Paramyxovirus-like nuclear inclusions identical to those of Paget's disease of bone detected in giant cells of primary oxalosis

Update on the pathogenesis and genetics of Paget’s disease of bone

Studies over the past two decades have led to major advances in the pathogenesis of Paget’s disease of bone (PDB) and particularly on the role of genetic factors. Germline mutations of different genes have been identified, as a possible cause of this disorder, and most of the underlying pathways are implicated in the regulation of osteoclast differentiation and function, whereas other are involved in cell autophagy mechanisms. In particular, about 30 different germline mutations of the Sequestosome 1 gene (SQSTM1) have been described in a significant proportion of familial and sporadic PDB cases. The majority of SQSTM1 mutations affect the ubiquitin-binding domain of the protein and are associated to a more severe clinical expression of the disease. Also, germline mutations in the ZNF687 and PFN1 genes have been associated to severe, early onset, polyostotic PDB with increased susceptibly to neoplastic degeneration, particularly giant cell tumor. Mutations in the VCP (Valosin Containing Protein) gene cause the autosomal dominant syndrome “Inclusion Body Myopathy, PDB, Fronto-temporal Dementia,” characterized by pagetic manifestations, associated with myopathy, amyotrophic lateral sclerosis and fronto-temporal dementia. Moreover, germline mutations in the TNFRSF11A gene, which encodes for RANK, were associated with rare syndromes showing some histopathological, radiological, and clinical overlap with PDB and in two cases of early onset PDB-like disease. Likewise, genome wide association studies performed in unrelated PDB cases identified other potential predisposition genes and/or susceptibility loci. Thus, it is likely that polygenic factors are involved in the PDB pathogenesis in many individuals and that modifying genes may contribute in refining the clinical phenotype. Moreover, the contribution of somatic mutations of SQSTM1 gene and/or epigenetic mechanisms in the pathogenesis of skeletal pagetic abnormalities and eventually neoplastic degeneration, cannot be excluded. Indeed, clinical and experimental observations indicate that genetic susceptibility might not be a sufficient condition for the clinical development of PDB without the concomitant intervention of viral infection, in primis paramixoviruses, and/or other environmental factors (e.g., pesticides, heavy metals or tobacco exposure), at least in a subset of cases. This review summarizes the most important advances that have been made in the field of cellular and molecular biology PDB over the past decades.

Bone impairment in oxalosis: An ultrastructural bone analysis

Deposition of calcium oxalate crystals in the kidney and bone is a hallmark of systemic oxalosis. Since the bone compartment can store massive amounts of oxalate, patients present with recurrent low-trauma fractures, bone deformations, severe bone pains and specific oxalate osteopathy on plain X-ray. Bone biopsy from the iliac crest displays specific features such as oxalate crystals surrounded by a granulomatous reaction due to an invasion of bone surface by macrophages. We present data obtained in 10 samples from 8 patients with oxalosis (16-68 years) who underwent iliac crest bone biopsy and bone quality analysis using modern methods (microradiography, microindentation, Fourier Transform InfraRed Microspectroscopy, transmission electron microscopy) in addition to histomorphometry. Disseminated calcium oxalate deposits (whewellite) were found in the bone marrow space (with a granulomatous reaction) but not in the bone matrix. Calcium oxalate deposits were totally surrounded by macrophages and multinucleated giant cells, and a phagocytosis activity was sometimes observed. Very few calcium oxalate crystals were directly in close contact with the mineral substance of the bone. Bone mineralization was not modified by the presence of calcium oxalate even in close vicinity. Bone quality analysis also revealed a harder bone than normal, perhaps in relationship with decreased carbonate content in the mineral. This increase in bone hardness could explain a more "brittle" bone. In patients with oxalosis, the formation and growth of calcium oxalate crystals in the bone appeared independent of apatite. The mechanisms leading to nucleation and growth of oxalate deposits are still unclear and deserve further studies.

Paget's disease of bone-genetic and environmental factors

Paget's disease of bone is generally diagnosed in individuals aged >50 years, usually manifests in one or several bones and is initiated by osteoclast-induced osteolytic lesions. Subsequently, over a period of many years, osteoblastic activity can result in sclerosis and deformation of bone. The prevalence of Paget's disease is highest in the UK and in countries where a large number of residents have ancestors from the UK. Currently, in many countries, the prevalence of the disorder has decreased. A considerable number of affected patients have a family history of Paget's disease and the disorder has an autosomal dominant pattern of inheritance but with incomplete penetrance. A large number of mutations in SQSTM1 (which encodes sequestosome-1; also known as ubiquitin-binding protein p62) seem to account for the susceptibility to develop Paget's disease in some families; the involvement of other genes is currently under investigation. In addition to a genetic cause, environmental factors have been proposed to have a role in the pathogenesis of Paget's disease. Although most evidence has been presented for measles virus as an aetiologic factor, some studies have not confirmed its involvement. The decreasing incidence of Paget's disease, which could be attributed to measles vaccination along with the measles virus nucleocapsid protein induction of Paget's disease lesions in transgenic mice, supports an aetiologic role of the virus.

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.

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.

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.

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.

Multicenter blinded analysis of RT-PCR detection methods for paramyxoviruses in relation to Paget's disease of bone

Conflicting results have been reported on the detection of paramyxovirus transcripts in Paget's disease, and a possible explanation is differences in the sensitivity of RT-PCR methods for detecting virus. In a blinded study, we found no evidence to suggest that laboratories that failed to detect viral transcripts had less sensitive RT-PCR assays, and we did not detect measles or distemper transcripts in Paget's samples using the most sensitive assays evaluated.

INTRODUCTION

There is conflicting evidence on the possible role of persistent paramyxovirus infection in Paget's disease of bone (PDB). Some workers have detected measles virus (MV) or canine distemper virus (CDV) transcripts in cells and tissues from patients with PDB, but others have failed to confirm this finding. A possible explanation might be differences in the sensitivity of RT-PCR methods for detecting virus. Here we performed a blinded comparison of the sensitivity of different RT-PCR-based techniques for MV and CDV detection in different laboratories and used the most sensitive assays to screen for evidence of viral transcripts in bone and blood samples derived from patients with PDB.

MATERIALS AND METHODS

Participating laboratories analyzed samples spiked with known amounts of MV and CDV transcripts and control samples that did not contain viral nucleic acids. All analyses were performed on a blinded basis.

RESULTS

The limit of detection for CDV was 1000 viral transcripts in three laboratories (Aberdeen, Belfast, and Liverpool) and 10,000 transcripts in another laboratory (Manchester). The limit of detection for MV was 16 transcripts in one laboratory (NIBSC), 1000 transcripts in two laboratories (Aberdeen and Belfast), and 10,000 transcripts in two laboratories (Liverpool and Manchester). An assay previously used by a U.S.-based group to detect MV transcripts in PDB had a sensitivity of 1000 transcripts. One laboratory (Manchester) detected CDV transcripts in a negative control and in two samples that had been spiked with MV. None of the other laboratories had false-positive results for MV or CDV, and no evidence of viral transcripts was found on analysis of 12 PDB samples using the most sensitive RT-PCR assays for MV and CDV.

CONCLUSIONS

We found that RT-PCR assays used by different laboratories differed in their sensitivity to detect CDV and MV transcripts but found no evidence to suggest that laboratories that previously failed to detect viral transcripts had less sensitive RT-PCR assays than those that detected viral transcripts. False-positive results were observed with one laboratory, and we failed to detect paramyxovirus transcripts in PDB samples using the most sensitive assays evaluated. Our results show that failure of some laboratories to detect viral transcripts is unlikely to be caused by problems with assay sensitivity and highlight the fact that contamination can be an issue when searching for pathogens by sensitive RT-PCR-based techniques.

Paget disease of bone

Paget disease of bone (PD) is characterized by excessive bone resorption in focal areas followed by abundant new bone formation, with eventual replacement of the normal bone marrow by vascular and fibrous tissue. The etiology of PD is not well understood, but one PD-linked gene and several other susceptibility loci have been identified, and paramyxoviral gene products have been detected in pagetic osteoclasts. In this review, the pathophysiology of PD and evidence for both a genetic and a viral etiology for PD will be discussed.

Paget's disease in an archeological population

The aim of this investigation was to study the prevalence and distribution of Paget's disease in an archeological population. Paget's disease, first described over 100 years ago, is a well-recognized chronic disorder involving abnormal bone turnover with established radiological features. Prevalence within modern populations varies both within individual countries and between them. Paleopathological examples are uncommon and sporadically reported both from Europe and the Americas and from many periods of history. A large skeletal assemblage (2,770 individuals) from Barton on Humber, UK, provided an opportunity to examine the prevalence of Paget's disease in one area of the northern England over the period 900-1,850 AD. All bones were examined visually for evidence of Paget's disease of the bone (PDB) and all abnormal bones were examined further by plain radiography. Fifteen cases of probable Paget's disease were found. The overall prevalence was 2.1% in those aged >40 years. The prevalence before 1500 AD was 1.7% and post-1500 AD was 3.1%. The distribution of disease mirrored modern disease, with the lumbar spine, pelvis, and proximal femur being the commonest sites. The prevalence of Paget's disease in the United Kingdom over the last 1,000 years has been assessed. Although there is a trend of increasing prevalence, this did not reach statistical significance. This is likely caused by the small sample size, but this is by far the greatest number of cases of PDB described in a single skeletal assemblage to date. The distribution of lesions within the skeleton is unchanged.

Osteoclasts formed by measles virus-infected osteoclast precursors from hCD46 transgenic mice express characteristics of pagetic osteoclasts

Pagetic osteoclasts (OCLs) are abnormal in size and contain paramyxoviral-like nuclear inclusions that cross-react with antibodies to measles virus (MV). However, the role that MV infection plays in Paget's disease is unknown, because no animal model of Paget's disease is available. Therefore, we targeted a cellular MV receptor, human CD46 (hCD46), to cells in the OCL lineage in transgenic mice using the mouse tartrate-resistant acid phosphatase (TRAP) gene promoter. In vitro infection of OCL precursors from hCD46 transgenic mice with MV significantly increased OCL formation in bone marrow cultures. The numbers of TRAP-positive mononuclear cells and CFU-GM, the earliest identifiable OCL precursor, were also significantly increased. MV-infected OCLs formed from hCD46 marrow were increased in size, contained markedly increased numbers of nuclei, and had increased bone-resorbing capacity per OCL compared with OCLs formed from marrow of nontransgenic littermates. Furthermore, IL-6 and 24-hydroxylase messenger RNA expression levels were increased in MV-infected hCD46 transgenic mouse bone marrow cultures. Treatment of MV-infected hCD46 marrow cultures with a neutralizing antibody to IL-6 blocked the increased OCL formation seen in these cultures. These data demonstrate that MV infection of OCL precursors results in OCLs that have many features of pagetic OCLs, that the enhanced OCL formation is in part mediated by increased IL-6 expression induced by MV infection, and suggest that the hCD46 transgenic mouse may be a useful model for examining the effects of MV infection on OCL formation in vivo.

Absence of measles virus and canine distemper virus transcripts in long-term bone marrow cultures from patients with Paget's disease of bone

The presence of intranuclear inclusions in pagetic osteoclasts with similar characteristics to those seen in some slow viral diseases has lead to the hypothesis that Paget's disease is caused by a similar infection. Bone marrow aspirates from seven patients with hemipelvic Paget's disease were taken from both sides of the pelvis and cultured under identical conditions. RNA was extracted after approximately 2 weeks of culture and reverse transcriptase-linked polymerase chain reaction used to investigate the expression of measles and canine distemper virus RNA. We were unable to detect the presence of measles virus (MV) or canine distemper virus (CDV) transcripts in bone marrow cultures from either affected or unaffected sites in any of our patients. The results of this study do not support a role for MV or CDV in the pathogenesis of Paget's disease of bone.

Are paramyxoviruses involved in Paget's disease? A negative view

We believe that the assembled data are consistent with the presence of mRNA species and/or proteins in pagetic bone that are recognized by some paramyxovirus antibodies and nucleic acid probes. The evidence presented so far is insufficient to substantiate claims for the "unequivocal" presence of paramyxovirus sequences in pagetic bone, because the molecular targets for these probes could be endogenous mRNA's and proteins rather than viruses. Positive reports of a viral presence in Paget's disease have so far been confined to two laboratories, both of which have consistently demonstrated evidence for the virus they have worked on most. We argue that independent replication of the aforementioned findings is necessary to conclude that pagetic bone can be considered a site of chronic paramyxovirus infection. For this to be convincing, we would expect to see colocalization of viral antigens, mRNA, and genomic RNA in cells that also show ultrastructural evidence of viral infection. If virus is indeed present, it should, in addition, be possible to clone and characterize extensive tracts of viral cDNA from samples of pagetic tissue. Although we acknowledge that the absence of evidence for viral mRNA in some RT-PCR studies does not constitute evidence of absence, the data implicating paramyxoviruses as causal agents is conflicting and insufficient to prove a cause-effect relationship. In view of this, we believe that the role of paramyxovirus infection as a cause Paget's disease remains uncertain.

Paget's disease of bone: indications for treatment and goals of therapy

Paget's disease of bone is a common disorder of unknown etiology characterized by increased bone remodeling and abnormal bone architecture. The pathologic process is initiated by an increase in osteoclast-mediated bone resorption, accompanied by a compensatory increase in bone formation. The increased bone remodeling results in a disorganized mosaic of woven and lamellar bone. This bone is highly vascular and gradually becomes enlarged and structurally weakened. Paget's disease is generally diagnosed in patients older than 40 years of age, usually as an incidental finding. The disease may be monostotic or polyostotic. The pelvis, femur, spine, tibia, skull, and humerus are most commonly involved. Most patients with Paget's disease are asymptomatic. Pain is the most common presenting symptom. Complications of the disease include bowing deformity of the long bones, fracture, and a variety of nerve compression syndromes. Malignant degeneration of Paget's disease is a rare complication. As safer, more effective therapies have become available, the indications for treatment and goals of therapy have changed. The difficult issue that clinicians are currently facing is whether to treat patients with asymptomatic disease. The progressive nature of the disease, the severity of its complications, its potential negative impact on quality of life, and the availability of therapy capable of controlling its activity have led many experts in the field to recommend treatment of asymptomatic patients who have active disease at sites where complications are likely to develop. There are, however, no data to prove that complications can be prevented by decreasing the rate of bone remodeling in Paget's disease, nor any data to define who is at risk for complications. Until more information is available, the management of patients with Paget's disease will continue to be based on clinical observation and theoretical considerations. This review examines the present understanding of Paget's disease, the rationale for the proposed indications for treatment and the goals of therapy.

Genetic linkage of Paget disease of the bone to chromosome 18q

Paget disease is a common bone disease characterized by abnormal osteoclasts that are large, multinucleated, and overactive and that contain paramyxovirus-like nuclear inclusions. There is evidence for a major genetic component to Paget disease, with up to 40% of patients having affected first-degree relatives; however, the locus (loci) and gene(s) involved are unknown. Another bone disorder, familial expansile osteolysis (FEO), although extremely rare, also is characterized by similar osteoclast abnormalities but has an earlier age at onset and a more aggressive clinical progression. The causative gene for FEO has been localized to a region of human chromosome 18q. On the basis of the presence of similar clinical findings and of viral-like nuclear inclusions in osteoclasts, we hypothesized that FEO and Paget disease are allelic versions of the same locus. Therefore, a large kindred with a high incidence of Paget disease was examined to determine if Paget disease was linked to genetic markers in the same region of chromosome 18 as that for FEO. Our analysis yielded a two-point LOD score of 3.40, with the genetic marker D18S42, a marker tightly linked to the FEO locus. This demonstrates that the gene(s) responsible for FEO and that for Paget disease are either closely linked or the same locus.

Paget's disease of bone

Paget's disease of bone is a relatively common condition in the UK affecting up to 5% of the population over the age of 55 years with particularly high prevalence in the North West of England. The majority of those affected are asymptomatic. Its precise cause remains unknown, and until recently, choice of treatment of this sometimes painful and debilitating disease has been limited. In this article, we review various aspects of this disease, concentrating particularly on recent advances in our understanding of its aetiology and its treatment.

Tartrate-resistant acid phosphate activity as osteoclastic marker: sensitivity of cytochemical assessment and serum assay in comparison with standardized osteoclast histomorphometry

Tartrate-resistant acid phosphatase (TRAP) activity is regarded as an important cytochemical marker of osteoclasts; its concentration in serum is utilized as a biochemical marker of osteoclast function and degree of bone resorption. This study was carried out to assess the sensitivity of TRAP activity both as a cytochemical marker in histological sections and as a biochemical marker in serum in comparison with the standardized histomorphometric variables of osteoclasts. To this end we investigated 24 patients (21 women, 3 men; 60 +/- 17 years of age) affected with various metabolic bone diseases. Osteoclast surface (OcS/BS) and osteoclast number (OcN/BS) were evaluated by standardized histomorphometry in iliac crest biopsies. On the basis of TRAP cytochemical activity, TRAP-positive osteoclast surface (TRAP + OcS/BS) and number (TRAP + OcN/BS) were measured. TRAP-positive cells adjacent to bone and showing one nucleus or no nuclei at all in the plane of section were included in the counts as osteoclasts. Serum TRAP activity was determined by spectrophotometric assay. Values of OcS/BS and OcN/BS were much lower than those of TRAP + OcS/BS (-50%) and TRAP + OcN/BS (-60%), respectively. Correlations between OcS/BS and TRAP + OcS/BS, and between OcN/BS and TRAP + OcN/BS, were highly significant. Serum TRAP was significantly correlated with OcS/BS, OcN/BS, and TRAP + OcN/BS. These correlations, however, were rather low. Moreover, serum TRAP did not correlate with TRAP + OcS/BS. From these results, the conclusion can be drawn that while TRAP activity is confirmed as a valid cytochemical marker for identification of osteoclasts, serum TRAP activity is an osteoclastic marker of weak sensitivity. This may be due to known factors, such as synthesis of the enzyme not being unique to osteoclasts, enzyme instability, and the presence of inhibitors in serum. Mononucleated osteoclasts do not significantly influence the serum enzyme levels.

Paget's disease of bone possible viral basis

In 1974, the first report of the presence of viral-like inclusions in the osteoclasts of patients with Paget's disease appeared (Rebel et al 1974). This observation, first made in France, was followed by confirmatory reports from North America, Europe, and Asia. Although no more compelling hypothesis than a viral etiology has been proposed subsequently, definitive proof of viral etiology is still lacking. This article summarizes the research of the past 22 years, which has been directed at defining the exact nature of the viral-like inclusions that are invariably found in the osteoclasts of Paget's disease.

Osteoclast function in Paget's disease and multiple myeloma

Paget's disease of bone and multiple myeloma are characterized by increased numbers of osteoclasts and markedly increased bone resorption at the sites of the disease. In Paget's disease the osteoclasts are abnormal morphologically and contain viral-like nuclear inclusions, but in multiple myeloma the osteoclasts are normal. The bone lesions in both Paget's disease and multiple myeloma appear to be due to local stimulation of osteoclast formation and bone resorption. In situ hybridization techniques, bone marrow cultures, and cytokine assays have been used to examine osteoclast function in Paget's disease and multiple myeloma. Interleukin-6 (IL-6) has been implicated as a potential mediator for the increased osteoclast activity in both diseases. In Paget's disease, IL-6 is produced by the osteoclasts, the osteoclasts express IL-6 receptors and IL-6 mRNA, and increased levels of IL-6 are present in the marrow plasma and serum of these patients. Similarly, increased levels of IL-6 have been detected in sera from some patients with multiple myeloma. Multiple myeloma cells do not produce IL-6 in vivo but marrow stromal cells or the osteoclasts may be the source of IL-6 in multiple myeloma. IL-6 is a growth factor for multiple myeloma cells, and treating patients with anti-IL-6 decreases the tumor burden in some patients. Thus, IL-6 may be an autocrine/paracrine factor in both Paget's disease and in multiple myeloma. Multiple myeloma cells also produce osteoclast activating factors (OAFs) that can stimulate osteoclast formation and activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Dogs, distemper and Paget's disease

The cause of Paget's disease is still unknown, despite many years of intensive study. During this time, evidence has sporadically emerged to suggest that the disease may result from a slow viral infection by one or more of the Paramyxoviruses. More recently, epidemiologic and molecular studies have suggested that the canine paramyxovirus, canine distemper virus, is the virus responsible for the disease. If true, then along with rabies, this would be a further example of a canine virus causing human disease. Studies in the natural host have now supported these findings. Further investigations have proposed that the bony abnormalities seen in Paget's disease are due to the effects of the virus on osteoclastic interleukin-6 and c-FOS production, possibly via the transcription factor NF-kappa B.