Differential gene expression in cultured osteoblasts and bone marrow stromal cells from patients with Paget's disease of bone

Molecular characterisation of osteoblasts from bone obtained from people of Polynesian and European ancestry undergoing joint replacement surgery

Population studies in Aotearoa New Zealand found higher bone mineral density and lower rate of hip fracture in people of Polynesian ancestry compared to Europeans. We hypothesised that differences in osteoblast proliferation and differentiation contribute to the differences in bone properties between the two groups. Osteoblasts were cultured from bone samples obtained from 30 people of Polynesian ancestry and 25 Europeans who had joint replacement surgeries for osteoarthritis. The fraction of cells in S-phase was determined by flow cytometry, and gene expression was analysed by microarray and real-time PCR. We found no differences in the fraction of osteoblasts in S-phase between the groups. Global gene expression analysis identified 79 differentially expressed genes (fold change > 2, FDR P < 0.1). Analysis of selected genes by real-time PCR found higher expression of COL1A1 and KRT34 in Polynesians, whereas BGLAP, DKK1, NOV, CDH13, EFHD1 and EFNB2 were higher in Europeans (P ≤ 0.01). Osteoblasts from European donors had higher levels of late differentiation markers and genes encoding proteins that inhibit the Wnt signalling pathway. This variability may contribute to the differences in bone properties between people of Polynesian and European ancestry that had been determined in previous studies.

Protective Effects of Vitamin K Compounds on the Proteomic Profile of Osteoblasts under Oxidative Stress Conditions

Oxidative stress, which accompanies the pathogenesis of many bone diseases, contributes to the reduction of osteoblast activity, resulting in the inhibition of differentiation. This study aimed to assess the effect of vitamins K1 and K2 (MK4 and MK7) on the proteomic profile of human osteoblasts cell line under oxidative conditions induced by hydrogen peroxide (H₂O₂). The analysis was performed using QExactiveHF mass spectrometer with a nanoelectrospray ionization source. The osteoblast protein exposed to oxidative stress and vitamin K was compared with the proteome of cells exposed only to oxidative stress. Our proteomic analysis identified 1234 proteins changed after 5 days, 967 after 15 days, and 1214 after 20 days of culture. We observed the most frequent changes in the expression of proteins with catalytic activity or protein/DNA binding properties (45% and 40%, respectively). Significant changes were also observed in proteins with transcription/translation regulator activity (2–6%), regulators of molecular functions (5–6%), signal transducers (1–4%), transporters (4–6%), and structural molecules (3–5%). Our results clearly show that vitamins K protect cells from H₂O₂-induced changes in protein expression, primarily through their effects on transcriptional regulators and transporter proteins. As a result, vitamins K can support the formation, remodeling, and mineralization of bone tissue.

Recent advances in understanding and managing Paget's disease

Paget’s disease is a condition which continues to challenge and surprise. The dramatic fall in its incidence over the last three decades has been an enormous surprise, as is the capacity of a single infusion of the potent bisphosphonate, zoledronate, to produce biochemical remission in 90% of patients, remissions which usually persist for many years and raise the possibility of a cure in some patients. However, challenges in its management remain. The trials carried out in Paget’s disease have almost always had biochemical indices as their primary endpoints. From these studies, we also know that bone pain is relieved, quality of life improved, bone histology normalised, and radiological lesions healed. Thus, disease progression is halted. Studies have not been powered to assess whether clinically important endpoints such as fracture and the need for joint replacement surgery are diminished, although these complications are well established as part of the natural history of the condition. Since disease progression is prevented by potent bisphosphonates, it is likely that disease complications will also be prevented. Zoledronate also reduces the frequency of follow-up needed and therefore provides a very cost-effective intervention in those who have symptomatic disease or are at risk of complications.

Inhibition of STAT5A promotes osteogenesis by DLX5 regulation

The regulation of osteogenesis is important for bone formation and fracture healing. Despite advances in understanding the molecular mechanisms of osteogenesis, crucial modulators in this process are not well-characterized. Here we demonstrate that suppression of signal transducer and activator of transcription 5A (STAT5A) activates distal-less homeobox 5 (DLX5) in human bone marrow-derived stromal cells (hBMSCs) and enhances osteogenesis in vitro and in vivo. We show that STAT5A negatively regulates expression of Dlx5 in vitro and that STAT5A deletion results in increased trabecular and cortical bone mass and bone mineral density in mice. Additionally, STAT5A deletion prevents age-related bone loss. In a murine fracture model, STAT5A deletion was found to significantly enhance bone remodeling by stimulating the formation of a fracture callus. Our findings indicate that STAT5A inhibition enhances bone formation by promoting osteogenesis of BMSCs.

Treatment of Paget's Disease of Bone with Denosumab: Case Report and Literature Review

Paget's disease is a condition involving focal overactivity of bone cells (osteoblasts and osteoclasts), which can result in significant skeletal morbidity. It is unclear in which bone cells the causative lesion resides. It is managed effectively with potent bisphosphonates, but treatment is difficult if these drugs are contraindicated. We describe a 75-year-old woman with Paget's disease involving the skull who was intolerant of bisphosphonates, so was treated with denosumab. This intervention normalized serum alkaline phosphatase for 4-8 months after each injection and led to some symptomatic improvement. Scintigraphic activity in the lesion was improved but not normalized. We conclude that reduction in RANKL activity by denosumab only partially corrects pagetic activity, indicating that the osteoclast overactivity of Paget's disease is not wholly mediated by RANKL. Denosumab has some clinical utility in Paget's disease and may become a second-line agent in those with contraindications to intravenous bisphosphonates.

CHMP5 controls bone turnover rates by dampening NF-κB activity in osteoclasts

Physiological bone remodeling requires that bone formation by osteoblasts be tightly coupled to bone resorption by osteoclasts. However, relatively little is understood about how this coupling is regulated. Here, we demonstrate that modulation of NF-κB signaling in osteoclasts via a novel activity of charged multivesicular body protein 5 (CHMP5) is a key determinant of systemic rates of bone turnover. A conditional deletion of CHMP5 in osteoclasts leads to increased bone resorption by osteoclasts coupled with exuberant bone formation by osteoblasts, resembling an early onset, polyostotic form of human Paget's disease of bone (PDB). These phenotypes are reversed by haploinsufficiency for Rank, as well as by antiresorptive treatments, including alendronate, zolendronate, and OPG-Fc. Accordingly, CHMP5-deficient osteoclasts display increased RANKL-induced NF-κB activation and osteoclast differentiation. Biochemical analysis demonstrated that CHMP5 cooperates with the PDB genetic risk factor valosin-containing protein (VCP/p97) to stabilize the inhibitor of NF-κBα (IκBα), down-regulating ubiquitination of IκBα via the deubiquitinating enzyme USP15. Thus, CHMP5 tunes NF-κB signaling downstream of RANK in osteoclasts to dampen osteoclast differentiation, osteoblast coupling and bone turnover rates, and disruption of CHMP5 activity results in a PDB-like skeletal disorder.

Paget's disease of bone

Paget's disease of bone is a common disorder characterized by increased but disorganized bone remodelling. Some patients are asymptomatic but others present with bone pain or other complications such as fracture and deformity. Major advances have been made in understanding the pathophysiology of Paget's disease in recent years and highly effective agents are now available with which to suppress the abnormal bone turnover that causes the disease. Here we review recent advances in the epidemiology, pathogenesis, clinical features and management of Paget's disease. We also reflect upon the future challenges that remain to be overcome to explain the unusual distribution of the disease and to favourably alter the natural history and prevent the development of complications.

Genetics of Paget's disease of bone

Paget's disease of bone (PDB) is a common condition, which is characterised by focal areas of increased and disorganized bone remodeling. Genetic factors play an important role in the disease. In some cases, Paget's disease is inherited in an autosomal dominant manner and the most common cause for this is a mutation in the SQSTM1 gene. Other familial cases have been linked to the OPTN locus on Chromosome 10p13 and still other variants have been identified by genome wide association studies that lie within or close to genes that play roles in osteoclast differentiation and function. Mutations in TNFRSF11A, TNFRSF11B and VCP have been identified in rare syndromes with PDB-like features. These advances have improved understanding of bone biology and the causes of PDB. The identification of genetic markers for PDB also raises the prospect that genetic profiling could identify patients at high risk of developing complications, permitting enhanced surveillance and early therapeutic intervention.

Increased IL-6 expression in osteoclasts is necessary but not sufficient for the development of Paget's disease of bone

Measles virus nucleocapsid protein (MVNP) expression in osteoclasts (OCLs) and mutation of the SQSTM1 (p62) gene contribute to the increased OCL activity in Paget's disease (PD). OCLs expressing MVNP display many of the features of PD OCLs. Interleukin-6 (IL-6) production is essential for the pagetic phenotype, because transgenic mice with MVNP targeted to OCLs develop pagetic OCLs and lesions, but this phenotype is absent when MVNP mice are bred to IL-6(-/-) mice. In contrast, mutant p62 expression in OCL precursors promotes receptor activator of NF-κB ligand (RANKL) hyperresponsivity and increased OCL production, but OCLs that form have normal morphology, are not hyperresponsive to 1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3 ), nor produce elevated levels of IL-6. We previously generated p62(P394L) knock-in mice (p62KI) and found that although OCL numbers were increased, the mice did not develop pagetic lesions. However, mice expressing both MVNP and p62KI developed more exuberant pagetic lesions than mice expressing MVNP alone. To examine the role of elevated IL-6 in PD and determine if MVNP mediates its effects primarily through elevation of IL-6, we generated transgenic mice that overexpress IL-6 driven by the tartrate-resistant acid phosphatase (TRAP) promoter (TIL-6 mice) and produce IL-6 at levels comparable to MVNP mice. These were crossed with p62KI mice to determine whether IL-6 overexpression cooperates with mutant p62 to produce pagetic lesions. OCL precursors from p62KI/TIL-6 mice formed greater numbers of OCLs than either p62KI or TIL-6 OCL precursors in response to 1,25-(OH)2 D3 . Histomorphometric analysis of bones from p62KI/TIL-6 mice revealed increased OCL numbers per bone surface area compared to wild-type (WT) mice. However, micro-quantitative CT (µQCT) analysis did not reveal significant differences between p62KI/TIL-6 and WT mice, and no pagetic OCLs or lesions were detected in vivo. Thus, increased IL-6 expression in OCLs from p62KI mice contributes to increased responsivity to 1,25-(OH)2 D3 and increased OCL numbers, but is not sufficient to induce Paget's-like OCLs or bone lesions in vivo.

Republished: Paget's disease of bone: clinical review and update

Paget's disease (PD) is a focal disorder of bone remodelling that occurs commonly in older people. In this article, we review clinical aspects of PD with an emphasis on recent findings. The epidemiology of PD appears to be changing rapidly, with several groups in different parts of the world reporting a marked reduction in the prevalence and incidence of PD, as well as in the severity of disease seen by clinicians. These findings seem most likely to be caused by changes in exposure to unknown environmental factors that have a role in the development of PD. However, genetic factors are also important. Mutations in SQSTM1 occur in 25-50% of familial PD. Genotype-phenotype relationships are present, as PD develops at an earlier age and is more extensive and severe in those with SQSTM1 mutations, and these findings are more pronounced in those with truncating mutations. However, the prevalence of PD in adults with SQSTM1 mutations is uncertain, and it is not known how such mutations might cause PD. Ultimately, if the cause of PD is determined, it seems likely that it will include both genetic and environmental factors. Lastly, clinical trials have shown that potent bisphosphonates are highly effective treatments for active PD, and reduce pain, improve quality of life, normalise bone turnover and heal lytic lesions on radiographs. They can also induce sustained remission that persists for many years.

Inflammatory cytokines in Paget's disease of bone

This study was undertaken to evaluate the expression of inflammatory cytokines in patients with Paget's disease of bone (PDB). Serum levels of tumoral necrosis factor-α, interleukin 1β, interleukin-6 and interleukin-17 were measured in 51 patients with PDB and in 24 controls with primary osteoarthritis. Compared to controls, patients with Paget's disease of bone presented higher levels of interleukin 6 and reduced interleukin 17, but levels of tumoral necrosis factor α and interleukin 1 β did not differ significantly. We found no significant differences when patients were compared according to disease activity or current treatment. There were no correlations between cytokine levels and bone-specific alkaline phosphatase or extension of Paget's disease of bone on bone scintigraphs. In conclusion, patients with PDB present significant differences on levels of certain cytokines in comparison to primary osteoarthritis patients, but these alterations did not appear to have a clear correlation with parameters of disease activity or severity.

Genetic association study of Dickkopf-1 and sclerostin genes with paget disease of bone

Increased expression of DKK1 gene was reported in pagetic osteoblasts and stromal cells, and increased serum levels of DKK1 and SOST proteins were reported in patients with Paget disease of bone (PDB). This study aimed at identifying rare genetic variants of the DKK1 and SOST genes and at testing for genetic association with PDB in the French-Canadian population. Exons, promoters, and exon-intron junctions of these genes were sequenced in patients with PDB and healthy controls. An association study of Tag SNPs of both genes was also performed in 239 pagetic patients and 297 healthy individuals. Three rare variants were identified in this study, all located in the DKK1 gene: one variant in the second exon leading to alteration in a highly conserved amino acid (p.R120L), one in the 5'-untranslated region (-50 C/A), and one in a splice site of intron 1 (IVS1 184 T/C), although none of these rare variants were associated with PDB. A genetic association of a Tag SNP of the DKK1 gene was found: the G allele of rs1569198 was significantly decreased in patients in comparison to controls (42 vs. 49 %, uncorrected P = 0.03, OR = 0.77, 95 % CI 0.61-0.98). In conclusion, this study identified three rare genetic variants in DKK1 in the French-Canadian population. In addition, a weak genetic association of a common variant of DKK1, rs1569198, which is located on a predicted new acceptor site for splicing of this gene, was observed in PDB, whereas no rare variant or genetic association was found in the SOST gene.

Paget's disease of bone: clinical review and update

Paget's disease (PD) is a focal disorder of bone remodelling that occurs commonly in older people. In this article, we review clinical aspects of PD with an emphasis on recent findings. The epidemiology of PD appears to be changing rapidly, with several groups in different parts of the world reporting a marked reduction in the prevalence and incidence of PD, as well as in the severity of disease seen by clinicians. These findings seem most likely to be caused by changes in exposure to unknown environmental factors that have a role in the development of PD. However, genetic factors are also important. Mutations in SQSTM1 occur in 25-50% of familial PD. Genotype-phenotype relationships are present, as PD develops at an earlier age and is more extensive and severe in those with SQSTM1 mutations, and these findings are more pronounced in those with truncating mutations. However, the prevalence of PD in adults with SQSTM1 mutations is uncertain, and it is not known how such mutations might cause PD. Ultimately, if the cause of PD is determined, it seems likely that it will include both genetic and environmental factors. Lastly, clinical trials have shown that potent bisphosphonates are highly effective treatments for active PD, and reduce pain, improve quality of life, normalise bone turnover and heal lytic lesions on radiographs. They can also induce sustained remission that persists for many years.

New insights into the role of sequestosome 1/p62 mutant proteins in the pathogenesis of Paget's disease of bone

Paget's disease of bone (PDB) is characterized by focal areas of aberrant and excessive bone turnover, specifically increased bone resorption and disorganized bone formation. Germline mutations in the sequestosome 1/p62 (SQSTM1/p62) gene are common in PDB patients, with most mutations affecting the ubiquitin-associated domain of the protein. In vitro, osteoclast precursor cells expressing PDB-mutant SQSTM1/p62 protein are associated with increases in nuclear factor κB activation, osteoclast differentiation, and bone resorption. Although the precise mechanisms by which SQSTM1/p62 mutations contribute to disease pathogenesis and progression are not well defined, it is apparent that as well as affecting nuclear factor κB signaling, SQSTM1/p62 is a master regulator of ubiquitinated protein turnover via autophagy and the ubiquitin-proteasome system. Additional roles for SQSTM1/p62 in the oxidative stress-induced Keap1/Nrf2 pathway and in caspase-mediated apoptosis that were recently reported are potentially relevant to the pathogenesis of PDB. Thus, SQSTM1/p62 may serve as a molecular link or switch between autophagy, apoptosis, and cell survival signaling. The purpose of this review is to outline recent advances in understanding of the multiple pathophysiological roles of SQSTM1/p62 protein, with particular emphasis on their relationship to PDB, including challenges associated with translating SQSTM1/p62 research into clinical diagnosis and treatment.

High dickkopf-1 levels in sera and leukocytes from children with 21-hydroxylase deficiency on chronic glucocorticoid treatment

Children with 21-hydroxylase deficiency (21-OHD) need chronic glucocorticoid (cGC) therapy to replace congenital deficit of cortisol synthesis, and this therapy is the most frequent and severe form of drug-induced osteoporosis. In this study, we enrolled 18 patients (9 females) and 18 sex- and age-matched controls. We found in 21-OHD patients high serum and leukocyte levels of dickkopf-1 (DKK1), a secreted antagonist of the Wnt/β-catenin signaling pathway known to be a key regulator of bone mass. In particular, we demonstrated by flow cytometry, confocal microscopy, and real-time PCR that monocytes, T lymphocytes, and neutrophils from patients expressed high levels of DKK1, which may be related to the cGC therapy. In fact, we showed that dexamethasone treatment markedly induced the expression of DKK1 in a dose- and time-dependent manner in leukocytes. The serum from patients containing elevated levels of DKK1 can directly inhibit in vitro osteoblast differentiation and receptor activator of NF-κB ligand (RANKL) expression. We also found a correlation between both DKK1 and RANKL or COOH-terminal telopeptides of type I collagen (CTX) serum levels in 21-OHD patients on cGC treatment. Our data indicated that DKK1, produced by leukocytes, may contribute to the alteration of bone remodeling in 21-OHD patients on cGC treatment.

Genotype-phenotype correlation in juvenile Paget disease: role of molecular alterations of the TNFRSF11B gene

Juvenile Paget disease (JPD) {MIM 239000} is a rare inherited bone disease that affects children. The patients affected with JPD present an altered bone turnover, therefore, show a phenotype characterized by progressive bone deformities, fractures, and short stature. Deletions or missense mutations of the TNFRSN11B gene are common in these children. This gene encodes a soluble protein, the osteoprotegerin, which leads to uncontrolled osteoclastogenesis when mutated. JPD is characterized by a strong genotype-phenotype correlation, so depending on the alteration of the TNFRSN11B gene, the phenotype is variable. This review describes the different clinical features which are characteristic of JPD and the correspondence with the different molecular alterations of the TNFRSN11B gene.

Pathogenesis of Paget disease of bone

Paget disease of bone (PDB) is a common disease characterized by focal areas of increased and disorganized bone turnover. Some patients are asymptomatic, whereas others develop complications such as pain, osteoarthritis, fracture, deformity, deafness, and nerve compression syndromes. PDB is primarily caused by dysregulation of osteoclast differentiation and function, and there is increasing evidence that this is due, in part, to genetic factors. One of the most important predisposing genes is SQSTM1, which harbors mutations that cause osteoclast activation in 5-20 % of PDB patients. Seven additional susceptibility loci for PDB have been identified by genomewide association studies on chromosomes 1p13, 7q33, 8q22, 10p13, 14q32, 15q24, and 18q21. Although the causal variants remain to be discovered, three of these loci contain CSF1, TNFRSF11A, and TM7SF4, genes that are known to play a critical role in osteoclast differentiation and function. Environmental factors are also important in the pathogenesis of PDB, as reflected by the fact that in many countries the disease has become less common and less severe over recent years. The most widely studied environmental trigger is paramyxovirus infection, but attempts to detect viral transcripts in tissues from patients with PDB have yielded mixed results. Although our understanding of the pathophysiology of PDB has advanced tremendously over the past 10 years, many questions remain unanswered, such as the mechanisms responsible for the focal nature of the disease and the recent changes in prevalence and severity.

Serum sclerostin levels in Paget's disease and prostate cancer with bone metastases with a wide range of bone turnover

Evidence has been accumulating for the role of osteocytes as key players in the regulation of bone remodeling. One of the main products of these cells, sclerostin, inhibits bone formation and may also stimulate bone resorption. Circulating sclerostin has been evaluated in humans, but data are scarce in patients with different rates of bone turnover. To address this issue we evaluated serum sclerostin levels in patients with Paget's disease of bone (PD) and in patients with prostate cancer metastatic to the skeleton (PC). Sclerostin levels were measured in 88 patients with PD, 20 patients with PC and 237 healthy individuals (113 men and 124 women, aged 20 to 77 years). Bone turnover was evaluated by measuring serum levels of procollagen type 1 amino-terminal propeptide (P1NP) in all individuals studied and β-carboxy-terminal cross-linking telopeptide of type I collagen (β-CTX) only in patients. Patients were aged between 45 and 88 years and had a wide range of bone turnover: serum P1NP 9.2 to 1872 ng/ml and β-CTX 50 to 3120 pg/ml. Patients with PD and with PC had significantly higher mean serum sclerostin levels (53.1 ± 22.7 pg/ml and 56.6 ± 25.8 pg/ml, respectively) compared to healthy controls (38.1 ± 12.1 pg/ml) (p<0.001). Serum sclerostin levels were significantly correlated with P1NP in all (n=345) studied subjects (r=0.32, p<0.001). Circulating sclerostin levels are significantly increased in patients with increased bone turnover, regardless of underlying pathology. These increased levels may be due to a compensatory response to the increased number of osteoblasts at affected skeletal sites and may contribute to the increased bone resorption in patients with PC .

Post-genomics of bone metabolic dysfunctions and neoplasias

Post-genomic research on osteoblastic and osteoclastic cells, in contrast to that on many other cell types, has only been undertaken recently. Nevertheless, important information has been gained from these investigations on the mechanisms involved in osteoblast differentiation and on markers relevant for tissue regeneration and therapeutic validation of drugs, hormones and growth factors. These protein indicators may also have a diagnostic and prognostic value for bone dysfunctions and tumors. Some reviews have already focused on the application of transcriptomics and/or proteomics for exploring skeletal biology and related disorders. The main goal of the present review is to systematically summarize the most relevant post-genomic studies on various metabolic bone diseases (osteoporosis, Paget's disease and osteonecrosis), neoplasias (osteosarcoma) and metabolic conditions that indirectly affect bone tissue, such as alkaptonuria.

Paget's disease of bone: an update

PURPOSE OF REVIEW

The review summarizes the recent findings relevant to the clinical management, genetic predisposition, and molecular mechanisms implicated in Paget's disease of bone (PDB).

RECENT FINDINGS

PDB is characterized by focal regions of increased bone remodeling and abnormal bone architecture. PDB is treated effectively with amino-bisphosphonates, which can produce very prolonged disease remission. The disease has a strong genetic component and a large number of studies focus on the cellular mechanisms affected by mutations in the SQSTM1 (sequestosome 1) gene which are associated with PDB. Identifying other genes associated with PDB is an additional active research focus.

SUMMARY

In recent years, there has been a great progress in the understanding of the epidemiology, genetics and molecular biology of PDB. However, an integrative view of the disease cause is still missing and is likely to be attained only with further discoveries of genetic factors, environmental factors, and the interactions between them. Investigations of the cellular mechanisms that are disrupted in PDB contribute greatly to the understanding of normal bone remodeling.

Ghrelin is an Osteoblast Mitogen and Increases Osteoclastic Bone Resorption In Vitro

Ghrelin is released in response to fasting, such that circulating levels are highest immediately prior to meals. Bone turnover is acutely responsive to the fed state, with increased bone resorption during fasting and suppression during feeding. The current study investigated the hypothesis that ghrelin regulates the activity of bone cells. Ghrelin increased the bone-resorbing activity of rat osteoclasts, but did not alter osteoclast differentiation in a murine bone marrow assay nor bone resorption in ex vivo calvarial cultures. Ghrelin showed mitogenic activity in osteoblasts, with a strong effect in human cells and a weaker effect in rat osteoblasts. The expression of the human ghrelin receptor, GHSR, varied among individuals and was detectable in 25–30% of bone marrow and osteoblast samples. However, the rodent Ghsr expression was undetectable in bone cells and cell lines from rat and mouse. These data suggest that elevated levels of ghrelin may contribute to the higher levels of bone turnover that occurs in the fasted state.

Emerging strategies and therapies for treatment of Paget's disease of bone

Paget's disease of bone (PDB) is a progressive monostotic or polyostotic metabolic bone disease characterized by focal abnormal bone remodeling, with increased bone resorption and excessive, disorganized, new bone formation. PDB rarely occurs before middle age, and it is the second most frequent metabolic bone disorder after osteoporosis, affecting up to 3% of adults over 55 years of age. One of the most striking and intriguing clinical features is the focal nature of the disorder, in that once the disease is established within a bone, there is only local spread within that bone and no systemic dissemination. Despite many years of intense research, the etiology of PDB has still to be conclusively determined. Based on a detailed review of genetic and viral factors incriminated in PDB, we propose a unifying hypothesis from which we can suggest emerging strategies and therapies. PDB results in weakened bone strength and abnormal bone architecture, leading to pain, deformity or, depending on the bone involved, fracture in the affected bone. The diagnostic assessment includes serum total alkaline phosphatase, total body bone scintigraphy, skull and enlarged view pelvis x-rays, and if needed, additional x-rays. The ideal therapeutic option would eliminate bone pain, normalize serum total alkaline phosphatase with prolonged remission, heal radiographic osteolytic lesions, restore normal lamellar bone, and prevent recurrence and complications. With the development of increasingly potent bisphosphonates, culminating in the introduction of a single intravenous infusion of zoledronic acid 5 mg, these goals of treatment are close to being achieved, together with long-term remission in almost all patients. Based on the recent pathophysiological findings, emerging strategies and therapies are reviewed: ie, pulse treatment with zoledronic acid; denosumab, a fully human monoclonal antibody directed against RANK ligand; tocilizumab, an interleukin-6 receptor inhibitor; odanacatib, a cathepsin K inhibitor; and proteasome and Dickkopf-1 inhibitors.

The emerging role of Dickkopf-1 in bone biology: is it the main switch controlling bone and joint remodeling?

BACKGROUND

Dickkopf-1 (DKK-1), an inhibitor of the Wnt pathway, has recently emerged as an important player in several critical aspects of bone biology.

METHODS

We performed an extensive internet search (MEDLINE) using the key words Dickkopf-1 and the abbreviation DKK-1.

RESULTS

DKK-1 is a regulator of bone mass with increased expression linked to osteopenia and decreased expression to high bone mass. Moreover, it appears to actively participate in joint remodeling in animal models of arthritis, with increased levels related to bone resorption and decreased levels to new bone formation. Recent studies indicate its possible involvement in the remodeling process of human systemic rheumatic diseases such as rheumatoid arthritis and ankylosing spondylitis. DKK-1 may also play a role in osteoarthritis, metabolic bone disease (osteoporosis and Paget's disease), as well as multiple myeloma-associated bone disease and prostate cancer bone metastases.

CONCLUSIONS

DKK-1 is a regulator of bone mass and joint remodeling. It may be a promising therapeutic target in osteoporosis; monoclonal antibody-based inhibition of Dkk-1 is already under development for osteoporosis treatment. Its role as a regulator of joint remodeling in animal models requires further exploration in humans.

New knowledge on critical osteoclast formation and activation pathways from study of rare genetic diseases of osteoclasts: focus on the RANK/RANKL axis

Functional, biochemical and genetic studies have over the past decade identified many causative genes in the osteoclast diseases osteopetrosis and Paget's disease of bone. Here, we outline all osteoclast diseases and their genetic associations and then focus specifically on those diseases caused by mutations in the critical osteoclast molecule Receptor Activator of Nuclear factor Kappa B (RANK). Both loss and gain-of-function mutations have been found in humans leading to osteopetrosis and high bone turnover phenotypes, respectively. Osteopetrosis-associated RANK mutations are widely distributed over the RANK molecule. It is likely that some negatively affect ligand binding, whereas others preclude appropriate association of RANK with downstream signalling molecules. In the Paget-like disorders, familial expansile osteolysis, early onset Paget's disease and expansile skeletal hyperphosphatasia, heterozygous insertion mutations are found in the RANK signal peptide. These prevent signal peptide cleavage, trapping the protein translated from the mutated allele in the endoplasmic reticulum. Whole animal studies replicate the hyperactive osteoclast phenotype associated with these disorders and present only with heterozygous expression of the mutation, suggesting an as yet unexplained effect of the mutant allele on normal RANK function. We discuss the cell biological studies and animal models that help us to understand the nature of these different RANK defects and describe how careful dissection of these conditions can help understand critical pathways in osteoclast development and function. We highlight areas that require further study, particularly in light of the pharmacological interest in targeting the RANK signalling pathway to treat diseases caused by excessive bone resorption.

Paget's disease of bone is not associated with common polymorphisms in interleukin-6, interleukin-8 and tumor necrosis factor alpha genes

BACKGROUND

Cytokines, specially interleukin (IL)-6, play an important role in the differentiation and activation of osteoclasts and might be involved in osteoblast stimulation in Paget's disease of bone (PDB).

OBJECTIVES

The aim of this study was to investigate the association of polymorphisms in IL-6, IL-8 and tumor necrosis factors-alpha (TNFA) genes among Spanish patients with PDB.

METHODS

We studied four single nucleotide polymorphisms (-174 G>C IL-6, -251 T>A IL-8, -238 G>A TNFA and -308 G>A TNFA) in 172 PDB patients and 150 healthy controls. Distribution of alleles and pro-inflammatory genotypes were studied for association with the presence of the disease and with clinical and laboratory data, as well as the response to bisphosphonate treatment in PDB patients.

RESULTS

We found no statistically significant association between genotype and allele distribution of any of the cytokines polymorphism studied and PDB. No association between the clinical and therapeutic characteristics of PDB and the investigated polymorphism were found.

CONCLUSIONS

This study does not support the hypothesis that the analyzed IL6, IL8 and TNFA polymorphism are associated with PDB.

Circulating and tissue-derived isoforms of bone alkaline phosphatase in Paget's disease of bone

BACKGROUND

Alkaline phosphatase (ALP) is routinely used in the assessment of Paget's disease of bone (PDB); however, the individual bone ALP isoforms (B/I, B1, and B2) have not been investigated in this disorder.

METHODS

Subjects comprised 37 patients (mean age 74 years) with symptomatic PDB confirmed by radiograph and stratified into high and low total ALP activity groups and 66 healthy individuals (mean age 64 years). Extracts of human cancellous and cortical bone tissues were also investigated. The bone ALP isoforms, measured by HPLC, were compared with two bone ALP immunoassays (Metra and Ostase), and the bone formation marker intact amino-terminal procollagen type I propeptide (iPINP).

RESULTS

All bone ALP isoforms were increased in high ALP activity PDB compared with the low ALP activity and control groups (p < 0.0001). The B2 isoform had the greater relative activity representing 36%, 50%, and 71%, of the total ALP activity in the control, low and high ALP activity groups, respectively. Compared with controls, B2 was increased in the low ALP activity PDB group (p < 0.05). ROC analysis showed a validity of approximately 80% for B2 to discriminate patients with PDB.

CONCLUSION

All bone ALP isoforms were increased in patients with high ALP activity PDB and the B2 isoform was even elevated in the low ALP activity PDB group. The bone ALP isoform B2 may be of use in the management of PDB but that has to be further elucidated in subsequent studies.

Dual-energy X-ray absorptiometry and quantitative ultrasound in patients with Paget's disease of bone before and after treatment with zoledronic acid: association with serum bone markers and Dickkopf-1

The main aim of this study was to determine the effect of zoledronic acid (ZOL) on parameters of dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) in unaffected bones of patients with Paget's disease of bone (PDB). The secondary aim was the association of bone markers and Dickkopf (DKK)-1 with parameters of DXA and QUS. Ten consecutive patients with polyostotic PDB (median age: 63 yr) received a single 5-mg ZOL infusion. The patients were subjected to calcaneal QUS and DXA of both lumbar spine (LS) and femoral neck (FN). Blood samples for serum bone markers and DKK-1 were serially obtained for 12 mo. There was a significant increase in LS (p=0.005) and FN bone mineral density (BMD) (p=0.021) 12 mo after ZOL infusion. QUS parameters remained unaffected throughout the study. A significant correlation between broadband ultrasound attenuation and DKK-1 (p<0.001) and between speed of sound and DKK-1 (p=0.033) at baseline was found, which remained significant after adjustment for gender, age, and body mass index. Our data suggest that a single ZOL infusion significantly increases nonpagetic BMD 12 mo after treatment but has no effect on QUS parameters or DKK-1. Significant correlations were observed between QUS parameters and DKK-1 at baseline.

Dickkopf-1 as a potential therapeutic target in Paget's disease of bone

IMPORTANCE OF THE FIELD

Wnt signalling plays a role in maintaining healthy bone mass. Dickkopf-1 (DKK-1) is a soluble inhibitor of Wnt signalling and its excessive expression contributes to bone loss in rheumatoid arthritis and multiple myeloma. New therapeutics have been developed for treatment of these conditions that target DKK-1 expression. DKK-1 is elevated in serum of patients with Paget's disease of the bone (PDB) and evidence is accumulating for a role of DKK-1 in PDB.

AREAS COVERED IN THIS REVIEW

The role of Wnt signalling and DKK-1 in bone health and disease and the aetiology of PDB in the light of recent advances in understanding of Wnt signalling.

WHAT THE READER WILL GAIN

PDB is a disorder of unknown aetiology characterised by localised increase in unregulated bone remodelling resulting in osteolytic and osteosclerotic lesions. Evidence is adduced for the involvement of Wnt signalling, DKK-1 and osteoblasts in PDB pathogenesis.

TAKE HOME MESSAGE

At present there is no cure for PDB and the current treatment of choice are bisphosphonates. These treat the resorptive phase of PDB but do not prevent its return. We present a new perspective on the aetiology of PDB and speculate on DKK-1 as a therapeutic target.

Gene expression profile in osteoclasts from patients with Paget's disease of bone

Paget's disease of bone (PDB) is a common metabolic bone disorder with a significant genetic component. To date, only one gene associated with PDB has been identified, the p62-Sequestosome1 gene (SQSTM1), and more than 20 mutations of this gene have been reported in PDB, the most common being the P392L substitution. In order to search for differentially expressed genes in PDB, we investigated the relative gene expression profile of candidate genes in osteoclast (OCL) cultures from 12 PDB patients and six unmatched healthy controls with known genetic status regarding p62, including healthy carriers of the P392L mutation. We selected 48 OCL-expressed candidate genes that may be involved in relevant pathways of PDB pathogenesis, such as OCL signaling, survival, bone resorption activity, or adhesion. In OCL cultures derived from peripheral blood mononuclear cells, total RNA extraction was performed, followed by real-time PCR experiments. Relative quantification analysis utilized the qBase method where relative expression levels were normalized with respect to a set of reference primer pairs for three housekeeping genes. When compared to non-mutated healthy controls, OCL cultures from PDB patients displayed a significant down-regulation in genes involved in apoptosis (CASP3 and TNFRSF10A), in cell signaling (TNFRSF11A), in the OCL bone resorbing function (ACP5 and CTSK) and in the gene coding for Tau protein (MAPT) (all comparisons, p<0.0001). Comparison of relative gene expression in PDB patients with P392L mutation versus PDB patients without SQSTM1 mutation did not provide significant differential gene expression. However, we observed a non-significant decrease in the expression of several genes such as IL6ST, HIF1A, OSTM1, TNFRSF-10B and -10D, PDK1, MAPT and CASP3 in healthy carriers of the P392L mutation. These results provide important information about the mis-regulated activities of pagetic OCL, and highlight the role of altered apoptosis pathways in these cells. They also suggest that the SQSTM1 P392L mutation plays a role in PDB pathogenesis, even at early preclinical stages in healthy carriers of the P392L mutation.

Paget's disease of bone

Paget's disease of bone is a focal bone disorder that is common among older people of Western European descent. It is an unusual disorder, for although we now have safe and highly effective treatment, there are many aspects of its pathogenesis and natural history that we do not yet understand. Recent years have seen significant advances in the understanding of its epidemiology, genetics and molecular biology, but an integrated view that incorporates all these aspects remains elusive. In this review we examine some of the outstanding problems, the solutions to which seem likely to change our understanding of bone cell biology.

Paget's disease of bone: emphasis on treatment with zoledronic acid

The treatment of Paget's disease of bone (PDB) aims at suppression of abnormal bone turnover and bisphosphonates (BPs) are currently the drugs of choice. Zoledronic acid, a third-generation nitrogen-containing BPs, is the newest BP approved for PDB and is administered by a single intravenous infusion. In vitro zoledronic acid has higher binding affinity for hydroxyapatite and is a stronger inhibitor of farnesyl pyrophosphate synthase compared with other BPs. In vivo zoledronic acid improves symptoms, normalizes bone turnover markers and scintigraphic imaging in the majority of patients, and maintains remission of PDB longer than other BPs. This review summarizes available data on the pathogenesis, epidemiology, clinical manifestation, biochemical assessment and management of PDB, giving special attention to the treatment of PDB with zoledronic acid, based on current evidence.

FGF-2 stimulation of RANK ligand expression in Paget's disease of bone

Receptor activator for nuclear factor-kappaB ligand (RANKL), a critical osteoclastogenic factor expressed in marrow stromal/preosteoblast cells is up-regulated in Paget's disease of bone (PDB). We previously demonstrated that heat-shock factor-2 (HSF-2) is a downstream target of fibroblast growth factor-2 (FGF-2) signaling to induce RANKL expression in bone marrow stromal/preosteoblast cells. In this study, we identified a 2.5-fold increase in serum FGF-2 levels in patients (n = 8) with PDB compared with normal subjects (n = 10). We showed that HSF-2 co-immunoprecipitates with heat-shock protein-27 (HSP-27) and that FGF-2 stimulation significantly increased phospho-HSP-27 levels in marrow stromal cells. Confocal microscopy revealed HSF-2 colocalization with HSP-27 in unstimulated cells and HSF-2 nuclear translocation upon FGF-2 stimulation. We further show that FGF-2 stimulation significantly increased the levels of phosphorylated signal transducers and activators of the transcription (p-STAT-1) in these cells. Western blot analysis confirmed that small interfering RNA suppression of STAT-1 significantly decreased (3.2-fold) RANKL expression and promoter activity in FGF-2-stimulated cells. Chromatin immunoprecipitation assay revealed STAT-1 binding to a putative motif located far upstream (-8 kb) in the hRANKL gene promoter region. These results suggest STAT-1 is a downstream effector of FGF-2 signaling and that elevated levels of FGF-2 stimulates RANKL expression in PDB.

Assessment of circulating Dickkopf-1 with a new two-site immunoassay in healthy subjects and women with breast cancer and bone metastases

The aim of our study was to investigate the sex- and age-related changes of serum Dickkopf-1 (Dkk-1), a soluble inhibitor of the Wnt signaling pathway, in healthy individuals and in patients with breast cancer (BC) and bone metastases (BM) using a new ELISA. Association of serum Dkk-1 with markers of bone turnover was also investigated. Serum Dkk-1 measurements were performed using a commercial sandwich ELISA in 150 healthy men, 175 healthy pre- and postmenopausal women (20-65 years), 22 women with BC and BM (mean age 63 years), and 16 women with BC and metastases at sites other than bone (mean age 53 years). Intra- and interassay coefficients of variation were below 7% and 12%, respectively. The detection limit was determined to be 0.018 microg/L. In healthy women and men, Dkk-1 did not change with age. Serum Dkk-1 modestly correlated with serum bone alkaline phosphatase (r = 0.19, P = 0.013) and serum C-terminal cross-linking telopeptide of type I collagen (r = 0.19, P = 0.014) in women but not in men. Dkk-1 levels were higher in women with BC and BM (5.57 +/- 5.50 microg/L) than in healthy age-matched controls (3.47 +/- 1.47 microg/L, P < 0.0001) and women with metastases at sites other than bone (3.57 +/- 1.66 microg/L, P = 0.0003). In conclusion, serum Dkk-1 is stable with age in healthy women and men and increases in patients with BC and BM. Measurements of circulating Dkk-1 with this new ELISA may be useful for the clinical investigation of patients with malignant bone diseases.

Absence of somatic SQSTM1 mutations in Paget's disease of bone

BACKGROUND

Paget's disease is a common focal bone disorder that appears to be caused by a combination of genetic and environmental factors. Mutations in the SQSTM1 gene are found in about one third of families with Paget's disease and 8% of sporadic cases. Other potential loci linked to the disease have also been identified, and a number of environmental factors have been suggested to be involved in the disease. However, the focal nature of Paget's is still unexplained. Therefore, we examined the possibility that somatic mutations in the SQSTM1 gene are present in the local lesions, using RNA collected from primary osteoblast and bone marrow cell cultures of patients with this condition.

METHODS

SQSTM1 was sequenced, and allelic discrimination for the common P392L mutation was performed in cDNA samples from 14 osteoblast cultures and from 14 cultures of bone marrow cells.

RESULTS

In these 28 samples drawn from 23 patients, the wild-type sequence of SQSTM1 was found in all but one marrow sample, which was heterozygous for the P392L mutation. DNA from peripheral blood in this subject had an identical sequence of SQSTM1, indicating that this was a germline mutation.

CONCLUSION

We conclude that somatic mutations for SQSTM1 are not commonly present in Paget's disease.

Paget's disease: epidemiology and pathophysiology

Paget's disease of bone is a focal disorder of aging bone. The classic late-onset Paget's disease is often caused by a P392L mutation in the gene SQSTM1, which disturbs signaling pathways in osteoclasts on cell activation. This prevalent mutation is neither necessary nor sufficient to cause Paget's disease. Its identification, along with the elucidation of other mutations underlying early-onset Paget's and Paget's disease seen in association with inclusion body myopathy and frontotemporal dementia, have redefined our understanding of genetic disorders of bone remodeling by emphasizing the importance of environmental determinants in their pathophysiology.

The role of peptides and receptors of the calcitonin family in the regulation of bone metabolism

The 'calcitonin family' is a group of peptide hormones that share structural similarities with calcitonin, and includes calcitonin gene-related peptide (CGRP), amylin, adrenomedullin and adrenomedullin 2 (intermedin). These hormones are produced by different tissues, with calcitonin being produced in thyroid C cells, alphaCGRP predominantly in neural tissue, amylin in beta-islet cells of the pancreas and adrenomedullin in many tissues and cell types. Bone appears to be a common target for all the peptides of the calcitonin family, although the specific bone effects of the peptides vary. Administration of calcitonin produces rapid lowering of serum calcium levels, mainly through inhibition of bone resorption by osteoclasts. In vitro and in a number of animal experimental models, amylin and CGRP are also effective in inhibiting osteoclast activity and bone resorption. Amylin, adrenomedullin and CGRP can also affect cells of the osteoblast lineage, inducing osteoblast proliferation and promoting bone formation. Receptors for the peptides of the calcitonin family are formed by heterodimerization of the calcitonin receptor (CTR) or calcitonin receptor-like receptor (CLR) with receptor activity modifying proteins (RAMPs). Although the different combinations of these proteins create receptors with distinct ligand specificities, there is a degree of cross-reactivity and the receptors are able to bind other ligands from the family, usually with lower affinity. Analysis of the expression of the receptors for the calcitonin family in 16 samples of human osteoblasts showed high levels of CLR and RAMP1, low levels of RAMP2 and no expression of RAMP3 or CTR. Recent studies of the bone phenotype of knockout animals lacking the calcitonin, alphaCGRP or amylin gene indicated that in this experimental system the main physiological role of amylin in bone is the inhibition of bone resorption, that of CGRP is the activation of bone formation, while calcitonin, unexpectedly appears to be inhibiting bone formation without affecting bone resorption. Further investigations will be required to determine the mechanisms of action of calcitonin peptides in bone and their significance to human bone physiology.

Pathogenesis of Paget's disease of bone

Paget's disease of bone is a common condition characterised by increased and disorganised bone turnover which can affect one or several bones throughout the skeleton. These abnormalities disrupt normal bone architecture and lead to various complications such as bone pain osteoarthritis, pathological fracture, bone deformity, deafness, and nerve compression syndromes. Genetic factors play an important role in PDB and mutations or polymorphisms have been identified in four genes that cause classical Paget's disease and related syndromes. These include TNFRSF11A, which encodes RANK, TNFRSF11B which encodes osteoprotegerin, VCP which encodes p97, and SQSTM1 which encodes p62. All of these genes play a role in the RANK-NFkappaB signalling pathway and it is likely that the mutations predispose to PDB by disrupting normal signalling, leading to osteoclast activation. Although Paget's has traditionally be considered a disease of the osteoclast there is evidence that stromal cell function and osteoblast function are also abnormal, which might account for the fact that the disease is associated with increased bone formation as well as resorption. Environmental factors also contribute to Paget's disease. Most research has focused on paramyxovirus infection as a possible environmental trigger but evidence in favour of the involvement of viruses in the disease remains conflicting. Other factors which have been implicated as possible disease triggers include mechanical loading, dietary calcium and environmental toxins. Further work will be required to identify additional genetic variants that predispose to Paget's disease and to determine how the causal mutations and predisposing polymorphisms interact with environmental factors to influence bone cell function and cause the focal bone lesions that are characteristic of the disease.

Paget disease of bone

Despite significant advances in management, Paget disease remains an enigmatic disorder. There are no animal models, and while its end result --a focal disorder of accelerated bone turnover--is easily recognized, the causes and evolution of the disorder remain uncertain. Recent evidence strongly implicates both genetic and environmental factors in its etiology. The authors consider some of the unresolved questions surrounding Paget disease, including the attenuating prevalence and severity of the disease; how these observations might be reconciled with an apparently highly penetrant genetic susceptibility; what the putative environmental triggers of Paget disease might be; and what relapse after treatment tells us. Most observations seem to fit best with the idea that Paget disease behaves as a multifocal benign neoplasm.

Pathogenesis and management of Paget's disease of bone

Paget's disease of bone is a common disease characterised by focal areas of increased bone turnover, affecting one or several bones throughout the skeleton. Paget's disease is often asymptomatic but can be associated with bone pain and other complications such as osteoarthritis, pathological fracture, bone deformity, deafness, and nerve compression syndromes. Genetic factors have an important role in this disease, and mutations have been identified in four genes that cause Paget's disease and related syndromes. The most important of these is Sequestosome 1 (SQSTM1), which is a scaffold protein in the nuclear factor kappaB (NFkappaB) signalling pathway. Patients with SQSTM1 mutations have severe Paget's disease of bone and a high degree of penetrance with increasing age. Environmental factors also contribute. Most research has focused on paramyxovirus infection as a possible trigger, but evidence for this notion is conflicting. Other potential triggers include deficiency of dietary calcium and repetitive mechanical loading of the skeleton. Medical management of Paget's disease of bone is based on giving inhibitors of osteoclastic bone resorption, and bisphosphonates are the treatment of first choice. Bisphosphonate therapy is primarily indicated for patients who have bone pain arising from increased metabolic activity in affected bones. Bisphosphonate therapy is highly effective at reducing bone turnover, and it has been shown to heal radiological lesions and restore normal histology; however, the long-term effects of bisphosphonates on disease progression have not been adequately studied. No firm evidence as yet exists to show that bisphosphonates can prevent the development of complications of Paget's disease of bone, and further work is needed to address the effects of treatment on long-term clinical outcome.

The LIM protein LIMD1 influences osteoblast differentiation and function

The balance between bone resorption and bone formation involves the coordinated activities of osteoblasts and osteoclasts. Communication between these two cell types is essential for maintenance of normal bone homeostasis; however, the mechanisms regulating this cross talk are not completely understood. Many factors that mediate differentiation and function of both osteoblasts and osteoclasts have been identified. The LIM protein Limd1 has been implicated in the regulation of stress osteoclastogenesis through an interaction with the p62/sequestosome protein. Here we show that Limd1 also influences osteoblast progenitor numbers, differentiation, and function. Limd1(-/-) calvarial osteoblasts display increased mineralization and accelerated differentiation. While no significant differences in osteoblast number or function were detected in vivo, bone marrow stromal cells isolated from Limd1(-/-) mice contain significantly more osteoblast progenitors compared to wild type controls when cultured ex vivo. Furthermore, we observed a significant increase in nuclear beta-catenin staining in differentiating Limd1(-/-) calvarial osteoblasts suggesting that Limd1 is a negative regulator of canonical Wnt signaling in osteoblasts. These results demonstrate that Limd1 influences not only stress osteoclastogenesis but also osteoblast function and osteoblast progenitor commitment. Together, these data identify Limd1 as a novel regulator of both bone osetoclast and bone osteoblast development and function.

Failure to detect measles virus ribonucleic acid in bone cells from patients with Paget's disease

BACKGROUND

Paget's disease is a condition of focal accelerated bone turnover. Electron-microscopy investigations of osteoclasts from pagetic lesions have identified nuclear inclusion bodies that have a similar appearance to viral nucleocapsid particles. Subsequently, RNA from several paramyxoviruses has been detected in pagetic tissue, and it was suggested that these viruses, in particular measles, might play a role in the etiology of Paget's disease. We have tested for measles virus sequences in osteoblasts and bone marrow cells collected from pagetic lesions and healthy bone.

METHODS

Bone and bone marrow samples were taken from Paget's patients and control subjects, and cells were cultured from each of these tissues. RNA was extracted from 13 osteoblast cultures and 13 cultures of bone marrow cells derived from pagetic lesions, and from 26 and 23 control osteoblast and bone marrow cultures, respectively. These samples were sourced from 22 patients with Paget's disease and 31 controls. RT-PCR-nested PCR amplification was used for the detection of the genes for the measles nucleocapsid and matrix proteins.

RESULTS

Measles virus sequences were not detected in any of the pagetic or control samples. However, measles virus sequences were identified in samples of a measles virus culture isolate included as a positive control, and in a brain sample from a patient with subacute sclerosing panencephalitis, a condition associated with chronic measles infection.

CONCLUSION

The results of the study do not support the hypothesis that measles virus plays a role in the pathogenesis of Paget's disease.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.