Mutations of SQSTM1 are associated with severity and clinical outcome in paget disease of bone

Diagnosis and treatment of Paget's disease of bone: position paper from the Italian Society of Osteoporosis, Mineral Metabolism and Skeletal Diseases (SIOMMMS)

INTRODUCTION

Paget's disease of bone is a focal skeletal disorder causing bone deformities and impairing bone quality. Despite the prevalence of asymptomatic cases is increasing, the progression of the disease can lead to invalidating complications that compromise the quality of life. Doubts on clinical and therapeutic management aspects exist, although beneficial effects of antiresorptive drugs, particularly bisphosphonates are known. However, limited information is available from randomized controlled trials on the prevention of disease complications so that somewhat contrasting positions about treatment indications between expert panels from the main scientific societies of metabolic bone diseases exist. This task force, composed by expert representatives appointed by the Italian Society of Osteoporosis, Mineral Metabolism and Skeletal Diseases and members of the Italian Association of Paget's disease of bone, felt the necessity for more specific and up to date indications for an early diagnosis and clinical management.

METHODS

Through selected key questions, we propose evidence-based recommendations for the diagnosis and treatment of the disease. In the lack of good evidence to support clear recommendations, available information from the literature together with expert opinion of the panel was used to provide suggestions for the clinical practice.

RESULTS AND CONCLUSION

Description of the evidence quality and support of the strength of the statements was provided on each of the selected key questions. The diagnosis of PDB should be mainly based on symptoms and the typical biochemical and radiological features. While treatment is mandatory to all the symptomatic cases at diagnosis, less evidence is available on treatment indications in asymptomatic as well as in previously treated patients in the presence of biochemical recurrence. However, given the safety and long-term efficacy of potent intravenous bisphosphonates such as zoledronate, a suggestion to treat most if not all cases at the time of diagnosis was released.

Randomised trial of genetic testing and targeted intervention to prevent the development and progression of Paget's disease of bone

INTRODUCTION

Paget's disease of bone (PDB) frequently presents at an advanced stage with irreversible skeletal damage. Clinical outcomes might be improved by earlier diagnosis and prophylactic treatment.

METHODS

We randomised 222 individuals at increased risk of PDB because of pathogenic SQSTM1 variants to receive 5 mg zoledronic acid (ZA) or placebo. The primary outcome was new bone lesions assessed by radionuclide bone scan. Secondary outcomes included change in existing lesions, biochemical markers of bone turnover and skeletal events related to PDB.

RESULTS

The median duration of follow-up was 84 months (range 0-127) and 180 participants (81%) completed the study. At baseline, 9 (8.1%) of the ZA group had PDB lesions vs 12 (10.8%) of the placebo group. Two of the placebo group developed new lesions versus none in the ZA group (OR 0.41, 95% CI 0.00 to 3.43, p=0.25). Eight of the placebo group had a poor outcome (lesions which were new, unchanged or progressing) compared with none of the ZA group (OR 0.08, 95% CI 0.00 to 0.42, p=0.003). At the study end, 1 participant in the ZA group had lesions compared with 11 in the placebo group. Biochemical markers of bone turnover were significantly reduced in the ZA group. One participant allocated to placebo required rescue therapy with ZA because of symptomatic disease. The number and severity of adverse events did not differ between groups.

CONCLUSIONS

Genetic testing for pathogenic SQSTM1 variants coupled with intervention with ZA is well tolerated and has favourable effects on the progression of early PDB.

TRIAL REGISTRATION NUMBER

ISRCTN11616770.

Paget's Disease of the Bone and Lynch Syndrome: An Exceptional Finding

Our objective is to present an exceptional case of a patient diagnosed with Paget's disease of the bone (PDB) while being confirmed with Lynch syndrome (LS). A 44-year-old woman was admitted for progressive pain in the left forearm 2 years ago, and was partially relieved since admission by non-steroidal anti-inflammatory drugs. Suggestive imaging findings and increased blood bone turnover markers helped the diagnosis of PDB. She was offered zoledronate 5 mg. She had two more episodes of relapse, and a decision of new medication was taken within the following years (a second dose of zoledronate, as well as denosumab 60 mg). Her family history showed PDB (mother) and colorectal cancer (father). Whole exome sequencing was performed according to the manufacturer's standard procedure (Ion AmpliSeq™ Exome RDY S5 Kit). A heterozygous pathogenic variant in the SQSTM1 gene (c.1175C>T, p.Pro392Leu) was confirmed, consistent with the diagnosis of PDB. Additionally, a heterozygous pathogenic variant of MSH2 gene (c.2634+1G>T) was associated with LS. The patient's first-degree relatives (her brother, one of her two sisters, and her only daughter) underwent specific genetic screening and found negative results, except for her daughter, who tested positive for both pathogenic variants while being clinically asymptomatic. The phenotype influence of either mutation is still an open issue. To our current knowledge, no similar case has been published before. Both genetic defects that led to the two conditions appeared highly transmissible in the patient's family. The patient might have an increased risk of osteosarcoma and chondrosarcoma, both due to PDB and LS, and a review of the literature was introduced in this particular matter. The phenotypic expression of the daughter remains uncertain and is yet to be a lifelong follow-up as the second patient harbouring this unique combination of gene anomalies.

Paget's disease: a review of the epidemiology, etiology, genetics, and treatment

Paget's disease of bone (PDB) is the second most prevalent metabolic bone disorder worldwide, with a prevalence rate of 1.5%-8.3%. It is characterized by localized areas of accelerated, disorganized, and excessive bone production and turnover. Typically, PDB develops in the later stages of life, particularly in the late 50s, and affects men more frequently than women. PDB is a complex disease influenced by both genetic and environmental factors. PDB has a complex genetic basis involving multiple genes, with SQSTM1 being the gene most frequently associated with its development. Mutations affecting the UBA domain of SQSTM1 have been detected in both familial and sporadic PDB cases, and these mutations are often associated with severe clinical expression. Germline mutations in other genes such as TNFRSF11A, ZNF687 and PFN1, have also been associated with the development of the disease. Genetic association studies have also uncovered several PDB predisposing risk genes contributing to the disease pathology and severity. Epigenetic modifications of genes involved in bone remodelling and regulation, including RANKL, OPG, HDAC2, DNMT1, and SQSTM1, have been implicated in the development and progression of Paget's disease of bone, providing insight into the molecular basis of the disease and potential targets for therapeutic intervention. Although PDB has a tendency to cluster within families, the variable severity of the disease across family members, coupled with decreasing incidence rates, indicates that environmental factors may also play a role in the pathophysiology of PDB. The precise nature of these environmental triggers and how they interact with genetic determinants remain poorly understood. Fortunately, majority of PDB patients can achieve long-term remission with an intravenous infusion of aminobisphosphonates, such as zoledronic acid. In this review, we discuss aspects like clinical characteristics, genetic foundation, and latest updates in PDB research.

Drug treatment strategies for Paget's disease: relieving pain and preventing progression

INTRODUCTION

Paget's disease of bone (PDB) is a focal bone disorder caused by a marked dysregulation of osteoblasts and osteoclasts in basic multicellular units, leading to abnormal and disorganized deposition of collagen fibers (the so-called "woven bone"). Therefore, pagetic bones are increased in size, and at increased risk for bone pain, deformities, fractures, osteoarthritis, and, more rarely, neoplastic degeneration.

AREAS COVERED

In this review we revise the available information concerning the pharmacological treatment of PDB.

EXPERT OPINION

PDB progresses slowly within the affected skeletal sites and, if untreated, often leads to bone overgrowth, with bone pain, deformity and a likely increased risk of complications. Thus, the primary goal of treatment is the restoration of a normal bone turnover, in order to relieve bone pain or other symptoms and possibly prevent the complications. PDB long remained a poorly treatable disorder until the discovery of antiresorptive agents such as calcitonin first and bisphosphonates (BPs) later. With the recent development of potent intravenous BPs like zoledronate, allowing a better control of disease activity over the long term with a single infusion, has contributed to a marked improvement of the clinical management of this invalidating disorder.

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.

Epigenetic DNA Methylation Signatures Associated With the Severity of Paget's Disease of Bone

Background: Paget's disease of bone (PDB) is characterized by focal areas of dysregulated bone turnover resulting in increased bone loss and abnormal bone formation with variable severity. PDB has a complex etiology and both genetics and environmental factors have been implicated. A recent study has identified many differentially methylated loci in PDB compared to healthy subjects. However, associations between DNA methylation profiles and disease severity of PDB have not been investigated. Objectives: To investigate the association between DNA methylation signals and PDB severity. Methods: Using 232 well-characterized PDB subjects from the PRISM trial, a disease severity score was devised based on the clinical features of PDB. DNA methylation profiling was performed using Illumina Infinium HumanMethylation 450K array. Results: We identified 100 CpG methylation sites significantly associated with PDB severity at FDR <0.05. Additionally, methylation profiles in 11 regions showed Bonferroni-significant association with disease severity including six islands (located in VCL, TBX5, CASZ1, ULBP2, NUDT15 and SQSTM1), two gene bodies (CXCR6 and DENND1A), and 3 promoter regions (RPL27, LINC00301 and VPS29). Moreover, FDR-significant effects from region analysis implicated genes with genetic variants previously associated with PDB severity, including RIN3 and CSF1. A multivariate predictor model featuring the top severity-associated CpG sites revealed a significant correlation (R = 0.71, p = 6.9 × 10-16) between observed and predicted PDB severity scores. On dichotomizing the severity scores into low and high severity, the model featured an area under curve (AUC) of 0.80, a sensitivity of 0.74 and a specificity of 0.68. Conclusion: We identified several CpG methylation markers that are associated with PDB severity in this pioneering study while also highlighting the novel molecular pathways associated with disease progression. Further work is warranted to affirm the suitability of our model to predict the severity of PDB in newly diagnosed patients or patients with family history of PDB.

Long-Term Efficacy of Intensive Zoledronate Therapy and Predictors of Retreatment in Paget's Disease of Bone

Despite the current debate on the best therapeutic approach, i.e. symptomatic vs intensive strategy, one zoledronate (Zol) infusion is effective in most patients with Paget's disease of bone (PDB), whereas few need retreatment, whose predictors are not well established. We aimed to evaluate long-term efficacy of intensive Zol therapy and predictors of retreatment in PDB. Pagetic complications, clinical and biochemical response to Zol together with frequency of retreatment were retrospectively assessed in forty-seven PDB patients (age, mean ± SD: 72.5 ± 8.9 years, M/F: 24/23; symptomatic/asymptomatic: 16/31). Statistical analysis for retreatment prediction were based on Mann-Whitney U test, Pearson's Χ2 and ROC curve analysis. During seven-year follow-up, all patients achieved pain relief and only one underwent arthroplasty. Bone alkaline phosphatase (BAP) detected three non-responder (6%) and six relapsing (13%) patients needing retreatment. Retreated patients had less old age (66.1 ± 11.2 vs 74.0 ± 7.7 years), higher frequency of polyostotic disease (78% vs 40%) and higher baseline (96.5 ± 24.8 vs 44.9 ± 27.7 mcg/l) and post-Zol nadir BAP levels (24.7 ± 24.1 vs 8.1 ± 4.1 mcg/l) than patients treated once (p < 0.05 for all comparisons). In multivariate analysis both serum baseline and post-Zol nadir BAP significantly predicted retreatment (OR 1.09, 95%CI 1.01-1.17 and 1.29, 1.03-1.62, respectively), with ROC curve analysis showing the greatest accuracies for threshold values of 75.6 and 9.9 mcg/l (sensitivity 88 and 90%, specificity 94 and 86%, AUC 0.92 and 0.93, respectively). Our data in mostly asymptomatic, metabolically active PDB patients treated with intensive Zol therapy show a negligible incidence of pagetic complications and long-term optimal disease control, with BAP being the best predictor of retreatment.

Genetic Determinants of Paget's Disease of Bone

PURPOSE OF REVIEW

To provide an overview of the role of genes and loci that predispose to Paget's disease of bone and related disorders.

RECENT FINDINGS

Studies over the past ten years have seen major advances in knowledge on the role of genetic factors in Paget's disease of bone (PDB). Genome wide association studies have identified six loci that predispose to the disease whereas family based studies have identified a further eight genes that cause PDB. This brings the total number of genes and loci implicated in PDB to fourteen. Emerging evidence has shown that a number of these genes also predispose to multisystem proteinopathy syndromes where PDB is accompanied by neurodegeneration and myopathy due to the accumulation of abnormal protein aggregates, emphasising the importance of defects in autophagy in the pathogenesis of PDB. Genetic factors play a key role in the pathogenesis of PDB and the studies in this area have identified several genes previously not suspected to play a role in bone metabolism. Genetic testing coupled to targeted therapeutic intervention is being explored as a way of halting disease progression and improving outcome before irreversible skeletal damage has occurred.

Pattern of SQSTM1 Gene Variants in a Hungarian Cohort of Paget's Disease of Bone

Paget's disease of bone (PDB) is characterized by focal or multifocal increase in bone turnover. One of the most well-established candidate genes for susceptibility to PDB is Sequestosome 1 (SQSTM1). Mutations in SQSTM1 have been documented among Western-European, British and American patients with PDB. However, there is no information on SQSTM1 mutation status in PDB patients from the Central- and Eastern-European regions. In this study, we conducted a mutation screening for SQSTM1 gene variants in 82 PDB patients and 100 control participants in Hungary. Mutations of SQSTM1 were detected in 18 PDB patients (21.95%); associations between genotype and clinical characteristics were also analyzed. Altogether, six different exonic alterations, including two types of UTR variants in the SQSTM1 gene, were observed in our PDB patients. Similarly, to previous genetic studies on Paget's disease, our most commonly detected variant was the c.1175C > T (p.Pro392Leu) in nine cases (four in monostotic and five in polyostotic form). We have surveyed the germline SQSTM1 variant distribution among Hungarian patients with PDB. We also highlighted that the pattern of the analyzed disease-associated pathophysiological parameters could partially discriminate PDB patients with normal or mutant SQSTM1 genotype. However, our findings also underline and strengthen that not solely SQSTM1 stands in the background of the complex PDB etiology.

Characteristics of Early Paget's Disease in SQSTM1 Mutation Carriers: Baseline Analysis of the ZiPP Study Cohort

Mutations in SQSTM1 are strongly associated with Paget's disease of bone (PDB), but little is known about the clinical characteristics of those with early disease. Radionuclide bone scans, biochemical markers of bone turnover, and clinical characteristics were analyzed in SQSTM1 mutation carriers who took part in the Zoledronic acid in the Prevention of Paget's disease (ZiPP) study. We studied 222 individuals, of whom 54.9% were female, with mean ± SE age of 50.1 ± 0.6 years. Twelve SQSTM1 mutations were observed, including p.Pro392Leu, which was present in 141 of 222 (63.5%) subjects. Bone scan examination revealed evidence of PDB in 20 subjects (9.0%), ten of whom (50%) had a single affected site. Participants with lesions were older than those without lesions but the difference was not significant (53.6 ± 9.1 versus 49.8 ± 8.9; p = .07). The mean age of participants with lesions was not significantly different from the age at which their parents were diagnosed with PDB (55 years versus 59 years, p = .17). All individuals with lesions were asymptomatic. Serum concentrations of total alkaline phosphatase (ALP) normalized to the upper limit of normal in each center were higher in those with lesions (0.75 ± 0.69 versus 0.42 ± 0.29 arbitary units; p < .0001). Similar findings were observed for other biochemical markers of bone turnover, but the sensitivity of ALP and other markers in detecting lesions was poor. Asymptomatic PDB is present in about 9% of SQSTM1 mutation carriers by the fifth decade. Further follow-up of this cohort will provide important information on the natural history of early PDB and its response to treatment. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Molecular modelling and dynamic simulations of sequestosome 1 (SQSTM1) missense mutations linked to Paget disease of bone

The Paget disease (PDB; OMIM is 167250) is a chronic bone disease caused by pathogenic mutations in Sequestome1/p62 (SQSTM1) gene. This study has aimed to interpret the relationship of PDB linked SQSTM1 mutations with protein structure and its molecular dynamic features. The disease causative missense mutations were initially collected, and then analyzed for their, exonic and domain distribution, impact on secondary and tertiary structures, and their ability on protein-ligand interactions, using a combination of systems biology approaches. Our results show that most PDB linked SQSTM1 missense mutations affect amino acid residues clustered within or near the UBA domain (aa 389-434), which participates in the ubiquitination of substrates. We also report that the majority mutations occurred in α-helices over β-strands but their effects on the secondary structure were mostly neutral. Global tertiary structure deviations were minimal; however, at amino acid residue level minor structural changes were evident. The molecular dynamics simulation analysis showed that both PB1 and UBA domains were under constant structural fluctuations resulting in closed form conformation of SQSMT1 protein structure, when it is bound to PRKCI ligand. We also found salt bridge conformation changes in the UBA domain of SQSTM1 mutants when they bound to the PRKCI interactor protein. This finding suggests the possibility that mutations in SQSTM1 could impair its ability to ubiquitinate the substrates, eventually affecting autophagy and apoptosis, especially in mature osteoclasts. This study presents the additional insight into structure and function relationship between SQSTM1 mutations and PDB pathogenesis. Communicated by Ramaswamy H. Sarma.

Preventive Role of Vitamin D Supplementation for Acute Phase Reaction after Bisphosphonate Infusion in Paget's Disease

CONTEXT

Intravenous aminobisphosphonates (N-BPs) can induce an acute phase reaction (APR) in up to 40% to 70% of first infusions, causing discomfort and often requiring intervention with analgesics or antipyretics.

OBJECTIVE

Our aim was to explore the risk factors of APR in a large sample of patients with Paget's disease of bone (PDB) and to assess the possible preventive effects of vitamin D administration.

METHODS

An observational analysis was performed in 330 patients with PDB at the time of N-BP infusion. Then, an interventional study was performed in 66 patients with active, untreated PDB to evaluate if vitamin D administration (oral cholecalciferol 50 000 IU/weekly for 8 weeks before infusion) may prevent APR.

RESULTS

In a retrospective study, APR occurred in 47.6% and 18.3% of naive or previously treated patients, respectively. Its prevalence progressively increased in relation to the severity of vitamin D deficiency, reaching 80.0% in patients with 25-hydroxyvitamin D (25OHD) levels below 10 ng/mL (relative risk (RR) = 3.7; 95% confidence interval (CI) 2.8-4.7, P < .0001), even in cases previously treated with N-BPs. Moreover, APR occurred more frequently in patients who experienced a previous APR (RR = 2.8; 95% CI 1.5-5.2; P < .001) or in carriers of SQSTM1 mutation (RR = 2.3; 95% CI 1.3-4.2; P = .005). In the interventional study, vitamin D supplementation prevented APR in most cases, equivalent to a RR of 0.31 (95% CI 0.14-0.67; P < .005) with respect to prevalence rates of the observational cohort. A similar trend was observed concerning the occurrence of hypocalcemia.

CONCLUSIONS

The achievement of adequate 25OHD levels is recommended before N-BP infusion in order to minimize the risk of APR or hypocalcemia in PDB.

The role of sequestosome 1/p62 protein in amyotrophic lateral sclerosis and frontotemporal dementia pathogenesis

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration are multifaceted diseases with genotypic, pathological and clinical overlap. One such overlap is the presence of SQSTM1/p62 mutations. While traditionally mutations manifesting in the ubiquitin-associated domain of p62 were associated with Paget’s disease of bone, mutations affecting all functional domains of p62 have now been identified in amyotrophic lateral sclerosis and frontotemporal lobar degeneration patients. p62 is a multifunctional protein that facilitates protein degradation through autophagy and the ubiquitin-proteasome system, and also regulates cell survival via the Nrf2 antioxidant response pathway, the nuclear factor-kappa B signaling pathway and apoptosis. Dysfunction in these signaling and protein degradation pathways have been observed in amyotrophic lateral sclerosis and frontotemporal lobar degeneration, and mutations that affect the role of p62 in these pathways may contribute to disease pathogenesis. In this review we discuss the role of p62 in these pathways, the effects of p62 mutations and the effect of mutations in the p62 modulator TANK-binding kinase 1, in relation to amyotrophic lateral sclerosis-frontotemporal lobar degeneration pathogenesis.

Zoledronate in the prevention of Paget's (ZiPP): protocol for a randomised trial of genetic testing and targeted zoledronic acid therapy to prevent SQSTM1-mediated Paget's disease of bone

INTRODUCTION

Paget's disease of bone (PDB) is characterised by increased and disorganised bone remodelling affecting one or more skeletal sites. Complications include bone pain, deformity, deafness and pathological fractures. Mutations in sequestosome-1 (SQSTM1) are strongly associated with the development of PDB. Bisphosphonate therapy can improve bone pain in PDB, but there is no evidence that treatment alters the natural history of PDB or prevents complications. The Zoledronate in the Prevention of Paget's disease trial (ZiPP) will determine if prophylactic therapy with the bisphosphonate zoledronic acid (ZA) can delay or prevent the development of PDB in people who carry SQSTM1 mutations.

METHODS AND ANALYSIS

People with a family history of PDB aged >30 years who test positive for SQSTM1 mutations are eligible to take part. At the baseline visit, participants will be screened for the presence of bone lesions by radionuclide bone scan. Biochemical markers of bone turnover will be measured and questionnaires completed to assess pain, health-related quality of life (HRQoL), anxiety and depression. Participants will be randomised to receive a single intravenous infusion of 5 mg ZA or placebo and followed up annually for between 4 and 8 years at which point baseline assessments will be repeated. The primary endpoint will be new bone lesions assessed by radionuclide bone scan. Secondary endpoints will include changes in biochemical markers of bone turnover, pain, HRQoL, anxiety, depression and PDB-related skeletal events.

ETHICS AND DISSEMINATION

The study was approved by the Fife and Forth Valley Research Ethics Committee on 22 December 2008 (08/S0501/84). Following completion of the trial, a manuscript will be submitted to a peer-reviewed journal. The results of this trial will inform clinical practice by determining if early intervention with ZA in presymptomatic individuals with SQSTM1 mutations can prevent or slow the development of bone lesions with an adverse event profile that is acceptable.

TRIAL REGISTRATION NUMBER

ISRCTN11616770.

Paget's Disease of Bone

Paget's disease of bone (PDB) is a chronic and focal bone disorder, characterized by increased osteoclast-mediated bone resorption and a subsequent compensatory increase in bone formation, resulting in a disorganized mosaic of woven and lamellar bone at one or more affected skeletal sites. As a result, bone pain, noticeable deformities, arthritis at adjacent joints, and fractures can occur. In a small proportion of cases neoplastic degeneration in osteosarcoma, or, less frequently, giant cell tumor has been also described at PDB sites. While recent epidemiological evidences clearly indicate a decrease in the prevalence and the severity of PDB, over the past 2 decades there have been consistent advances on the genetic mechanisms of disease. It is now clear that PDB is a genetically heterogeneous disorder, with mutations in at least two different genes (SQSTM1, ZNF687) and more common predisposing variants. As a counterpart to the genetic hypothesis, the focal nature of lesions, the decline in prevalence rates, and the incomplete penetrance of the disease among family members suggest that one or more environmental triggers may play a role in the pathophysiology of PDB. The exact nature of these triggers and how they might interact with the genetic factors are less understood, but recent experimental data from mice models suggest the implication of paramixoviral infections. The clinical management of PDB has also evolved considerably, with the development of potent aminobisphosphonates such as zoledronic acid which, given as a single intravenous infusion, now allows a long-term disease remission in the majority of patients.

Molecular insights into an ancient form of Paget's disease of bone

We identify an ancient and atypical form of Paget’s disease of bone (PDB) in a collection of medieval skeletons exhibiting unusually extensive pathological changes, high disease prevalence, and low age-at-death estimations. Proteomic analysis of ancient bone-preserved proteins combined with analysis of small RNAs supports a retrospective diagnosis of PDB. Remains affected by other skeletal disorders may therefore hold a chemical memory amenable to similar molecular interrogation. Abnormalities in a contemporary PDB-linked protein detected in ancient tooth samples indicate that dentition may represent an unexplored storehouse for the study of skeletal disorders. Our work provides insights into the natural history of PDB and prompts a similar revaluation of other archaeological collections.

Paget’s disease of bone (PDB) is a chronic skeletal disorder that can affect one or several bones in individuals older than 55 y of age. PDB-like changes have been reported in archaeological remains as old as Roman, although accurate diagnosis and natural history of the disease is lacking. Six skeletons from a collection of 130 excavated at Norton Priory in the North West of England, which dates to medieval times, show atypical and extensive pathological changes resembling contemporary PDB affecting as many as 75% of individual skeletons. Disease prevalence in the remaining collection is high, at least 16% of adults, with age at death estimations as low as 35 y. Despite these atypical features, paleoproteomic analysis identified sequestosome 1 (SQSTM1) or p62, a protein central to the pathological milieu of PDB, as one of the few noncollagenous human sequences preserved in skeletal samples. Targeted proteomic analysis detected >60% of the ancient p62 primary sequence, with Western blotting indicating p62 abnormalities, including in dentition. Direct sequencing of ancient DNA excluded contemporary PDB-associated SQSTM1 mutations. Our observations indicate that the ancient p62 protein is likely modified within its C-terminal ubiquitin-associated domain. Ancient miRNAs were remarkably preserved in an osteosarcoma from a skeleton with extensive disease, with miR-16 expression consistent with that reported in contemporary PDB-associated bone tumors. Our work displays the use of proteomics to inform diagnosis of ancient diseases such as atypical PDB, which has unusual features presumably potentiated by yet-unidentified environmental or genetic factors.

Targeted sequencing of DCSTAMP in familial Paget's disease of bone

Paget's disease of bone (PDB) has a strong genetic component. Variants in SQSTM1 are found in up to 40% of patients with a family history of the disease, where a pattern of autosomal dominance with incomplete penetrance is apparent. By contrast, SQSTM1 variants are only found in up to 10% of patients with sporadic disease. It has been hypothesised that the remaining genetic susceptibility to PDB, particularly in familial cases, could be explained by rare genetic variants in loci previously identified by Genome Wide Association Studies. It is likely that polygenic factors are involved in many individuals. In this study we utilised whole exome sequencing to investigate predisposing genetic factors in an unsolved PDB kindred and identified a c.1189C > T p.L397F variant in DC-STAMP, also known as TM7SF4, that co-segregated with disease. DCSTAMP was identified as a gene of interest in PDB following Genome Wide Association Studies and has been previously shown to play critical roles in osteoclast fusion. The variant we identified has also been reported in association with PDB in a French-Canadian cohort however the significance of this variant was inconclusive. Targeted screening of DCSTAMP in our familial cohort of PDB patients revealed an additional 8 variants; however we did not find a significant association between any of these, including p.L397F, with PDB. Osteoclastogenesis assays from the affected proband and his unaffected brother demonstrated an increase in osteoclast number and nucleation, consistent with the pagetic phenotype. In converse to other established Paget's associated genetic variations such as SQSTM1, TNFRSF11A and OPTN, expression of the mutant DC-STAMP protein attenuated the activation of transcription factors NFκB and AP-1 when exogenously expressed. We found that the p.L397F variant did not influence the subcellular localization of the protein. Based on these findings we conclude that genetic variation in DCSTAMP is not a significant predisposing factor in our specific cohort of PDB patients and the p.L397F variant is unlikely to be a contributing factor in PDB pathogenesis.

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Variants in DC-STAMP do not appear to be significantly associated with Paget’s disease of bone in our cohort.

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The DC-STAMP p.L397F variant attenuates both NFkB and AP-1 signalling compared to the wild type protein.

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No significant differences in cellular colocalisation were found between DC-STAMP wild type and p.L397F.

Genetic regulatory mechanisms in human osteoclasts suggest a role for the STMP1 and DCSTAMP genes in Paget's disease of bone

Paget’s disease of bone (PDB) is characterised by focal abnormalities of bone remodelling, with increased osteoclastic resorption the primary feature of the disease. Genetic factors have been shown to play an important role in PDB, and genome-wide association studies (GWAS) have identified 7 genetic loci as associated with PDB at the genome-wide level. Expression quantitative trait locus (eQTL) studies using cell types that are directly relevant to the disease of interest are increasingly being used to identify putative effector genes for GWAS loci. We have recently constructed a unique osteoclast-specific eQTL resource using cells differentiated in vitro from 158 subjects for study of the genetics of bone disease. Considering the major role osteoclasts have in PDB, we used this resource to investigate potential genetic regulatory effects for the 7 PDB genome-wide significant loci on genes located within 500 kb of each locus. After correction for multiple testing, we observed statistically significant associations for rs4294134 with expression of the gene STMP1, and rs2458413 with expression of the genes DPYS and DCSTAMP. The eQTL associations observed for rs4294134 with STMP1, and rs2458413 with DCSTAMP were further supported by eQTL data from other tissue types. The product of the STMP1 gene has not been extensively studied, however the DCSTAMP gene has an established role in osteoclast differentiation and the associations seen between rs2458413 and PDB are likely mediated through regulatory effects on this gene. This study highlights the value of eQTL data in determining which genes are relevant to GWAS loci.

Paget's disease of bone

Paget's disease of bone is a focal disorder of bone remodelling that progresses slowly and leads to changes in the shape and size of affected bones and to skeletal, articular and vascular complications. In some parts of the world it is the second most common bone disorder after osteoporosis though in recent years its prevalence and severity appear to decrease. The disease is easily diagnosed and effectively treated but its pathogenesis remains incompletely understood.

The Changing Presentation of Paget's Disease of Bone in Australia, A High Prevalence Region

Studies from several countries suggest that the incidence of Paget's disease of bone (PDB) and the severity of newly diagnosed cases are declining. The aim of this study was to examine secular changes in clinical presentation of PDB in Australia, which historically had the highest prevalence outside the United Kingdom. The participants were 293 patients (61% male) diagnosed between 1956 and 2013 with details recorded in the database of the Paget's Disease Research Group of Western Australia. The mean age at diagnosis was 62 years (range 28-90); 26% of participants had a family history of PDB and 11% had Sequestosome 1 (SQSTM1) mutations. After adjustment for covariates (SQSTM1 mutation status, family history, country of birth, smoking and dog exposure), there was a significant positive relationship between year of diagnosis and age at diagnosis (P < 0.001) and significant negative relationships between year of diagnosis and both pre-treatment total plasma alkaline phosphatase activity (ALP) and number of involved bones (P < 0.001 for each). Patients with SQSTM1 mutations had more extensive disease (P < 0.001) and higher pre-treatment ALP (P = 0.013). In subgroup analyses, relationships between year of diagnosis and each of age at diagnosis, number of involved bones and ALP were similar in patients with sporadic or familial disease, and in patients with and without SQSTM1 mutations. We conclude that the severity of PDB in Western Australia has declined over recent decades. This is likely to reflect altered exposure to one or more environmental agents involved in pathogenesis.

Determinants of quality of life in Paget's disease of bone

OBJECTIVE

To evaluate the parameters associated with quality of life in patients with Paget's disease of bone.

METHODS

Patients with Paget's disease of bone were evaluated with SF-36 and WHOQOL-bref questionnaires. Patients with other diseases that could cause significant impairment of their quality of life were excluded. We searched for correlations between the results and: age, time from diagnosis, type of involvement, pain related to Paget's disease of bone, limitation to daily activities, deformities, bone specific alkaline phosphatase, the extent of involvement and treatment.

RESULTS

Fifty patients were included. Results of the SF-36 total score and its domains, physical and mental health, were significantly correlated with bone pain and deformities. Marital status was significantly correlated with the SF-36 total score and Mental Health Domain. BAP levels and disease extension were significantly correlated to SF-36 Physical Health Domain. After multivariate analysis, the only parameters that remained significantly associated with the SF-36 total score and to its Mental Health and Physical Health Domains were pain and marital status. The WHOQOL-bref total score was significantly associated with pain, physical impairment and deformities. WHOQOL-bref Domain 1 (physical) score was significantly associated with marital status, pain and deformities, while Domain 2 (psychological) score was associated with marital status, physical impairment and kind of involvement. After multivariate analysis, the presence of pain, deformities, and marital status were significantly associated with results of the WHOQOL-bref total score and its Domain 1. WHOQOL-bref domain 2 results were significantly predicted by pain and marital status.

CONCLUSION

The main disease-related factor associated with SF-36 results in Paget's disease of bone patients was bone pain, while bone pain and deformities were associated with WHOQOL-bref.

Antibody Response to Paramyxoviruses in Paget's Disease of Bone

Paget's disease of bone (PDB) is a common skeletal disorder characterised by focal abnormalities of increased and disorganised bone turnover. Genetic factors play a central role in the pathogenesis of PDB but environmental factors also contribute. Measles virus (MV), respiratory syncytial virus (RSV) and canine distemper virus (CDV) have all been implicated as potential disease triggers but the data are conflicting. Since chronic paramyxovirus infection with measles is known to be accompanied by increased production of antiviral antibodies, we have analysed circulating concentrations of antibodies to MV, CDV, and RSV as well as mumps, rubella and varicella zoster virus (VZV) in 463 patients with PDB and 220 aged and gender-matched controls. We also studied the relation between viral antibody concentrations and various markers of disease severity and extent in 460 PDB patients. A high proportion of cases and controls tested positive for antiviral antibodies but there was no significant difference in circulating antibody concentrations between PDB cases and controls for MV, CDV, RSV, rubella or VZV. However, mumps virus antibody levels were significantly higher in the PDB cases (mean ± SD = 3.1 ± 0.84 vs. 2.62 ± 0.86. p < 0.001). There was no association between disease severity and circulating antibody concentrations to any of the viruses. In conclusion, we found no evidence to suggest that PDB is associated with abnormalities of immune response to measles or other paramyxoviruses, although there was evidence of a greater antibody response to mumps. The results do not support that hypothesis that PDB is associated with a persistent infection with measles or other paramyxoviruses.

Clinical and Genetic Advances in Paget's Disease of Bone: a Review

Paget’s disease of bone (PDB) is the second most common metabolic bone disorder, after osteoporosis. It is characterised by focal areas of increased and disorganised bone turnover, coupled with increased bone formation. This disease usually appears in the late stages of life, being slightly more frequent in men than in women. It has been reported worldwide, but primarily affects individuals of British descent. Majority of PDB patients are asymptomatic, but clinical manifestations include pain, bone deformity and complications, like pathological fractures and deafness. The causes of the disease are poorly understood and it is considered as a complex trait, combining genetic predisposition with environmental factors. Linkage analysis identified SQSTM1, at chromosome 5q35, as directly related to the disease. A number of mutations in this gene have been reported, pP392L being the most common variant among different populations. Most of these variants affect the ubiquitin-associated (UBA) domain of the protein, which is involved in autophagy processes. Genome-wide association studies enlarged the number of loci associated with PDB, and further fine-mapping studies, combined with functional analysis, identified OPTN and RIN3 as causal genes for Paget’s disease. A combination of risk alleles identified by genome-wide association studies led to the development of a score to predict disease severity, which could improve the management of the disease. Further studies need to be conducted to elucidate other important aspects of the trait, such as its focal nature and the epidemiological changes found in some populations. In this review, we summarize the clinical characteristics of the disease and the latest genetic advances to identify susceptibility genes. We also list current available treatments and prospective options.

Paget's Disease in an Omani: Long-term Improvement Following a Single Injection of Zoledronic Acid

Paget's disease of bone is a patchy skeletal disorder characterized by an increase in bone resorption and formation in the affected areas. It affects up to 3% of individuals of Anglo-Saxon origin over the age of 40 years but is rare in Arabs. Although most patients are asymptomatic, a variety of symptoms and complications may develop directly from bone involvement or secondarily to compression by bone expansion and increased blood flow. The disease can be treated by using medications that inhibit bone resorption, such as calcitonin and the bisphosphonates. Here we describe the case of an Omani patient with the disease, involving the skull, spine, pelvis, and tibia. He presented to the endocrine clinic in Sultan Qaboos University Hospital with a six-year history of headache, bone pain, progressive skull enlargement, and left-sided deafness. His alkaline phosphatase (ALP) level was 1500 U/L. His disease responded gradually to six months of subcutaneous and nasal calcitonin followed by a single 5 mg intravenous injection of zoledronic acid. This resulted in a further progressive reduction of his bone pain, skull size, and improvement in his hearing, as well as normalization of his serum ALP levels after one-year. This effect has been sustained for 3 years.

Paget's Disease of Bone: Approach to Its Historical Origins

Paget's disease of bone is the second most common bone disease after osteoporosis. It is characterized by focal regions of highly exaggerated bone remodeling, with abnormalities in all phases of the remodeling process. This study aims to investigate the hypothesis of a possible British origin of Paget's disease of bone by studying the worldwide geographic distribution of cases identified in ancient skeletons excavated from archaeological sites. The methodology consists in reviewing cases of Paget's disease of bone described in the literature.

Genetics of Paget's disease of bone

Paget's disease of bone (PDB) is a common metabolic bone disease characterised by focal areas of increased bone turnover, which primarily affects people over the age of 55 years. Genetic factors have a fundamental role in the pathogenesis of PDB and are probably the main predisposing factor for the disease. The genetic contribution to PDB susceptibility ranges from rare pathogenic mutations in the single gene SQSTM1 to more common, small effect variants in at least seven genetic loci that predispose to the disease. These loci have additive effects on disease susceptibility and interact with SQSTM1 mutations to affect disease severity, making them a potentially useful tool in predicting disease risk and complication and in managing treatments. Many of these loci harbour genes that have important function in osteoclast differentiation such as CSF1, DCSTAMP and TNFRSF11A. Other susceptibility loci have highlighted new molecular pathways that have not been previously implicated in regulation of bone metabolism such as OPTN, which was recently found to negatively regulate osteoclast differentiation. PDB-susceptibility variants exert their effect either by affecting the protein coding sequence such as variants found in SQSTM1 and RIN3 or by influencing gene expression such as those found in OPTN and DCSTAMP. Epidemiological studies indicate that environmental triggers also have a key role in PDB and interact with genetic factors to influence manifestation and severity of the disease; however, further studies are needed to identify these triggers.

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.

Paget's sarcoma of the patella

Paget's sarcoma is a rare complication of Paget's disease and isolated Paget's disease of the patella is extremely rare. We describe a unique case of Paget's sarcoma of the patella in a 69-year-old male farmer who had a remote history of a fracture in the same patella 40 years previously. In this case, imaging and pathogenesis of Paget's disease of bone is described and factors implicated in the development of Paget's disease in this patient are evaluated.

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.

Clinical presentation of Paget's disease: evaluation of a contemporary cohort and systematic review

Paget's disease of bone (PDB) has become less common over recent decades but it is unclear if this has impacted on clinical presentation. Here we evaluated the presenting features of PDB in a contemporary cohort of UK patients and conducted a systematic review of studies in which the presenting features had been reported. The case series comprised 88 patients referred to a specialist clinic between 2005 and 2013. Bone pain was the most common presenting feature occurring in 73.8% of patients. Others included bone deformity (18.1%), deafness (7.9%) and pathological fracture (5.7%). The disease was asymptomatic in 22% of cases. Antiresorptive treatment was given for pain in 34 cases and 61.7% of patients responded. Patients with a shorter disease duration were more likely to respond (p = 0.047). In the systematic review, bone pain was the most common presenting feature (52.2% of cases) followed by deformity (21.5%), deafness (8.9%) and fracture (8.5%). Time trend analysis in subjects of European descent showed that fracture was less common in studies performed during the past 25 years as compared with older studies (5.5 vs. 10.8% p < 0.001) whereas pain was more common (54.3 vs. 48.3%, p = 0.003). While changes in the mode of presentation of PDB have occurred over recent years, many patients present with complications such as fracture and deformity. Further research is required to determine if early detection and therapeutic intervention might be of value in preventing the morbidity associated with this common disease.

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.

The role of ubiquitin-binding domains in human pathophysiology

Ubiquitination, a fundamental post-translational modification (PTM) resulting in the covalent attachment of ubiquitin (Ub) to a target protein, is currently implicated in several key cellular processes. Although ubiquitination was initially associated with protein degradation, it is becoming increasingly evident that proteins labeled with polyUb chains of specific topology and length are activated in an ever-expanding repertoire of specific cellular processes. In addition to their involvement in the classical protein degradation pathways they are involved in DNA repair, kinase regulation and nuclear factor-κB (NF-κB) signaling. The sorting and processing of distinct Ub signals is mediated by small protein motifs, known as Ub-binding domains (UBDs), which are found in proteins that execute disparate biological functions. The involvement of UBDs in several biological pathways has been revealed by several studies which have highlighted the vital role of UBDs in cellular homeostasis. Importantly, functional impairment of UBDs in key regulatory pathways has been related to the development of pathophysiological conditions, including immune disorders and cancer. In this review, we present an up-to-date account of the crucial role of UBDs and their functions, with a special emphasis on their functional impairment in key biological pathways and the pathogenesis of several human diseases. The still under-investigated topic of Ub-UBD interactions as a target for developing novel therapeutic strategies against many diseases is also discussed.

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.

Paget disease of bone-associated UBA domain mutations of SQSTM1 exert distinct effects on protein structure and function

SQSTM1 mutations are common in patients with Paget disease of bone (PDB), with most affecting the C-terminal ubiquitin-associated (UBA) domain of the SQSTM1 protein. We performed structural and functional analyses of two UBA domain mutations, an I424S mutation relatively common in UK PDB patients, and an A427D mutation associated with a severe phenotype in Southern Italian patients. Both impaired SQSTM1's ubiquitin-binding function in pull-down assays and resulted in activation of basal NF-κB signalling, compared to wild-type, in reporter assays. We found evidence for a relationship between the ability of different UBA domain mutants to activate NF-κB signalling in vitro and number of affected sites in vivo in 1152 PDB patients from the UK and Italy, with A427D-SQSTM1 producing the greatest level of activation (relative to wild-type) of all PDB mutants tested to date. NMR and isothermal titration calorimetry studies were able to demonstrate that I424S is associated with global structural changes in the UBA domain, resulting in 10-fold weaker UBA dimer stability than wild-type and reduced ubiquitin-binding affinity of the UBA monomer. Our observations provide insights into the role of SQSTM1-mediated NF-κB signalling in PDB aetiology, and demonstrate that different mutations in close proximity within loop 2/helix 3 of the SQSTM1 UBA domain exert distinct effects on protein structure and stability, including indirect effects at the UBA/ubiquitin-binding interface.

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The I424S and A427D SQSTM1 mutations affect ubiquitin-binding and NF-κB signalling.

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Mutant SQSTM1's ability to activate NF-κB signalling may be related to disease extent in PDB.

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A427D-SQSTM1 produces the greatest activation (relative to wild-type) of all PDB mutants.

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The I424S mutant destabilises the UBA dimer causing unfolding of the monomer.

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UBA domain mutations of SQSTM1 exert distinct effects on protein structure and stability.

Diagnosis and treatment of Paget's disease of bone: a mini-review

Paget's disease of bone (PDB) is a chronic progressive disorder of bone metabolism that may go undetected for many years, and endocrinologists should be alert to its clinical signs and promptly diagnose and treat PDB before it results in irreversible complications, such as deformity, fracture or neurological sequelae. Most commonly, PDB is suspected upon the incidental finding of elevated serum alkaline phosphatase levels or a radiographic abnormality in an otherwise healthy individual above 55 years of age. Some of these individuals may have symptoms such as bone pain or enlargement with increased warmth. In general, a basic laboratory evaluation of bone metabolism, plain radiographies of affected bones and bone scintigraphy are sufficient to corroborate the diagnosis. Antiresorptive therapy with bisphosphonates is the mainstay of treatment of symptomatic PDB, and intravenous zoledronic acid has emerged as an effective and safe treatment option, leading to sustained remission and improved quality of life. It is extremely important, though, to ensure calcium and vitamin D sufficiency before and during treatment in order to prevent hypocalcemia. The benefit of treating all asymptomatic patients is not clear, but treatment is warranted if the pagetic lesion is located in a site where progression to fracture, deformity, or compression would significantly impair the patient quality of life. This mini-review focuses on important aspects of the diagnosis and treatment of PDB.

Common susceptibility alleles and SQSTM1 mutations predict disease extent and severity in a multinational study of patients with Paget's disease

Paget's disease of bone (PDB) has a strong genetic component. Here, we investigated possible associations between genetic variants that predispose to PDB and disease severity. Allelic variants identified as predictors of PDB from genome-wide association studies were analyzed in 1940 PDB patients from the United Kingdom, Italy, Western Australia, and Spain. A cumulative risk allele score was constructed by adding the variants together and relating this to markers of disease severity, alone and in combination with SQSTM1 mutations. In SQSTM1-negative patients, risk allele scores in the highest tertile were associated with a 27% increase in disease extent compared with the lowest tertile (p < 0.00001) with intermediate values in the middle tertile (20% increase; p = 0.0007). The effects were similar for disease severity score, which was 15% (p = 0.01) and 25% (p < 0.00001) higher in the middle and upper tertiles, respectively. Risk allele score remained a significant predictor of extent and severity when SQSTM-positive individuals were included, with an effect size approximately one-third of that observed with SQSTM1 mutations. A genetic risk score was developed by combining information from both markers, which identified subgroups of individuals with low, medium, and high levels of severity with a specificity of 70% and sensitivity of 55%. Risk allele scores and SQSTM1 mutations both predict extent and severity of PDB. It is possible that with further refinement, genetic profiling may be of clinical value in identifying individuals at high risk of severe disease who might benefit from enhanced surveillance and early intervention.

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.

Secular changes in Paget's disease: contrasting changes in the number of new referrals and in disease severity in two neighboring regions of Spain

SUMMARY

We studied the changes in the number of new referrals with Paget's disease of bone (PDB) and severity of PDB in a high prevalence focus and its neighboring region. Referral of patients changed only in the high prevalence focus. The severity of PDB decreased in both regions. These results could suggest the effects of an environmental influence on disease activity.

INTRODUCTION

The prevalence and severity of PDB have decreased in several countries over recent years. We previously reported a high radiological prevalence of PDB in Vitigudino. Here we sought to determine if secular changes in the number of new referrals and severity of PDB had occurred over recent years.

METHODS

We studied 280 patients with clinically diagnosed PDB who were evaluated at a regional referral center for metabolic bone disease between 1986 and 2009. Changes in the number of new referrals were calculated by relating these data to the number of subjects at risk as determined by population registers. Trends in disease severity were analyzed with alkaline phosphatase (ALP) activity and disease extent on scan.

RESULTS

Referrals from the Vitigudino region increased substantially between 1986 and 2003 but fell markedly between 2004 and 2009, although by this time there had been depopulation of the region due to emigration. No significant changes in the rates of referral occurred in the remainder of Salamanca. ALP activity and disease extent decreased in Salamanca, but only ALP activity decreased in Vitigudino. Referrals rate and severity of PDB in Vitigudino were greater than in the remainder of Salamanca.

CONCLUSIONS

Referral of patients with clinically diagnosed PDB has remained stable for most of Salamanca during the past 24 years, but substantial changes have been observed in Vitigudino. In agreement with other reports, the severity of PDB has decreased in both regions consistent with the effects of an environmental influence on disease activity.

Giant cell tumor occurring in familial Paget's disease of bone: report of clinical characteristics and linkage analysis of a large pedigree

Neoplastic degeneration represents a rare but serious complication of Paget's disease of bone (PDB). Although osteosarcomas have been described in up to 1% of PDB cases, giant cell tumors are less frequent and mainly occur in patients with polyostotic disease. We recently characterized a large pedigree with 14 affected members of whom four developed giant cell tumors at pagetic sites. The high number of affected subjects across multiple generations allowed us to better characterize the clinical phenotype and look for possible susceptibility loci. Of interest, all the affected members had polyostotic PDB, but subjects developing giant cell tumors showed an increased disease severity with a reduced clinical response to bisphosphonate treatment and an increased prevalence of bone pain, deformities, and fractures. Together with an increased occurrence of common pagetic complications, affected patients of this pedigree also evidenced a fivefold higher prevalence of coronary artery disease with respect to either the unaffected family members or a comparative cohort of 150 unrelated PDB cases from the same geographical area. This association was further enhanced in the four cases with PDB and giant cell tumors, all of them developing coronary artery disease before 60 years of age. Despite the early onset and the severe phenotype, PDB patients from this pedigree were negative for the presence of SQSTM1 or TNFRSF11A mutations, previously associated with enhanced disease severity. Genome-wide linkage analysis identified six possible candidate regions on chromosomes 1, 5, 6, 8, 10, and 20. Because the chromosome 8 and 10 loci were next to the TNFRSF11B and OPTN genes, we extended the genetic screening to these two genes, but we failed to identify any causative mutation at both the genomic and transcription level, suggesting that a different genetic defect is associated with PDB and potentially giant cell tumor of bone in this pedigree.

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.

Radiological features of Paget disease of bone associated with VCP myopathy

OBJECTIVE

Mutations in the Valosin-containing protein (VCP) gene cause a unique disorder characterized by classic Paget disease of bone (PDB), inclusion body myopathy, and frontotemporal dementia (IBMPFD). Our objective was to analyze the radiographic features of PDB associated with VCP mutations since there is a dearth of literature on the PDB component of VCP disease.

MATERIALS AND METHODS

Radiographic bone surveys were examined in 23 individuals with VCP mutation and compared with their unaffected relatives. Laboratory testing relevant for VCP disease was performed in all individuals.

RESULTS

Of the 17 affected individuals with clinical manifestations of VCP disease, 16 of whom had myopathy, radiographic analysis revealed classic PDB in 11 individuals (65%). The mean age of diagnosis for myopathy was 43.8 years and for PDB was 38.1 years of age. Radiological evidence of PDB was seen in one individual (16%) amongst six clinically asymptomatic VCP mutation carriers. Alkaline phosphatase was a useful marker for diagnosing PDB in VCP disease.

CONCLUSIONS

Radiographic findings of classic PDB are seen in 52% of individuals carrying VCP mutations at a significantly younger age than conventional PDB. Screening for PDB is warranted in at-risk individuals because of the benefit of early treatment with the new powerful bisphosphonates that hold the potential for prevention of disease.