Mutations in prion-like domains in hnRNPA2B1 and hnRNPA1 cause multisystem proteinopathy and ALS

Algorithms designed to identify canonical yeast prions predict that around 250 human proteins, including several RNA-binding proteins associated with neurodegenerative disease, harbour a distinctive prion-like domain (PrLD) enriched in uncharged polar amino acids and glycine. PrLDs in RNA-binding proteins are essential for the assembly of ribonucleoprotein granules. However, the interplay between human PrLD function and disease is not understood. Here we define pathogenic mutations in PrLDs of heterogeneous nuclear ribonucleoproteins (hnRNPs) A2B1 and A1 in families with inherited degeneration affecting muscle, brain, motor neuron and bone, and in one case of familial amyotrophic lateral sclerosis. Wild-type hnRNPA2 (the most abundant isoform of hnRNPA2B1) and hnRNPA1 show an intrinsic tendency to assemble into self-seeding fibrils, which is exacerbated by the disease mutations. Indeed, the pathogenic mutations strengthen a 'steric zipper' motif in the PrLD, which accelerates the formation of self-seeding fibrils that cross-seed polymerization of wild-type hnRNP. Notably, the disease mutations promote excess incorporation of hnRNPA2 and hnRNPA1 into stress granules and drive the formation of cytoplasmic inclusions in animal models that recapitulate the human pathology. Thus, dysregulated polymerization caused by a potent mutant steric zipper motif in a PrLD can initiate degenerative disease. Related proteins with PrLDs should therefore be considered candidates for initiating and perhaps propagating proteinopathies of muscle, brain, motor neuron and bone.

TDP-43 in the ubiquitin pathology of frontotemporal dementia with VCP gene mutations

Frontotemporal dementia with inclusion body myopathy and Paget disease of bone is a rare, autosomal-dominant disorder caused by mutations in the gene valosin-containing protein (VCP). The CNS pathology is characterized by a novel pattern of ubiquitin pathology distinct from sporadic and familial frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) without VCP mutations. TAR DNA binding protein 43 (TDP-43) was recently identified as a major disease protein in the ubiquitin-positive inclusions of sporadic and familial FTLD-U. To determine whether the ubiquitin pathology associated with mutations in VCP is characterized by the accumulation of TDP-43, we analyzed TDP-43 in the CNS pathology of five patients with VCP gene mutations. Accumulations of TDP-43 colocalized with ubiquitin pathology in inclusion body myopathy and Paget disease of bone, including both intranuclear inclusions and dystrophic neurites. Similar to FTLD-U, phosphorylated TDP-43 was detected only in insoluble brain extracts from affected brain regions. Identification of TDP-43, but not VCP, within ubiquitin-positive inclusions supports the hypothesis that VCP gene mutations lead to a dominant negative loss or alteration of VCP function culminating in impaired degradation of TDP-43. TDP-43 is a common pathologic substrate linking a variety of distinct patterns of FTLD-U pathology caused by different genetic alterations.

Collagen type II C-telopeptide fragments as an index of cartilage degradation

We report the development of an assay for measurement of the urinary concentration of collagen type II C-telopeptide fragments. This assay was developed for providing a specific marker of joint metabolism. A monoclonal antibody, recognizing a linear six amino acid epitope from the middle region of the collagen type II C-telopeptide was used in a competitive enzyme-linked immunoassay (ELISA) format for measurement of urine samples. The technical performance and specificity of the assay was evaluated and a panel of samples from patients with rheumatoid arthritis (RA) (n = 27), osteoarthritis (OA) (n = 29), Paget's disease (n = 9), and healthy controls (n = 428) was measured in the assay. The ELISA was specific for the peptide EKGPDP derived from collagen type II C-telopeptide: it did not recognize peptides from the N-telopeptide of the molecule or from other collagen types. Collagen type II C-telopeptide fragments measured in the assay resisted seven freeze-thaw cycles and >20 h of storage at room temperature. RA and OA patients showed significant 2.33-fold (95% confidence interval [CI] 1.50-3.16) and 1.53-fold (CI 1.24-1.82) elevations in CartiLaps concentration, respectively. Paget's disease patients did not have elevated CartiLaps levels. RA patients with radiological evidence of cartilage damage had significantly higher (1.79-fold, CI 1.04-2.54) CartiLaps levels than RA patients without radiological evidence of cartilage destruction. The Cartilaps assay showed high technical precision and an ability to differentiate populations with an elevated joint metabolism from normal controls. This suggests that the assay may have clinical value in assisting in the diagnosis of joint diseases and in monitoring progression and therapy in RA and OA.

Nuclear inclusions in Paget's disease of bone

The ultrastructure of bone cells was examined in biopsies from 18 patients with Paget's disease of bone and from 60 patients with a variety of other bone diseases. A characteristic nuclear inclusion was found in the osteoclasts of each patient with Paget's disease. The nuclear inclusion most closely resembles viral nucleocapsids of the measles type.

Paget disease of bone

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

Molecular pathogenesis of osteosarcoma

Osteosarcoma is a devastating but rare disease, whose study has illuminated both the basic biology and clinical management of cancer over the past 30 years. These contributions have included insight into the roles of key cancer genes such as the retinoblastoma tumor suppressor gene and TP53, the identification of familial cancer syndromes implicating DNA helicases, and dramatic improvements in survival by the use of adjuvant chemotherapy. This review provides a synoptic overview of our current understanding of the molecular causes of osteosarcoma, and suggests future directions for study.

Treatment of Paget's disease with (3-amino-1-hydroxypropylidene)-1, 1-bisphosphonate (A.P.D.)

18 patients with Paget's disease were treated orally with (3-amino-1-hydroxypropylidene)-1, 1-bisphosphonate (A.P.D.). In most cases bone resorption became normal within a week of treatment, whereas the return to normal bone formation took 3-6 months; this difference produced a transient imbalance between resorption and formation. In biopsy specimens taken during treatment the numbers of osteoclasts and osteoblasts decreased towards normal and excess osteoid disappeared.

Valosin-containing protein disease: inclusion body myopathy with Paget's disease of the bone and fronto-temporal dementia

Mutations in valosin-containing protein (VCP) cause inclusion body myopathy (IBM) associated with Paget's disease of the bone (PDB) and fronto-temporal dementia (FTD) or IBMPFD. Although IBMPFD is a multisystem disorder, muscle weakness is the presenting symptom in greater than half of patients and an isolated symptom in 30%. Patients with the full spectrum of the disease make up only 12% of those affected; therefore it is important to consider and recognize IBMPFD in a neuromuscular clinic. The current review describes the skeletal muscle phenotype and common muscle histochemical features in IBMPFD. In addition to myopathic features; vacuolar changes and tubulofilamentous inclusions are found in a subset of patients. The most consistent findings are VCP, ubiquitin and TAR DNA-binding protein 43 (TDP-43) positive inclusions. VCP is a ubiquitously expressed multifunctional protein that is a member of the AAA+ (ATPase associated with various activities) protein family. It has been implicated in multiple cellular functions ranging from organelle biogenesis to protein degradation. Although the role of VCP in skeletal muscle is currently unknown, it is clear that VCP mutations lead to the accumulation of ubiquitinated inclusions and protein aggregates in patient tissue, transgenic animals and in vitro systems. We suggest that IBMPFD is novel type of protein surplus myopathy. Instead of accumulating a poorly degraded and aggregated mutant protein as seen in some myofibrillar and nemaline myopathies, VCP mutations disrupt its normal role in protein homeostasis resulting in the accumulation of ubiquitinated and aggregated proteins that are deleterious to skeletal muscle.

Novel ubiquitin neuropathology in frontotemporal dementia with valosin-containing protein gene mutations

Frontotemporal dementia (FTD) with inclusion body myopathy and Paget disease of bone (IBMPFD) is a rare, autosomal-dominant disorder caused by mutations in the valosin-containing protein (VCP) gene, a member of the AAA-ATPase gene superfamily. The neuropathology associated with sporadic FTD is heterogeneous and includes tauopathies and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). However, there is limited information on the neuropathology in IBMPFD. We performed a detailed, systematic analysis of the neuropathologic changes in 8 patients with VCP mutations. A novel pattern of ubiquitin pathology was identified in IBMPFD that was distinct from sporadic and familial FTLD-U without VCP gene mutations. This was characterized by ubiquitin-positive neuronal intranuclear inclusions and dystrophic neurites. In contrast to FTLD-U, only rare intracytoplasmic inclusions were identified. The ubiquitin pathology was abundant in the neocortex, less robust in limbic and subcortical nuclei, and absent in the dentate gyrus. Only rare inclusions were detected with antibodies to VCP and there was no biochemical alteration in the VCP protein. VCP is associated with a variety of cellular activities, including regulation of the ubiquitin-proteasome system. Our findings are consistent with the hypothesis that the pathology associated with VCP gene mutations is the result of impairment of ubiquitin-based degradation pathways.

Focal osteomalacia due to low-dose diphosphonate therapy in Paget's disease

Transiliac bone biopsies carried out on 13 patients with Paget's disease to evaluate the effects of low-dose diphosphonate (disodium etidronate) therapy showed focal osteomalacia in the 9 patients in whom post-therapy specimens were taken through pagetic bone. Active bone resorption persisted in 5 of these. A mineralisation defect not amounting to osteomalacia--ie, osteoid of increased thickness but of normal extent--was present in the 4 specimens taken through non-pagetic bone. Although 9 patients experienced symptomatic improvement, 2 suffered fissure fractures in affected lower limbs. In Paget's disease, the combination of osteomalacia and continuing active resorption within a lytic lesion may increase the risk of fracture in a weight-bearing bone. It is suggested that although disodium etidronate often provides effective pain relief it should be administered with caution until the optimum dose and duration of therapy are further evaluated.

Clinical delineation and localization to chromosome 9p13.3-p12 of a unique dominant disorder in four families: hereditary inclusion body myopathy, Paget disease of bone, and frontotemporal dementia

Autosomal dominant myopathy, Paget disease of bone, and dementia constitute a unique disorder (MIM 605382). Here we describe the clinical, biochemical, radiological, and pathological characteristics of 49 affected (23 male, 26 female) individuals from four unrelated United States families. Among these affected individuals 90% have myopathy, 43% have Paget disease of bone, and 37% have premature frontotemporal dementia. EMG shows myopathic changes and muscle biopsy reveals nonspecific myopathic changes or blue-rimmed vacuoles. After candidate loci were excluded, a genome-wide screen in the large Illinois family showed linkage to chromosome 9 (maximum LOD score 3.64 with marker D9S301). Linkage analysis with a high density of chromosome 9 markers generated a maximum two-point LOD score of 9.29 for D9S1791, with a maximum multipoint LOD score of 12.24 between D9S304 and D9S1788. Subsequent evaluation of three additional families demonstrating similar clinical characteristics confirmed this locus, refined the critical region, and further delineated clinical features of this unique disorder. Hence, autosomal dominant inclusion body myopathy (HIBM), Paget disease of bone (PDB), and frontotemporal dementia (FTD) localizes to a 1.08-6.46 cM critical interval on 9p13.3-12 in the region of autosomal recessive IBM2.

Sarcomas of bone complicating osteitis deformans (Paget's disease): fifty years' experience

Osteitis deformans (Paget's disease of bone) may be complicated by osseous cancer. Of 3964 patients between 1927 and 1977, 38 had primary malignant bone tumors. This represents an incidence of sarcomatous change of 0.95%. The bones of the pelvis were most often involved; the humerus and the femur were next in frequency. No region of the skeleton was spared, with the exception of the forearms and hands. Of the 38 tumors, six were fibrosarcomas and 32 were osteosarcomas. Irrespective of the site of involvement, the histopathologic extremely poor. The 5-year survival rate was 7.9%, with a mortality rate of 86.8% 36 months after diagnosis. The main cause of death was pulmonary metastasis or local extension of tumor growth. Three patients were long-term survivors, but no clinical or pathologic elements could be identified which differentiated these survivors from the other patients in the study.

Lumbar spinal stenosis in the elderly: an overview

Lumbar spinal stenosis is a common condition in elderly patients and also one of the most common reasons to perform spinal surgery at an advanced age. Disc degeneration, facet degeneration and hypertrophy, and ligamentum flavum hypertrophy and calcification usually participate in the genesis of a stenotic condition in the elderly. These changes can lead to symptoms by themselves or decompensate a preexisting narrow canal. Although some lesions are more central or more lateral, this classic dichotomy is less present in the elderly patient, in whom the degenerative process usually encroaches both central and lateral pathways. Some less common causes of lumbar spinal stenosis are found in the aging subject, such as Paget's disease. However, it must be stressed that so-called stenotic images (sometimes severe) are present on imaging studies in a great number of symptom-free individuals, and that the relationship between degenerative lesions, importance of abnormal images, and complaints is still unclear. Lumbar stenosis is a very common reason for decompressive surgery and/or fusion. Various conditions can lead to a narrowing of the neural pathways and differential diagnosis with vascular troubles, also common in the elderly, can be challenging. The investigation of stenotic symptoms should be extremely careful and thorough and include a choice of technical examinations including vascular investigations. This is of utmost importance, especially if a surgical sanction is considered to avoid disappointing results.

Pathological consequences of VCP mutations on human striated muscle

Mutations in the valosin-containing protein (VCP, p97) gene on chromosome 9p13-p12 cause a late-onset form of autosomal dominant inclusion body myopathy associated with Paget disease of the bone and frontotemporal dementia (IBMPFD). We report on the pathological consequences of three heterozygous VCP (R93C, R155H, R155C) mutations on human striated muscle. IBMPFD skeletal muscle pathology is characterized by degenerative changes and filamentous VCP- and ubiquitin-positive cytoplasmic and nuclear protein aggregates. Furthermore, this is the first report demonstrating that mutant VCP leads to a novel form of dilatative cardiomyopathy with inclusion bodies. In contrast to post-mitotic striated muscle cells and neurons of IBMPFD patients, evidence of protein aggregate pathology was not detected in primary IBMPFD myoblasts or in transient and stable transfected cells using wild-type-VCP and R93C-, R155H-, R155C-VCP mutants. Glutathione S-transferase pull-down experiments showed that all three VCP mutations do not affect the binding to Ufd1, Npl4 and ataxin-3. Structural analysis demonstrated that R93 and R155 are both surface-accessible residues located in the centre of cavities that may enable ligand-binding. Mutations at R93 and R155 are predicted to induce changes in the tertiary structure of the VCP protein. The search for putative ligands to the R93 and R155 cavities resulted in the identification of cyclic sugar compounds with high binding scores. The latter findings provide a novel link to VCP carbohydrate interactions in the complex pathology of IBMPFD.

Effects of disodium dichloromethylene diphosphonate on Paget's disease of bone

19 patients with Paget's disease were treated orally for 6 months with disodium dichloromethylene diphosphonate. 1600 mg/day (10 patients) significantly reduced urine hydroxyproline, serum alkaline phosphatase, urine calcium, and the number of pagetic bone osteoclasts. Tetracycline double labelling revealed undisturbed bone mineralisation. There was improvement on quantitative bone-scans and bone pain diminished. There was a transient increase in parathyroid hormone level in 13 of the 19 patients during treatment, which was associated with a high serum 1,25 (OH)2D3. No adverse clinical side-effects have been observed and biochemical remission has persisted for 9 months.

Pathogenic VCP mutations induce mitochondrial uncoupling and reduced ATP levels

Valosin-containing protein (VCP) is a highly expressed member of the type II AAA+ ATPase family. VCP mutations are the cause of inclusion body myopathy, Paget's disease of the bone, and frontotemporal dementia (IBMPFD) and they account for 1%-2% of familial amyotrophic lateral sclerosis (ALS). Using fibroblasts from patients carrying three independent pathogenic mutations in the VCP gene, we show that VCP deficiency causes profound mitochondrial uncoupling leading to decreased mitochondrial membrane potential and increased mitochondrial oxygen consumption. This mitochondrial uncoupling results in a significant reduction of cellular ATP production. Decreased ATP levels in VCP-deficient cells lower their energy capacity, making them more vulnerable to high energy-demanding processes such as ischemia. Our findings propose a mechanism by which pathogenic VCP mutations lead to cell death.

From the archives of the AFIP. Radiologic spectrum of Paget disease of bone and its complications with pathologic correlation

Paget disease of bone is a common disorder affecting approximately 3%-4% of the population over 40 years of age. The pathologic abnormality in Paget disease is excessive and abnormal remodeling of bone. Three pathologic phases have been described: the lytic phase (incipient-active), in which osteoclasts predominate; the mixed phase (active), in which osteoblasts cause repair superimposed on the resorption; and the blastic phase (late-inactive) in which osteoblasts predominate. Radiographic appearance of Paget disease reflects these pathologic changes and is often characteristic. Initially, there is osteolysis, particularly affecting the skull (osteoporosis circumscripta) and subchondral long bones, with subsequent development of trabecular and cortical thickening and enlargement of bone in the mixed phase of the disease. Finally, areas of sclerosis may develop in the blastic phase. Frequent sites of involvement include the skull (25%-65% of cases), spine (30%-75%), pelvis (30%-75%), and proximal long bones (25%-30%). Bone scintigraphy typically demonstrates marked increased uptake of radionuclide in all phases of Paget disease. Computed tomography and magnetic resonance imaging often show changes similar to those seen radiographically in noncomplicated Paget disease with maintenance of yellow marrow. Complications of Paget disease include the effects of osseous weakening (deformity and fracture), arthritis, neurologic symptoms, and neoplastic involvement. Sarcomatous transformation is the most feared complication, occurring in approximately 1% of cases, and is seen on images as focal bone destruction extending through the cortex with an associated soft-tissue mass. Recognition of the radiologic spectrum of the appearances of Paget disease usually allows prospective diagnosis and differentiation of its associated complications, which helps guide therapy and improve patient management.

Canine distemper virus localised in bone cells of patients with Paget's disease

The technique of in situ hybridisation was applied using radioactively labelled riboprobes to examine for the presence of canine distemper (CDV) and measles (MV) RNA in Paget's disease of bone. The results indicate that in 41% of Paget's patients, CDV RNA could be detected in osteoclasts, osteoblasts, and osteocytes, but not in controls. In contrast, RNA to the measles virus was not detected. We suggest that CDV may in some cases play a role in the aetiology of Paget's disease.

Interleukin-6, IL-6 receptor, and IL-6 nuclear factor gene expression in Paget's disease

The cytokine interleukin-6 (IL-6) is considered an important regulator of bone cell function and may play a central role in bone disease states characterized by increased bone remodeling, such as Paget's disease. Indeed, recent in vitro data suggest that IL-6 may be an autocrine/paracrine factor for pagetic osteoclasts. However, its expression and role in vivo are not known. Using in situ hybridization we investigated the spatial localization of expression of IL-6, IL-6 receptor (IL-6R), and the transcription factor (NF-IL-6) in pagetic bone. Our results show that osteoblasts in the normal remodeling bone of osteoarthritis (controls) and in Paget's disease express IL-6, IL-6R, and NF-IL-6 genes with higher levels of IL-6 and IL-6R mRNA in pagetic bone. Osteoclasts in both osteoarthritic and pagetic bone express IL-6R mRNA and NF-IL-6, but only pagetic osteoclasts expressed IL-6, suggesting that in Paget's disease IL-6 can act as an autocrine factor on osteoclasts. These results provide evidence for a major role of the IL-6 regulatory pathway in the phenotype of the pagetic osteoclasts and lead us to suggest a model linking possible paramyxovirus infection and IL-6 regulation in the pagetic osteoclast.

Enhanced RANK ligand expression and responsivity of bone marrow cells in Paget's disease of bone

Paget's disease is characterized by highly localized areas of increased osteoclast (OCL) activity. This suggests that the microenvironment in pagetic lesions is highly osteoclastogenic, or that OCL precursors in these lesions are hyperresponsive to osteoclastogenic factors (or both). To examine these possibilities, we compared RANK ligand (RANKL) mRNA expression in a marrow stromal cell line developed from a pagetic lesion (PSV10) with that in a normal stromal cell line (Saka), and expression in marrow samples from affected bones of Paget's patients with that in normal marrow. RANKL mRNA was increased in PSV10 cells and pagetic marrow compared with Saka cells and normal marrow, and was also increased in marrow from affected bones compared with uninvolved bones from Paget's patients. Furthermore, pagetic marrow cells formed OCLs at much lower RANKL concentrations than did normal marrow. Anti-IL-6 decreased the RANKL responsivity of pagetic marrow to normal levels, whereas addition of IL-6 to normal marrow enhanced RANKL responsivity. Thus, RANKL expression and responsivity is increased in pagetic lesions, in part mediated by IL-6. These data suggest that the combination of enhanced expression of RANKL in affected bones and increased RANKL sensitivity of pagetic OCL precursors may contribute to the elevated numbers of OCLs in Paget's disease.

Osteogenic sarcoma associated with Paget's disease of bone. A clinicopathologic study of 65 patients

Among 1177 osteogenic sarcoma patients diagnosed and treated at Memorial Hospital, 65 (5.5%) were associated with either monostotic or polyostotic Paget's disease. The overall median age was 64 years (range, 39-82 years). In those patients older than 40 years of age, the frequency of sarcomatous transformation rose to 27%. There were slightly more men (55%) than women. The most common skeletal sites were the pelvic bones (34%), the humerus (22%), the femur (19%), and the craniofacial bones (14%). Unrelenting pain and tender swelling were the most common presenting symptoms (85%), with pathologic fracture in 14 (22%) patients. In two-thirds of the cases, the radiographic presentation was that of a lytic destructive lesion; while in the others it showed a sclerotic, mixed, or permeative character. In almost one-half of the cases, the histologic appearance of the osteogenic sarcomas was either fibrohistocytomatous or osteoblastic. In spite of radical surgical amputations, only three patients survived longer than 5 years. The prognosis of Paget's sarcoma is significantly less favorable than in osteogenic sarcoma arising de novo in patients of comparable age.

Bone histomorphometry in Paget's disease. Quantitative and dynamic analysis of pagetic and nonpagetic bone tissue

Transiliac bone biopsies from 136 untreated pagetic patients, taken from both pagetic (72 cases) and nonpagetic bone (64 cases), were quantitatively analyzed. Tetracycline double labeling analysis demonstrated that osteosclerosis of pagetic bone results from an overproduction of woven bone by the osteoblasts. Increased bone cell populations appeared as the consequence of an increased birthrate of the basic multicellular units. In 45% of patients biopsied in nonpagetic bone, there were prints of an increased bone remodeling attributed to a hyperparathyroidism secondary to the high calcium demand of pagetic bones.