Early-onset Paget's Disease Of Bone Research Articles

Osteolytic Bone Loss and Skeletal Deformities in a Mouse Model for Early-Onset Paget's Disease of Bone with PFN1 Mutation Are Treatable by Alendronate.

A novel osteolytic disorder due to PFN1 mutation was discovered recently as early-onset Paget's disease of bone (PDB). Bone loss and pain in adult PDB patients have been treated using bisphosphonates. However, therapeutic strategies for this specific disorder have not been established. Here, we evaluated the efficiency of alendronate (ALN) on a mutant mouse line, recapitulating this disorder. Five-week-old conditional osteoclast-specific Pfn1-deficient mice (Pfn1-cKOOCL) and control littermates (33 females and 22 males) were injected with ALN (0.1 mg/kg) or vehicle twice weekly until 8 weeks of age. After euthanizing, bone histomorphometric parameters and skeletal deformities were analyzed using 3D μCT images and histological sections. Three weeks of ALN administration significantly improved bone mass at the distal femur, L3 vertebra, and nose in Pfn1-cKOOCL mice. Histologically increased osteoclasts with expanded distribution in the distal femur were normalized in these mice. Geometric bone shape analysis revealed a partial recovery from the distal femur deformity. A therapeutic dose of ALN from 5 to 8 weeks of age significantly improved systemic bone loss in Pfn1-cKOOCL mice and femoral bone deformity. Our study suggests that preventive treatment of bony deformity in early-onset PDB is feasible.

VCP/p97 inhibitor CB-5083 modulates muscle pathology in a mouse model of VCP inclusion body myopathy

BackgroundPathogenic gain of function variants in Valosin-containing protein (VCP) cause a unique disease characterized by inclusion body myopathy with early-onset Paget disease of bone and frontotemporal dementia (also known as Multisystem proteinopathy (MSP)). Previous studies in drosophila models of VCP disease indicate treatment with VCP inhibitors mitigates disease pathology. Earlier-generation VCP inhibitors display off-target effects and relatively low therapeutic potency. New generation of VCP inhibitors needs to be evaluated in a mouse model of VCP disease. In this study, we tested the safety and efficacy of a novel and potent VCP inhibitor, CB-5083 using VCP patient-derived myoblast cells and an animal model of VCP disease.MethodsFirst, we analyzed the effect of CB-5083 in patient-derived myoblasts on the typical disease autophagy and TDP-43 profile by Western blot. Next, we determined the maximum tolerated dosage of CB-5083 in mice and treated the 2-month-old VCPR155H/R155H mice for 5 months with 15 mg/kg CB-5083. We analyzed motor function monthly by Rotarod; and we assessed the end-point blood toxicology, and the muscle and brain pathology, including autophagy and TDP-43 profile, using Western blot and immunohistochemistry. We also treated 12-month-old VCPR155H/+ mice for 6 months and performed similar analysis. Finally, we assessed the potential side effects of CB-5083 on retinal function, using electroretinography in chronically treated VCPR155H/155H mice.ResultsIn vitro analyses using patient-derived myoblasts confirmed that CB-5083 can modulate expression of the proteins in the autophagy pathways. We found that chronic CB-5083 treatment is well tolerated in the homozygous mice harboring patient-specific VCP variant, R155H, and can ameliorate the muscle pathology characteristic of the disease. VCP-associated pathology biomarkers, such as elevated TDP-43 and p62 levels, were significantly reduced. Finally, to address the potential adverse effect of CB-5083 on visual function observed in a previous oncology clinical trial, we analyzed retinal function in mice treated with moderate doses of CB-5083 for 5 months and documented the absence of permanent ocular toxicity.ConclusionsAltogether, these findings suggest that long-term use of CB-5083 by moderate doses is safe and can improve VCP disease-associated muscle pathology. Our results provide translationally relevant evidence that VCP inhibitors could be beneficial in the treatment of VCP disease.

MON-LB70 The Association of Paget’s Disease With Inclusion Body Myositis and Fronto Temporal Dementia (IBMFTD)

Background: Inclusion body myopathy associated with Paget disease of bone (PDB) and/or frontotemporal dementia (IBMPFD) is a rare, autosomal dominant condition, characterized by adult-onset muscle weakness, early-onset PDB, and premature frontotemporal dementia. Paget’s disease is a chronic disorder of bone resulting in increased bone resorption, followed by a disorganized and excessive formation of bone. Clinical Case: A 43 year old gentleman was referred to neurology services with foot drop, limb weakness and cognitive impairment. Following a prolonged period of diagnostic evaluation a mutation in valosin-containing protein (VCP) gene was uncovered IBMPFD has a variable phenotype which may include PDB. This gentleman denied bony pain and had an alkaline phosphatase within reference range. Plain film radiographs at multiple sights demonstrated no signs of PDB. An MRI whole body was performed which reported coarse trabecular markings in L2 vertebral body and multilevel degenerative changes with bridging osteophytes in the lumbar spine consistent with PDB.At initial review in endocrine clinic, he denied fractures or bone pain. He had no signs of increased cardiac output or cranial nerve deficits. A radionuclide bone scan identified intense radiopharmaceutical accumulation in L2 vertebral body consistent with MRI findings and also curvilinear increased activity in the left occipital bone and low-grade activity in the left hip, thus confirming polyostotic Paget’s disease.He received a 5mg IV infusion of zolendronate, side effects of which included myalgia, pyrexia and lethargy.Six months following the zoledronate infusion a repeat bone scan demonstrated that the extent of uptake at affected sites had decreased significantly.He subsequently fractured his left femur following a mechanical fall. PDB can affect up to 50% of patients with IBMFTD. PDB can lead to complications such as bone pain, localized pain and deformity of the long bones, pathologic fractures and deafness. This case highlights the association of Paget’s disease with IBMFTD and as it can be asymptomatic, as in our case, radiological imaging is required for diagnosis. It also reminds us that Paget’s disease can be due to genetic causes. Understanding the role of VCP in the cell cycle may help in further understanding bone physiology.

Genetic variation in the TNFRSF11A gene encoding RANK is associated with susceptibility to Paget's disease of bone

RANK (receptor activator of nuclear factor-κB), encoded by TNFRSF11A, is a key protein in osteoclastogenesis. TNFRSF11A mutations cause Paget's disease of bone (PDB)-like diseases (ie, familial expansile osteolysis, expansile skeletal hyperphosphatasia, and early-onset PDB) and an osteoclast-poor form of osteopetrosis. However, no TNFRSF11A mutations have been found in classic PDB, neither in familial nor in isolated cases. To investigate the possible relationship between TNFRSF11A polymorphisms and sporadic PDB, we conducted an association study including 32 single-nucleotide polymorphisms (SNPs) in 196 Belgian sporadic PDB patients and 212 control individuals. Thirteen SNPs and 3 multimarker tests (MMTs) turned out to have a p value of between .036 and 3.17 × 10(-4) , with the major effect coming from females. Moreover, 6 SNPs and 1 MMT withstood the Bonferroni correction (p < .002). Replication studies were performed for 2 nonsynonymous SNPs (rs35211496 and rs1805034) in a Dutch and a British cohort. Interestingly, both SNPs resulted in p values ranging from .013 to 8.38 × 10(-5) in both populations. Meta-analysis over three populations resulted in p = .002 for rs35211496 and p = 1.27 × 10(-8) for rs1805034, again mainly coming from the female subgroups. In an attempt to identify the underlying causative SNP, we performed functional studies for the coding SNPs as well as resequencing efforts of a 31-kb region harboring a risk haplotype within the Belgian females. However, neither approach resulted in significant evidence for the causality of any of the tested genetic variants. Therefore, further studies are needed to identify the real cause of the increased risk to develop PDB shown to be present within TNFRSF11A.

Hereditary Inclusion Body Myopathy-Linked p97/VCP Mutations in the NH2 Domain and the D1 Ring Modulate p97/VCP ATPase Activity and D2 Ring Conformation

Hereditary inclusion body myopathy associated with early-onset Paget disease of bone and frontotemporal dementia (hIBMPFTD) is a degenerative disorder caused by single substitutions in highly conserved residues of p97/VCP. All mutations identified thus far cluster within the NH(2) domain or the D1 ring, which are both required for communicating conformational changes to adaptor protein complexes. In this study, biochemical approaches were used to identify the consequences of the mutations R155P and A232E on p97/VCP structure. Assessment of p97/VCP oligomerization revealed that p97(R155P) and p97(A232E) formed hexameric ring-shaped structures of approximately 600 kDa. p97(R155P) and p97(A232E) exhibited an approximately 3-fold increase in ATPase activity compared to wild-type p97 (p97(WT)) and displayed increased sensitivity to heat-induced upregulation of ATPase activity. Protein fluorescence analysis provided evidence for conformational differences in the D2 rings of both hIBMPFTD mutants. Furthermore, both mutations increased the proteolytic susceptibility of the D2 ring. The solution structures of all p97/VCP proteins revealed a didispersed distribution of a predominant hexameric population and a minor population of large-diameter complexes. ATP binding significantly increased the abundance of large-diameter complexes for p97(R155P) and p97(A232E), but not p97(WT) or the ATP-binding mutant p97(K524A). Therefore, we propose that hIBMPFTD p97/VCP mutants p97(R155P) and p97(A232E) possess structural defects that may compromise the mechanism of p97/VCP activity within large multiprotein complexes.

Early onset Paget's disease of bone caused by a novel mutation (78dup27) of the TNFRSF11A gene in a Chinese family

A previous study showed that individuals of Japanese descent affected by early onset familial Paget's disease of bone (PDB) carried a 27-bp duplication at position 75 (75dup27) in the TNFRSF11A gene encoding RANK. Here we report the identification of a novel mutation (78dup27) in exon 1 of TNFRSF11A in a Chinese family with early onset PDB. We conducted clinical and genetic studies in a non-consanguineous Chinese family with early onset PDB. The entire coding region of TNFRSF11A was amplified and directly sequenced directly. A novel 27-bp duplication in exon 1 (78dup27) in TNFRSF11A was found in four affected individuals and one asymptomatic individual. Although this duplication was the same length as the previously identified mutation (27 bp, from bases 78 to 104), in our patients the nine duplicated amino acids in the RANK signal peptide were LLLLCALLA. The phenotypes of affected individuals in this family overlapped with both early onset PDB and classic PDB, but several distinguishing features were found in our patients. The key difference between our familial PDB and the Japanese early onset PDB was the age of onset, which in most of our patients was during their late 20s (except for the propositus' niece). Another notable difference was that the propositus' son (24 years old), who carried the 78dup27 mutation, had no clinical symptoms or bone abnormalities, except for increased serum ALP, OC and CTX. Our findings may provide a better understanding of the clinical features of early onset PDB and support the notion of a hot spot for mutations in exon 1 of the TNFRSF11A gene.

Inclusion body myopathy with Paget disease and frontotemporal dementia (IBMPFD): clinical features including sphincter disturbance in a large pedigree

Autosomal dominant inclusion body myopathy (IBM) associated with Paget disease of bone (PDB) and frontotemporal dementia (FTD), or IBMPFD, is a rare recently described multisystem disorder caused by missense mutations...

Pathophysiology and Genetics of Metabolic Bone Disorders Characterized by Increased Bone Turnover

Bone is the most important supportive tissue in the human body, and in order to maintain its integrity, it is continuously renewed by a process called "remodeling". Paget's disease of bone (PDB), familial expansile osteolysis (FEO), expansile skeletal hyperphosphatasia (ESH), early-onset Paget's disease of bone (EOPDB), and juvenile Paget's disease (JPD) are all metabolic bone disorders characterized by accelerated bone remodeling. Histological studies have shown that bone-resorbing osteoclasts are the primary disease-causing cells in these disorders. In this review, we provide an overview of the clinical differences between diseases with increased bone turnover. Our main focus is on Paget's disease because this is, by far, the most common form of this type of disease. Molecular genetic studies of these disorders have revealed key players in bone remodeling and have provided further insights in signal transduction in osteoclasts. Moreover, a syndromal form of PDB has been characterized in which PDB is associated with inclusion body myopathy and frontotemporal dementia, pointing toward similar biological pathways in osteoclasts, muscle, and brain cells. However, several additional genes underlying conditions with increased bone turnover remain to be identified.

Genetics of Paget's disease of bone

PDB (Paget's disease of bone) is a common condition characterized by focal increases in bone turnover affecting one or more sites throughout the skeleton. Genetic factors are important in the pathogenesis of PDB and many families have been described where PDB is inherited in an autosomal-dominant fashion. Several candidate loci for susceptibility to PDB and related syndromes have been identified by genome-wide scans and recent evidence suggests that mutations in genes that encode components of the RANK [receptor activator of NF-kappaB (nuclear factor-kappaB)]/NF-kappaB signalling pathway play an important role in the pathogenesis of this group of diseases. Insertion mutations in the TNFRSF11A gene encoding RANK have been identified as the cause of familial expansile osteolysis, some cases of early onset PDB and expansile skeletal hyperphosphatasia. Inactivating mutations in the TNFRSF11B gene that encodes OPG (osteoprotegerin) have been found to cause the syndrome of juvenile PDB. Polymorphisms in OPG also appear to increase the risk of developing PDB. The most important causal gene for classical PDB is Sequestosome 1 (SQSTM1), which is a scaffold protein in the NF-kappaB signalling pathway, and mutations affecting the UBA (ubiquitin-associated) domain of this protein occur in between 20-50% of familial and 10-20% of sporadic PDB cases. The rare syndrome of IBMPFD (inclusion body myopathy, PDB and fronto-temporal dementia) is due to mutations in the VCP gene and these also cluster in the domain of VCP that interacts with ubiquitin, suggesting a common disease mechanism with SQSTM1-mediated PDB.