotype and milder Pyle disease-like to osteopetrosis and DOS. To date, only a few patients carrying biallelic CSF1R variants have been reported. In this clinical report, we describe three siblings with variable skeletal findings along with neurological symptoms ranging from mild to severe in whom exome sequencing revealed a novel homozygous splice site variant in canonical splice donor site of intron 21 adjacent to an exon, which encoding part of kinase domain of CSF1R along with a review of the literature.

The third case of TNFRSF11A-associated dysosteosclerosis with a mutation producing elongating proteins

Dysosteosclerosis (DOS) is a distinct form of sclerosing bone disease characterized by platyspondyly and progressive osteosclerosis. DOS is genetically heterogeneous. Three causal genes, SLC29A3, CSF1R, and TNFRSF11A are reported. TNFRSF11A-associated DOS has been identified in two patients; however, TNFRSF11A is also a causal gene for osteopetrosis, autosomal recessive 7 (OP-AR7). Whole-exome sequencing in a patient with sclerosing bone disease identified novel compound heterozygous variants (c.414_427 + 7del, c.1664del) in TNFRSF11A. We examined the impact of the two variants on five splicing isoforms of TNFRSF11A by RT-PCR. We found that c.1664del resulted in elongated proteins (p.S555Cfs*121, etc.), while c.414_427 + 7del generated two aberrant splicing products (p.A139Wfs*19 and p.E132Dfs*19) that lead to nonsense mediated mRNA decay (NMD). In the previous two cases of TNFRSF11A-associated DOS, their mutations produced truncated TNFRSF11A protein isoforms. The mutations in all three cases thus contrast with TNFRSF11A mutations reported in OP-AR7, which does not generated truncated or elongated TNFRSF11A proteins. Thus, we identified the third case of TNFRSF11A-associated DOS and reinforced the genotype-phenotype correlation that aberrant protein-producing TNFRSF11A mutations cause DOS.

Adult Osteosclerotic Metaphyseal Dysplasia With Progressive Osteonecrosis of the Jaws and Abnormal Bone Resorption Pattern Due to a LRRK1 Splice Site Mutation

Osteosclerotic metaphyseal dysplasia (OSMD) is a rare autosomal recessive sclerosing skeletal dysplasia. We report on a 34-year-old patient with sandwich vertebrae, platyspondyly, osteosclerosis of the tubular bones, pathologic fractures, and anemia. In the third decade, he developed osteonecrosis of the jaws, which was progressive in spite of repeated surgical treatment over a period of 11 years. An iliac crest bone biopsy revealed the presence of hypermineralized cartilage remnants, large multinucleated osteoclasts with abnormal morphology, and inadequate bone resorption typical for osteoclast-rich osteopetrosis. After exclusion of mutations in TCIRG1 and CLCN7 we performed trio-based exome sequencing. The novel homozygous splice-site mutation c.261G>A in the gene LRRK1 was found and co-segregated with the phenotype in the family. cDNA sequencing showed nearly complete skipping of exon 3 leading to a frameshift (p.Ala34Profs*33). Osteoclasts differentiated from the patient's peripheral blood monocytes were extremely large. Instead of resorption pits these cells were only capable of superficial erosion. Phosphorylation of L-plastin at position Ser5 was strongly reduced in patient-derived osteoclasts showing a loss of function of the mutated LRRK1 kinase protein. Our analysis indicates a strong overlap of LRRK1-related OSMD with other forms of intermediate osteopetrosis, but an exceptional abnormality of osteoclast resorption. Like in other osteoclast pathologies an increased risk for progressive osteonecrosis of the jaws should be considered in OSMD, an intermediate form of osteopetrosis. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

TNFRSF11A-Associated Dysosteosclerosis: A Report of the Second Case and Characterization of the Phenotypic Spectrum

Dysosteosclerosis (DOS) is a distinct form of sclerosing bone disease characterized by irregular osteosclerosis and platyspondyly. DOS is genetically heterogeneous; however, only five cases with SLC29A3 mutations and a single case with a splice-site mutation of TNFRSF11A have been reported, and TNFRSF11A is also a causal gene for osteopetrosis, autosomal recessive 7 (OP-AR7). Thus, the causal genes of DOS and their genotype-phenotype associations remain unclear. In this study, we examined a Japanese patient with DOS and found a novel variant in TNFRSF11A. The homozygous variant was a G to T transversion at the first nucleotide of exon 9 (c.784G>T). Although the variant was predicted to cause a stop codon mutation (p.E262*), in silico evaluation of the exonic splicing elements followed by RT-PCR for the patient-derived cells showed that it caused aberrant splicing due to the change in the exonic splicing element and produced two types of aberrant transcripts: One caused a premature stop codon (p.E262Vfs*17) leading to nonsense mutation-mediated mRNA decay; the other produced a protein with interstitial deletion (p.E262_Q279del). The effects of the mutation on five splicing isoforms of TNFRSF11A were different from those in OP-AR7, but comparable with those in the first DOS with the TNFRSF11A mutation. Thus, we identified the second case of DOS caused by the TNFRSF11A splice-site mutation and confirmed the novel disease entity. © 2019 American Society for Bone and Mineral Research.

Sclerosing bone dysplasias with hallmarks of dysosteosclerosis in four patients carrying mutations in SLC29A3 and TCIRG1

The osteopetroses and related sclerosing bone dysplasias can have a broad range of manifestations. Especially in the milder forms, sandwich vertebrae are an easily recognizable and reliable radiological hallmark. We report on four patients from three families presenting with sandwich vertebrae and platyspondyly. The long bone phenotypes were discordant with one patient showing modeling defects and patchy osteosclerosis, while the second displayed only metaphyseal sclerotic bands, and the third and fourth had extreme metaphyseal flaring with uniform osteosclerosis. Two of the four patients had experienced pathological fractures, two had developmental delay, but none showed cranial nerve damage, hepatosplenomegaly, or bone marrow failure. According to these clinical features the diagnoses ranged between intermediate autosomal recessive osteopetrosis and dysosteosclerosis. After exclusion of mutations in CLCN7 we performed gene panel and exome sequencing. Two novel mutations in SLC29A3 were found in the first two patients. In the third family a TCIRG1 C-terminal frameshift mutation in combination with a mutation at position +4 in intron 2 were detected. Our study adds two cases to the small group of individuals with SLC29A3 mutations diagnosed with dysosteosclerosis, and expands the phenotypic variability. The finding that intermediate autosomal recessive osteopetrosis due to TCIRG1 splice site mutations can also present with platyspondyly further increases the molecular heterogeneity of dysosteosclerosis-like sclerosing bone dysplasias.

Unique Variant of NOD2 Pediatric Granulomatous Arthritis With Severe 1,25-Dihydroxyvitamin D-Mediated Hypercalcemia and Generalized Osteosclerosis

Pediatric granulomatous arthritis (PGA) refers to two formerly separate entities: autosomal dominant Blau syndrome (BS) and its sporadic phenocopy early-onset sarcoidosis (EOS). In 2001 BS and in 2005 EOS became explained by heterozygous mutations within the gene that encodes nucleotide-binding oligomerization domain-containing protein 2 (NOD2), also called caspase recruitment domain-containing protein 15 (CARD15). NOD2 is a microbe sensor in leukocyte cytosol that activates and regulates inflammation. PGA is characterized by a triad of autoinflammatory problems (dermatitis, uveitis, and arthritis) in early childhood, which suggests the causal NOD2/CARD15 mutations are activating defects. Additional complications of PGA were recognized especially when NOD2 mutation analysis became generally available. However, in PGA, hypercalcemia is only briefly mentioned, and generalized osteosclerosis is not reported, although NOD2 regulates NF-κB signaling essential for osteoclastogenesis and osteoclast function. Herein, we report a 4-year-old girl with PGA uniquely complicated by severe 1,25(OH)₂ D-mediated hypercalcemia, nephrocalcinosis, and compromised renal function together with radiological and histopathological features of osteopetrosis (OPT). The classic triad of PGA complications was absent, although joint pain and an antalgic gait accompanied wrist, knee, and ankle swelling and soft non-tender masses over her hands, knees, and feet. MRI revealed tenosynovitis in her hands and suprapatellar effusions. Synovial biopsy demonstrated reactive synovitis without granulomas. Spontaneous resolution of metaphyseal osteosclerosis occurred while biochemical markers indicated active bone turnover. Anti-inflammatory medications suppressed circulating 1,25(OH)₂ D, corrected the hypercalcemia, and improved her renal function, joint pain and swelling, and gait. Mutation analysis excluded idiopathic infantile hypercalcemia, type 1, and known forms of OPT, and identified a heterozygous germline missense mutation in NOD2 common in PGA (c.1001G>A, p.Arg334Gln). Thus, radiological and histological findings of OPT and severe hypercalcemia from apparent extrarenal production of 1,25(OH)₂ D can complicate NOD2-associated PGA. Although the skeletal findings seem inconsequential, treatment of the hypercalcemia is crucial to protect the kidneys. © 2018 American Society for Bone and Mineral Research.

Dual effects of baicalin on osteoclast differentiation and bone resorption

Osteoclasts (OC) are critical cells responsible for many bone diseases such as osteoporosis. It is of great interest to identify agents that can regulate the activity of OC to treat osteolytic bone diseases. In this study, we found that baicalin exerted a two‐way regulatory effect on OC in a concentration‐dependent manner in vitro and in vivo. In detail, baicalin at a low concentration (below 1 μmol/L) enhanced OC differentiation and bone resorption, but baicalin at a high concentration (above 2 μmol/L) exhibited inhibitory effects on OC. We demonstrated that baicalin at low concentrations enhanced the mitogen‐activated protein kinase (MAPK) (ERK) signalling pathway and activated c‐Fos and NFATc1 expression, and thus enhanced gene expression, OC differentiation and bone resorption. However, baicalin at higher levels not only suppressed ERK phosphorylation and c‐fos and NFATc1 expression, but also altered the expression of apoptosis‐related proteins, and therefore inhibiting OC function. This dual effect was further verified in an LPS‐induced mouse calvarial osteolysis model, evidenced by enhanced osteolysis at a lower concentration but reduced bone loss at a higher concentration. Overall, our findings indicate that baicalin exerts dose‐dependent effects on OC formation and function. Therefore, caution should be applied when using baicalin to treating OC‐related bone diseases.

[Osteomyelitis of the mandible and dysosteosclerosis]

Dysosteosclerosis is a rare genetic disorder with a poor prognosis. It is an osteochondrodysplasia similar to osteopetrosis but it is typically characterized by platyspondyly and expanded metaphyses. It shows complications such as compression of cranial nerves, especially the optic nerve, hematologic complications, fractures following mild injury, abnormal dentition, neurological and psychological deterioration, in addition to osteomyelitis of the mandible. We report a new case of dysosteosclerosis complicated by osteomyelitis of the lower maxilla.

Rapid skeletal turnover in a radiographic mimic of osteopetrosis

Among the high bone mass disorders, the osteopetroses reflect osteoclast failure that prevents skeletal resorption and turnover, leading to reduced bone growth and modeling and characteristic histopathological and radiographic findings. We report an 11-year-old boy with a new syndrome that radiographically mimics osteopetrosis (OPT), but features rapid skeletal turnover. He presented at age 21 months with a parasellar, osteoclast-rich giant cell granuloma. Radiographs showed a dense skull, generalized osteosclerosis and cortical thickening, medullary cavity narrowing, and diminished modeling of tubular bones. His serum alkaline phosphatase was >5000 IU/L (normal <850 IU/L). After partial resection, the granuloma re-grew but then regressed and stabilized during 3 years of uncomplicated pamidronate treatment. His hyperphosphatasemia transiently diminished, but all bone turnover markers, especially those of apposition, remained elevated. Two years after pamidronate therapy stopped, bone mineral density (BMD) Z-scores reached +9.1 and +5.8 in the lumbar spine and hip, respectively, and iliac crest histopathology confirmed rapid bone remodeling. Serum multiplex biomarker profiling was striking for low sclerostin. Mutation analysis was negative for activation of lipoprotein receptor-related protein 4 (LRP4), LRP5, or TGFβ1, and for defective sclerostin (SOST), osteoprotegerin (OPG), RANKL, RANK, SQSTM1, or sFRP1. Microarray showed no notable copy number variation. Studies of his nonconsanguineous parents were unremarkable. The etiology and pathogenesis of this unique syndrome are unknown.

Sclerosing bone dysplasias with involvement of the craniofacial skeleton

In this review we provide a complete overview of the existing sclerosing bone dysplasias with craniofacial involvement. Clinical presentation, disease course, the craniofacial symptoms, genetic transmission pattern and pathophysiology are discussed. There is an emphasis on radiologic features with a large collection of CT and MRI images. In previous reviews the craniofacial area of the sclerosing bone dysplasias was underexposed. However, craniofacial symptoms are often the first symptoms to address a physician. The embryology of the skull and skull base is explained and illustrated for a better understanding of the affected areas.

Mechanism of human tooth eruption: review article including a new theory for future studies on the eruption process

Human eruption is a unique developmental process in the organism. The aetiology or the mechanism behind eruption has never been fully understood and the scientific literature in the field is extremely sparse. Human and animal tissues provide different possibilities for eruption analyses, briefly discussed in the introduction. Human studies, mainly clinical and radiological, have focused on normal eruption and gender differences. Why a tooth begins eruption and what enables it to move eruptively and later to end these eruptive movements is not known. Pathological eruption courses contribute to insight into the aetiology behind eruption. A new theory on the eruption mechanism is presented. Accordingly, the mechanism of eruption depends on the correlation between space in the eruption course, created by the crown follicle, eruption pressure triggered by innervation in the apical root membrane, and the ability of the periodontal ligament to adapt to eruptive movements. Animal studies and studies on normal and pathological eruption in humans can support and explain different aspects in the new theory. The eruption mechanism still needs elucidation and the paper recommends that future research on eruption keeps this new theory in mind. Understanding the aetiology of the eruption process is necessary for treating deviant eruption courses.

Osteogenesis response to implanted materials in endocortical bone in rat femora

BACKGROUND

Orthopedic surgeons and dentists often implant materials to repair bone tissue defects and restore physiological functions of bone organs. The clinical success depends on adequate bone formation in operation sites. However, the real cause of osteogenesis has not yet been fully elucidated. To investigate the bone response to implanted materials, this study examined the bone tissue reaction in rat femoral medullary canal, which received gelatin and collagen as foreign-body materials.

METHODS

A total of 36 six-month-old Sprague-Dawley rats were randomly and meanly divided into three groups. In the gelatin group, the bilateral femora received gelatin material; in the collagen group, they were implanted with type I collagen, and in the control group, the femora suffered from sham operation with no materials inserted. After 2, 4, 8, and 12 weeks, specimens were harvested and subjected to a series of examinations.

RESULTS

After 2 weeks of healing, a significant upregulation of both alkaline phosphatase and osteocalcin by both kinds of implanted materials relative to the control (sham implantation group) was seen in gene expression analysis. Strong reactivity of osteoprotegerin and receptor activator of NFκB ligand was detected in the two test groups in immunohistochemistry at 4 weeks of healing. Also, micro-CT revealed an increase in cortical bone thickness in the two test groups as compared to the control group. Densitometry showed increased bone mineral density in the bone receiving materials after 12 weeks, leading to the enhanced maximum load in the test groups.

CONCLUSIONS

These results indicated that the implanted materials led to an osteogenesis response in rat femoral medullary canal. Thus, we probably should reconsider the potential cascades of tissue reaction when utilizing orthopedic and dental implants and other materials to recover bone related-organ function and repair bone defects.

Whole-exome sequencing identifies mutations in the nucleoside transporter gene SLC29A3 in dysosteosclerosis, a form of osteopetrosis

Dysosteosclerosis (DSS) is the form of osteopetrosis distinguished by the presence of skin findings such as red-violet macular atrophy, platyspondyly and metaphyseal osteosclerosis with relative radiolucency of widened diaphyses. At the histopathological level, there is a paucity of osteoclasts when the disease presents. In two patients with DSS, we identified homozygous or compound heterozygous missense mutations in SLC29A3 by whole-exome sequencing. This gene encodes a nucleoside transporter, mutations in which cause histiocytosis-lymphadenopathy plus syndrome, a group of conditions with little or no skeletal involvement. This transporter is essential for lysosomal function in mice. We demonstrate the expression of Slc29a3 in mouse osteoclasts in vivo. In monocytes from patients with DSS, we observed reduced osteoclast differentiation and function (demineralization of calcium surface). Our report highlights the pleomorphic consequences of dysfunction of this nucleoside transporter, and importantly suggests a new mechanism for the control of osteoclast differentiation and function.

Neuropathology and craniofacial lesions of osteopetrotic Red Angus calves

Inherited osteopetrosis was identified in cattle herds in Wyoming, Nebraska, and Missouri in 2008 to 2010. Ten affected Red Angus calves were examined to characterize lesions in brain, teeth, and skull. Six affected aborted or stillborn calves were homozygous for the recently characterized deletion mutation in SLC4A2. Four affected calves were heterozygous for the SLC4A2 mutation and survived 1 to 7 days after birth. Gross lesions were similar in all 10 calves. Brains were rectangular and dorsoventrally compressed, with concave depressions in the parietal cortex owing to thickened parietal bone. Cerebellar hemispheres were compressed with herniation of the cerebellar vermis into the foramen magnum. Moderate bilateral chromatolysis affected multiple cranial nerve nuclei and, in some calves, the red nucleus. There was loss of retinal ganglion cells with severe atrophy of optic nerves. Periventricular corpora amylacea were in the thalamus, caudate nucleus, and midbrain. Vessels and neuropil in the dorsomedial aspect of the thalamus were mineralized. Dysplastic change in premolar and molar teeth comprised intra-alveolar intermingling of dentin, enamel, cementum, and bone, contributing to dental ankylosis. Changes in the heads of osteopetrotic calves are similar to those in children with malignant forms of homozygous recessive osteopetrosis.

Camurati-Engelmann disease: unique variant featuring a novel mutation in TGFβ1 encoding transforming growth factor beta 1 and a missense change in TNFSF11 encoding RANK ligand

We report a 32-year-old man and his 59-year-old mother with a unique and extensive variant of Camurati-Engelmann disease (CED) featuring histopathological changes of osteomalacia and alterations within TGFβ1 and TNFSF11 encoding TGFβ1 and RANKL, respectively. He suffered leg pain and weakness since childhood and reportedly grew until his late 20s, reaching 7 feet in height. He had deafness, perforated nasal septum, torus palatinus, disproportionately long limbs with knock-knees, low muscle mass, and pseudoclubbing. Radiographs revealed generalized skeletal abnormalities, including wide bones and cortical and trabecular bone thickening in keeping with CED, except that long bone ends were also affected. Lumbar spine and hip BMD Z-scores were + 7.7 and + 4.4, respectively. Biochemical markers of bone turnover were elevated. Hypocalciuria accompanied low serum 25-hydroxyvitamin D (25[OH]D) levels. Pituitary hypogonadism and low serum insulin-like growth factor (IGF)-1 were present. Karyotype was normal. Despite vitamin D repletion, iliac crest histology revealed severe osteomalacia. Exon 1 of TNFRSF11A (RANK), exons 2, 3, and 4 of LRP5, and all coding exons and adjacent mRNA splice junctions of TNFRSF11B (OPG), SQSTM1 (sequestosome 1), and TNSALP (tissue nonspecific alkaline phosphatase) were intact. His asymptomatic and less dysmorphic 5'11″ mother, also with low serum 25(OH)D, had milder clinical, radiological, biochemical, and histopathological findings. Both individuals were heterozygous for a novel 12-bp duplication (c.27_38dup, p.L10_L13dup) in exon 1 of TGFβ1, predicting four additional leucine residues in the latency-associated-peptide segment of TGFβ1, consistent with CED. The son was also homozygous for a single base transversion in TNFSF11, predicting a nonconservative amino acid change (c.107C > G, p.Pro36Arg) in the intracellular domain of RANKL that was heterozygous in his nonconsanguineous parents. This TNFSF11 variant was not found in the SNP Database, nor in published TNFSF11 association studies, but it occurred in four of the 134 TNFSF11 alleles (3.0%) we tested randomly among individuals without CED. Perhaps the unique phenotype of this CED family is conditioned by altered RANKL activity.

Elevated serum lactate dehydrogenase isoenzymes and aspartate transaminase distinguish Albers-Schönberg disease (Chloride Channel 7 Deficiency Osteopetrosis) among the sclerosing bone disorders

Osteopetrosis (OPT) refers to the consequences of generalized failure of skeletal resorption during growth. Most cases are explained by loss-of-function mutation within the genes that encode either chloride channel 7 (CLCN7) or a vacuolar proton pump subunit (TCIRG1), each compromising acid secretion by osteoclasts. Patients suffer fractures and sometimes cranial nerve entrapment and insufficient medullary space for hematopoiesis. In 1996, we reported that a high serum level of the brain isoenzyme of creatine kinase (BB-CK), the CK of osteoclasts, characterizes OPT dueamong the sclerosing bone disorders (J Clin Endocrinol Metab. 1996;11:1438). Now, we show that elevation in serum of multiple lactate dehydrogenase (LDH) isoenzymes with aspartate transaminase (AST) distinguishes autosomal dominant OPT due to loss-of-function mutation in CLCN7 [Albers-Schönberg disease (A-SD)] among these conditions. Serum total LDH and AST levels as high as 3× and 2×, respectively, the upper limits of normal for age-appropriate controls, were persistent and essentially concordant in A-SD. Serum LDH was elevated in 7 of 9 children and in the 2 adults studied with A-SD. LDH isoenzyme quantitation showed excesses of LDH-2, -3, and -4. Neither total LDH nor AST increases were found in other forms of OPT, including bisphosphonate-induced OPT, or in 41 children and 6 adults representing 20 additional sclerosing bone disorders. Serum TRACP-5b and BB-CK also were markedly elevated in A-SD. Hence, high serum levels of several enzymes characterize A-SD. Elevated serum LDH isoenzymes and AST indicate a disturbance (of uncertain clinical significance) within multiple extraosseous tissues when there is CLCN7 deficiency.