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

Genetic Screening of ZNF687 and PFN1 in a Paget's Disease of Bone Cohort Indicates an Important Role for the Nuclear Localization Signal of ZNF687

Paget's disease of bone (PDB) is a common, late-onset bone disorder, characterized by focal increases of bone turnover that can result in bone lesions. Heterozygous pathogenic variants in the Sequestosome 1 (SQSTM1) gene are found to be the main genetic cause of PDB. More recently, PFN1 and ZNF687 have been identified as causal genes in patients with a severe, early-onset, polyostotic form of PDB, and an increased likelihood to develop giant cell tumors. In our study, we screened the coding regions of PFN1 and ZNF687 in a Belgian PDB cohort (n = 188). In the PFN1 gene, no variants could be identified, supporting the observation that variants in this gene are extremely rare in PDB. However, we identified 3 non-synonymous coding variants in ZNF687. Interestingly, two of these rare variants (p.Pro937His and p.Arg939Cys) were clustering in the nuclear localization signal of the encoded ZNF687 protein, also harboring the p.Pro937Arg variant, a previously reported disease-causing variant. In conclusion, our findings support the involvement of genetic variation in ZNF687 in the pathogenesis of classical PDB, thereby expanding its mutational spectrum.

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.

A mutation in the ZNF687 gene that is responsible for the severe form of Paget's disease of bone causes severely altered bone remodeling and promotes hepatocellular carcinoma onset in a knock-in mouse model

Paget's disease (PDB) is a late-onset bone remodeling disorder with a broad spectrum of symptoms and complications. One of the most aggressive forms is caused by the P937R mutation in the ZNF687 gene. Although the genetic involvement of ZNF687 in PDB has been extensively studied, the molecular mechanisms underlying this association remain unclear. Here, we describe the first Zfp687 knock-in mouse model and demonstrate that the mutation recapitulates the PDB phenotype, resulting in severely altered bone remodeling. Through microcomputed tomography analysis, we observed that 8-month-old mutant mice showed a mainly osteolytic phase, with a significant decrease in the trabecular bone volume affecting the femurs and the vertebrae. Conversely, osteoblast activity was deregulated, producing disorganized bone. Notably, this phenotype became pervasive in 16-month-old mice, where osteoblast function overtook bone resorption, as highlighted by the presence of woven bone in histological analyses, consistent with the PDB phenotype. Furthermore, we detected osteophytes and intervertebral disc degeneration, outlining for the first time the link between osteoarthritis and PDB in a PDB mouse model. RNA sequencing of wild-type and Zfp687 knockout RAW264.7 cells identified a set of genes involved in osteoclastogenesis potentially regulated by Zfp687, e.g., Tspan7, Cpe, Vegfc, and Ggt1, confirming its role in this process. Strikingly, in this mouse model, the mutation was also associated with a high penetrance of hepatocellular carcinomas. Thus, this study established an essential role of Zfp687 in the regulation of bone remodeling, offering the potential to therapeutically treat PDB, and underlines the oncogenic potential of ZNF687.

Gene Sequencing Identifies Perturbation in Nitric Oxide Signaling as a Nonlipid Molecular Subtype of Coronary Artery Disease

BACKGROUND

A key goal of precision medicine is to disaggregate common, complex diseases into discrete molecular subtypes. Rare coding variants in the low-density lipoprotein receptor gene (LDLR) are identified in 1% to 2% of coronary artery disease (CAD) patients, defining a molecular subtype with risk driven by hypercholesterolemia.

METHODS

To search for additional subtypes, we compared the frequency of rare, predicted loss-of-function and damaging missense variants aggregated within a given gene in 41 081 CAD cases versus 217 115 controls.

RESULTS

Rare variants in LDLR were most strongly associated with CAD, present in 1% of cases and associated with 4.4-fold increased CAD risk. A second subtype was characterized by variants in endothelial nitric oxide synthase gene (NOS3), a key enzyme regulating vascular tone, endothelial function, and platelet aggregation. A rare predicted loss-of-function or damaging missense variants in NOS3 was present in 0.6% of cases and associated with 2.42-fold increased risk of CAD (95% CI, 1.80-3.26; P=5.50×10-9). These variants were associated with higher systolic blood pressure (+3.25 mm Hg; [95% CI, 1.86-4.65]; P=5.00×10-6) and increased risk of hypertension (adjusted odds ratio 1.31; [95% CI, 1.14-1.51]; P=2.00×10-4) but not circulating cholesterol concentrations, suggesting that, beyond lipid pathways, nitric oxide synthesis is a key nonlipid driver of CAD risk.

CONCLUSIONS

Beyond LDLR, we identified an additional nonlipid molecular subtype of CAD characterized by rare variants in the NOS3 gene.

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.

Effects of Bisphosphonate Treatment on Circulating Lipid and Glucose Levels in Patients with Metabolic Bone Disorders

Bisphosphonates are the first-choice treatment of osteoporosis and Paget's disease of bone. Among the bisphosphonates, the non-amino-bisphosphonates, such as clodronic acid, are intracellular converted into toxic analogues of ATP and induce cellular apoptosis whereas the amino-bisphosphonates, such as zoledronic acid, inhibit the farnesyl-diphosphate-synthase, an enzyme of the mevalonate pathway. This pathway regulates cholesterol and glucose homeostasis and is a target for statins. In this retrospective cohort study, we evaluated the effects of an intravenous infusion of zoledronic acid (5 mg) or clodronic acid (1500 mg) on blood lipid (i.e. total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol and triglycerides) and glucose levels in patients with osteoporosis and Paget's disease of bone. All patients were evaluated before, 1 and 6 months after bisphosphonate treatment. Pagetic and osteoporotic patients treated with zoledronic acid showed a significant reduction in glucose and atherogenic lipids during follow-up whereas these phenomena were not observed after clodronic treatment. The effect on circulating lipid levels was similar in naïve and re-treated Pagetic patients. Zoledronic acid treatment was associated with a reduction in blood glucose and atherogenic lipids in patients with metabolic bone disorders. The extent of change was similar to that obtained with the regular assumption of a low-intensity statin. Further studies are warranted to better evaluate the clinical implications of these observations.

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.

ZNF687 mutations are frequently found in pagetic patients from South Italy: implication in the pathogenesis of Paget's disease of bone

Paget's disease of bone (PDB) is a skeletal disorder whose molecular basis is not fully elucidated. However, 10% of patients show a familial PDB and 35% of them carry mutations in the SQSTM1 gene. We recently reported a founder mutation (p.Pro937Arg) in the ZNF687 gene, underlying PDB complicated by giant cell tumor (GCT/PDB) and rarely occurring in PDB patients without neoplastic degeneration. Since 80% of Italian GCT/PDB patients derive from Avellino, we hypothesized that ZNF687 mutation rate was higher in this region than elsewhere. Interestingly, our molecular analysis on 30 PDB patients showed that 33% hosted ZNF687 mutations, with the p.Pro937Arg identified in 8 familial cases. Two novel ZNF687 mutations (p.Pro665Leu and p.Gln784Glu) were detected in 2 sporadic patients. Only 2 subjects were positive for the p.Pro392Leu mutation in SQSTM1. ZNF687-mutated patients showed a severe PDB, with a remarkable number of affected sites. in vitro studies revealed that the ZNF687-mutant osteoclasts appeared as giant sized with up to 150 nuclei, never described in PDB. Finally, we also confirmed the causality of the p.Pro937Arg mutation in 4 additional GCT/PDB cases deriving from the same geographic area, indicating that PDB and GCT/PDB represent 2 sides of the same coin.

ZNF687 Mutations in Severe Paget Disease of Bone Associated with Giant Cell Tumor

Paget disease of bone (PDB) is a skeletal disorder characterized by focal abnormalities of bone remodeling, which result in enlarged and deformed bones in one or more regions of the skeleton. In some cases, the pagetic tissue undergoes neoplastic transformation, resulting in osteosarcoma and, less frequently, in giant cell tumor of bone (GCT). We performed whole-exome sequencing in a large family with 14 PDB-affected members, four of whom developed GCT at multiple pagetic skeletal sites, and we identified the c.2810C>G (p.Pro937Arg) missense mutation in the zinc finger protein 687 gene (ZNF687). The mutation precisely co-segregated with the clinical phenotype in all affected family members. The sequencing of seven unrelated individuals with GCT associated with PDB (GCT/PDB) identified the same mutation in all individuals, unravelling a founder effect. ZNF687 is highly expressed during osteoclastogenesis and osteoblastogenesis and is dramatically upregulated in the tumor tissue of individuals with GCT/PDB. Interestingly, our preliminary findings showed that ZNF687, indicated as a target gene of the NFkB transcription factor by ChIP-seq analysis, is also upregulated in the peripheral blood of PDB-affected individuals with (n = 5) or without (n = 6) mutations in SQSTM1, encouraging additional studies to investigate its potential role as a biomarker of PDB risk.

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.

Clinical characteristics and evolution of giant cell tumor occurring in Paget's disease of bone

Patients with Paget's bone disease (PDB) have an increased risk of developing giant cell tumor (GCT). This study was performed to evaluate the clinical characteristics and evolution of GCT complicating PDB and to compare these clinical characteristics to those observed in two large PDB cohorts, the PDB Italian Registry and the United Kingdom's Multi-Centre Randomised Controlled Trial of Symptomatic Versus Intensive Bisphosphonate Therapy for Paget's Disease (PRISM) study. A systematic literature review identified 117 cases of PDB complicated by GCT (PDB-GCT), which involved the skeletal sites affected by PDB (110 patients) or the extraskeletal tissues adjacent to affected bones (7 patients). In contrast to what previously reported for GCT patients without GCT patients (83.2%) were white and one-fourth of them (24.8%) had multifocal GCTs. Compared to PDB patients without GCT, PDB-GCT patients showed a higher male/female ratio (2.1 versus 1.2) and more severe disease (age at PDB onset 52.1 ± 12.1 versus 63.3 ± 10.6 years; number of affected sites 6.1 ± 2.9 versus 2.34 ± 1.6; prevalence of polyostotic PDB 93.3% versus 60.6%). The mortality rate of PDB-GCT patients was higher than those occurring in GCT patients without PDB (about 50% versus 0% to 5% at 5 years) or in PDB patients without GCT (log rank = 29.002). Moreover, up to 98% of PDB-GCT cases had elevated total alkaline phosphatase levels at neoplasm diagnosis, suggestive of active PDB. Importantly, PDB-GCT patients from Southern Italy (45.6% of all GCT patients) showed a higher prevalence of multifocal GCT (51.7%) and of positive familial history for PDB (70.8%) and GCT (65.0%). Finally, indirect evidence suggests a decline in the incidence of GCT in PDB patients. The occurrence of GCT in PDB patients is associated with severe disease and reduced life expectancy of affected patients. The increased prevalence of familial diseases in PDB-GCT patients from Southern Italy suggests a founder effect. The observed changes over time in the incidence of GCT in PDB patients could be related to improved clinical management and/or living conditions of patients.

Rapid skeletal turnover in a radiographic mimic of osteopetrosis

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