Hereditary Multiple Exostoses-A Review of the Molecular Background, Diagnostics, and Potential Therapeutic Strategies

Exostoisns (EXT1/2) in Head and Neck Cancers: An In Silico Analysis and Clinical Correlates

OBJECTIVES

The exostosins (EXT), which are responsible for heparan sulfate backbone synthesis and play a vital role in tissue homeostasis, have been reported to be correlated with prognosis of various cancers. However, the expression, prognostic value, and immune infiltration of EXT1 and EXT2 in head and neck squamous cell carcinoma (HNSC) remain uncertain.

METHODS

GEPIA, UALCAN, and Xiantao bioinformatics tools were used to explore the EXT1 and EXT2 expression level in HNSC. GEPIA and Sangerbox were utilised to obtain the prognostic value of EXT1 and EXT2 in HNSC. Genetic alterations, immune cell infiltration, and single-cell analysis were conducted in cBioPortal, TIMER, and TISCH2. In addition, the expressions of EXT1 and EXT2 were validated by real-time polymerase chain reaction (PCR) in HNSC samples.

RESULTS

EXT1 and EXT2 were highly expressed in HNSC, especially in malignant cells. Only EXT2 was significantly negatively correlated to the prognosis of patients with HNSC. EXT1 and EXT2 were found to be associated with focal adhesin and cell adhesin molecule binding. EXT1 expression levels were considerably connected with CD8+ T cell infiltrating levels, whilst EXT2 expression levels were considerably negatively connected with infiltrating levels of CD4+ T cells, macrophages, neutrophils, and dendritic cells in HNSC. The gene mutation rates of EXT1 and EXT2 in HNSC were 7% and 2.8%, respectively. Moreover, EXT2 was validated to be highly expressed in HNSC samples by real-time PCR.

CONCLUSION

EXT2 was highly expressed and presented negative correlation with the prognosis and immune infiltration of HNSC, which might be a potential biomarker for HNSC.

Prenatal Diagnosis by Trio Clinical Exome Sequencing: Single Center Experience

Fetal anomalies, characterized by structural or functional abnormalities occurring during intrauterine life, pose a significant medical challenge, with a notable prevalence, affecting approximately 2-3% of live births and 20% of spontaneous miscarriages. This study aims to identify the genetic cause of ultrasound anomalies through clinical exome sequencing (CES) analysis. The focus is on utilizing CES analysis in a trio setting, involving the fetuses and both parents. To achieve this objective, prenatal trio clinical exome sequencing was conducted in 51 fetuseses exhibiting ultrasound anomalies with previously negative results from chromosomal microarray (CMA) analysis. The study revealed pathogenic variants in 24% of the analyzed cases (12 out of 51). It is worth noting that the findings include de novo variants in 50% of cases and the transmission of causative variants from asymptomatic parents in 50% of cases. Trio clinical exome sequencing stands out as a crucial tool in advancing prenatal diagnostics, surpassing the effectiveness of relying solely on chromosomal microarray analysis. This underscores its potential to become a routine diagnostic standard in prenatal care, particularly for cases involving ultrasound anomalies.

Defining priorities in the transition from paediatric to adult healthcare for rare bone disease patients: a dialogic approach

The Italian patient association for Multiple Osteochondromas, Ollier Disease, and Maffucci Syndrome, Associazione Conto Alla Rovescia-ACAR Aps, conducted a mixed-methods study at its 2023 annual conference. The study included the Open Dialogue Approach and a feedback survey to identify the main priorities in the transitioning process from paediatric to adult healthcare for patients with Multiple Osteochondromas, Ollier Disease, and Maffucci Syndrome. The common needs identified by patients, families, caregivers, and healthcare professionals were coordination and continuity of care, patient empowerment and communication, social and practical support, and transition planning and support. This experience fostered a sense of collaboration and cooperation among stakeholders, helping to build trust and create a shared vision for improving the quality of care for these patients. Furthermore, it could be considered a starting point for other patient associations interested in using different approaches to identify the needs of their members and actively involve all stakeholders.

Rare coexistence of multiple osteochondromas and solitary osteoid osteoma: A case report

Multiple osteochondromas (MOs) are inherited in an autosomal-dominant manner, with a penetrance of ~96 and 100% in female and male patients, respectively. Osteochondromas primarily involve the metaphyses and diaphyses of long bones, including the ribs. Osteoid osteomas account for ~3 and 11% of all bone tumors and benign bone tumors, respectively. Furthermore,1 the male-to-female ratio is 2-3:1, and they generally occur in the long bones of the lower extremities, with the femoral neck being the most frequent site. The present study describes the case of a 16-year-old male patient with a bony mass around the left knee joint and pain in the left calf. Radiography revealed MOs in the upper and lower extremities, while computed tomography showed a nidus in the cortex of the tibial shaft. The patient's family history included the presence of MOs, and the patient was diagnosed with MOs and a solitary osteoid osteoma. Surgical excision of the osteochondroma and curettage of the osteoid osteoma in the proximal tibia and tibial shaft, respectively, were performed simultaneously. Postoperative pathological examination revealed osteochondroma and osteoid osteoma. Furthermore, the pain resolved, and no recurrence was observed 7 months post-operation. To the best of our knowledge, no reports exist on coexisting MOs and osteoid osteoma; therefore, the present study describes the first case of such a condition. Marginal excision for osteochondroma and curettage for osteoid osteoma effectively improved the symptoms.

The exostosin glycosyltransferase 1/STAT3 axis is a driver of breast cancer aggressiveness

The epithelial-mesenchymal transition (EMT) program is crucial for transforming carcinoma cells into a partially mesenchymal state, enhancing their chemoresistance, migration, and metastasis. This shift in cell state is tightly regulated by cellular mechanisms that are not yet fully characterized. One intriguing EMT aspect is the rewiring of the proteoglycan landscape, particularly the induction of heparan sulfate proteoglycan (HSPG) biosynthesis. This proteoglycan functions as a co-receptor that accelerates cancer-associated signaling pathways through its negatively-charged residues. However, the precise mechanisms through which EMT governs HSPG biosynthesis and its role in cancer cell plasticity remain elusive. Here, we identified exostosin glycosyltransferase 1 (EXT1), a central enzyme in HSPG biosynthesis, to be selectively upregulated in aggressive tumor subtypes and cancer cell lines, and to function as a key player in breast cancer aggressiveness. Notably, ectopic expression of EXT1 in epithelial cells is sufficient to induce HSPG levels and the expression of known mesenchymal markers, subsequently enhancing EMT features, including cell migration, invasion, and tumor formation. Additionally, EXT1 loss in MDA-MB-231 cells inhibits their aggressiveness-associated traits such as migration, chemoresistance, tumor formation, and metastasis. Our findings reveal that EXT1, through its role in HSPG biosynthesis, governs signal transducer and activator of transcription 3 (STAT3) signaling, a known regulator of cancer cell aggressiveness. Collectively, we present the EXT1/HSPG/STAT3 axis as a central regulator of cancer cell plasticity that directly links proteoglycan synthesis to oncogenic signaling pathways.

Exostosis of Ulna With Developmental Deformity of the Left Forearm: A Rare Case

This case report presents a rare occurrence of exostosis of the ulna associated with a developmental deformity of the left forearm in a 15-year-old female. The patient reported a history of trauma resulting in a supracondylar humerus fracture managed conservatively eight years prior. The patient presented with a two-year history of pain and swelling over the left forearm. Clinical examination revealed a firm, non-tender, immobile swelling closely associated with the ulna, accompanied by a 20-degree cubitus varus deformity and forearm shortening. Radiographs and computed tomography scans confirmed the presence of a solitary external bony protuberance over the ulna shaft, communicating with the medullary cavity. A preliminary diagnosis of osteochondroma was established based on clinical and imaging findings. The patient underwent extraperiosteal en bloc resection of the lesion under supraclavicular nerve block anesthesia. A histopathological examination confirmed the diagnosis. Postoperative physiotherapy was initiated, and at the one-month follow-up, the patient reported being pain-free. This case highlights the rarity of exostosis of the ulna with associated developmental deformity, emphasizing the importance of a comprehensive diagnostic approach. Early surgical intervention resulted in a successful outcome, underscoring the significance of timely management in improving patient outcomes and quality of life.

Phenotypic and Molecular Spectrum of a Turkish Cohort with Hereditary Multiple Osteochondromas

OBJECTIVE

Hereditary multiple osteochondromas is an autosomal dominant disorder caused by heterozygous pathogenic variants in EXT1 or EXT2. We aimed to evaluate the clinical and molecular findings of a Turkish cohort with hereditary multiple osteochondroma.

MATERIALS AND METHODS

Thirty-two patients aged 1.3-49.6 years from 22 families were enrolled. Genetic analyses were made by EXT1 and/or EXT2 sequencing and chromosomal microarray analyses.

RESULTS

We found 17 intragenic pathogenic variants in EXT1 (13/17) and EXT2 (4/17), 12 of which are novel. Four probands had EXT1 deletions, including 2 patients with partial EXT1 microdeletions involving exons 2-11 and 5-11, and 2 patients with whole-gene deletions. In 21 variants, the frequency of truncating and missense variants was 76.1% and 23.8%, respectively. Two families had no detectable variants in EXT1 and EXT2. All patients had multiple osteochondromas at the long bones, mainly at the tibia, forearm, femur, and humerus. Bowing deformity of the forearms (9/32) and the lower extremities (2/32), and scoliosis (6/32) were observed. The clinical severity was not different between patients with EXT1 or EXT2 variants. One patient with an EXT2 variant and another with an EXT1 microdeletion had the most severe phenotype with class III disease. Four patients with no EXT1 or EXT2 variants had milder phenotypes. Intrafamilial variability in disease severity was not observed.

CONCLUSION

We report a hereditary multiple osteochondroma cohort with clinical and molecular data including 12 novel intragenic variants in EXT1 or EXT2, and 4 microdeletions involving EXT1. Taken together, our data expand the existing knowledge of the phenotype-genotype spectrum in hereditary multiple osteochondroma.

Hereditary multiple exostoses caused by a chromosomal inversion removing part of EXT1 gene

BACKGROUND

Hereditary multiple exostoses (HME) is an autosomal dominant skeletal disorder characterized by the development of multiple, circumscript and usually symmetric bony protuberances called osteochondromas. Most HME are caused by EXT1 and EXT2 loss of function mutations. Most pathogenic mutations are nonsense followed by missense mutations and deletions.

CASE PRESENTATION

Here we report on a patient with a rare and complex genotype resulting in a typical HME phenotype. Initial point mutation screening in EXT1 and EXT2 genes by Sanger sequencing did not reveal any pathogenic variants. The patient along with the healthy parents was subsequently referred for karyotype and array-Comparative Genomic Hybridization (CGH) analyses. Chromosomal analysis revealed two independent de novo apparently balanced rearrangements: a balanced translocation between the long arms of chromosomes 2 and 3 at breakpoints 2q22 and 3q13.2 and a pericentric inversion with breakpoints at 8p23.1q24.1. Both breakpoints were confirmed by Fluorescence In Situ Hybridization (FISH). Subsequently, array-CGH revealed a novel heterozygous deletion within the EXT1 gene at one of the inversion breakpoints, rendering the inversion unbalanced. The mode of inheritance, as well as the size of the deletion were further investigated by Quantitative Real-time PCR (qPCR), defining the deletion as de novo and of 3.1 kb in size, removing exon 10 of EXT1. The inversion in combination with the 8p23.1 deletion most likely abolishes the transcription of EXT1 downstream of exon 10 hence resulting in a truncated protein.

CONCLUSIONS

The identification of a rare and novel genetic cause of HME, highlights the importance of additional comprehensive investigation of patients with typical clinical manifestations, even when EXT1 and EXT2 mutation analysis is negative.

Structural basis for heparan sulfate co-polymerase action by the EXT1-2 complex

Heparan sulfate (HS) proteoglycans are extended (-GlcAβ1,4GlcNAcα1,4-)n co-polymers containing decorations of sulfation and epimerization that are linked to cell surface and extracellular matrix proteins. In mammals, HS repeat units are extended by an obligate heterocomplex of two exostosin family members, EXT1 and EXT2, where each protein monomer contains distinct GT47 (GT-B fold) and GT64 (GT-A fold) glycosyltransferase domains. In this study, we generated human EXT1-EXT2 (EXT1-2) as a functional heterocomplex and determined its structure in the presence of bound donor and acceptor substrates. Structural data and enzyme activity of catalytic site mutants demonstrate that only two of the four glycosyltransferase domains are major contributors to co-polymer syntheses: the EXT1 GT-B fold β1,4GlcA transferase domain and the EXT2 GT-A fold α1,4GlcNAc transferase domain. The two catalytic sites are over 90 Å apart, indicating that HS is synthesized by a dissociative process that involves a single catalytic site on each monomer.

Clinical utility of liquid biopsy and integrative genomic profiling in early-stage and oligometastatic cancer patients treated with radiotherapy

BACKGROUND

Liquid biopsy and Integrative Genomic Profiling (IGP) are yet to be implemented into routine Radiation Oncology. Here we assess the utility of germline, tumour and circulating cell-free DNA-based genomic analyses for the clinical management of early-stage and oligometastatic cancer patients treated by precision radiotherapy.

METHODS

We performed germline, tissue- and liquid biopsy NGS panels on 50 early-stage/oligometastatic cancer patients undergoing radiotherapy. We also monitored ctDNA variants in serial liquid biopsies collected during radiotherapy and follow-up and evaluated the clinical utility of such comprehensive approach.

RESULTS

The integration of different genomic studies revealed that only 1/3 of the liquid biopsy variants are of tumour origin. Altogether, 55 tumour variants (affecting 3/4 of the patients) were considered potentially actionable (for treatment and prognosis), whereas potential follow-up biomarkers were identified in all cases. Germline cancer-predisposing variants were present in three patients, which would have not been eligible for hereditary cancer testing according to clinical guidelines. The presence of detectable ctDNA variants before radiotherapy was associated with progression-free survival both in oligometastatic patients and in those with early-stage.

CONCLUSIONS

IGP provides both valuable and actionable information for personalised decision-making in Radiation Oncology.

Structure of the human heparan sulfate polymerase complex EXT1-EXT2

Heparan sulfates are complex polysaccharides that mediate the interaction with a broad range of protein ligands at the cell surface. A key step in heparan sulfate biosynthesis is catalyzed by the bi-functional glycosyltransferases EXT1 and EXT2, which generate the glycan backbone consisting of repeating N-acetylglucosamine and glucuronic acid units. The molecular mechanism of heparan sulfate chain polymerization remains, however, unknown. Here, we present the cryo-electron microscopy structure of human EXT1-EXT2, which reveals the formation of a tightly packed hetero-dimeric complex harboring four glycosyltransferase domains. A combination of in vitro and in cellulo mutational studies is used to dissect the functional role of the four catalytic sites. While EXT1 can catalyze both glycosyltransferase reactions, our results indicate that EXT2 might only have N-acetylglucosamine transferase activity. Our findings provide mechanistic insight into heparan sulfate chain elongation as a nonprocessive process and lay the foundation for future studies on EXT1-EXT2 function in health and disease.

Genetic analysis of seven pateints with Hereditary Multiple Osteochondromas (HMO)

BACKGROUND

HMO (Hereditary Multiple Osteochondroma), an uncommon autosomal dominant disorder, is characterized by the development of multiple osteochondromas, which are nonmalignant cartilage-capped bone tumors growing outwards from long bone metaphyses.

METHODS

The present work retrospectively analyzed seven children with HMO who were enrolled for routine clinical diagnosis and treatment, including X-ray examination. Subsequent genetic detection was carried out using whole exome sequencing (WES). In addition, this work applied Sanger sequencing to be the validation approach. Moreover, this work also examined amino acid (AA) evolutionary conservatism under the influence of certain missense variants.

RESULTS

The clinical indications of all seven patients and their family members were thoroughly indexed. WES identified diagnostic variants in the EXT1 or EXT2 gene in these patients. In these variants, four were reported for the first time, namely EXT1: c.1285-2A>T, EXT2: c.1139delT, EXT1: c.203G>A, and EXT1: c.1645_1673del. Familial validation revealed that three of the variants were hereditary, while the other four were de novo, which was consistent with the phenotype in each case.

CONCLUSION

Our results expanded HMO variation spectrum, and laid certain foundations for the precise counseling of those affected families.

Management of Unresectable Localized Pelvic Bone Sarcomas: Current Practice and Future Perspectives

Simple Summary

Some locally advanced pelvic bone tumors are deemed unresectable and, as such, not suitable for curative surgery. In this setting, treatment options are generally limited and not unanimous, with decisions being made on an individual basis after multidisciplinary discussion. Ultimately, and notwithstanding the bright prospects raised by novel therapeutic approaches, treatment should be patient-tailored, weighing a panoply of patient- and tumor-related factors.

Abstract

Bone sarcomas (BS) are rare mesenchymal tumors usually located in the extremities and pelvis. While surgical resection is the cornerstone of curative treatment, some locally advanced tumors are deemed unresectable and hence not suitable for curative intent. This is often true for pelvic sarcoma due to anatomic complexity and proximity to vital structures, making treatment options for these tumors generally limited and not unanimous, with decisions being made on an individual basis after multidisciplinary discussion. Several studies have been published in recent years focusing on innovative treatment options for patients with locally advanced sarcoma not amenable to local surgery. The present article reviews the evidence regarding the treatment of patients with locally advanced and unresectable pelvic BS, with the goal of providing an overview of treatment options for the main BS histologic subtypes involving this anatomic area and exploring future therapeutic perspectives. The management of unresectable localized pelvic BS represents a major challenge and is hampered by the lack of comprehensive and standardized guidelines. As such, the optimal treatment needs to be individually tailored, weighing a panoply of patient- and tumor-related factors. Despite the bright prospects raised by novel therapeutic approaches, the role of each treatment option in the therapeutic armamentarium of these patients requires solid clinical evidence before becoming fully established.

Clinical survey of a pedigree with hereditary multiple exostoses and identification of EXT‑2 gene deletion mutation

The aim of the present study was to report a clinical survey of hereditary multiple exostoses (HME) in a large Chinese pedigree, and the identification of a novel deletion mutation of exostosin glycosyltransferase 2 (EXT‑2) gene. A patient with multiple exostoses with huge cartilage‑capped tumors in scapula, knees and ankles received surgery in Department of Orthopedics (Shanghai Changhai Hospital). A total of 20 family members were recruited to the study, with seven members (five male; two female) diagnosed as HME. The family members of the patients with HME were examined, clinical data and peripheral blood samples were collected, and their DNA was sequenced. The incidence of HME in this family pedigree was 35%. Exostoses were most frequently in the tibiae with occurrence in six patients, followed by ribs, femurs, radii, fibulae, scapulae and humeri. DNA sequencing of peripheral blood revealed a novel deletion mutation, c.824‑826delGCA, in exon 5 of the EXT‑2 gene, which was observed in all the patients with HME, but not in the healthy family members. Several characteristics of HME in the pedigree were observed, such as susceptibility of male gender, decreased average age of onset and height and increased severity of clinical symptoms with generations.