Clinical and animal research findings in pycnodysostosis and gene mutations of cathepsin K from 1996 to 2011

Craniofacial dysmorphism of osteogenesis imperfecta mouse and effect of cathepsin K knockout: Preliminary craniometry observations

OBJECTIVES

In addition to bone fragility, patients with osteogenesis imperfecta (OI) type III have typical craniofacial abnormalities, such as a triangular face and maxillary micrognathism. However, in the osteogenesis imperfecta mouse (oim), a validated model of OI type III, few descriptions exist of craniofacial phenotype. Treatment of OI mostly consists of bisphosphonate administration. Cathepsin K inhibition has been tested as a promising therapeutic approach for osteoporosis and positive results were observed in long bones of cathepsin K knocked out oim (oim/CatK-/-). This craniometry study aimed to highlight the craniofacial characteristics of oim and Cathepsin K KO mouse.

MATERIALS AND METHODS

We analyzed the craniofacial skeleton of 51 mice distributed in 4 genotype groups: Wt (control), oim, CatK-/-, oim/CatK-/-. The mice were euthanized at 13 weeks and their heads were analyzed using densitometric (pQCT), X-ray cephalometric, and histomorphometric methods.

RESULTS

The craniofacial skeleton of the oim mouse is frailer than the Wt one, with a reduced thickness and mineral density of the cranial vault and mandibular ramus. Different cephalometric data attest a dysmorphism similar to the one observed in humans with OI type III. Those abnormalities were not improved in the oim/CatK-/- group.

CONCLUSION

These results suggest that oim mouse could serve as a complete model of the human OI type III, including the craniofacial skeleton. They also suggest that invalidation of cathepsin K has no impact on the craniofacial abnormalities of the oim model.

Genetic background of walking ability and its relationship with leg defects, mortality, and performance traits in turkeys (Meleagris gallopavo)

This study aimed to explore the genetic basis of walking ability and potentially related performance traits in turkey purebred populations. Phenotypic, pedigree, and genomic datasets from 2 turkey lines hatched between 2010 and 2023 were included in the study. Walking ability data, defined based on a scoring system ranging from 1 (worst) to 6 (best), were collected on 192,019 animals of a female line and 235,461 animals of a male line. Genomic information was obtained for 46,427 turkeys (22,302 from a female line and 24,125 from a male line) using a 65K single nucleotide polymorphism (SNP) panel. Variance components and heritability for walking ability were estimated. Furthermore, genetic and phenotypic correlations among walking ability, mortality and disorders, and performance traits were calculated. A genome-wide association study (GWAS) was also conducted to identify SNPs associated with walking ability. Walking ability is moderately heritable (0.23 ± 0.01) in both turkey lines. The genetic correlations between walking ability and the other evaluated traits ranged from -0.02 to -0.78, with leg defects exhibiting the strongest negative correlation with walking ability. In the female line, 31 SNPs were associated with walking ability and overlapped with 116 genes. These positional genes are linked to 6 gene ontology (GO) terms. Notably, genes such as CSRP2, DDX1, RHBDL1, SEZ6L, and CTSK are involved in growth, development, locomotion, and bone disorders. GO terms, including fibronectin binding (GO:0001968), peptide cross-linking (GO:0018149), and catabolic process (GO:0009057), are directly linked with mobility. In the male line, 66 markers associated with walking ability were identified and overlapped with 281 genes. These genes are linked to 12 GO terms. Genes such as RB1CC1, TNNI1, MSTN, FN1, SIK3, PADI2, ERBB4, B3GNT2, and BACE1 are associated with cell growth, myostatin development, and disorders. GO terms in the male line are predominantly related to lipid metabolism. In conclusion, walking ability is moderately heritable in both populations. Furthermore, walking ability can be enhanced through targeted genetic selection, emphasizing its relevance to both animal welfare and productivity.

Heparan sulfate selectively inhibits the collagenase activity of cathepsin K

Cathepsin K (CtsK) is a cysteine protease with potent collagenase activity. CtsK is highly expressed by bone-resorbing osteoclasts and plays an essential role in resorption of bone matrix. Although CtsK is known to bind heparan sulfate (HS), the structural details of the interaction, and how HS regulates the biological functions of CtsK, remains largely unknown. In this report, we discovered that HS is a multifaceted regulator of the structure and function of CtsK. Structurally, HS forms a highly stable complex with CtsK and induces its dimerization. Co-crystal structures of CtsK with bound HS oligosaccharides reveal the location of the HS binding site and suggest how HS may support dimerization. Functionally, HS plays a dual role in regulating the enzymatic activity of CtsK. While it preserves the peptidase activity of CtsK by stabilizing its active conformation, it inhibits the collagenase activity of CtsK in a sulfation level-dependent manner. These opposing effects can be explained by our finding that the HS binding site is remote from the active site, which allows HS to specifically inhibit the collagenase activity without affecting the peptidase activity. At last, we show that structurally defined HS oligosaccharides effectively block osteoclast resorption of bone in vitro without inhibiting osteoclast differentiation, which suggests that HS-based oligosaccharide might be explored as a new class of selective CtsK inhibitor for many diseases involving exaggerated bone resorption.

Pathological Fractures in Patients Affected by Pycnodysostosis: A Case Series

Background/Objectives: Pycnodysostosis is a rare genetic disorder causing skeletal dysplasia. It is determined by a gene mutation leading to cathepsin K deficiency and predisposes a patient to osteosclerosis, resulting in increased bone fragility. The altered bone quality typical of this disease is responsible for an increased risk of fractures. The purpose of our study was to evaluate the orthopedic manifestations and potential pitfalls in the surgical treatments of pathological fractures in a series of patients treated in our institution who were affected by pycnodysostosis. Methods: We retrospectively evaluated clinical and radiographic characteristics of five patients with pycnodysostosis treated for pathological fractures at our hospital in the past 5 years. Results: Two male and three female patients were included in this study. Four patients had a family history of pycnodysostosis. All the patients were of short stature, but only two underwent growth hormone treatment. All the patients experienced fractures, mostly in their lower limbs and occurring as a result of low-energy trauma. Most of the patients experienced either consolidation delay or nonunion. Conclusions: The orthopedic management of fractures in patients with pycnodysostosis poses an ongoing challenge for orthopedic surgeons. The fact that the bone is simultaneously sclerotic and brittle makes any orthopedic surgical treatment challenging and at a high risk of nonunion in any case.

Pathological mandibular fracture complicated by osteonecrosis in an adult patient with pycnodysostosis: clinical report and review of the literature

Pycnodysostosis is an ultra-rare osteosclerotic skeletal disorder characterized by short stature, susceptibly to fractures, acroosteolysis of the distal phalanges, and craniofacial features (frontal bossing, prominent nose, obtuse mandibular angle, micrognathia). Dental abnormalities (delayed eruption of teeth, hypodontia, malocclusion, dental crowding, persistence of deciduous teeth, enamel hypoplasia, and increased caries) are also frequent; due to bone metabolism alteration, the patients have an increased risk for jaw osteomyelitis, especially after tooth extraction or mandible fracture. Other complications are obstructive sleep apnea, endocrine alterations and cytopenia. Pycnodysostosis is caused by biallelic loss of function variants in CTSK gene, coding the lysosomal protease cathepsin K. CTSK is involved in the degradation of bone matrix proteins, such as type I and type II collagen. In pycnodysostosis, this degradation is decreased, leading to increased bone density and bone fragility with pathological fractures and poor healing. We present a clinical report of a female adult patient with typical pycnodysostosis phenotype. At the age of 52 years, she had a pathological spontaneous fracture of the right mandible complicated by osteonecrosis, treated with load bearing osteosynthesis. The direct sequencing of CTSK gene revealed the presence of the pathogenic homozygous variant c.746T>A, (p.Ile249Asn), that confirmed the diagnosis of pycnodysostosis. We also review the literature case series published to date, that suggest to always consider the diagnosis of pycnodysostosis in case of osteosclerosis, even in the absence of brachydactyly or short stature. This report details the natural history of the disease in this patient, from childhood to adulthood, and highlights the importance of a quality of life assessment. In addition, we describe a case of mandibular osteonecrosis and spontaneous fracture in pycnodysostosis, drawing attention on the maxillofacial complications in these patients and on the importance of a personalized follow-up.

Heparan sulfate selectively inhibits the collagenase activity of cathepsin K

Cathepsin K (CtsK) is a cysteine protease with potent collagenase activity. CtsK is highly expressed by bone-resorbing osteoclasts and plays an essential role in bone remodeling. Although CtsK is known to bind heparan sulfate (HS), the structural details of the interaction, and how HS ultimately regulates the biological functions of CtsK, remains largely unknown. In this report, we determined that CtsK preferably binds to larger HS oligosaccharides, such as dodecasaccharides (12mer), and that the12mer can induce monomeric CtsK to form a stable dimer in solution. Interestingly, while HS has no effect on the peptidase activity of CtsK, it greatly inhibits the collagenase activity of CtsK in a manner dependent on sulfation level. By forming a complex with CtsK, HS was able to preserve the full peptidase activity of CtsK for prolonged periods, likely by stabilizing its active conformation. Crystal structures of Ctsk with a bound 12mer, alone and in the presence of the endogenous inhibitor cystatin-C reveal the location of HS binding is remote from the active site. Mutagenesis based on these complex structures identified 6 basic residues of Ctsk that play essential roles in mediating HS-binding. At last, we show that HS 12mers can effectively block osteoclast resorption of bone in vitro. Combined, we have shown that HS can function as a multifaceted regulator of CtsK and that HS-based oligosaccharide might be explored as a new class of selective CtsK inhibitor in many diseases that involve exaggerated bone resorption.

Elucidating the role of RBM5 in osteoclastogenesis: a novel potential therapeutic target for osteoporosis

Osteoporosis is a prevalent bone disease with multigene involved, and the molecular mechanisms of its pathogenesis are not entirely understood. This study aims to identify novel key genes involved in osteoporosis to discover potential pharmacological targets. We analyzed three microarray datasets and identified four differentially expressed genes. The LASSO model indicated that RNA-binding motif protein 5 (RBM5) is associated with osteoporosis and is a potential drug target. We conducted the Spearman correlation analysis and found 52 genes that were significantly related to RBM5. Enrichment analysis showed that these genes were primarily involved in RNA splicing and osteoclast differentiation pathways. By using lentivirus-based shRNA, we successfully knocked down RBM5 expression in RAW264.7 cell line, which showed that RBM5 knockdown significantly impaired their differentiation potential to mature osteoclasts and significantly inhibited bone-resorbing activity. RT-qPCR analyses revealed the expression of osteoclastogenesis marker genes was downregulated along with RBM5 expression. These findings suggest that RBM5 plays a crucial role in the pathogenesis of osteoporosis and provides a new potential pharmacological target.

Analysis of cuproptosis-related genes in Ulcerative colitis and immunological characterization based on machine learning

Cuproptosis is a novel form of cell death, mediated by protein lipid acylation and highly associated with mitochondrial metabolism, which is regulated in the cell. Ulcerative colitis (UC) is a chronic inflammatory bowel disease that recurs frequently, and its incidence is increasing worldwide every year. Currently, a growing number of studies have shown that cuproptosis-related genes (CRGs) play a crucial role in the development and progression of a variety of tumors. However, the regulatory role of CRGs in UC has not been fully elucidated. Firstly, we identified differentially expressed genes in UC, Likewise, CRGs expression profiles and immunological profiles were evaluated. Using 75 UC samples, we typed UC based on the expression profiles of CRGs, followed by correlative immune cell infiltration analysis. Using the weighted gene co-expression network analysis (WGCNA) methodology, the cluster's differentially expressed genes (DEGs) were produced. Then, the performances of extreme gradient boosting models (XGB), support vector machine models (SVM), random forest models (RF), and generalized linear models (GLM) were constructed and predicted. Finally, the effectiveness of the best machine learning model was evaluated using five external datasets, receiver operating characteristic curve (ROC), the area under the curve of ROC (AUC), a calibration curve, a nomogram, and a decision curve analysis (DCA). A total of 13 CRGs were identified as significantly different in UC and control samples. Two subtypes were identified in UC based on CRGs expression profiles. Immune cell infiltration analysis of subtypes showed significant differences between immune cells of different subtypes. WGCNA results showed a total of 8 modules with significant differences between subtypes, with the turquoise module being the most specific. The machine learning results showed satisfactory performance of the XGB model (AUC = 0.981). Finally, the construction of the final 5-gene-based XGB model, validated by the calibration curve, nomogram, decision curve analysis, and five external datasets (GSE11223: AUC = 0.987; GSE38713: AUC = 0.815; GSE53306: AUC = 0.946; GSE94648: AUC = 0.809; GSE87466: AUC = 0.981), also proved to predict subtypes of UC with accuracy. Our research presents a trustworthy model that can predict the likelihood of developing UC and methodically outlines the complex relationship between CRGs and UC.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

Cathepsin K mutation-A subtle clinical presentation

Introduction

Pyknodysostosis is an uncommon inherited disorder associated with consanguinity; often presenting with sclerotic bone disease, short stature, dysmorphic features and recurrent fragility fractures at an early age.

Case history

A 34-year-old lady was evaluated for the cause of recurrent fragility fractures. She was born of a third-degree consanguineous marriage and had a twin brother who was short statured. The index patient had a height of 141 cm, dysmorphic features including frontoparietal bossing, blue sclera with short stubby fingers and toes. Radiological evaluation revealed diffuse osteosclerosis with acro-osteolysis exclusively in the toes, apart from mid-facial hypoplasia, lack of pneumatisation of the paranasal sinuses, dental abnormalities and scoliosis. Dual-energy X-ray absorptiometry revealed increased bone mineral density. Based on the clinical features, the patient was tested for Cathepsin K gene variants using Next Generation Sequencing, and was found to be positive for a novel homozygous c.224T>C, p. Met75Thr likely pathogenic missense variant.

Discussion

This patient presented at a later age than expected with recurrent fragility fractures and the diagnosis was not suspected till adulthood, owing to the subtle clinical features. Confirmation with genetic testing helped in establishing the diagnosis.

Conclusion

Pyknodysostosis, although uncommon, is one of the differential diagnoses for diffuse osteosclerosis presenting with recurrent fragility fractures. Next generation sequencing in an appropriate setting may confirm the diagnosis.

CTSK variant implicated in suspected pyknodysostosis in a domestic cat

Case summary

A 9-month-old entire male domestic longhair cat presented with a history of pathological fractures, chronic musculoskeletal pain and poor growth. Multiple facial and skeletal abnormalities were identified on physical examination and advanced imaging (CT and radiographs). A variant in CTSK was identified in the affected cat following whole-exome sequencing (WES). The cat was managed symptomatically with diet, environmental modifications and analgesia.

Relevance and novel information

This is the first report of a cat with a similar clinical presentation and genetic variant to the hereditary human genetic disorder pyknodysostosis. In this case, WES was performed, which often facilitates the diagnosis of various hereditary disorders (ie, a conceptual framework for practicing feline genomic medicine). Despite the severe skeletal and appendicular abnormalities described, the cat was alive more than 2 years after its initial presentation.

Clinical and genetic characterization of three Russian patients with pycnodysostosis due to pathogenic variants in the CTSK gene

BACKGROUND

Pycnodysostosis (PD, OMIM # 265800) is a rare variant of skeletal dysplasia with an autosomal recessive type of inheritance, characterized by a combination of specific features such as disproportionate nanism, generalized osteosclerosis, and distinct craniofacial dysmorphism. Radiographic features include acro-osteolysis of the distal phalanges in association with sclerosing bone lesions with multiple fractures. The polymorphism of the clinical manifestations of pycnodysostosis and low prevalence of the disorder lead to the difficulties with early.

METHODS

The following tests were used for diagnostics: genealogical analysis, clinical examination, neurological examination according to the standard method with an assessment of the psychoemotional sphere, radiological analysis, searching for pathogenic variants in the CTSK gene by the automated Sanger sequencing.

RESULTS

We describe first clinical and genetic characteristics of three Russian patients with pycnodysostosis from unrelated families. Two patients have a novel homozygous nucleotide substitution c.746T>A (p. Ile249Asn), and one has a previously described homozygous pathogenic variant c.746T>C (p.Ile249Thr) in the CTSK gene. In all three cases, a transition or transversion was found at nucleotide position 746 in exon 6 of the CTSK gene, leading to two different amino acid substitutions in the polypeptide chain. The obtained results may indicate the presence of a major pathogenic variant in the CTSK gene, leading to the typical manifestation of the disease.

CONCLUSION

The data presented in the study enlarge the clinical, radiological, and mutational spectrum of pycnodysostosis. Typical clinical manifestations and the small size of the CTSK gene make the automated Sanger sequencing the optimal method for diagnosis of pycnodysostosis.

Identification of Periosteal Osteogenic Progenitors in Jawbone

Unlike long bones, jawbone development is mainly accomplished by intramembranous ossification resulting from the differentiation of periosteal progenitor cells. However, the spatiotemporal ontogeny of periosteal progenitor cells during jawbone development and repair remains elusive. In this study, we mapped the transcriptional landscape of the human jawbone periosteum at single-cell resolution and identified a cathepsin K (Ctsk)⁺ periosteal subset. Lineage tracing analysis indicated that Ctsk-Cre-labeled periosteal cells could make contributions to jawbone development. However, different from the periosteal-specific location of Ctsk⁺ cells in long bone, we also identified Ctsk⁺ stromal cells in jawbone marrow and implied the heterogeneity of jawbone Ctsk⁺ hierarchy. In further analysis of the periosteal progenitor cell subset of heterogeneous Ctsk⁺ hierarchy, we identified a unique Ctsk⁺Ly6a⁺ subset of cells. The additional marker Ly6a helped to further confine the progenitor subset to the jawbone periosteum and was nearly undetectable in the bone marrow. Defects in the jawbone could activate the migration and osteogenic differentiation of Ctsk⁺Ly6a⁺ cells. Local ablation of Ctsk⁺ cells by diphtheria reduced the number of Ctsk⁺Ly6a⁺ cells and delayed the repair of the bone defect. Taken together, we identify a novel periosteal osteogenic progenitor subset that is active in jawbone osteogenesis and healing.

Pycnodysostosis- a rare disorder with distinctive craniofacial dysmorphia. A case report

Pycnodysostosis is a rare autosomal recessive condition caused by the mutation of CTSK gene. CTSK regulates the activity of Cathepsin K which is responsible for osteoclast-mediated bone resorption. This mutation causes the bones to become dense, sclerotic, brittle, and thus, prone to fracture. Affected individuals have normal cognitive development and life expectancy, however, the quality of life depends on the early diagnosis of the condition. The patient presents with striking clinical (short stature, brachydactyly) and radiological (frontal and parieto-occipital bossing, open sutures, and fontanelles, acro-osteolysis of terminal phalanges) features making the diagnosis clinico-radiographic. In atypical or mild cases with overlapping features, gene mapping is advocated. A plethora of dental anomalies and characteristic craniofacial dysmorphia puts the dentist in a position to diagnose such a case.

Genetic and Molecular Evaluation: Reporting Three Novel Mutations and Creating Awareness of Pycnodysostosis Disease

Pycnodysostosis is a rare autosomal recessive disorder with characteristic diagnostic manifestations. This study aims to phenotype and provide molecular characterization of Egyptian patients, with emphasis on identifying unusual phenotypes and raising awareness about pycnodysostosis with different presentations to avoid a mis- or under-diagnosis and consequent mismanagement. We report on 22 Egyptian pycnodysostosis patients, including 9 new participants, all descending from consanguineous families and their ages ranging from 6 to 15 years. In addition, prenatal diagnosis was performed in one family with affected siblings. They all presented with short stature, except for one patient who presented with pancytopenia as her primary complaint. Moreover, 41.2% of patients had sleep apnea, 14% presented with craniosynostosis, and 44.4% had failure of tooth development. Molecular analysis via direct exome sequencing of the cathepsin K gene revealed three novel mutations ((NM_000396.3) c.761_763delCCT, c.864_865delAA, and c.509G>T) as well as two previously reported mutations among nine new cases. The following is our conclusion: This study expands the molecular spectrum of pycnodysostosis by identifying three novel mutations and adds to the clinical and orodental aspects of the disease. The link between the CTSK gene mutations and the failure of tooth development has not been established, and further studies could help to improve our understanding of the molecular pathology.

Pycnodysostosis: a case report and literature review concerning oral and maxillofacial complications and their management

OBJECTIVE

There is a lack of knowledge regarding pycnodysostosis (PYCD), which is commonly misdiagnosed as other, similar malformations. This study aims to report a patient with PYCD and conjointly present a comprehensive literature review regarding oral complications after oral surgery procedures.

STUDY DESIGN

This study aims to report a noteworthy case of a 40-year-old woman with PYCD who suffered from a midface defect after iatrogenic fracture during extraction of the upper right molars. A comprehensive electronic search was carried out in January 2020 for detection and analysis of the most commonly encountered dentoalveolar PYCD-related complications. The study was granted an exemption from the local institutional review board.

RESULTS

The electronic search yielded 35 articles reporting 41 PYCD cases with 62 various reported dentoalveolar complications. The survey reported a prevalence of osteomyelitis (n = 39) followed by pathologic fracture (n = 17), iatrogenic fracture (n = 5), and oronasal communication (n = 1).

CONCLUSIONS

This study advocates handling patients with PYCD with care through the use of extensive clinical and radiographic examinations, giving priority to any conservative treatment modalities, atraumatic surgical procedures, prophylactic antibiotic prescriptions, and a regular follow-up schedule to tackle any anticipated complications.

Phenotypic and genotypic spectrum of CTSK variants in a cohort of twenty-five Indian patients with pycnodysostosis

BACKGROUND

Pycnodysostosis is an autosomal recessive skeletal dysplasia with easily recognizable clinical features and marked molecular heterogeneity. In this study, we explored the clinical and molecular spectrum of 25 Indian patients with pycnodysostosis from 20 families.

METHODS

Clinical information was collected on a predesigned clinical proforma. Sanger method was employed to sequence all the exons and exon/intron boundaries of the CTSK gene. Novel variants were systematically assessed by prediction softwares and protein modelling. The pathogenicity of variant was established based on ACMG-AMP criteria. An attempt was also made to establish a genotype-phenotype correlation and devise a diagnostic scoring system based on clinical and radiological findings.

RESULTS

Consanguinity and positive family history were present in 65% (13/20) and 45% (9/20) of the families respectively. Short stature and fractures were the predominant presenting complaints and was evident in 96% (24/25) and 32% (8/25) of affected individuals respectively. Gestalt facial phenotype and acro-osteolysis were present in 76% (19/25) and 82.6% (19/23) of the individuals respectively. Hepatosplenomegaly was present in 15% (3/20) of the individuals with one of them having severe anaemia. Causative sequence variations were identified in all of them. A total of 19 variants were identified from 20 families amongst which 10 were novel. Homozygous variants were identified in 90% (18/20) families. Amongst the novel variants, there was a considerable proportion (40%) of frameshift variants (4/10). No significant genotype-phenotype correlation was noted. Scoring based on clinical and radiological findings led to the proposal that a minimum of 2 scores in each category is required in addition to high bone density to diagnose pycnodysostosis with certainty.

CONCLUSION

This study delineated the genotypic and phenotypic characterisation of Indian patients with pycnodysostosis with identification of 10 novel variants. We also attempted to develop a clinically useful diagnostic scoring system which requires further validation.

Cathepsin K maintains the compartment of bone marrow T lymphocytes in vivo

In this study, we investigated the influence of the loss of cathepsin K (Ctsk) gene on the hematopoietic system in vitro and in vivo. We found that cultures with lineage^- SCA1⁺ KIT⁺ (LSK) cells on Ctsk deficient stromal cells display reduced colony formation and proliferation, with increased differentiation, giving rise to repopulating cells with reduced ability to repopulate the donor LSKs and T cell compartments in the bone marrow (BM). Subsequent in vivo experiments showed impairment of lymphocyte numbers, but, gross effects on early hematopoiesis or myelopoiesis were not found. Most consistently in in vivo experimental settings, we found a significant reduction of (donor) T cell numbers in the BM. Lymphocyte deregulation is also found in transplantation experiments, which revealed that Ctsk is required for optimal regeneration of small populations of T cells, particularly in the BM, but also of thymic B cells. Interestingly, cell nonautonomous Ctsk regulates both B and T cell numbers, but T cell numbers in the BM require an additional autonomous Ctsk-dependent process. Thus, we show that Ctsk is required for the maintenance of hematopoietic stem cells in vitro, but in vivo, Ctsk deficiency most strongly affects lymphocyte homeostasis, particularly of T cells in the BM.

Increased Bone Resorption during Lactation in Pycnodysostosis

Pycnodysostosis, a rare autosomal recessive skeletal dysplasia, is caused by a deficiency of cathepsin K. Patients have impaired bone resorption in the presence of normal or increased numbers of multinucleated, but dysfunctional, osteoclasts. Cathepsin K degrades collagen type I and generates N-telopeptide (NTX) and the C-telopeptide (CTX) that can be quantified. Levels of these telopeptides are increased in lactating women and are associated with increased bone resorption. Nothing is known about the consequences of cathepsin K deficiency in lactating women. Here we present for the first time normalized blood and CTX measurements in a patient with pycnodysostosis, exclusively related to the lactation period. In vitro studies using osteoclasts derived from blood monocytes during lactation and after weaning further show consistent bone resorption before and after lactation. Increased expression of cathepsins L and S in osteoclasts derived from the lactating patient suggests that other proteinases could compensate for the lack of cathepsin K during the lactation period of pycnodysostosis patients.

Osteomyelitis of the jaws in patients with pycnodysostosis: a systematic review

Introduction

Pycnodysostosis is a rare autosomal recessive syndrome that provides the abnormal bone metabolism that increases the susceptibility of patients to develop osteomyelitis.

Objective

This systematic review was conducted to analyze the risk factors associated with the development of complications in the jaws (fractures and osteomyelitis), as well as their clinical-pathological characteristics and therapeutic approaches in patients with pycnodysostosis.

Methods

Searches were performed in the PubMed, Web of Science, Scopus, Lilacs, and Cochrane databases. Case reports or case series that met the eligibility criteria according to the PRISMA statement were included. The full texts of 31 articles were retrieved. Twenty of these articles published between 1969 and 2018 were selected, which described 26 cases of osteomyelitis in patients with pycnodysostosis.

Results

The mean age of the patients was 37.84 years; the male-to-female was 1.36:1. The mandible was the most affected site (76.9%). Tooth extraction was the main risk factor for osteomyelitis (61.5%), followed by infection (26.8%) and mandibular fracture (23.0%). Antibiotic therapy alone or combined with some surgical procedure was the treatment used in most cases (80.7%).

Conclusion

The findings of this review showed that patients with pycnodysostosis are more likely to develop osteomyelitis of the jaws after surgical procedures, especially tooth extraction which remains the main risk factor for its establishment. In addition, prophylactic antibiotic-therapy in the pre- and postoperative periods may prevent the development of osteomyelitis in pycnodysostosis.

Clinical and genetic evaluation of Danish patients with pycnodysostosis

BACKGROUND

Pycnodysostosis is a rare autosomal recessive osteosclerotic skeletal dysplasia caused by variants in the cathepsin K gene (CTSK). Clinical features include short stature, bone fragility, characteristic facial features and acro-osteolysis of the distal phalanges. Usually, patients suffer from multiple bone fractures. The purpose of this study was to describe the Danish population of pycnodysostosis patients with respect to genotype, phenotype and the prevalence of complications. We collected medical history, performed clinical examination, collected blood- and urine samples, performed dual-energy x-ray absorptiometry scan (DXA) and high-resolution peripheral quantitative computed tomography scan (HRpQCT) and obtained clinical photos. Information about complications, bone mineral density and bone markers in the blood were collected and analysed.

RESULTS

Ten patients with a median age of 32 years ranging from five to 51 years participated. The pycnodysostosis phenotype varied with respect to the number of bone fractures and degree of complications. DXA and HRpQCT showed high bone mineral density. A tendency of growth hormone treatment escalating growth and increasing final height was seen. A marker of bone resorption measured in blood was within normal range in nine patients and elevated in one patient. A novel pathogenic variant in CSTK causing pycnodysostosis was detected in two related patients. Moreover information about the patients' own health perception was reported. An example being they rated their mental health to be good despite multiple bone fractures.

CONCLUSION

This study provides information about genotypes and phenotypes in a Danish pycnodysostosis population. It reports new data about the complications such as bone fractures and it elucidates the levels of bone turnover markers as well as the density of the bones in one of the biggest cohort of pycnodysostosis patients ever published. An individualised approach to treatment in this patient group is necessary as the phenotype including complications varies between patients. Additional studies are needed to further understand genotype-phenotype correlations.

PYKNODYSOSTOSIS (OSTEOPETROSIS ACRO-OSTEOLYTICA)

Objective

To present a case of pyknodysostosis (PKND), a rare genetic cause of skeletal dysplasia that often goes undiagnosed even in patients with classic features.

Methods

We report a case of PKND that went undiagnosed over many years despite classic features. We performed physical examination, imaging studies, and genetic testing on the patient.

Results

A 21-year-old female presented to endocrinology to establish care. On evaluation, she was noted to have disproportionate short stature and a past medical history notable for bilateral blindness due to optic atrophy secondary to bone enlargement and thickening of the optic nerve canal before age 7 years. She also had a history of foot fractures occurring with ambulation. Her family history was significant for consanguineous parents and relatives with similar clinical features. Physical examination revealed a short, 128-cm tall female with open anterior and mastoid fontanels, mild frontal bossing and micrognathia, evidence of double rows of teeth, and digits of varied length in both hands and feet. Plain radiographs demonstrated diffuse sclerosis and marked cortical thickening of the pelvis, femurs, metacarpals, proximal phalanges, and metatarsals as well as decreased phalangeal length and acro-osteolysis of the hands and feet. Dual energy X-ray absorptiometry demonstrated increased bone mineral density (z scores +2.5 lumbar spine, +3.7 femoral neck, +4.5 total hip). Genetic testing revealed a exon 5-homozygous mutation in the cathepsin K (CTSK) gene consistent with PKND.

Conclusion

Patients with PKND come to medical attention for a variety of reasons but often go undiagnosed even when presenting with classic features due to the rarity of the condition and the overlap with other skeletal dysplasias.

Osteoblast-Osteoclast Communication and Bone Homeostasis

Bone remodeling is tightly regulated by a cross-talk between bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoblasts and osteoclasts communicate with each other to regulate cellular behavior, survival and differentiation through direct cell-to-cell contact or through secretory proteins. A direct interaction between osteoblasts and osteoclasts allows bidirectional transduction of activation signals through EFNB2-EPHB4, FASL-FAS or SEMA3A-NRP1, regulating differentiation and survival of osteoblasts or osteoclasts. Alternatively, osteoblasts produce a range of different secretory molecules, including M-CSF, RANKL/OPG, WNT5A, and WNT16, that promote or suppress osteoclast differentiation and development. Osteoclasts also influence osteoblast formation and differentiation through secretion of soluble factors, including S1P, SEMA4D, CTHRC1 and C3. Here we review the current knowledge regarding membrane bound- and soluble factors governing cross-talk between osteoblasts and osteoclasts.

A First-Case Report of Pycnodysostosis in an Omani Boy

Here we reported on the genetic findings of a 9-year-old Omani boy with a rare inherited bone disorder. The patient's clinical features include dysmorphic facial features, short stature, and skeletal abnormalities. Exome sequence of the patient's deoxyribonucleic acid revealed a variant in the cathepsin K gene, which was confirmed by Sanger sequencing. These findings established the diagnosis of pycnodysostosis (PKND). To the best of the authors' knowledge, this case is the first case to be reported in the Gulf Cooperative Region of the novel PKND with molecular confirmation.

Alternative Method for Full Oral Rehabilitation in Patients with Pycnodysostosis Syndrome: A Case Report

Pycnodysostosis (PYCD) is a rare autosomal recessive skeletal dysplasia arising from a change in the production of the cathepsin K enzyme and it is also known as Maroteaux-Lamy Syndrome. The main changes in the buccal and maxillofacial region are modifications of the facial bones (leading to the loss of the mandibular angle due to micrognathia), deep palate, premature and/or delayed tooth eruption, hypopneumatization of the maxillary sinuses, chin hypoplasia, hypercementosis, enamel hypoplasia, hyperdontia, incomplete dentin calcification, root hypoplasia, pulp chamber obliteration, and increased free functional space. This paper aims to report a case of a patient with PYCD, in which are highlighted the oral manifestations of this syndrome and present an option of oral rehabilitative treatment through a removable overdenture made on natural tooth of the patient. The technique of dental coating through overdenture is a simple, viable and conservative alternative for oral rehabilitation of patients with large maxillomandibular discrepancies, as in cases of pycnodysostosis, especially in the presence of increased free space - characteristic of patients with this syndrome. The result was quite satisfactory both aesthetically and functionally and provided a better life quality for the patient.

Whole-exome sequencing identified a novel variant in an Iranian patient affected by pycnodysostosis

BACKGROUND

Whole-exome sequencing (WES) has emerged as a successful diagnostic tool in molecular genetics laboratories worldwide. In this study, we aimed to find the potential genetic cause of skeletal disease, a heterogeneous disease, revealing the obvious short stature phenotype. In an Iranian family, we used solo-WES in a suspected patient to decipher the potential genetic cause(s).

METHODS

A comprehensive clinical and genotyping examination was applied to suspect the disease of the patient. The solo clinical WES was exploited, and the derived data were filtered according to the standard pipelines. In order to validate the WES finding, the region harboring the candidate variant in the CTSK gene was amplified from genomic DNA and sequenced directly by Sanger sequencing.

RESULTS

Sequence analysis revealed a rare novel nonsense variant, p.(Trp320*); c.905G>A, in the CTSK gene (NM_000396.3). In silico analysis shed light on the contribution of the variant to the pathogenicity of pycnodysostosis. This variant was confirmed by Sanger sequencing and further clinical examinations of the patient confirmed the disease.

CONCLUSION

The present study shows a rare variant of the CTSK gene, which inherited as autosomal recessive, in an Iranian male patient with pycnodysostosis. Taken together, the novel nonsense CTSK variant meets the criteria of being likely pathogenic according to the American College of Medical Genetics and Genomics-the Association for Molecular Pathology (ACMG-AMP) variant interpretation guidelines.

A rare case of pycnodysostosis: Technical difficulties in managing long bone fractures

Pycnodysostosis is a rare inherited disorder of autosomal recessive trait causing cathepsin K deficiency, leading to failure of osteoclastic activity. Brittle and sclerotic bones which are prone for frequent fractures is the characteristic feature of this congenital disorder. Despite good healing potential there are few issues in the management of fractures in pycnodysostosis patients. In this article we report the challenges faced in managing a fracture of the femoral shaft in a 12 year old girl with pycnodysostosis. For early rehabilitation and to avoid deformity and shortening, we opted for surgical fixation over conservative treatment. Narrow medullary canal ruled out the option for titanium elastic nail fixation. 4.5mm dynamic compression plate was used to fix the fracture. Sclerotic bone made drilling extremely difficult. Deformed femoral shaft allowed plating over the anterior surface only, instead of the routine lateral surface plating. Postoperative fracture healing was satisfactory. Implant was removed after 18 months.

Multiple Fractures and Impaired Bone Fracture Healing in a Patient with Pycnodysostosis and Hypophosphatasia

Pycnodysostosis (PYCD) is a rare recessive inherited skeletal disease, characterized by short stature, brittle bones, and recurrent fractures, caused by variants in the Cathepsin K encoding gene that leads to impaired osteoclast-mediated bone resorption. Hypophosphatasia (HPP) is a dominant or recessive inherited condition representing a heterogeneous phenotype with dental symptoms, recurrent fractures, and musculoskeletal problems. The disease results from mutation(s) in the tissue non-specific alkaline phosphate encoding gene with reduced activity of alkaline phosphatase and secondarily defective mineralization of bone and teeth. Here, we present the first report of a patient with the coexistence of PYCD and HPP. This patient presented typical clinical findings of PYCD, including short stature, maxillary hypoplasia, and sleep apnoea. However, the burden of disease was caused by over 30 fractures, whereupon most showed delayed healing and non-union. Biochemical analysis revealed suppressed bone resorption and low bone formation capacity. We suggest that the coexistence of impaired bone resorption and mineralization may explain the severe bone phenotype with poor fracture healing.

Sleep-disordered breathing in children with pycnodysostosis

Upper airway obstruction is a common feature in pycnodysostosis and may cause obstructive sleep apnea (OSA). The aim of our study was to analyze sleep-disordered breathing and respiratory management in children with pycnodysostosis. A retrospective review of the clinical charts and sleep studies of 10 consecutive children (three girls and seven boys) with pycnodysostosis seen over a time period of 10 years was performed. Six patients had severe OSA and/or nocturnal hypoventilation and were started on continuous positive airway pressure (CPAP) as a first treatment at a median age of 3.4 ± 2.6 years, because of the lack of indication of any surgical treatment. Three patients could be weaned after several years from CPAP after spontaneous improvement (two patients) or multiple upper airway surgeries (one patient). Three patients had upper airway surgery prior to their first sleep study with two patients still needing CPAP during their follow-up. Only one patient never developed OSA. Patients with pycnodysostosis are at a high risk of severe OSA, underlying the importance of a systematic screening for sleep-disordered breathing. Multidisciplinary care is mandatory because of the multilevel airway obstruction. CPAP is very effective and well accepted for treating OSA.

Pycnodysostosis: Natural history and management guidelines from 27 French cases and a literature review

Pycnodysostosis is a lysosomal autosomal recessive skeletal dysplasia characterized by osteosclerosis, short stature, acro-osteolysis, facial features and an increased risk of fractures. The clinical heterogeneity of the disease and its rarity make it difficult to provide patients an accurate prognosis, as well as appropriate care and follow-up. French physicians from the OSCAR network have been asked to fill out questionnaires collecting molecular and clinical data for 27 patients issued from 17 unrelated families. All patients showed short stature (mean = -3.5 SD) which was more severe in females (P = .006). The mean fracture rate was moderate (0.21 per year), with four fractures in total average. About 75% underwent at least one surgery, with an average number of 2.1 interventions per patient. About 50% required non-invasive assisted ventilation due to sleep apnea (67%). About 29% showed psychomotor difficulties and 33% needed a school assistant or adapted schooling. No patient had any psychological evaluation or follow-up. Molecular data were available for 14 families. Growth hormone administration was efficient on linear growth in 40% of cases. We propose several axis of management, such as systematic cerebral MRI for Chiari malformation screening at diagnosis and regular psychological follow-up.

Disturbed remodeling and delayed fracture healing in pediatric pycnodysostosis patients

Pycnodysostosis is an autosomal recessive disease caused by a gene mutation leading cathepsin K deficiency. Pathological fractures of the long bones are common, but guidelines on fracture treatment in these patients are still lacking. We have treated 5 fractures in 2 pediatric pycnodysostosis patients. We hypothesize that pycnodysostosis patients have an incomplete remodeling process in fracture healing because of cathepsin K deficiency. Therefore, to minimize the role of endochondral bone formation (indirect) after a fracture, it seems prudent to strive for direct bone healing (intramembranous) instead of indirect bone healing. Open reduction with internal fixation should be the goal.

A Novel Variant c.847T>C in CTSK Gene Leading to Pycnodysostosis: A Case Report

Pycnodysostosis is a rare genetic disorder with a prevalence of 1.7 per million births; it usually presents with short stature, osteosclerosis, increased bone fragility, and acro-osteolysis of distal phalanges. There are less than 200 cases reported worldwide and very few from South-East Asia. We present a case of pycnodysostosis who presented with short stature, acro-osteolysis of distal phalanges, and on genetic testing revealing a variant c.847T>C, p.Y283H, in exon 7 of the CTSK in homozygous state: not reported till date to the best of our knowledge.

AP-1 and Mitf interact with NFATc1 to stimulate cathepsin K promoter activity in osteoclast precursors

Cathepsin K (CTSK) is a secreted protease that plays an essential role in osteoclastic bone resorption and osteoporotic bone loss. We have previously shown that activator protein 1 (AP-1) stimulates CTSK promoter activity and that proximal nuclear factor of activated T cells cytoplasmic 1 (NFATc1)-binding sites play a major role in the stimulation of CTSK gene expression by receptor activator of NFκB ligand (RANKL). In the present study, we have extended these observations and further dissected the effects of transcription factors involved in the regulation of CTSK gene expression. Our aim was to investigate the cooperative interplay among transcription factors AP-1, microphthalmia-associated transcription factor (Mitf), and NFATc1, and the consequent regulatory effects on CTSK transcription. Experiments were carried out in RAW 264.7 cells, which can be readily differentiated to osteoclasts upon RANKL stimulation. Our data show that AP-1, Mitf, and NFATc1 are capable of independently stimulating CTSK promoter activity. A combination of any two factors further enhances CTSK promoter activity, with the combination of AP-1 (c-fos/c-jun) and NFATc1 inducing the largest increase. We further identify a synergistic effect when all three factors cooperate intimately at the proximal promoter region, yielding maximal transcriptional upregulation of the CTSK promoter. RANKL induces temporal localization of AP-1 and NFATc1 to the CTSK promoter. These results suggest that the interaction of multiple transcription factors mediate a maximal response to RANKL-induced CTSK gene expression.

Not all pycnodysostosis-related mutants of human cathepsin K are inactive - crystal structure and biochemical studies of an active mutant I249T

Human cathepsin K (CTSK) is a collagenolytic lysosomal cysteine protease that plays an important role in bone turnover. Mutation in CTSK gene is associated with loss of collagenolytic activity of CTSK leading to an autosomal recessive bone disorder called pycnodysostosis. Although a number of pycnodysostotic missense mutations have been reported, underlying mechanism of the disease is not clear. In this study, we investigated in vitro six recombinant pycnodysostosis-related mutants of human CTSK (G79E, I249T, G243E, G303E, G319C and Q187P). While all the mutants, like wild-type, show similar high levels of expression in Escherichia coli, four of them (G79E, G303E, G319C and Q187P) are inactive, unstable and spontaneously degrade during purification process. In contrast, proteolytic/collagenolytic activity, zymogen activation kinetics and stability of G243E and I249T mutants are nominally affected. Crystal structure of I249T at 1.92 Å resolution shows that the mutation in R-domain causes conformational changes of a surface loop in the L-domain although the catalytic cleft remains unaltered. Molecular simulation, normal mode analysis and fluorescence lifetime measurement eliminated the possibility that the change in L-domain surface loop orientation is a crystallization artefact. CD-based thermal melting profile indicates that stability of I249T is significantly higher than wild-type. Our studies first time reports that pycnodysostosis-related mutations do not always lead to complete loss of general proteolytic activity or specific collagenolytic activity of CTSK. The first crystal structure of a pycnodysostotic mutant (I249T) provides critical information that may pave new avenues towards understanding the disease at molecular level. DATABASE: The atomic co-ordinates and structure factors for I249T mutant of human CTSK (codes 5Z5O) have been deposited in the Protein Data Bank (http://wwpdb.org/).

Genetic study of eight Egyptian patients with pycnodysostosis: identification of novel CTSK mutations and founder effect

This is the first Egyptian study with detailed clinical and orodental evaluation of eight patients with pycnodysostosis and identification of four mutations in CTSK gene with two novel ones and a founder effect.

INTRODUCTION

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia due to mutations in the CTSK gene encoding for cathepsin K, a lysosomal cysteine protease.

METHODS

We report on the clinical, orodental, radiological, and molecular findings of eight patients, from seven unrelated Egyptian families with pycnodysostosis.

RESULTS

All patients were offspring of consanguineous parents and presented with the typical clinical picture of the disorder including short stature, delayed closure of fontanels, hypoplastic premaxilla, obtuse mandibular angle, and drum stick terminal phalanges with dysplastic nails. Their radiological findings showed increased bone density, acro-osteolysis, and open cranial sutures. Mutational analysis of CTSK gene revealed four distinct homozygous missense mutations including two novel ones, c.164A>C (p. K55T) and c.433G>A (p.V145M). The c.164A>C (p. K55T) mutation was recurrent in three unrelated patients who also shared similar haplotype, suggesting a founder effect.

CONCLUSION

Our findings expand the mutational spectrum of CTSK gene and emphasize the importance of full clinical examination of all body systems including thorough orodental evaluation in patients with pycnodysostosis.

Bone health in patients with inborn errors of metabolism

Inborn errors of metabolism encompass a wide spectrum of disorders, frequently affecting bone. The most important metabolic disorders that primarily influence calcium or phosphate balance, resulting in skeletal pathology, are hypophosphatemic rickets and hypophosphatasia. Conditions involving bone marrow or affecting skeletal growth and development are mainly the lysosomal storage disorders, in particular the mucopolysaccharidoses. In these disorders skeletal abnormalities are often the presenting symptom and early recognition and intervention improves outcome in many of these diseases. Many disorders of intermediary metabolism may impact bone health as well, resulting in higher frequencies of osteopenia and osteoporosis. In these conditions factors contributing to the reduced bone mineralization can be the disorder itself, the strict dietary treatment, reduced physical activity or sunlight exposure and/or early ovarian failure. Awareness of these primary or secondary bone problems amongst physicians treating patients with inborn errors of metabolism is of importance for optimization bone health and recognition of skeletal complications.

Genetics of Osteopetrosis

PURPOSE OF REVIEW

The term osteopetrosis refers to a group of rare skeletal diseases sharing the hallmark of a generalized increase in bone density owing to a defect in bone resorption. Osteopetrosis is clinically and genetically heterogeneous, and a precise molecular classification is relevant for prognosis and treatment. Here, we review recent data on the pathogenesis of this disorder.

RECENT FINDINGS

Novel mutations in known genes as well as defects in new genes have been recently reported, further expanding the spectrum of molecular defects leading to osteopetrosis. Exploitation of next-generation sequencing tools is ever spreading, facilitating differential diagnosis. Some complex phenotypes in which osteopetrosis is accompanied by additional clinical features have received a molecular classification, also involving new genes. Moreover, novel types of mutations have been recognized, which for their nature or genomic location are at high risk being neglected. Yet, the causative mutation is unknown in some patients, indicating that the genetics of osteopetrosis still deserves intense research efforts.

Genetic Risk Factors for Atypical Femoral Fractures (AFFs): A Systematic Review

Atypical femoral fractures (AFFs) are uncommon and have been associated particularly with long‐term antiresorptive therapy, including bisphosphonates. Although the pathogenesis of AFFs is unknown, their identification in bisphosphonate‐naïve individuals and in monogenetic bone disorders has led to the hypothesis that genetic factors predispose to AFF. Our aim was to review and summarize the evidence for genetic factors in individuals with AFF. We conducted structured literature searches and hand‐searching of conference abstracts/reference lists for key words relating to AFF and identified 2566 citations. Two individuals independently reviewed citations for (i) cases of AFF in monogenetic bone diseases and (ii) genetic studies in individuals with AFF. AFFs were reported in 23 individuals with the following 7 monogenetic bone disorders (gene): osteogenesis imperfecta (COL1A1/COL1A2), pycnodysostosis (CTSK), hypophosphatasia (ALPL), X‐linked osteoporosis (PLS3), osteopetrosis, X‐linked hypophosphatemia (PHEX), and osteoporosis pseudoglioma syndrome (LRP5). In 8 cases (35%), the monogenetic bone disorder was uncovered after the AFF occurred. Cases of bisphosphonate‐naïve AFF were reported in pycnodysostosis, hypophosphatasia, osteopetrosis, X‐linked hypophosphatemia, and osteoporosis pseudoglioma syndrome. A pilot study in 13 AFF patients and 268 controls identified a greater number of rare variants in AFF cases using exon array analysis. A whole‐exome sequencing study in 3 sisters with AFFs showed, among 37 shared genetic variants, a p.Asp188Tyr mutation in the GGPS1 gene in the mevalonate pathway, critical to osteoclast function, which is also inhibited by bisphosphonates. Two studies completed targeted ALPL gene sequencing, an ALPL heterozygous mutation was found in 1 case of a cohort of 11 AFFs, whereas the second study comprising 10 AFF cases did not find mutations in ALPL. Targeted sequencing of ALPL, COL1A1, COL1A2, and SOX9 genes in 5 cases of AFF identified a variant in COL1A2 in 1 case. These findings suggest a genetic susceptibility for AFFs. A large multicenter collaborative study of well‐phenotyped AFF cases and controls is needed to understand the role of genetics in this uncommon condition. © 2017 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Pycnodysostosis with novel gene mutation and sporadic medullary thyroid carcinoma: A case report

RATIONALE

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia caused by a mutation in the cathepsin K encoded by cathepsin K gene (CTSK). Medullary thyroid carcinoma (MTC) is also a relatively rare type of primary thyroid carcinoma.

PATIENT CONCERNS

A 31-year-old woman presenting a short stature and a palpable nodule in the front of her neck that had gradually increased in size during the last 2 years was referred to our department. She has experienced multiple fractures at lower limbs in the last 2 decades.

DIAGNOSES

The patient's clinical examination revealed short stature, underweight, a prominent forehead, stubby fingers, and a fixed nodule in the right thyroid lobe. Intraoral examination revealed multiple clinically malposed and missing teeth, as well as chronic periodontitis with a narrow and grooved palate. Radiographic examination revealed typical widely separated cranial sutures and an open anterior/posterior fontanel with an obtuse gonial angle, acroosteolysis, and osteosclerosis with narrowed medullary cavities. Ultrasonography of the thyroid gland showed a marked hypoechoic solid nodule in the right lobe in which tumor cell clusters were confirmed by ultrasound-guided fine needle aspiration biopsy and was suspected to be MTC. Laboratory tests revealed dramatically elevated serum calcitonin >2000 pg/L (reference range: 0-5 pg/L) and carcinoembryonic antigen (CEA) 134.37 ng/mL (reference range: 0-5 ng/mL). Genotypic screening revealed compound heterozygous mutations in the CTSK gene (c.158delA, P.Asn53Thr/c.C830T, P.Ala277Val) but no mutation associated with the familial forms of MTC.

INTERVENTIONS

The patient underwent a total thyroidectomy with right-sided functional neck dissection.

OUTCOMES

CEA and serum calcitonin decreased significantly postthyroidectomy, and no further fracture has been reported by the patient so far.

LESSONS

The present study is the first to report a rare case of the coexistence of pycnodysostosis with a compound CTSK gene mutation and sporadic MTC. Radiological techniques and gene analysis play key roles in the definitive diagnosis.

Clinical and radiographic features of pycnodysostosis: A case report

Pycnodysostosis is a rare disorder that was first described in 1962; however, it was only in 1996 that the defective gene was discovered, which led to a better understanding of this disease. This study reports and discuss a case of pycnodysostosis. In addition, a search of articles published in PubMed-Medline was performed. The case was a 13-year-old girl who was referred to a private clinic for dental treatment. Clinical examination showed midface hypoplasia, prominent cheeks, a high nasal bridge, beaked nose, spoon-shaped fingers, frontal bossing, open fontanelles and dental alterations, findings compatible with pycnodysostosis. Patients with this disease also suffer from fractures because of bone hardness with almost no elasticity, a fact that requires special care particularly in the case of children and adolescents. The diagnosis of pycnodysostosis is made based on clinical and radiographic findings. Clinicians should be aware of this disorder to provide adequate dental treatment.

Key words:Pycnodysostosis, developmental bone disease, imaging diagnosis.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

Pycnodysostosis: Novel Variants in CTSK and Occurrence of Giant Cell Tumor

Pycnodysostosis is an autosomal recessive skeletal dysplasia caused by pathogenic variants in the cathepsin K ( CTSK ) gene. We report seven patients from four unrelated families with this condition in whom we have identified three novel pathogenic variants, c.120 + 1G > T in intron 2, c.399 + 1G > A in intron 4, and c.148T > G (p.W50G) in exon 2, and a known variant, c.568C > T (p.Q190*) in exon 5 of CTSK . We present the clinical, radiographic, and molecular findings of all individuals with molecularly proven pycnodysostosis from the present cohort. We also report the occurrence of giant cell tumor in the skull of a patient with this condition.

A case report of pycnodysostosis with atypical femur fracture diagnosed by next-generation sequencing of candidate genes

RATIONALE

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia characterized by short stature, craniofacial dysmorphism, acro-osteolysis, osteosclerosis, and brittle bone with poor healing. Pycnodysostosis results from the deficient activity of cathepsin K, a lysosomal cysteine protease that is encoded by CTSK.

PATIENT CONCERNS

We report a Korean adult patient with pycnodysostosis and atypical femur fracture whose diagnosis was confirmed by next-generation sequencing (NGS) of candidate genes. A 41-year-old female patient was presented with a left femur fracture after falling down. Underlying sclerotic bone disease was suspected as a radiographic skeletal survey showed thickened cortical bones, and the total body bone density was increased (T score was 5.3, and Z score was 4.9).

DIAGNOSES

We performed candidate gene sequencing of various sclerotic bone diseases for the differential molecular diagnosis of underlying sclerosing bone disease. Two heterozygous variants of CTSK were detected. One was a frameshift variant in exon 5, c.426delT (p.Phe142Leufs*19), which was previously reported, and the other was a novel missense variant in exon 6, c.755G>A (p.Ser252Asn). Sanger sequencing of CTSK confirmed the 2 heterozygous variants and thus the patient was diagnosed with pycnodysostosis.

INTERVENTIONS

The patient had emergency surgery for subtrochantic femoral fracture.

OUTCOMES

After 4 months of surgery, the patient had almost a full range of hip and knee movements and radiographs show the substantial bridging callus across the fracture.

LESSONS

Candidate gene sequencing could be a useful diagnostic tool for the genetically heterogeneous skeletal dysplasia group, especially in cases with a mild or atypical clinical phenotype.

Distribution of Cathepsin K in Late Stage of Tooth Germ Development and Its Function in Degrading Enamel Matrix Proteins in Mouse

Cathepsin K (CTSK) is a member of cysteine proteinase family, and is predominantly expressed in osteoclastsfor degradationof bone matrix proteins. Given the similarity in physical properties of bone and dental mineralized tissues, including enamel, dentin and cementum, CTSK is likely to take part in mineralization process during odontogenesis. On the other hand, patients with pycnodysostosis caused by mutations of the CTSK gene displayedmultipledental abnormalities, such as hypoplasia of the enamel, obliterated pulp chambers, hypercementosis and periodontal disease. Thereforeitis necessary to study the metabolic role of CTSK in tooth matrix proteins. In this study, BALB/c mice at embryonic day 18 (E18), post-natal day 1 (P1), P5, P10 and P20 were used (5 mice at each time point)for systematic analyses of CTSK expression in the late stage of tooth germ development. We found that CTSK was abundantly expressed in the ameloblasts during secretory and maturation stages (P5 and P10) by immunohistochemistry stainings.During dentinogenesis, the staining was also intense in the mineralization stage (P5 and P10),but not detectable in the early stage of dentin formation (P1) and after tooth eruption (P20).Furthermore, through zymography and digestion test in vitro, CTSK was proved to be capable of hydrolyzing Emdogain and also cleaving Amelogenininto multiple products. Our resultsshed lights on revealing new functions of CTSK and pathogenesis of pycnodysostosis in oral tissues.