Clinical characteristics of hereditary multiple exostoses: a retrospective study of mainland chinese cases in recent 23 years

Hereditary multiple exostoses: an educational review

Hereditary multiple exostoses (HME), an autosomal dominant disorder with an incidence of 1:50,000 to 1:100,000, is characterised by the formation of multiple osteochondromas arising from the metaphyses of long and flat bones. These osteochondromas often present as painless palpable lumps, though some cases are symptomatic due to mechanical compression or bursitis. Diagnosis of HME is typically clinical and radiological. WHO diagnostic criteria include ≥ 2 radiological osteochondromas in the juxta-epiphyseal region of the long bones. Genetic testing is reserved for ambiguous cases. HME is associated with mutations in the EXT-1 (exostosin-1) and EXT-2 (exostosin-2) genes. Imaging techniques, including conventional radiography, CT, MRI, ultrasound, and nuclear medicine, play a crucial role in diagnosing and assessing HME, with each modality offering distinct advantages in visualising the lesions and associated complications. Common complications include skeletal deformities, fractures, bursitis, as well as neural and vascular abnormalities. Notably, there is a 10% risk of malignant transformation into secondary chondrosarcoma in HME patients, compared to only a 1% risk in those with solitary osteochondromas. Malignant transformation should be suspected in patients with new-onset pain or specific imaging features in an osteochondroma, such as growth of de cartilaginous cap. In these cases, an MRI should be performed to assess the cartilage cap thickness. Advances in imaging techniques and genetic understanding have improved the management and prognosis of HME. Follow-up is essential to rule out malignant transformation. This review summarises current knowledge on the clinical presentation, pathogenesis, imaging characteristics, complications, and treatment of HME. CRITICAL RELEVANCE STATEMENT: HME is a disorder characterised by the formation of osteochondromas arising from long and flat bones. Multi-modality imaging characteristics, clinical presentation, complications, and treatment are highlighted to familiarise the readers with this entity and offer optimal patient care. KEY POINTS: HME is characterised by multiple osteochondromas on long and flat bones. Imaging for HME includes radiography, CT, MRI, ultrasound, and nuclear medicine studies. Complications include non-malignant complications, such as bone deformities and malignant transformation. Cartilage-cap measurement with MRI or US is key to exclude malignancy. Follow-up is essential to rule out malignant transformation of the osteochondromas.

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.

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

Hereditary multiple exostoses (HMEs) syndrome, also known as multiple osteochondromas, represents a rare and severe human skeletal disorder. The disease is characterized by multiple benign cartilage-capped bony outgrowths, termed exostoses or osteochondromas, that locate most commonly in the juxta-epiphyseal portions of long bones. Affected individuals usually complain of persistent pain caused by the pressure on neighboring tissues, disturbance of blood circulation, or rarely by spinal cord compression. However, the most severe complication of this condition is malignant transformation into chondrosarcoma, occurring in up to 3.9% of HMEs patients. The disease results mainly from heterozygous loss-of-function alterations in the EXT1 or EXT2 genes, encoding Golgi-associated glycosyltransferases, responsible for heparan sulfate biosynthesis. Some of the patients with HMEs do not carry pathogenic variants in those genes, hence the presence of somatic mutations, deep intronic variants, or another genes/loci is suggested. This review presents the systematic analysis of current cellular and molecular concepts of HMEs along with clinical characteristics, clinical and molecular diagnostic methods, differential diagnosis, and potential treatment options.

Mutational Analysis of EXT1in a Chinese Family Affected by Hereditary Multiple Osteochondroma

Objectives

To discuss the mutational features and their relationships with disease in a family with hereditary multiple osteochondroma (HMO) from Guangxi Province (GXBB-1 family), China.

Methods

Genomic DNA and total mRNA were extracted from peripheral blood cells of GXBB-1 family members. Whole elements of the EXT1gene and its transcript, including exons, introns, exon-intron boundaries, and coding sequence (CDS) clones, were amplified and sequenced. Allele-specific PCR was used to confirm the position and type of mutation.

Results

All patients from the GXBB-1 family harbored the cosegregating heterozygous c.1056+1G>A mutation located in EXT1at an exon-intron boundary. Another three single-nucleotide polymorphisms (SNPs) were also detected in the patients, including IVS2+1G>A in intron 2, c.1844 T>C [p.Pro (CCT) 614Pro (CCC)] in exon 3, and c.2534G>A [p.Glu (GAG) 844Glu (GAA)] in exon 9. The latter two SNPs were synonymous variations.

Conclusions

The heterozygous c.1056+1G>A mutation cosegregated with the phenotype, indicating that it is a pathogenic mutation in the GXBB-1 family. This mutation is reported for the first time in Chinese HMO patients. IVS2+1G>A and c.2534G>A have no relationship with the occurrence of disease. However, c.1844 T>C and c.1056+1G>A are linked, and their interaction needs to be further studied. c.1844T>C is a new SNP that has not been reported internationally.

Novel Mutations in Chinese Patients with Multiple Osteochondromas Identified Using Whole Exome Sequencing

Background: Multiple osteochondromas (MO) are an autosomal-dominant disease characterized by the growth of multiple cartilage-capped prominences in the growth plate region of the metaphysis in long and flat bones. Materials and Methods: To detect genetic mutations related to MO, a three-generation Chinese family with MO was evaluated using whole exome sequencing for mutation screening. The candidate pathogenic mutation was validated by Sanger sequencing. Results: A novel frameshift (NM_000401.3:c.1321del:p.Leu441TrpfsTer28) in exon 8 of the exotosin 2 (EXT2) gene was identified in two affected individuals. Codons 441 and 468 in the EXT2 gene are highly conserved among vertebrates as demonstrated by multiple sequence alignment. The c.1321 del C resulted in an amino acid change at codon 441, which generated a premature stop codon at position 468, causing complete loss of the glycosyltransferase domain. Conclusions: A novel frameshift mutation c.1321delC detected in the EXT2 gene may help in prenatal genetic screening and early diagnosis of MO.

Forearm Deformity and Radial Head Dislocation in Pediatric Patients with Hereditary Multiple Exostoses: A Prospective Study Using Proportional Ulnar Length as a Scale to Lengthen the Shortened Ulna

BACKGROUND

Ulnar lengthening is a consensus treatment for hereditary multiple exostoses with radial head dislocation in pediatric patients; however, the optimal amount of ulnar lengthening remains unclear. It is necessary to look for a parameter to decide the amount of ulnar lengthening that will avoid recurrence and complications. The purpose of the present study was to confirm that proportional ulnar length (ulnar length/radial length) can be used as a scale for ulnar lengthening in pediatric patients.

METHODS

The normal lengths of the ulna and radius in the pediatric population were measured in different age groups. The proportional ulnar length was calculated as ulnar length/radial length in each group. Thirty forearms in 26 patients with radial head dislocation were treated with ulnar lengthening and deformity correction. The goal of ulnar lengthening was to recover the normal proportional ulnar length. The function of the forearm was evaluated at the time of the latest follow-up. The preoperative and postoperative values for radial bowing, radioarticular angle, ulnar variance, and carpal slip were also compared.

RESULTS

The value of proportional ulnar length in the normal population consistently averaged approximately 1.1. In all cases, proportional ulnar length recovered to the normal value of 1.1. Reduction of the dislocated radial head was achieved in 28 forearms (93%); in 16 of these forearms, good-quality reduction was achieved and no recurrence of radial head dislocation was observed during follow-up. The function of the forearm improved markedly (p < 0.001). Ulnar variance improved from 2.51 to -0.79 cm (p < 0.001). Radial deformities improved according to measurements of radial bowing and the radioarticular angle (p < 0.001). All parents were satisfied with the postoperative appearance and function of the forearm.

CONCLUSIONS

Proportional ulnar length could be used as a scale to decide the amount of ulnar lengthening for radial head dislocation in pediatric patients with hereditary multiple exostoses. Ulnar lengthening according to proportional ulnar length and deformity correction can prevent recurrence of ulnar variance and avoid impingement of the wrist.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Rib Exostoses Presenting as Mediastinal Masses: A Rare Presentation and Minireview of the Literature

Costal osteocartilaginous exostoses, also known as osteochondromas, are the most common neoplasms of the long bones but are rare tumors of the ribs. Osteochondroma is often asymptomatic and incidentally observed. Tumors typically begin to grow before puberty and continue until bone maturation is reached. Our paper presents the case of a 16-year-old young male who was admitted to the hospital with nonspecific symptoms and having a family history of exostosis. Chest X-ray and computed tomography imaging revealed multiple costosternal exostoses, manifested as mediastinal masses, with protrusion into the thoracic cavity, exerting compressive effects on the ascending aorta and pulmonary parenchyma. Surgery is required in childhood if lesions are painful. But if tumor formation occurs in adulthood, such pathological bony outgrowths should always be resected for avoiding further complications. In this patient, surgical intervention removed the tumoral masses and improved the symptoms. Subsequently, histological exam confirmed the diagnosis of osteocartilaginous exostoses and showed the lack of dysplastic changes.

Identification of a novel mutation in EXT2 in a fourth-generation Korean family with multiple osteochondromas and overview of mutation spectrum

Multiple osteochondromas (MOs) or hereditary multiple exostoses is a rare autosomal-dominant disease characterized by growths of MOs, which are benign cartilage-capped bone tumors that grow away from the growth plates. Almost 90% of MOs have a molecular explanation and 10% are unexplained. MOs are genetically heterogeneous with two causal genes on 8q24.11 (EXT1) and 11p12 (EXT2), with a higher frequency in EXT1. MO is a very rare genetic disorder, and the genotype-phenotype of MO with EXT2 mutation has not been well investigated in Korea. We present the clinical radiographic and molecular analysis of a four-generation Korean family with 11 MO-affected members (seven males and four females). The affected members from the third generation available for molecular analysis and their detailed medical histories showed moderate-to-severe phenotypes (clinical classes II-III), including bony deformities and limb misalignment with pain requiring surgical correction. The x-rays showed MOs in multiple sites. A novel EXT2 frameshift mutation (c.590delC, p.P197Qfs*73) was revealed by targeted exome sequencing in the affected members of this family. In this article, we not only expand the phenotypic-genotypic spectrum of MOs but also highlight the phenotypic heterogeneity in a family with the same mutation. In addition, we compiled the mutation spectrum of EXT2 from a literature review and identified that exon 2 of EXT2 is a mutation hot spot. Early medical attention with diagnosis of MO through careful examination of the clinical manifestations and genetic analysis can provide the opportunity to establish coordinated multispecialty management of the patient.

Current paediatric orthopaedic practice in hereditary multiple osteochondromas of the forearm: a systematic review

Introduction: This systematic review aims to answer three research questions concerning the management of hereditary multiple osteochondromas of forearm in children: What is the best available evidence for the currently employed surgical procedures? What patient characteristics are associated with better prognosis? What disease characteristics are associated with better prognosis?

Methods: We searched the literature using three major databases with no publication date restrictions. To enhance search sensitivity and maintain precision we used keywords/subject terms correlating with patient population, problem and interventions. We used strict inclusion/exclusion criteria to improve validity evidence.

Results: The search process yielded 34 eligible studies with a total of 282 patients (315 forearms). We comprehensively analysed study and patient demographics and interventions and outcomes. Eleven studies (32%) had a long-term follow-up and 31 studies (91%) were retrospective. Of the total number of forearms, ulnar lengthening +/− associated procedures was used in 210 forearms (66.7%), isolated osteochondroma excision in 65 forearms (20.6%) and isolated distal radius hemiepiphysiodesis in 15 forearms (4.7%) among others.

Discussion: Ulnar lengthening can restore radiologic anatomy, improve appearance and to a lesser extent objective clinical parameters like joint range of motion on the short/intermediate term. Isolated osteochondroma excision can relief pain and satisfy cosmetic concerns occasionally. There is poor evidence to suggest that surgery improves quality of life or function. Predictors of surgical success in regard to patient and disease characteristics remain elusive. Natural history and prospective randomized control studies where the control group receives no treatment should be rethought. They have the potential for bias control and identification of the ideal surgical candidate. The complex interplay between the confounding variables has undermined the capability of most studies to provide well-grounded evidence to support and generalize their conclusions. Valid quality of life scales should supplement objective outcome measures.

Analysis of mutations in EXT1 and EXT2 in Brazilian patients with multiple osteochondromas

Background

Multiple osteochondromas is a dysplasia characterized by growth of two or more osteochondromas. It is genetically heterogeneous, caused by pathogenic variants in EXT1 or EXT2 genes in 70%–90% of patients. The EXT1 is more often mutated than EXT2 gene, with a variable prevalence between populations. There are no data about EXT1 and EXT2 pathogenic variants in patients with multiple osteochondromas in Brazilian population. The aim of this survey is to characterize these to determine the genotype profile of this population.

Methods

DNA sequencing (Sanger Method) and MLPA analysis were performed to identify point mutations and deletions/duplications in the sample of 153 patients in 114 families.

Results

Germline variants were identified in 83% of families in which EXT2 variants were detected in 46% and EXT1 in 37% of cases. No variants were detected in 17% of them. We identified 50 different variants, 33 (13 frameshift, 11 nonsense, 5 missense, 2 splice site mutation, and 2 large deletions) in EXT1 and 17 (6 frameshift, 6 splice site mutation, 3 nonsense, 1 missense, and 1 large deletion) in EXT2. Of all 50 variants, 31 (62%) were novel, including 20 out of 33 (60,6%) EXT1 and 11 out of 17 (64.7%) EXT2 alleles. The vast majority of variants (88%) were “loss‐of‐function” and two novel hotspots in EXT2 gene were observed in our study.

Conclusion

The prevalence of variants detected in the EXT2 gene differs from other researches from Latin America, European, and Asian population. This uncommon prevalence could be related with the newly characterized variant hotspot sites detected in EXT2 gene (p.Ala409Profs*26 and p.Ser290*). A high number of novel variants were also identified indicating that Brazilian population has a unique genetic profile. Characterizing this population and establishing its genotype is essential to understand the molecular pathogenesis of this disease in Brazil.

Magnetic Resonance Imaging in Symptomatic Children With Hereditary Multiple Exostoses of the Hip

BACKGROUND

Magnetic resonance imaging (MRI) is useful in evaluating nontraumatic hip pain. It provides information about associated injuries like labral/chondral tears or ischiofemoral impingement (IFI). However, in hereditary multiple exostoses (HME) there has been no report about MRI findings in symptomatic children with hip involvement.

METHODS

Records of children with HME and hip osteochondromas, who had hip MRI/magnetic resonance arthrography, were reviewed. The presence of chondral lesions and labral tears, as well the presence of IFI, was recorded. IFI was defined as edema or fatty replacement/atrophy in the quadratus femoris muscle or decrease of the space for this muscle between the ischium and the proximal femur. The measurements used to determine the space included the ischiofemoral space, the quadratus femoris space, and the minimum ischiofemoral space (MIFS). All measurements were performed on axial T1-weighted images.

RESULTS

Ten children were included (4 males, 6 females). In 2 patients, MRI was unilateral, therefore a total of 18 hips were analyzed. The indication for MRI was hip pain. Mean age, when MRI was performed, was 11.7 years. Labral tears were found in 44% (8/18) and chondral lesions in 33% (6/18) of the hips. The mean ischiofemoral space was 17.2 mm (SD, 7.3), the mean quadratus femoris space was 14.9 mm (SD, 5.3), and the mean MIFS was of 12.8 mm (SD, 5.9). IFI was seen in 44% (8/18) of hips. Two patients had bilateral IFI. MIFS was <10 mm in all hips with IFI (8/8). Of these hips, 88% (7/8) had edema of the quadratus femoris muscle and 38% (3/8) had fatty replacement/atrophy in the muscle. Osteochondromas were seen in the lesser trochanter in all hips with IFI (8/8) and in the ischium in 50% of them (4/8).

CONCLUSIONS

In symptomatic children with HME of the hip, MRI is helpful in detecting the source of pain. A high percentage of these children have IFI and intra-articular lesions. These findings can play an important role in the indication and planning of the surgical approach.

LEVEL OF EVIDENCE

Level IV-diagnostic study.

A genotype-phenotype study of hereditary multiple exostoses in forty-six Chinese patients

BACKGROUND

Hereditary multiple exostoses (HME) is a rare autosomal dominant skeletal disorder that can cause a variety of clinical manifestations. We aimed to evaluate the general clinical phenotypic severity of HME by using a scoring system and correlate the genotypes with different clinical phenotypes in Chinese patients.

METHODS

Forty-six patients from different families were prospectively enrolled. The mutations were identified by direct sequencing of PCR-amplified genomic DNA or by multiplex ligation-dependent probe amplification (MLPA). Patients' demographic data, height, age of onset, number of anatomical sites, forearm deformity, and lower extremity alignment were analysed according to genotype and gender. A scoring system was used to assess the severity of the clinical phenotype.

RESULTS

Thirty (60%) patients presented mutations in the EXT1 gene, and 16 (32%) presented mutations in the EXT2 gene. The mean age of onset was 2.96 years. The mean number of involved anatomic sites was 15.35. Male patients had more lesion sites than female patients (15.97 vs. 13.77, p = 0.046). The height evaluation illustrated that 67% of the patients (31 of 46) were below the 50th percentile, and the patients with EXT1 mutations were shorter than those with EXT2 mutations (p = 0.005). Forearm deformity showed a significant correlation with the number of involved anatomical sites (r = 0.382, p = 0.009). Moreover, a higher total score was found in patients with EXT1 mutations (p = 0.001).

CONCLUSIONS

The clinical manifestations of 46 Chinese HME patients were similar to those in previous reports of Western populations. Patients with EXT1 mutations have a more severe clinical phenotype than patients with EXT2 mutations.

NFAT restricts osteochondroma formation from entheseal progenitors

Osteochondromas are common benign osteocartilaginous tumors in children and adolescents characterized by cartilage-capped bony projections on the surface of bones. These tumors often cause pain, deformity, fracture, and musculoskeletal dysfunction, and they occasionally undergo malignant transformation. The pathogenesis of osteochondromas remains poorly understood. Here, we demonstrate that nuclear factor of activated T cells c1 and c2 (NFATc1 and NFATc2) suppress osteochondromagenesis through individual and combinatorial mechanisms. In mice, conditional deletion of NFATc1 in mesenchymal limb progenitors, Scleraxis-expressing (Scx-expressing) tendoligamentous cells, or postnatally in Aggrecan-expressing cells resulted in osteochondroma formation at entheses, the insertion sites of ligaments and tendons onto bone. Combinatorial deletion of NFATc1 and NFATc2 gave rise to larger and more numerous osteochondromas in inverse proportion to gene dosage. A population of entheseal NFATc1- and Aggrecan-expressing cells was identified as the osteochondroma precursor, previously believed to be growth plate derived or perichondrium derived. Mechanistically, we show that NFATc1 restricts the proliferation and chondrogenesis of osteochondroma precursors. In contrast, NFATc2 preferentially inhibits chondrocyte hypertrophy and osteogenesis. Together, our findings identify and characterize a mechanism of osteochondroma formation and suggest that regulating NFAT activity is a new therapeutic approach for skeletal diseases characterized by defective or exaggerated osteochondral growth.