A nonsynonymous TNFRSF11A variation increases NFκB activity and the severity of Paget's disease

Hereditary Metabolic Bone Diseases: A Review of Pathogenesis, Diagnosis and Management

Hereditary metabolic bone diseases are characterized by genetic abnormalities in skeletal homeostasis and encompass one of the most diverse groups among rare diseases. In this review, we examine 25 selected hereditary metabolic bone diseases and recognized genetic variations of 78 genes that represent each of the three groups, including sclerosing bone disorders, disorders of defective bone mineralization and disorder of bone matrix and cartilage formation. We also review pathophysiology, manifestation and treatment for each disease. Advances in molecular genetics and basic sciences has led to accurate genetic diagnosis and novel effective therapeutic strategies for some diseases. For other diseases, the genetic basis and pathophysiology remain unclear. Further researches are therefore crucial to innovate ways to overcome diagnostic challenges and develop effective treatment options for these orphan diseases.

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.

Genomic Medicine in Periodontal Disease: Old Issue, New Insights

Genetic variability is the main cause of phenotypic variation. Some variants may be associated with several diseases and can be used as risk biomarkers, identifying animals with higher susceptibility to develop the pathology. Genomic medicine uses this genetic information for risk calculation, clinical diagnosis and prognosis, allowing the implementation of more effective preventive strategies and/or personalized therapies. Periodontal disease (PD) is the inflammation of the periodontium induced mainly by bacterial plaque and is the leading cause of tooth loss. Microbial factors are responsible for the PD initiation; however, several studies support the genetic influence on the PD progression. The main purpose of the present publication is to highlight the main steps involved in the genomic medicine applied to veterinary patients, describing the flowchart from the characterization of the genetic variants to the identification of potential associations with specific clinical data. After investigating which genes might potentially be implicated in canine PD, the RANK gene, involved in the regulation of osteoclastogenesis, was selected to illustrate this approach. A case-control study was performed using DNA samples from a population of 90 dogs – 50 being healthy and 40 with PD. This analysis allowed for the discovery of four new intronic variations that were banked in GenBank (g.85A>G, g.151G>T, g.268A>G and g.492T>C). The results of this study are not intended to be applied exclusively to PD. On the contrary, this genetic information is intended to be used by other researchers as a foundation for the development of multiple applications in the veterinary clinical field.

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.

Genomic and Genetic Approaches to Deciphering Acute Respiratory Distress Syndrome Risk and Mortality

Significance: Acute respiratory distress syndrome (ARDS) is a severe, highly heterogeneous critical illness with staggering mortality that is influenced by environmental factors, such as mechanical ventilation, and genetic factors. Significant unmet needs in ARDS are addressing the paucity of validated predictive biomarkers for ARDS risk and susceptibility that hamper the conduct of successful clinical trials in ARDS and the complete absence of novel disease-modifying therapeutic strategies. Recent Advances: The current ARDS definition relies on clinical characteristics that fail to capture the diversity of disease pathology, severity, and mortality risk. We undertook a comprehensive survey of the available ARDS literature to identify genes and genetic variants (candidate gene and limited genome-wide association study approaches) implicated in susceptibility to developing ARDS in hopes of uncovering novel biomarkers for ARDS risk and mortality and potentially novel therapeutic targets in ARDS. We further attempted to address the well-known health disparities that exist in susceptibility to and mortality from ARDS. Critical Issues: Bioinformatic analyses identified 201 ARDS candidate genes with pathway analysis indicating a strong predominance in key evolutionarily conserved inflammatory pathways, including reactive oxygen species, innate immunity-related inflammation, and endothelial vascular signaling pathways. Future Directions: Future studies employing a system biology approach that combines clinical characteristics, genomics, transcriptomics, and proteomics may allow for a better definition of biologically relevant pathways and genotype-phenotype connections and result in improved strategies for the sub-phenotyping of diverse ARDS patients via molecular signatures. These efforts should facilitate the potential for successful clinical trials in ARDS and yield a better fundamental understanding of ARDS pathobiology.

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.

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.

Effects of receptor activator nuclear factor κB gene polymorphisms on the susceptibility to knee osteoarthritis: A case-control study

The present study aimed to explore genetic association of receptor activator nuclear factor κB (RANK) polymorphisms with individual susceptibility to knee osteoarthritis (OA) in different Kellgren-Lawrence (KL) grades.This case-control study included 138 knee OA patients and 145 healthy individuals. RANK rs1805034 and rs8086340 polymorphisms were genotyped through polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The effects of RANK polymorphisms on knee OA risk were analyzed via χ test or Fisher exact test, and the results were expressed using odds ratios (ORs) with corresponding 95% confidence intervals (CIs).The C allele of rs1805034 polymorphism had significantly higher frequency in knee OA patients than in controls (P = .044), indicating that this allele could increase the risk of knee OA (OR = 1.424, 95% CI = 1.010-2.008). Besides, the CC genotype and C allele of the rs1805034 polymorphism were significantly associated with elevated risk of knee OA in moderate grade (CC vs TT: P = .018, OR = 3.071, 95% CI = 1.187-7.941; C vs T: P = .012, OR = 1.787, 95% CI = 1.131-2.823). However, rs8086340 polymorphism had no significant association with knee OA riskThe C allele of RANK rs1805034 polymorphism is closely correlated with increased risk of knee OA, especially for moderate grade.

Human Genetics of Sclerosing Bone Disorders

PURPOSE OF REVIEW

The group of sclerosing bone disorders encompasses a variety of disorders all marked by increased bone mass. In this review, we give an overview of the genetic causes of this heterogeneous group of disorders and briefly touch upon the value of these findings for the development of novel therapeutic agents.

RECENT FINDINGS

Advances in the next-generation sequencing technologies are accelerating the molecular dissection of the pathogenic mechanisms underlying skeletal dysplasias. Throughout the years, the genetic cause of these disorders has been extensively studied which resulted in the identification of a variety of disease-causing genes and pathways that are involved in bone formation by osteoblasts, bone resorption by osteoclasts, or both processes. Due to this rapidly increasing knowledge, the insights into the regulatory mechanisms of bone metabolism are continuously improving resulting in the identification of novel therapeutic targets for disorders with reduced bone mass and increased bone fragility.

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.

Osteoimmunology: The Conceptual Framework Unifying the Immune and Skeletal Systems

The immune and skeletal systems share a variety of molecules, including cytokines, chemokines, hormones, receptors, and transcription factors. Bone cells interact with immune cells under physiological and pathological conditions. Osteoimmunology was created as a new interdisciplinary field in large part to highlight the shared molecules and reciprocal interactions between the two systems in both heath and disease. Receptor activator of NF-κB ligand (RANKL) plays an essential role not only in the development of immune organs and bones, but also in autoimmune diseases affecting bone, thus effectively comprising the molecule that links the two systems. Here we review the function, gene regulation, and signal transduction of osteoimmune molecules, including RANKL, in the context of osteoclastogenesis as well as multiple other regulatory functions. Osteoimmunology has become indispensable for understanding the pathogenesis of a number of diseases such as rheumatoid arthritis (RA). We review the various osteoimmune pathologies, including the bone destruction in RA, in which pathogenic helper T cell subsets [such as IL-17-expressing helper T (Th17) cells] induce bone erosion through aberrant RANKL expression. We also focus on cellular interactions and the identification of the communication factors in the bone marrow, discussing the contribution of bone cells to the maintenance and regulation of hematopoietic stem and progenitors cells. Thus the time has come for a basic reappraisal of the framework for understanding both the immune and bone systems. The concept of a unified osteoimmune system will be absolutely indispensable for basic and translational approaches to diseases related to bone and/or the immune system.

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 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.

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.

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.

Exclusion of TNFRSF11B as Candidate Gene for Otosclerosis in Campania Population

The etiology of otosclerosis is unknown. The etiopathogenesis of otosclerosis seems similar to that occurring in Paget's disease of bone, for which mutations or polymorphisms in several genes have been identified. Among these, TNFRSF11B gene encoding the osteoprotegerin is produced at high levels in the normal inner ear and at low level in active otosclerotic stapes footplates. The aim of this work was to verify the presence of a correlation between the rs2073618 (N3K) polymorphism in the TNFRSF11B gene and otosclerosis. Mutational screening in the TNFRSF11B gene was performed by direct sequencing. SNPs analysis was performed by PCR and by specific restriction enzyme assay with HpaI. The significance of the association was analyzed by statistical specific software. No causative mutation has been identified but the data suggested a strong correlation between the rs2073618 (N3K) polymorphism and otosclerosis. This correlation, however, has been excluded in a case-control study. This study excluded the association between the N3K polymorphism and otosclerosis in Campania region population.

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.

Distinct disease phenotypes linked to different combinations of GAA mutations in a large late-onset GSDII sibship

Background

Glycogenosis type II (GSDII or Pompe disease) is an autosomal recessive disease, often characterized by a progressive accumulation of glycogen within lysosomes caused by a deficiency of α-1,4-glucosidase (GAA; acid maltase), a key enzyme of the glycogen degradation pathway. To date, more than 326 different mutations in the GAA gene have been identified in patients with GSDII but the course of the disease is difficult to be predicted on the basis of molecular genetic changes. Studies on large informative families are advisable to better define how genetics and non genetics factors like exercise and diet may influence the clinical phenotype.

Methods and results

In this study, we report on clinical, instrumental, and pathological features as well as on molecular analysis of a family with 10 out of 13 siblings affected by late-onset Pompe disease. Three mutations segregated in the family, two of which are novel mutations. Siblings showing a more severe phenotype were compound heterozygous for c.118C > T [p.R40X] and c.2647-7G > A [p.N882fs] on GAA, whereas, two patients showing a mild phenotype were compound heterozygous c.2647-7G > A [p.N882fs] and c.2276G > C [p.G759A] mutations. Quantitative expression analysis showed, in the patients carrying p.R40X/ p.N882fs, a significant (p 0.01) correlation between the levels of expression of the mutated allele and the age at onset of the disease.

Conclusions

As far as we know, this is the largest informative family with late-onset Pompe disease described in the literature showing a peculiar complex set of mutations of GAA gene that may partially elucidate the clinical heterogeneity of this family.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

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.

Digenic mutational inheritance of the integrin alpha 7 and the myosin heavy chain 7B genes causes congenital myopathy with left ventricular non-compact cardiomyopathy

Background

We report an Italian family in which the proband showed a severe phenotype characterized by the association of congenital fiber type disproportion (CFTD) with a left ventricular non-compaction cardiomyopathy (LVNC). This study was focused on the identification of the responsible gene/s.

Methods and results

Using the whole-exome sequencing approach, we identified the proband homozygous missense mutations in two genes, the myosin heavy chain 7B (MYH7B) and the integrin alpha 7 (ITGA7). Both genes are expressed in heart and muscle tissues, and both mutations were predicted to be deleterious and were not found in the healthy population.

The R890C mutation in the MYH7B gene segregated with the LVNC phenotype in the examined family. It was also found in one unrelated patient affected by LVNC, confirming a causative role in cardiomyopathy.

The E882K mutation in the ITGA7 gene, a key component of the basal lamina of muscle fibers, was found only in the proband, suggesting a role in CFTD.

Conclusions

This study identifies two novel disease genes. Mutation in MYH7B causes a classical LVNC phenotype, whereas mutation in ITGA7 causes CFTD. Both phenotypes represent alterations of skeletal and cardiac muscle maturation and are usually not severe. The severe phenotype of the proband is most likely due to a synergic effect of these two mutations.

This study provides new insights into the genetics underlying Mendelian traits and demonstrates a role for digenic inheritance in complex phenotypes.

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.

New insights into osteoclastogenic signaling mechanisms

Bone is continuously renewed through a dynamic balance between bone resorption and formation. This process is the fundamental basis for the maintenance of normal bone mass and architecture. Osteoclasts play a crucial role in both physiological and pathological bone resorption, and receptor activator of nuclear factor-κB ligand (RANKL) is the key cytokine that induces osteoclastogenesis. Here we summarize the recent advances in the understanding of osteoclastogenic signaling by focusing on the investigation of RANKL signaling and RANKL-expressing cells in the context of osteoimmunology. The context afforded by osteoimmunology will provide a scientific basis for future therapeutic approaches to diseases related to the skeletal and immune systems.

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.