Current and Emerging Therapeutic Options for the Management of Rare Skeletal Diseases

Novel Therapeutic Targets for Fibrodysplasia Ossificans Progressiva: Emerging Strategies and Future Directions

Fibrodysplasia ossificans progressiva (FOP), also known as Stoneman syndrome, is a rare genetic disorder characterized by abnormal bone development caused by activating mutations of the ACVR1 gene. FOP affects both the developmental and postnatal stages, resulting in musculoskeletal abnormalities and heterotopic ossification. Current treatment options for FOP are limited, emphasizing the need for innovative therapeutic approaches. Challenges in the development of management criteria for FOP include difficulties in recruitment due to the rarity of FOP, disease variability, the absence of reliable biomarkers, and ethical considerations regarding placebo-controlled trials. This narrative review provides an overview of the disease and explores emerging strategies for FOP treatment. Gene therapy, particularly the CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) system, holds promise in treating FOP by specifically targeting the ACVR1 gene mutation. Another gene therapy approach being investigated is RNA interference, which aims to silence the mutant ACVR1 gene. Small molecule inhibitors targeting glycogen synthase kinase-3β and modulation of the bone morphogenetic protein signaling pathway are also being explored as potential therapies for FOP. Stem cell-based approaches, such as mesenchymal stem cells and induced pluripotent stem cells, show potential in tissue regeneration and inhibiting abnormal bone formation in FOP. Immunotherapy and nanoparticle delivery systems provide alternative avenues for FOP treatment.

Pharmacological options in the treatment of osteogenesis imperfecta: A comprehensive review of clinical and potential alternatives

Osteogenesis imperfecta (OI) is a genetically heterogeneous connective tissue disorder characterized by bone fragility and different extra-skeletal manifestations. The severity of these manifestations makes it possible to classify OI into different subtypes based on the main clinical features. This review aims to outline and describe the current pharmacological alternatives for treating OI, grounded on clinical and preclinical reports, such as antiresorptive agents, anabolic agents, growth hormone, and anti-TGFβ antibody, among other less used agents. The different options and their pharmacokinetic and pharmacodynamic properties will be reviewed and discussed, focusing on the variability of their response and the molecular mechanisms involved to attain the main clinical goals, which include decreasing fracture incidence, improving pain, and promoting growth, mobility, and functional independence.

A Comprehensive Review on Collagen Type I Development of Biomaterials for Tissue Engineering: From Biosynthesis to Bioscaffold

Collagen is the most abundant structural protein found in humans and mammals, particularly in the extracellular matrix (ECM). Its primary function is to hold the body together. The collagen superfamily of proteins includes over 20 types that have been identified. Yet, collagen type I is the major component in many tissues and can be extracted as a natural biomaterial for various medical and biological purposes. Collagen has multiple advantageous characteristics, including varied sources, biocompatibility, sustainability, low immunogenicity, porosity, and biodegradability. As such, collagen-type-I-based bioscaffolds have been widely used in tissue engineering. Biomaterials based on collagen type I can also be modified to improve their functions, such as by crosslinking to strengthen the mechanical property or adding biochemical factors to enhance their biological activity. This review discusses the complexities of collagen type I structure, biosynthesis, sources for collagen derivatives, methods of isolation and purification, physicochemical characteristics, and the current development of collagen-type-I-based scaffolds in tissue engineering applications. The advancement of additional novel tissue engineered bioproducts with refined techniques and continuous biomaterial augmentation is facilitated by understanding the conventional design and application of biomaterials based on collagen type I.

A Network Pharmacology Study: Reveal the Mechanisms of Palovarotene Against Heterotopic Ossification

Heterotopic ossification (HO) occurs when bone forms within non-ossifying tissues, such as in muscle. Palovarotene, an activator of retinoic acid receptor γ (RAR-γ), has been shown to inhibit the formation of ectopic bone in HO model mice, but its specific mechanism of action remains unclear. This study will explore the target and molecular mechanism of Palovarotene's action on HO by network pharmacology study. We collected the relevant targets of Palovarotene and HO from the database, obtained the potential targets of Palovarotene acting on HO through Venn analysis, and constructed the protein-protein interaction (PPI) network. Then, Gene Ontology (GO) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment Analysis and Module-based Network Analysis were performed for potential targets, and in addition, PPI Network Topology Analysis and Gene-Phenotype Correlation Analysis were performed. The results suggested that MAPK1, MDM2, and other targets as well as P53 signaling pathway and PI3K–Akt signaling pathway may be closely related to Palovarotene treatment of HO. We carried out verification experiments to confirm our finding, alkaline phosphatase and alizarin red staining in vitro and Micro-CT as well as hematoxylin-eosin staining in vivo were performed to verify treatment for HO of Palovarotene, reverse transcription polymerase chain reaction was also used to explore the transcription changes of MAPK1, MDM2, and osteogenic genes. This study systematically elucidated the possible mechanism of Palovarotene in the treatment of HO through network pharmacology study, revealing a new direction for the further application of Palovarotene in the treatment of HO.

Palovarotene: First Approval

Palovarotene (Sohonos™) is an orally bioavailable selective retinoic acid receptor (RAR)γ agonist being developed by Ipsen for the reduction of heterotopic ossification (HO) formation in patients with fibrodysplasia ossificans progressiva (FOP). By binding to RARγ, palovarotene inhibits bone morphogenetic protein and SMAD 1/5/8 signalling: interfering with these pathways prevents chondrogenesis and ultimately HO by permitting normal muscle tissue repair or regeneration to occur. Palovarotene received its first approval on 21 January 2022 to reduce the formation of HO in adults and children aged 8 years and above for females and 10 years and above for males with FOP in Canada. This article summarizes the milestones in the development of palovarotene leading to this first approval.

Vosoritide: First Approval

Vosoritide (VOXZOGO^®) is a modified recombinant human C-type natriuretic peptide (CNP) analogue, being developed by BioMarin Pharmaceutical for the treatment of achondroplasia. Achondroplasia is caused by a gain-of-function mutation in the fibroblast growth factor receptor 3 gene (FGFR3), which is a negative regulator of bone growth. Vosoritide acts to restore chondrogenesis through its binding to natriuretic peptide receptor B (NPR-B), resulting in the inhibition of downstream signalling pathways of the overactive FGFR3 gene. Vosoritide was approved in August 2021 in the EU for the treatment of achondroplasia in patients aged ≥ 2 years whose epiphyses are not closed; the diagnosis of achondroplasia should be confirmed by appropriate genetic testing. The drug is also under regulatory review in the USA for the treatment of achondroplasia and clinical development is underway in several countries. This article summarizes the milestones in the development of vosoritide leading to this first approval for achondroplasia in patients aged ≥ 2 years whose epiphyses are not closed.

Clinical trials in skeletal dysplasia: a paradigm for treating rare diseases

BACKGROUND

Genetic skeletal dysplasia conditions (GSDs) account for 5% of all birth defects. Until recently, targeted treatments were only available for select few conditions; 1 however, opportunities arising from developments in molecular diagnostic technologies are now leading to unparalleled therapeutic advances. This review explores current GSD clinical trials, their challenges and the hopes for the future.

SOURCES OF DATA

A systematic literature search of relevant original articles, reviews and meta-analyses restricted to English was conducted using PubMed up to February 2020 regarding emerging GSD therapies.

AREAS OF AGREEMENT

We discuss current clinical trials for in achondroplasia, osteopetrosis, osteogenesis imperfecta, hypophosphataemic rickets, hypophosphatasia and fibrous ossificans progressiva.

AREAS OF CONTROVERSY

We explore challenges in GSD drug development from clinician input, cost-effectiveness and evidenced-based practice.

GROWING POINTS

We explore opportunities brought by earlier diagnosis, its treatment impact and the challenges of gene editing.

AREAS TIMELY FOR DEVELOPING RESEARCH

We horizon scan for future clinical trials.

Rare skeletal disorders: a multidisciplinary postnatal approach to diagnosis and management

Skeletal disorders are inherited disorders with significant skeletal involvement and most of them are rare or extremely rare. Based on the clinical, radiological and genetic phenotype, the group of skeletal disorder comprises more than 450 different and highly heterogeneous disorders. In skeletal disorders rapid and precise diagnoses are urgently needed for patient care and are based on the combination of clinical, radiological and genetic analysis. Novel genetic techniques have revolutionized diagnostics and have a huge impact on counseling of patients and families. Disease-specific long-term management in a multidisciplinary healthcare team in highly specialized centers is recommended to optimize care for these patients. Here we describe a multidisciplinary postnatal approach for the diagnosis and management of patients and families with rare skeletal disorders at the Vienna Bone and Growth Center. We discuss the value of a multidisciplinary diagnostic and management approach in the postnatal setting and provide a diagnostic flowchart for rare skeletal disorders.

A bedridden young lady with hypophosphatemic rickets treated with denosumab: a case report

Background

Hypophosphatemic rickets is associated with delayed walking, bone deformities, growth failure and physical dysfunction that can limit daily activities. Treatment consists of phosphate salts and calcitriol. We report a case that received denosumab with marked improvement in her condition.

Case presentation

A 24-year-old Yemeni female with hypophosphatemic rickets presented to an endocrinologist with severe weakness and severe pain in the extremities, she had been bedridden for the last 4 years. Bone density showed severe osteoporosis (T score of hip was − 5.0 and Z score of hip was − 5.0, T score of the spine was − 6.0 and Z score of the spine was − 6.1) so the patient was started on denosumab in addition to calcitriol and after 7months she was feeling stronger and felt she could stand assisted and was walking with assistance within 9 months and after 1.5 years of treatment she was walking unassisted.

Conclusion

Denosumab is an effective treatment for osteoporosis, we used it in our patient in addition to calcitriol because she had severe osteoporosis due to long standing hypophosphatemic rickets that had not been treated properly, the patient improved markedly and regained the ability to walk again after being bedridden for 4 years. It may be a drug to consider in such cases although further studies need to be done to confirm this.

An Overview of the NF-kB mechanism of pathophysiology in rheumatoid arthritis, investigation of the NF-kB ligand RANKL and related nutritional interventions

Nuclear Factor Kappa-Β (NF-kB) is recognized as one of the main inflammatory pathways in the Autoimmune Disease (AD) Rheumatoid Arthritis (RA), which exhibits high levels of inflammatory cytokines such as IL-1, TNFa and IL-6 linked to bone erosion and disease progression. NF-kB is also the most studied pathophysiological mechanism in RA, however, over the last few decades, a more recently discovered Receptor Activator of Nuclear Factor Kappa-Β Ligand (RANKL), also linked to NF-kB activation and bone erosion, has been the topic of interest for research in the area of AD management. As the non-discriminative long term suppression of the NF-kB pathway by pharmacological agents in the management of RA has been linked with a number of side effects and with the discovery of the RANKL mechanism, which may present a more targeted approach to the management of the AD, there has been renewed interest in research on the potential impact of nutritional interventions influencing the NF-kB pathway, RANKL as well as RA disease outcomes. Existing research highlights the potential utility of nutrients such as Omega 3 and Vitamin D, which may lower NF-kB activation in RA. There is, however, a gap in the knowledge of the effects of nutritional interventions on pathophysiological mechanisms contributing to RA and a more robust systematic analysis of whether nutrients or specific vitamins can have an effect on the NF-kB and RANKL main drivers of pathology in RA. Findings from this study suggest the potential of Vitamin D supplementation in lowering the levels of RANKL and related markers/cytokines such as Th17 cell levels, OPG/RANKL ratio and CXCL10 pathway, which may present as a viable nutrition intervention for the management of RA. The methodology of this review involved a Systematic Search of the Literature with a Critical Appraisal of papers. It incorporated three tranche searches of 1. review, 2. animal/in vitro and 3. intervention peer reviewed research published in the last 10 years, resulting in a total of 119 papers. Results provide an overview of the NF-kB pathway, a detailed mechanistic examination of the Receptor Activator of Nuclear Factor Kappa-Β Ligand (RANKL) which is linked to bone erosion, and finally a review of nutritional interventions relating to this mechanism of pathophysiology. The accepted papers were critically appraised using SIGN50 for human studies and the ARRIVE guidelines for animal studies; the narrative was and the extracted information coded into key themes.

Osteogenesis imperfecta in a male holstein calf associated with a possible oligogenic origin

Background: Neuromusculoskeletal anomalies generally in combination with severe clinical symptoms, comprise a heterogeneous group of fairly common and mostly fatal disorders in man and animals. Osteogenesis imperfecta (OI), also known as brittle bone disease, causes bone fragility and deformity. Prominent extra-skeletal accessory manifestations of OI comprise blue/gray sclerae, hearing impairment, lung abnormalities and hypercalciuria. Cases of OI in cattle have been reported. However, no causative mutations have been identified in cattle so far.Aim: To report a possible oligogenic origin identified in a calf from clinically healthy parents suffering from OI.Materials and Methods: A neonatal embryo transfer male Holstein calf developing multiple fractures with bone tissue showing marked osteopenia was used for whole genome re-sequencing as well as its parents. In addition, 2,612 randomly chosen healthy Holstein cattle were genotyped as well as controls.Results: Sixteen candidate genes with potential protein-altering variants were selected revealing non-synonymous variants only within IFITM5 and CRTAP genes. However, in-depth gene analysis did not result in the identification of a single causative mutation in the OI calf.Conclusion: The analysis of the OI case revealed a possible oligogenic origin of the disease attributable to additive effects of three candidate genes, i.e., ABCA13, QRFPR, and IFTIM5.Clinical relevance: Most OI cases in humans and domestic animals reported so far are caused by distinct dominant or recessive monogenic mutations, therefore a potential oligogenic additive genetic effect is a novel finding. Furthermore, the case presented here demonstrates that cross-species genetic analyses might not always be straightforward.

Proceedings of the 2019 Santa Fe Bone Symposium: New Concepts in the Care of Osteoporosis and Rare Bone Diseases

The 20th annual Santa Fe Bone Symposium was held August 9-10, 2019, in Santa Fe, New Mexico, USA. This is an annual meeting devoted to clinical applications of recent advances in skeletal research that impact the care of patients with osteoporosis, metabolic bone diseases, and inherited bone diseases. Participants included practicing and academic physicians, fellows, advanced practice providers, fracture liaison service (FLS) coordinators, clinical researchers, and bone density technologists. The symposium consisted of lectures, case presentations, and panel discussions, with an emphasis on learning through interaction of all attendees. Topics included new approaches in the use of anabolic agents for the treatment osteoporosis, a review of important events in skeletal health over the past year, new and emerging treatments for rare bone diseases, the use of genetic testing for bone diseases in clinical practice, medication-associated causes of osteoporosis, new concepts in the use of estrogen therapy for osteoporosis, new Official Positions of the International Society for Clinical Densitometry, skeletal consequences of bariatric surgery, and update on the progress and potential of Bone Health TeleECHO, a virtual community of practice using videoconferencing technology to link healthcare professionals for advancing the care of osteoporosis worldwide. Sessions on rare bone diseases were developed in collaboration with the Rare Bone Disease Alliance. Symposium premeetings included an FLS workshop by the National Osteoporosis Foundation and others devoted to the use of new therapeutic agents for the care of osteoporosis and related disorders.

High Fidelity of Mouse Models Mimicking Human Genetic Skeletal Disorders

The 2019 International Skeletal Dysplasia Society nosology update lists 441 genes for which mutations result in rare human skeletal disorders. These genes code for enzymes (33%), scaffolding proteins (18%), signal transduction proteins (16%), transcription factors (14%), cilia proteins (8%), extracellular matrix proteins (5%), and membrane transporters (4%). Skeletal disorders include aggrecanopathies, channelopathies, ciliopathies, cohesinopathies, laminopathies, linkeropathies, lysosomal storage diseases, protein-folding and RNA splicing defects, and ribosomopathies. With the goal of evaluating the ability of mouse models to mimic these human genetic skeletal disorders, a PubMed literature search identified 260 genes for which mutant mice were examined for skeletal phenotypes. These mouse models included spontaneous and ENU-induced mutants, global and conditional gene knockouts, and transgenic mice with gene over-expression or specific base-pair substitutions. The human X-linked gene ARSE and small nuclear RNA U4ATAC, a component of the minor spliceosome, do not have mouse homologs. Mouse skeletal phenotypes mimicking human skeletal disorders were observed in 249 of the 260 genes (96%) for which comparisons are possible. A supplemental table in spreadsheet format provides PubMed weblinks to representative publications of mutant mouse skeletal phenotypes. Mutations in 11 mouse genes (Ccn6, Cyp2r1, Flna, Galns, Gna13, Lemd3, Manba, Mnx1, Nsd1, Plod1, Smarcal1) do not result in similar skeletal phenotypes observed with mutations of the homologous human genes. These discrepancies can result from failure of mouse models to mimic the exact human gene mutations. There are no obvious commonalities among these 11 genes. Body BMD and/or radiologic dysmorphology phenotypes were successfully identified for 28 genes by the International Mouse Phenotyping Consortium (IMPC). Forward genetics using ENU mouse mutagenesis successfully identified 37 nosology gene phenotypes. Since many human genetic disorders involve hypomorphic, gain-of-function, dominant-negative and intronic mutations, future studies will undoubtedly utilize CRISPR/Cas9 technology to examine transgenic mice having genes modified to exactly mimic variant human sequences. Mutant mice will increasingly be employed for drug development studies designed to treat human genetic skeletal disorders.

SIGNIFICANCE

Great progress is being made identifying mutant genes responsible for human rare genetic skeletal disorders and mouse models for genes affecting bone mass, architecture, mineralization and strength. This review organizes data for 441 human genetic bone disorders with regard to heredity, gene function, molecular pathways, and fidelity of relevant mouse models to mimic the human skeletal disorders. PubMed weblinks to citations of 249 successful mouse models are provided.