Osteomesopyknosis associated with a novel ALOX5 variant that impacts the RANKL pathway.

BACKGROUND: Bone tissue homeostasis relies on the coordinated activity of the bone-forming osteoblasts and bone-resorbing osteoclasts. Osteomesopyknosis is considered a distinctive rare sclerosing skeletal disorder of unelucidated pathophysiology and presumably autosomal dominant transmission. However, the causal genes are unknown. METHODS: We present a case report encompassing clinical assessments, imaging studies, and whole-exome sequencing analysis, complemented by functional in vitro experiments. RESULTS: This new case of osteomesopyknosis was associated with a missense ALOX5 variant predicted to induce protein misfolding and proteasomal degradation. Transfection experiments demonstrated that the variant was associated with reduced protein levels restored by proteasomal inhibition with bortezomib. Likewise, gene expression analysis showed that the mutated gene was associated with a decreased RANKL/OPG ratio, which is a critical driver of osteoclast precursor differentiation. CONCLUSION: Our data indicate impaired bone resorption as the underlying mechanism of this rare osteosclerosis, implicating ALOX5 pathogenic variants as potential etiological factors.

Gingival proteomics reveals the role of TGF beta and YAP/TAZ signaling in Raine syndrome fibrosis.

Raine syndrome (RNS) is a rare autosomal recessive osteosclerotic dysplasia. RNS is caused by loss-of-function disease-causative variants of the FAM20C gene that encodes a kinase that phosphorylates most of the secreted proteins found in the body fluids and extracellular matrix. The most common RNS clinical features are generalized osteosclerosis, facial dysmorphism, intracerebral calcifications and respiratory defects. In non-lethal RNS forms, oral traits include a well-studied hypoplastic amelogenesis imperfecta (AI) and a much less characterized gingival phenotype. We used immunomorphological, biochemical, and siRNA approaches to analyze gingival tissues and primary cultures of gingival fibroblasts of two unrelated, previously reported RNS patients. We showed that fibrosis, pathological gingival calcifications and increased expression of various profibrotic and pro-osteogenic proteins such as POSTN, SPARC and VIM were common findings. Proteomic analysis of differentially expressed proteins demonstrated that proteins involved in extracellular matrix (ECM) regulation and related to the TGFß/SMAD signaling pathway were increased. Functional analyses confirmed the upregulation of TGFß/SMAD signaling and subsequently uncovered the involvement of two closely related transcription cofactors important in fibrogenesis, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). Knocking down of FAM20C confirmed the TGFß-YAP/TAZ interplay indicating that a profibrotic loop enabled gingival fibrosis in RNS patients. In summary, our in vivo and in vitro data provide a detailed description of the RNS gingival phenotype. They show that gingival fibrosis and calcifications are associated with, and most likely caused by excessed ECM production and disorganization. They furthermore uncover the contribution of increased TGFß-YAP/TAZ signaling in the pathogenesis of the gingival fibrosis.

Metformin alleviates osteoarthritis in mice by inhibiting chondrocyte ferroptosis and improving subchondral osteosclerosis and angiogenesis.

BACKGROUND: Osteoarthritis (OA) is the most common musculoskeletal disease, and it has a complex pathology and unknown pathogenesis. Chondrocyte ferroptosis is closely associated with the development of OA. As a common drug administered for the treatment of type 2 diabetes, metformin (Met) is known to inhibit the development of ferroptosis. However, its therapeutic effect in OA remains unknown. The present study aimed to explore the effects of Met on cartilage and subchondral bone in a mouse OA model and to explore the potential underlying mechanisms. METHODS: A mouse OA model was induced using destabilization of the medial meniscus (DMM) surgery, chondrocyte ferroptosis was induced using an intra-articular injection of Erastin, and Met (200 mg/kg/day) was intragastrically administered for 8 weeks after surgery. H&E and Safranin O­fast green staining were used to evaluate cartilage degeneration, and µ­computed tomography was used to evaluate changes in subchondral bone microarchitecture. Moreover, immunohistochemical staining was performed to detect mechanistic metalloproteinases 13, type II collagen, glutathione peroxidase 4, acyl-CoA synthetase long-chain family member 4, solute carrier family 7 member 11 and p53. Runt-associated transcription factor 2 and CD31 were detected using immunofluorescent staining. RESULTS: Met protected articular cartilage and reversed the abnormal expression of ferroptosis-related proteins in the chondrocytes of DMM mice. Moreover, intra-articular injection of Erastin induced ferroptosis in mouse chondrocytes, and Met eliminated the ferroptosis effects induced by Erastin and protected articular cartilage. In addition, the results of the present study demonstrated that Met alleviated the microstructural changes of subchondral osteosclerosis and reduced heterotypic angiogenesis in DMM mice. CONCLUSION: Met alleviates the pathological changes of OA by inhibiting ferroptosis in OA chondrocytes, alleviating subchondral sclerosis and reducing abnormal angiogenesis in subchondral bone in advanced OA.

FAM20C Overview: Classic and Novel Targets, Pathogenic Variants and Raine Syndrome Phenotypes.

FAM20C is a gene coding for a protein kinase that targets S-X-E/pS motifs on different phosphoproteins belonging to diverse tissues. Pathogenic variants of FAM20C are responsible for Raine syndrome (RS), initially described as a lethal and congenital osteosclerotic dysplasia characterized by generalized atherosclerosis with periosteal bone formation, characteristic facial dysmorphisms and intracerebral calcifications. The aim of this review is to give an overview of targets and variants of FAM20C as well as RS aspects. We performed a wide phenotypic review focusing on clinical aspects and differences between all lethal (LRS) and non-lethal (NLRS) reported cases, besides the FAM20C pathogenic variant description for each. As new targets of FAM20C kinase have been identified, we reviewed FAM20C targets and their functions in bone and other tissues, with emphasis on novel targets not previously considered. We found the classic lethal and milder non-lethal phenotypes. The milder phenotype is defined by a large spectrum ranging from osteonecrosis to osteosclerosis with additional congenital defects or intellectual disability in some cases. We discuss our current understanding of FAM20C deficiency, its mechanism in RS through classic FAM20C targets in bone tissue and its potential biological relevance through novel targets in non-bone tissues.

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.

Osteal Tissue Macrophages Are Involved in Endplate Osteosclerosis through the OSM-STAT3/YAP1 Signaling Axis in Modic Changes.

Modic changes (MCs) are radiographic manifestations of lumbar degenerative diseases. Various types of MCs are often associated with endplate osteosclerosis. Osteal tissue macrophages (Osteomacs) were reported to be crucial for bone homeostasis and bone repair, but whether osteomacs participate in the endplate osteosclerosis in MCs remained unclear. In this study, we tried to explore the critical role of osteomacs in regulating osteogenesis in MCs. We collected MCs from patient samples and developed a Propionibacterium acnes-induced rat MCs model, using microcomputed tomography and immunohistochemistry to detect the endplate bone mass and distribution of osteomacs. In patients' MCs, osteomacs increased in endplate subchondral bone, especially in Modic type II. Endplate in Modic type III presented a stable osteosclerosis. In rat MCs model, osteomacs increased in the bone hyperplasia area but not in the inflammation area of the endplate region, whereas the distribution of osteomacs was consistent with the area of osteosclerosis. To further explore the functions of osteomacs in vitro, we isolated osteomacs using MACS technology and found osteomacs secreted oncostatin M (OSM) and strongly promoted osteoblast differentiation rather than osteoclast through the mechanism of OSM-mediated tyrosine phosphorylation and interaction of STAT3 and Yes-associated protein 1 (YAP1). STAT3 phosphorylation inhibition or YAP1 knockdown attenuated OSM-mediated osteoblast differentiation. Finally, we confirmed that blockade of OSM in vivo using anti-OSM-neutralizing Ab prevented endplate osteosclerosis in rat MCs model. Taken together, these findings confirmed that endplate osteosclerosis in MCs was accompanied by an increased number of osteomacs, which regulated osteogenesis via the OSM-STAT3/YAP1 signaling axis.

Pediatric myelofibrosis: WHO 2024 update on myeloproliferative neoplasms calling?

OBJECTIVES: Pediatric myelofibrosis is a rare entity with the largest reported series of 19 cases. We describe here the clinicopathological spectrum and outcomes of 15 cases of pediatric myelofibrosis. METHODS: Case files of myelofibrosis of patients less than 18 years were retrieved from January 2016 to January 2019, and patients with idiopathic myelofibrosis after exhaustive work-up were studied. Their clinicopathological profiles were studied and then followed up for resolution and malignant transformation. RESULTS: Of the 15 cases of idiopathic myelofibrosis, transfusion-dependent anemia (14/15) was most common presentation. Only one patient showed leukoerythroblastosis with dacryocytes. Myeloid hyperplasia was seen in 13 of 15 patients and megakaryocytic hyperplasia in 10 patients. Dysmegakaryopoiesis was seen in 8 of 15 patients, and only three had small loose megakaryocytic clustering. None showed hyperchromatic megakaryocytes, intrasinusoidal hematopoiesis, or osteosclerosis. One patient with trisomy 8 tested positive for JAK2V617F. Bone marrow biopsy was hypercellular in 13, and 8 had world health organization (WHO) MF-3 fibrosis. None of the patients developed malignancy, one had spontaneous resolution, and one patient required allogenic stem cell transplant. CONCLUSIONS: Pediatric myelofibrosis is a distinct entity from primary myelofibrosis in adults and merits mention in the WHO manual as a distinct entity.

Insulin-like growth factor-II and bioactive proteins containing a part of the E-domain of pro-insulin-like growth factor-II.

Insulin-like growth factor (IGF)-II is considered to function as an important fetal growth factor, which is structurally and functionally related to IGF-I and proinsulin. At least in vitro, IGF-II actions are mediated through the IGF-I receptor and to a lesser extent the insulin receptor. After birth, the function of IGF-II is less clear although in adults the serum level of IGF-II exceeds that of IGF-I several fold. The IGF-II gene is maternally imprinted, with exception of the liver and several parts of the brain, where it is expressed from both alleles. The regulation, organization, and translation of the IGF-II gene is complex, with five different putative promotors leading to a range of noncoding and coding mRNAs. The 180-amino acid pre-pro-IGF-II translation product can be divided into five domains and include a N-terminal signal peptide of 24 amino acid residues, the 67 amino acid long mature protein, and an 89 residues extension at the COOH terminus, designated as the E-domain. After removal of the signal peptide, the processing of pro-IGF-II into mature IGF-II requires various steps including glycosylation of the E-domain followed by the action of endo-proteases. Several of these processing intermediates can be found in the human circulation. There is increasing evidence that, besides IGF-II, several incompletely processed precursor forms of the protein, and even a 34-amino acid peptide (preptin) derived from the E-domain of pro-IGF-II, exhibit distinct biological activities. This review will focus on the current insights regarding the specific roles of the latter proteins in cancer, glucose homeostasis, and bone physiology. To address this topic clearly in the right context, a concise overview of the biological and biochemical properties of IGF-II and several relevant aspects of the IGF system will be provided.

Two Novel FAM20C Variants in A Family with Raine Syndrome.

Two siblings from a Mexican family who carried lethal Raine syndrome are presented. A newborn term male (case 1) and his 21 gestational week brother (case 2), with a similar osteosclerotic pattern: generalized osteosclerosis, which is more evident in facial bones and cranial base. Prenatal findings at 21 weeks and histopathological features for case 2 are described. A novel combination of biallelic FAM20C pathogenic variants were detected, a maternal cytosine duplication at position 456 and a paternal deletion of a cytosine in position 474 in exon 1, which change the reading frame with a premature termination at codon 207 and 185 respectively. These changes are in concordance with a negative detection of the protein in liver and kidney as shown in case 2. Necropsy showed absence of pancreatic Langerhans Islets, which are reported here for the first time. Corpus callosum absence is added to the few reported cases of brain defects in Raine syndrome. This report shows two new FAM20C variants not described previously, and negative protein detection in the liver and the kidney. We highlight that lethal Raine syndrome is well defined as early as 21 weeks, including mineralization defects and craniofacial features. Pancreas and brain defects found here in FAM20C deficiency extend the functional spectrum of this protein to previously unknown organs.

Congenital lipodystrophy induces severe osteosclerosis.

Berardinelli-Seip congenital generalized lipodystrophy is associated with increased bone mass suggesting that fat tissue regulates the skeleton. Because there is little mechanistic information regarding this issue, we generated "fat-free" (FF) mice completely lacking visible visceral, subcutaneous and brown fat. Due to robust osteoblastic activity, trabecular and cortical bone volume is markedly enhanced in these animals. FF mice, like Berardinelli-Seip patients, are diabetic but normalization of glucose tolerance and significant reduction in circulating insulin fails to alter their skeletal phenotype. Importantly, the skeletal phenotype of FF mice is completely rescued by transplantation of adipocyte precursors or white or brown fat depots, indicating that adipocyte derived products regulate bone mass. Confirming such is the case, transplantation of fat derived from adiponectin and leptin double knockout mice, unlike that obtained from their WT counterparts, fails to normalize FF bone. These observations suggest a paucity of leptin and adiponectin may contribute to the increased bone mass of Berardinelli-Seip patients.

Diffuse osteosclerosis as a presentation of recurrent breast cancer: role of endothelin 1.

We report a 46-yr-old woman with a history of breast cancer who presented with diffuse myalgias, bone pain, and osteosclerosis. She was found to have recurrent breast cancer producing endothelin-1. INTRODUCTION: Acquired osteosclerosis can be caused by various disorders. Endothelin -1 is believed to contribute to osteosclerosis caused by breast cancer. METHODS: Although the bone marrow biopsy did not reveal breast cancer, she developed skin lesions consistent with metastatic breast cancer. She ultimately died from progressive disease. At autopsy immunohistochemistry for endothelin-1 was performed on a section from the L5 vertebral body. RESULTS: The section from the L5 vertebral body showed small foci of cells consistent with metastatic carcinoma and a prominent sclerotic response. Immunohistochemistry for endothelin-1 was strongly positive. CONCLUSIONS: Recurrent breast cancer may present with diffuse osteosclerosis. Endothelin-1 may be a paracrine factor responsible for increased bone formation and osteosclerosis.

Conditional mouse models support the role of SLC39A14 (ZIP14) in Hyperostosis Cranialis Interna and in bone homeostasis.

Hyperostosis Cranialis Interna (HCI) is a rare bone disorder characterized by progressive intracranial bone overgrowth at the skull. Here we identified by whole-exome sequencing a dominant mutation (L441R) in SLC39A14 (ZIP14). We show that L441R ZIP14 is no longer trafficked towards the plasma membrane and excessively accumulates intracellular zinc, resulting in hyper-activation of cAMP-CREB and NFAT signaling. Conditional knock-in mice overexpressing L438R Zip14 in osteoblasts have a severe skeletal phenotype marked by a drastic increase in cortical thickness due to an enhanced endosteal bone formation, resembling the underlying pathology in HCI patients. Remarkably, L438R Zip14 also generates an osteoporotic trabecular bone phenotype. The effects of osteoblastic overexpression of L438R Zip14 therefore mimic the disparate actions of estrogen on cortical and trabecular bone through osteoblasts. Collectively, we reveal ZIP14 as a novel regulator of bone homeostasis, and that manipulating ZIP14 might be a therapeutic strategy for bone diseases.

Genetic and Molecular Insights Into Genotype-Phenotype Relationships in Osteopathia Striata With Cranial Sclerosis (OSCS) Through the Analysis of Novel Mouse Wtx Mutant Alleles.

The X-linked WTX/AMER1 protein constitutes an important component of the ß-catenin destruction complex that can both enhance and suppress canonical ß-catenin signaling. Somatic mutations in WTX/AMER1 have been found in a proportion of the pediatric kidney cancer Wilms' tumor. By contrast, germline mutations cause the severe sclerosing bone dysplasia osteopathia striata congenita with cranial sclerosis (OSCS), a condition usually associated with fetal or perinatal lethality in male patients. Here we address the developmental and molecular function of WTX by generating two novel mouse alleles. We show that in addition to the previously reported skeletal abnormalities, loss of Wtx causes severe midline fusion defects including cleft palate and ectopic synostosis at the base of the skull. By contrast, deletion of the C-terminal part of the protein results in only mild developmental abnormalities permitting survival beyond birth. Adult analysis, however, revealed skeletal defects including changed skull morphology and an increased whole-body bone density, resembling a subgroup of male patients carrying a milder, survivable phenotype. Molecular analysis in vitro showed that while ß-catenin fails to co-immunoprecipitate with the truncated protein, partial recruitment appears to be achieved in an indirect manner using AXIN/AXIN2 as a molecular bridge. Taken together our analysis provides a novel model for WTX-caused bone diseases and explains on the molecular level how truncation mutations in this gene may retain some of WTX-protein functions. © 2018 American Society for Bone and Mineral Research.

Loading-Induced Reduction in Sclerostin as a Mechanism of Subchondral Bone Plate Sclerosis in Mouse Knee Joints During Late-Stage Osteoarthritis.

OBJECTIVE: To establish an unbiased, 3-dimensional (3-D) approach that quantifies subchondral bone plate (SBP) changes in mouse joints, and to investigate the mechanism that mediates SBP sclerosis at a late stage of osteoarthritis (OA). METHODS: A new micro-computed tomography (micro-CT) protocol was developed to characterize the entire thickness of the SBP in the distal femur of a normal mouse knee. Four mouse models of severe joint OA were generated: cartilage-specific Egfr-knockout (Egfr-CKO) mice at 2 months after surgical destabilization of the medial meniscus (DMM), Egfr-CKO mice with aging-related spontaneous OA, wild-type (WT) mice at 10 months after DMM, and WT mice at 14 weeks after DMM plus hemisectomy of the meniscus (DMMH) surgery. As an additional model, mice with knockout of the sclerostin gene (Sost-KO) were subjected to DMMH surgery. Knee joints were examined by micro-CT, histology, and immunohistochemical analyses. RESULTS: Examination of the mouse distal femur by 3-D micro-CT revealed a positive correlation between SBP thickness and the loading status in normal knees. In all 4 mouse models of late-stage OA, SBP sclerosis was restricted to the areas under severely eroded articular cartilage. This was accompanied by elevated bone formation at the bone marrow side of the SBP and a drastic reduction in the levels of sclerostin in osteocytes within the SBP. Unlike in WT mice, no further increase in the thickness of the SBP was observed in response to DMMH in Sost-KO mice. CONCLUSION: Since focal stress on the SBP underlying sites of cartilage damage increases during late stages of OA, these findings establish mechanical loading-induced attenuation of sclerostin expression and elevation of bone formation along the SBP surface as the major mechanisms characterizing subchondral bone phenotypes associated with severe late-stage OA in mice.

Prognostic significance of a comprehensive histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis in primary myelofibrosis patients.

AIMS: To evaluate whether a comprehensive histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis in bone marrow trephine biopsies (BMBs) of primary myelofibrosis (PMF) patients may have prognostic implications. METHODS AND RESULTS: Reticulin fibrosis, collagen deposition and osteosclerosis were graded from 0 to 3 in a series of 122 baseline BMBs. Then, we assigned to each case a comprehensive score [reticulin, collagen, osteosclerosis (RCO) score, ranging from 0 to 9] that allowed us to distinguish two groups of patients, with low-grade (RCO score 0-4) and high-grade (RCO score 5-9) stromal changes. Of 122 patients, 88 displayed a low-grade and 34 a high-grade RCO score. The latter was associated more frequently with anaemia, thrombocytopenia, peripheral blood blasts and increased lactate dehydrogenase levels. The RCO score was correlated strictly with overall mortality (P = 0.013) and International Prognostic Scoring System (IPSS) risk categories, and was able to discriminate the overall survival of both low- and high-grade patients (log-rank test: P < 0.001). Moreover, it proved to be more accurate than the European Consensus on Grading of Bone Marrow Fibrosis (ECGMF grade) in identifying high-risk patients with poor prognosis. Finally, a combined analysis of RCO scores and IPSS risk categories in an integrated clinical-pathological evaluation was able to increase the positive predictive value (PPV) for mortality in high-risk patients. CONCLUSION: The comprehensive RCO score, obtained by histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis was prognostically significant and more accurate than ECGMF grade in identifying high-risk patients and improved PPV when applied in addition to IPSS.

The vitamin D receptor is involved in the regulation of human breast cancer cell growth via a ligand-independent function in cytoplasm.

Vitamin D has pleiotropic effects on multiple tissues, including malignant tumors. Vitamin D inhibits breast cancer growth through activation of the vitamin D receptor (VDR) and via classical nuclear signaling pathways. Here, we demonstrate that the VDR can also function in the absence of its ligand to control behaviour of human breast cancer cells both outside and within the bone microenvironment. Stable shRNA expression was used to knock down VDR expression in MCF-7 cells, generating two VDR knockdown clonal lines. In ligand-free culture, knockdown of VDR in MCF-7 cells significantly reduced proliferation and increased apoptosis, suggesting that the VDR plays a ligand-independent role in cancer cell growth. Implantation of these VDR knockdown cells into the mammary fat pad of nude mice resulted in reduced tumor growth in vivo compared with controls. In the intra-tibial xenograft model, VDR knockdown greatly reduced the ability of the cells to form tumors in the bone microenvironment. The in vitro growth of VDR knockdown cells was rescued by the expression of a mutant form of VDR which is unable to translocate to the nucleus and hence accumulates in the cytoplasm. Thus, our data indicate that in the absence of ligand, the VDR promotes breast cancer growth both in vitro and in vivo and that cytoplasmic accumulation of VDR is sufficient to produce this effect in vitro. This new mechanism of VDR action in breast cancer cells contrasts the known anti-proliferative nuclear actions of the VDR-vitamin D ligand complex.

Raine Syndrome (OMIM #259775), Caused By FAM20C Mutation, Is Congenital Sclerosing Osteomalacia With Cerebral Calcification (OMIM 259660).

In 1985, we briefly reported infant sisters with a unique, lethal, autosomal recessive disorder designated congenital sclerosing osteomalacia with cerebral calcification. In 1986, this condition was entered into Mendelian Inheritance In Man (MIM) as osteomalacia, sclerosing, with cerebral calcification (MIM 259660). However, no attestations followed. Instead, in 1989 Raine and colleagues published an affected neonate considering unprecedented the striking clinical and radiographic features. In 1992, "Raine syndrome" entered MIM formally as osteosclerotic bone dysplasia, lethal (MIM #259775). In 2007, the etiology emerged as loss-of-function mutation of FAM20C that encodes family with sequence similarity 20, member C. FAM20C is highly expressed in embryonic calcified tissues and encodes a kinase (dentin matrix protein 4) for most of the secreted phosphoproteome including FGF23, osteopontin, and other regulators of skeletal mineralization. Herein, we detail the clinical, radiological, biochemical, histopathological, and FAM20C findings of our patients. Following premortem tetracycline labeling, the proposita's non-decalcified skeletal histopathology after autopsy indicated no rickets but documented severe osteomalacia. Archival DNA revealed the sisters were compound heterozygotes for a unique missense mutation and a novel deletion in FAM20C. Individuals heterozygous for the missense mutation seemed to prematurely fuse their metopic suture and develop a metopic ridge sometimes including trigonocephaly. Our findings clarify FAM20C's role in hard tissue formation and mineralization, and show that Raine syndrome is congenital sclerosing osteomalacia with cerebral calcification. © 2016 American Society for Bone and Mineral Research.

Role of Endothelin-1 in a Syndrome of Myelofibrosis and Osteosclerosis.

CONTEXT: Primary myelofibrosis is one of the chronic myeloproliferative disorders characterized by bone marrow fibrosis associated with extramedullary hematopoiesis and osteosclerosis. Endothelin-1 (ET1) is a potent vasoconstrictor that is also a key mediator of osteoblastic bone metastases by stimulating osteoblast proliferation and new bone formation. CASE DESCRIPTION: We report laboratory, radiographic, bone densitometry, and bone histology data of a patient presenting with newly diagnosed, biopsy-proven myelofibrosis and osteosclerosis. We were able to demonstrate abundant ET1 signaling in the bones of our patient. CONCLUSIONS: We believe that ET1 is responsible for the osteosclerosis that develops with advanced myelofibrosis and suggest that ET1 signaling may play a role in other osteosclerotic settings as well.

Sclerosing bone dysplasias: leads toward novel osteoporosis treatments.

Sclerosing bone dysplasias are a group of rare, monogenic disorders characterized by increased bone density resulting from the disturbance in the fragile equilibrium between bone formation and resorption. Over the last decade, major contributions have been made toward better understanding of the pathogenesis of these conditions. These studies provided us with important insights into the bone biology and yielded the identification of numerous drug targets for the prevention and treatment of osteoporosis. Here, we review this heterogeneous group of disorders focusing on their utility in the development of novel osteoporosis therapies.

Exome sequencing reveals FAM20c mutations associated with fibroblast growth factor 23-related hypophosphatemia, dental anomalies, and ectopic calcification.

Fibroblast growth factor 23 (FGF23) plays a crucial role in renal phosphate regulation, exemplified by the causal role of PHEX and DMP1 mutations in X-linked hypophosphatemic rickets and autosomal recessive rickets type 1, respectively. Using whole exome sequencing we identified compound heterozygous mutations in family with sequence similarity 20, member C (FAM20C) in two siblings referred for hypophosphatemia and severe dental demineralization disease. FAM20C mutations were not found in other undiagnosed probands of a national Norwegian population of familial hypophosphatemia. Our results demonstrate that mutations in FAM20C provide a putative new mechanism in human subjects leading to dysregulated FGF23 levels, hypophosphatemia, hyperphosphaturia, dental anomalies, intracerebral calcifications and osteosclerosis of the long bones in the absence of rickets.