This gene encodes an endoplasmic reticulum-resident type II transmembrane glycosyltransferase involved in the chain elongation step of heparan sulfate biosynthesis. Mutations in this gene cause the type I form of multiple exostoses. [provided by RefSeq, Jul 2008]
EXT1 abnormalities are associated with hereditary multiple exostoses, an autosomal dominant bone disorder (also associated with EXT2 and EXT3 gene mutations). A small proportion of cases exhibit malignant transformation resulting in osteosarcoma or chondrosarcoma. Mutation of EXT1 has also been implicated in sporadic chondrosarcoma.
EXT1 mutations in Secondaty Chondrosarcoma Osteochondroma (the most common type of benign bone tumor) is frequently characterised by mutations of EXT1 and EXT2 genes, often sporadic but sometimes germline, as seen in Multiple Hereditary Exostoses. Osteochondromas occasionally undergo neoplastic transformation resulting in secondary chondrosarcoma.
BACKGROUND: Multiple osteochondroma (MO) is an autosomal dominant skeletal disorder characterized by the formation of multiple osteochondromas, and exostosin-1 (EXT1) and exostosin-2 (EXT2) are major causative genes in MO. In this study, we evaluated the genetic backgrounds and mutational patterns in Japanese families with MO. RESULTS: We evaluated 112 patients in 71 families with MO. Genomic DNA was isolated from peripheral blood leucocytes. The exons and exon/intron junctions of EXT1 and EXT2 were directly sequenced after PCR amplification. Fifty-two mutations in 47 families with MO in either EXT1 or EXT2, and 42.3% (22/52) of mutations were novel mutations. Twenty-nine families (40.8%) had mutations in EXT1, and 15 families (21.1%) had mutations in EXT2. Interestingly, three families (4.2%) had mutations in both EXT1 and EXT2. Twenty-four families (33.8%) did not exhibit mutations in either EXT1 or EXT2. With regard to the types of mutations identified, 59.6% of mutations were inactivating mutations, and 38.5% of mutations were missense mutations. CONCLUSIONS: We found that the prevalence of EXT1 mutations was greater than that of EXT2 mutations in Japanese MO families. Additionally, we identified 22 novel EXT1 and EXT2 mutations in this Japanese MO cohort. This study represents the variety of genotype in MO.
Musso N, Caronia FP, Castorina S, et al. Somatic loss of an EXT2 gene mutation during malignant progression in a patient with hereditary multiple osteochondromas. Cancer Genet. 2015; 208(3):62-7 [PubMed] Related Publications
Multiple osteochondromas (MO) is an autosomal-dominant skeletal disorder caused by mutations in the exostosin-1 (EXT1) or exostosin-2 (EXT2) genes. In this study, we report the analysis of the mutational status of the EXT2 gene in tumor samples derived from a patient affected by hereditary MO, documenting the somatic loss of the germline mutation in a giant chondrosarcoma and in a rapidly growing osteochondroma. The sequencing of all exons and exon-intron junctions of the EXT1 and EXT2 genes from blood DNA of the proband did not reveal any mutation in the EXT1 gene but did demonstrate the presence of the transition point mutation c.67C > T in the EXT2 gene, determining the introduction of a stop codon in the coding sequence (p.Arg23*). A mutational analysis of other members of the family and the presence of osteochondromas in the metaphysis of long bones confirmed the diagnosis of hereditary multiple osteochondromas. Direct sequencing from DNA extracted from different sites of two tumor samples (a small rapidly growing osteochondroma and a giant peripheral secondary chondrosarcoma, each located at different chondrocostal junctions) revealed the loss of the germline EXT2 mutation. Analysis of microsatellite polymorphic markers in the 11p region harboring the EXT2 gene did not reveal any loss of heterozygosity. This observation supports a recent model of sarcomagenesis in which osteochondroma cells bear EXT homozygous inactivation, whereas chondrosarcoma-initiating cells are EXT-expressing cells.
Cammarata-Scalisi F, Cozar M, Grinberg D, et al. [Double mutant alleles in the EXT1 gene not previously reported in a teenager with hereditary multiple exostoses]. Arch Argent Pediatr. 2015; 113(2):e109-12 [PubMed] Related Publications
Hereditary forms of multiple exostoses, now called EXT1/EXT2-CDG within Congenital Disorders of Glycosylation, are the most common benign bone tumors in humans and clinical description consists of the formation of several cartilage-capped bone tumors, usually benign and localized in the juxta-epiphyseal region of long bones, although wide body dissemination in severe cases is not uncommon. Onset of the disease is variable ranging from 2-3 years up to 13-15 years with an estimated incidence ranging from 1/18,000 to 1/50,000 cases in European countries. We present a double mutant alleles in the EXT1 gene not previously reported in a teenager and her family with hereditary multiple exostoses.
Peripheral chondrosarcoma (PCS) develops as malignant transformation of an osteochondroma, a benign cartilaginous outgrowth at the bone surface. Its invasive, lobular growth despite low-grade histology suggests a loss of chondrocyte polarity. The known genetics of osteochondromagenesis include mosaic loss of EXT1 or EXT2 in both hereditary and non-hereditary cases. The most frequent genetic aberrations in human PCS also include disruptions of CDKN2A or TP53. In order to test the sufficiency of either of these to drive progression of an osteochondroma to PCS, we added conditional loss of Trp53 or Ink4a/Arf in an Ext1-driven mouse model of osteochondromagenesis. Each additional tumour suppressor silencing efficiently drove the development of growths that mimic human PCS. As in humans, lobules developed from both Ext1-null and Ext1-functional clones within osteochondromas. Assessment of their orientation revealed an absence of primary cilia in the majority of mouse PCS chondrocytes, which was corroborated in human PCSs. Loss of primary cilia may be responsible for the lost polarity phenotype ascribed to PCS. Cilia deficiency blocks proliferation in physeal chondrocytes, but cell cycle deregulation is sufficient to rescue chondrocyte proliferation following deciliation. This provides a basis of selective pressure for the frequent cell-cycle regulator silencing observed in peripheral chondrosarcomagenesis. Mosaic loss of Ext1 combined with loss of cell cycle regulators promotes peripheral chondrosarcomagenesis in the mouse and reveals deficient ciliogenesis in both the model and the human disease, explaining biological behaviour including lobular and invasive growth.
Goud AL, Wuyts W, Bessems J, et al. Intraosseous atypical chondroid tumor or chondrosarcoma grade 1 in patients with multiple osteochondromas. J Bone Joint Surg Am. 2015; 97(1):24-31 [PubMed] Related Publications
BACKGROUND: The autosomal dominant condition multiple osteochondromas, formerly called multiple hereditary exostoses, is associated with a risk of malignant progression of osteochondroma into secondary peripheral chondrosarcoma. Most patients with multiple osteochondromas have exostosin-1 or exostosin-2 gene mutations. To our knowledge, it has not been previously reported that patients may also harbor intraosseous (central) chondroid neoplasms, enchondromas, or atypical chondroid tumors or central chondrosarcomas. The combination of osteochondroma and enchondromas also exists in patients with metachondromatosis, a disorder associated with a protein tyrosine phosphatase non-receptor type 11 gene mutation. This study aims to establish any correlation between multiple osteochondromas and intraosseous cartilaginous neoplasms. METHODS: We retrospectively reviewed all histologically proven intraosseous atypical chondroid tumors or chondrosarcomas in our prospective nationwide Dutch tertiary referral multiple osteochondromas database. Demographic, clinical, radiographic, histological, and genetic data were recorded. The institutional medical ethics review board approved the study. RESULTS: From 195 adult patients, seven (3.6%) were identified with intraosseous atypical chondroid tumor or chondrosarcoma World Health Organization grade 1 and had a mean age of forty-two years; five of these patients were male. In all cases, radiographic and genetic findings were consistent with multiple osteochondromas, not metachondromatosis; three patients had an exostosin-1 mutation, four patients had an exostosin-2 mutation, and no patients had a protein tyrosine phosphatase, non-receptor type 11 mutation. Six patients underwent successful operative treatment without complications or recurrences after a mean follow-up duration of forty-eight months (range, twelve to 144 months). One patient was scheduled for surgery after biopsy and histologic confirmation. Of the seven patients, five (71%) also developed a peripheral chondrosarcoma in a known osteochondroma during the study period. CONCLUSIONS: Apart from osteochondromas or peripheral chondrosarcomas, multiple osteochondromas are also associated with intraosseous chondroid neoplasms, potentially resulting in central chondrosarcoma. Therefore, intraosseous lesions should not automatically be regarded as innocuous in this patient population.
Exotosin (EXT) proteins are involved in the chain elongation step of heparan sulfate (HS) biosynthesis, which is intricately involved in organ development. Loss of function mutations (LOF) in EXT1 and EXT2 result in hereditary exostoses (HME). Interestingly, HS plays a role in pancreas development and beta-cell function, and genetic variations in EXT2 are associated with an increased risk for type 2 diabetes mellitus. We hypothesized that loss of function of EXT1 or EXT2 in subjects with hereditary multiple exostoses (HME) affects pancreatic insulin secretion capacity and development. We performed an oral glucose tolerance test (OGTT) followed by hyperglycemic clamps to investigate first-phase glucose-stimulated insulin secretion (GSIS) in HME patients and age and gender matched non-affected relatives. Pancreas volume was assessed with magnetic resonance imaging (MRI). OGTT did not reveal significant differences in glucose disposal, but there was a markedly lower GSIS in HME subjects during hyperglycemic clamp (iAUC HME: 0.72 [0.46-1.16] vs. controls 1.53 [0.69-3.36] nmol·l-1·min-1, p<0.05). Maximal insulin response following arginine challenge was also significantly attenuated (iAUC HME: 7.14 [4.22-10.5] vs. controls 10.2 [7.91-12.70] nmol·l-1·min-1 p<0.05), indicative of an impaired beta-cell reserve. MRI revealed a significantly smaller pancreatic volume in HME subjects (HME: 72.0±15.8 vs. controls 96.5±26.0 cm3 p = 0.04). In conclusion, loss of function of EXT proteins may affect beta-cell mass and insulin secretion capacity in humans, and render subjects at a higher risk of developing type 2 diabetes when exposed to environmental risk factors.
Sgariglia F, Pedrini E, Bradfield JP, et al. The type 2 diabetes associated rs7903146 T allele within TCF7L2 is significantly under-represented in Hereditary Multiple Exostoses: insights into pathogenesis. Bone. 2015; 72:123-7 [PubMed] Free Access to Full ArticleRelated Publications
Hereditary Multiple Exostoses (HME) is an autosomal-dominant disorder characterized by benign cartilage tumors (exostoses) forming near the growth plates, leading to severe health problems. EXT1 and EXT2 are the two genes known to harbor heterozygous loss-of-function mutations that account for the vast majority of the primary genetic component of HME. However, patients present with wide clinical heterogeneity, suggesting that modifier genes play a role in determining severity. Our previous work has pointed to an imbalance of β-catenin signaling being involved in the pathogenesis of osteochondroma formation. TCF7L2 is one of the key 'gate-keeper' TCF family members for Wnt/β-catenin signaling pathway, and TCF7L2 and EXT2 are among the earliest associated loci reported in genome wide appraisals of type 2 diabetes (T2D). Thus we investigated if the key T allele of single nucleotide polymorphism (SNP) rs7903146 within the TCF7L2 locus, which is strongly over-represented among T2D cases, was also associated with HME. We leveraged genotype data available from ongoing GWAS efforts from genomics and orthopedic centers in the US, Canada and Italy. Collectively 213 cases and 1890 controls were analyzed and, surprisingly, the T allele was in fact significantly under-represented in the HME patient group [P = 0.009; odds ratio = 0.737 (95% C.I. 0.587-0.926)]; in addition, the direction of effect was consistent within each individual cohort. Immunohistochemical analyses revealed that TCF7L2 is differentially expressed and distributed in normal human growth plate zones, and exhibits substantial variability in human exostoses in terms of staining intensity and distribution. In summary, the data indicate that there is a putative genetic connection between TCF7L2 and EXT in the context of HME. Given this observation, we suggest that these loci could possibly modulate shared pathways, in particular with respect to β-catenin, and their respective variants interplay to influence HME pathogenesis as well as T2D.
Mooij HL, Cabrales P, Bernelot Moens SJ, et al. Loss of function in heparan sulfate elongation genes EXT1 and EXT 2 results in improved nitric oxide bioavailability and endothelial function. J Am Heart Assoc. 2014; 3(6):e001274 [PubMed] Free Access to Full ArticleRelated Publications
BACKGROUND: Heparanase is the major enzyme involved in degradation of endothelial heparan sulfates, which is associated with impaired endothelial nitric oxide synthesis. However, the effect of heparan sulfate chain length in relation to endothelial function and nitric oxide availability has never been investigated. We studied the effect of heterozygous mutations in heparan sulfate elongation genes EXT1 and EXT2 on endothelial function in vitro as well as in vivo. METHODS AND RESULT: Flow-mediated dilation, a marker of nitric oxide bioavailability, was studied in Ext1(+/-) and Ext2(+/-) mice versus controls (n=7 per group), as well as in human subjects with heterozygous loss of function mutations in EXT1 and EXT2 (n=13 hereditary multiple exostoses and n=13 controls). Endothelial function was measured in microvascular endothelial cells under laminar flow with or without siRNA targeting EXT1 or EXT2. Endothelial glycocalyx and maximal arteriolar dilatation were significantly altered in Ext1(+/-) and Ext2(+/-) mice compared to wild-type littermates (glycocalyx: wild-type 0.67±0.1 μm, Ext1(+/-) 0.28±0.1 μm and Ext2(+/-) 0.25±0.1 μm, P<0.01, maximal arteriolar dilation during reperfusion: wild-type 11.3±1.0%), Ext1(+/-) 15.2±1.4% and Ext2(+/-) 13.8±1.6% P<0.05). In humans, brachial artery flow-mediated dilation was significantly increased in hereditary multiple exostoses patients (hereditary multiple exostoses 8.1±0.8% versus control 5.6±0.7%, P<0.05). In line, silencing of microvascular endothelial cell EXT1 and EXT2 under flow led to significant upregulation of endothelial nitric oxide synthesis and phospho-endothelial nitric oxide synthesis protein expression. CONCLUSIONS: Our data implicate that heparan sulfate elongation genes EXT1 and EXT2 are involved in maintaining endothelial homeostasis, presumably via increased nitric oxide bioavailability.
Li L, Li X, Liu Y, et al. [Mutation analysis of EXT2 gene in a family with hereditary multiple exostosis]. Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2014; 31(6):743-6 [PubMed] Related Publications
OBJECTIVE: To investigate EXT1 and EXT2 genes mutations in a family with hereditary multiple osteochondromas (HME). METHODS: A four-generation family with HME from Linyi city of Shandong Province was studied. There were 6 affected individuals among the 17 family members. Physical examination and radiographical evaluations were carried out for all family members. Genomic DNA was extracted from peripheral venous blood and the samples were subjected to mutation screening by PCR of the coding regions of EXT1 and EXT2 genes. RESULTS: The family has featured an autosomal dominant inheritance pattern. Sequencing of the EXT1 and EXT2 genes suggested the causative gene in this family was in linkage with the second exon of EXT2. A c.244delG mutation was detected, which has resulted in a frameshift mutation p.Asp81IlefsX30. The mutation was found in all of the 6 affected individuals but not in normal family members. And the mutation has co-segregated with the phenotype. CONCLUSION: The mutation c.244delG in the EXT2 gene is the probably the cause of the disease in this family.
Hereditary multiple exostosis (HME) is an autosomal inherited skeletal disease whose etiology is not fully understood. To further understand the genetic spectrum of the disease, we analyzed a five-generation Chinese family with HME that have observable inheritance. Exome sequencing was performed on three HME individuals and three unaffected individuals from the family. A downstream study confirmed a new C deletion at codon 442 on exon 5 of the exostosin-1 (EXT1) gene as the only pathogenic site which generated a stop codon and caused the truncation of the protein. We rediscovered the deletion in other affected individuals but not in the unaffected individuals from the family. Upon immunohistochemistry assay, we found that the EXT1 protein level of the patients with the novel mutation in our study was less than the level in the patients without the EXT1 mutation from another unrelated family. For a deeper understanding, we analyzed the mutation spectrum of the EXT1 gene. The present study should facilitate a further understanding of HME.
Multiple osteochondromatosis (MO), or EXT1/EXT2-CDG, is an autosomal dominant O-linked glycosylation disorder characterized by the formation of multiple cartilage-capped tumors (osteochondromas). In contrast, solitary osteochondroma (SO) is a non-hereditary condition. EXT1 and EXT2, are tumor suppressor genes that encode glycosyltransferases involved in heparan sulfate elongation. We present the clinical and molecular analysis of 33 unrelated Latin American patients (27 MO and 6 SO). Sixty-three percent of all MO cases presented severe phenotype and two malignant transformations to chondrosarcoma (7%). We found the mutant allele in 78% of MO patients. Ten mutations were novel. The disease-causing mutations remained unknown in 22% of the MO patients and in all SO patients. No second mutational hit was detected in the DNA of the secondary chondrosarcoma from a patient who carried a nonsense EXT1 mutation. Neither EXT1 nor EXT2 protein could be detected in this sample. This is the first Latin American research program on EXT1/EXT2-CDG.
Nakane T, Goi K, Oshiro H, et al. Pre-B-cell acute lymphoblastic leukemia in a boy with hereditary multiple exostoses caused by EXT1 deletion. Pediatr Hematol Oncol. 2014; 31(7):667-9 [PubMed] Related Publications
Granulin-epithelin precursor (GEP) is a pluripotent secretory growth factor which promotes cancer progression in a number of human cancers. However, how cancer cells interact with GEP remains unknown. In this study, we aimed to identify the cell surface-binding partner of GEP on liver cancer cells. Human recombinant GEP (rGEP) was expressed and purified to homogeneity. The rGEP was shown to trigger phosphorylation of AKT and ERK1/2 in liver cancer cells. We demonstrated cell surface attachment of rGEP, which was blocked by prebinding of platelet-derived growth factor-AA, platelet-derived growth factor-BB and fibroblast growth factor-2. Therefore, heparan sulfate (HS) had been reasoned as the binding partner of rGEP. Heparinase digestion validated the role of HS on supporting the attachment. The heparin-binding domain of GEP was mapped to RRH(555-557) in the C-terminal region. Suppression of the HS polymerase exostosin-1 reduced the rGEP binding and rGEP-mediated signaling transduction. Suppression of a specific HS proteoglycan, glypican-3, also showed a partial reduction of rGEP binding and an inhibition on rGEP-mediated activation of AKT. Furthermore, glypican-3 was shown to correlate with the expressions of GEP in clinical samples (Spearman's ρ = 0.363, P = 0.001). This study identified HS, partly through glypican-3, as a novel binding partner of GEP on the surface of liver cancer cells.
Wang W, Qiu ZQ, Song HM [A splicing mutation of EXT1 in a Chinese pedigree with hereditary multiple exostoses]. Zhongguo Dang Dai Er Ke Za Zhi. 2014; 16(2):174-80 [PubMed] Related Publications
OBJECTIVE: Hereditary multiple exostoses (HME) is an autosomal dominant monogenic disorder of paraplasia ossium. Mutations in EXT1 and EXT2 have been suggested to be responsible for over 70% of HME cases. This study aimed to analyze the clinical features and pathogenic mutations in a Chinese family with HME (6 patients in 24 members of 3 generations) and to review the relative literature regarding mutations in EXT1 and EXT2 in the Chinese population. METHODS: Clinical pedigree dada from a Chinese family of HME were collected and analysed. EXT gene mutations in this pedigree assessed by PCR and sequencing. Pubmed and Wanfang (a Chinese database) were searched for the literature related to gene mutations in Chinese HME patients. RESULTS: In the pedigree analyzed, the age of onset of HME was becoming younger, the disease was becoming more severe, and the number of osteochondromas was increasing, in successive generations. A splicing mutation IVS5+1G>A, first identified in Chinese population, was found in all diseased members of this pedigree. According the currently available literature, EXT1 and EXT2 mutations have been detected in 29% (26/90) and 43% (39/90) Chinese families with HME. CONCLUSIONS: HME starts earlier and becomes more severe and extensive with each successive generation in members of the pedigree analyzed. A splicing mutation, IVS5+1G>A, of EXT1, first identified in Chinese population, may be responsible for HME in the studied pedigree. EXT1 and EXT2 mutation rates may be different between the Chinese and Western populations.
Hereditary multiple exostosis is an intriguing genetic condition with a clinical impact in the field of orthopaedics, paediatrics and oncology. In this review we highlight the current knowledge about this condition from a clinical and scientific point of view. This gives us more insight into the molecular mechanisms and current models on which therapeutic agents are based. It allows for a multidisciplinary approach to the management of this complex condition. There is currently no exact pathological model that can accurately describe all the findings in the research on Hereditary Multiple Exostosis. Promising treatments with blocking agents are currently under investigation.
Hereditary multiple exostoses (HME) also known as multiple osteochondromas represent one of the most frequent bone tumor disorder in humans. Its clinical presentation is characterized by the presence of multiple benign cartilage-capped tumors located most commonly in the juxta-epiphyseal portions of long bones. HME are usually inherited in autosomal dominant manner, however de novo mutations can also occur. In most patients, the disease is caused by alterations in the EXT1 and EXT2 genes. In this study we investigated 33 unrelated Polish probands with the clinical and radiological diagnosis of HME by means of Sanger sequencing and MLPA for all coding exons of EXT1 and EXT2. We demonstrated EXT1 and EXT2 heterozygous mutations in 18 (54.6 %) and ten (30.3 %) probands respectively, which represents a total of 28 (84.9 %) index cases. Sequencing allowed for the detection of causative changes in 26 (78.8 %) probands, whereas MLPA showed intragenic deletions in two (6.1 %) further cases (15 mutations represented novel changes). Our paper is the first report on the results of exhaustive mutational screening of both EXT1/EXT2 genes in Polish patients. The proportion of EXT1/EXT2 mutations in our group was similar to other Caucasian cohorts. However, we found that EXT1 lesions in Polish patients cluster in exons 1 and 2 (55.6 % of all EXT1 mutations). This important finding should lead to the optimization of cost-effectiveness rate of HME diagnostic testing. Therefore, the diagnostic algorithm for HME should include EXT1 sequencing (starting with exons 1-2), followed by EXT2 sequencing, and MLPA/qPCR for intragenic copy number changes.
Guo XL, Deng Y, Liu HG Clinical characteristics of hereditary multiple exostoses: a retrospective study of mainland chinese cases in recent 23 years. J Huazhong Univ Sci Technolog Med Sci. 2014; 34(1):42-50 [PubMed] Related Publications
Hereditary multiple exostoses (HME) are an autosomal dominant skeletal disease with wide variations in clinical manifestations among different ethnic groups. This study investigated the epidemiology, clinical presentations, pathogenetic features and treatment strategies of HME in mainland China. We searched and reviewed the related cases published since 1990 by searching electronic databases, namely SinoMed database, Wanfang database, CNKI, Web of Science and PubMed as well as Google search engines. A total of 1051 cases of HME (male-to-female ratio 1.5:1) were investigated and the diagnosis was made in 83% before the age of 10 years. Approximately 96% patients had a family history. Long bones, ribs, scapula and pelvis were the frequently affected sites. Most patients were asymptomatic with multiple palpable masses. Common complications included angular deformities, impingement on neighbouring tissues and impaired articular function. Chondrosarcomas transformation occurred in 2% Chinese cases. Among the cases examined, about 18% had mutations in EXT1 and 28% in EXT2. Frameshift, nonsense and missense mutations represented the majority of HME-causing mutations. Diagnosis of HME was made based on the clinical presentations and radiological documentations. Most patients needed no treatment. Surgical treatment was often directed to remove symptomatic exostoses, particularly those of suspected malignancy degeneration, and correction of skeletal deformities. This study shows some variance from current literature regarding other ethnic populations and may provide valuable baseline assessment of the natural history of HME in mainland China.
Clement ND, Porter DE Hereditary multiple exostoses: anatomical distribution and burden of exostoses is dependent upon genotype and gender. Scott Med J. 2014; 59(1):35-44 [PubMed] Related Publications
BACKGROUND AND AIMS: We describe the novel anatomical distribution of exostoses in patients with hereditary multiple exostoses according to their gender and genotype. METHODS AND RESULTS: A prospective database of 143 patients from 65 families with hereditary multiple exostoses was compiled. Patient demographics, genotype and number of exostoses according to anatomical site were recorded. The hand was affected by the greatest proportion of exostoses for both EXT1 (19%) and EXT2 (14%) genotypes and was the most prevalent site for exostoses in patients with an EXT1 genotype (92%). Patients with an EXT1 genotype had a significantly greater number of exostoses compared to those with an EXT2 genotype (2680 vs. 1828, p = 0.006); however, this was only significantly different for 10 of the 19 anatomical regions examined. Male patients with an EXT1 genotype had a significantly (p < 0.05) greater number of exostoses affecting their hands, distal radius, proximal humerus, scapular and ribs compared to female patients with the same genotype and males with an EXT2 genotype. CONCLUSION: The anatomical distribution of exostoses varies according to genotype and gender; however, the reason for this difference is not clear and may relate to different biochemical pathways.
Jones KB, Pacifici M, Hilton MJ Multiple hereditary exostoses (MHE): elucidating the pathogenesis of a rare skeletal disorder through interdisciplinary research. Connect Tissue Res. 2014; 55(2):80-8 [PubMed] Related Publications
Abstract An interdisciplinary and international group of clinicians and scientists gathered in Philadelphia, PA, to attend the fourth International Research Conference on Multiple Hereditary Exostoses (MHE), a rare and severe skeletal disorder. MHE is largely caused by autosomal dominant mutations in EXT1 or EXT2, genes encoding Golgi-associated glycosyltransferases responsible for heparan sulfate (HS) synthesis. HS chains are key constituents of cell surface- and extracellular matrix-associated proteoglycans, which are known regulators of skeletal development. MHE affected individuals are HS-deficient, can display skeletal growth retardation and deformities, and consistently develop benign, cartilage-capped bony outgrowths (termed exostoses or osteochondromas) near the growth plates of many skeletal elements. Nearly 2% of patients will have their exostoses progress to malignancy, becoming peripheral chondrosarcomas. Current treatments are limited to the surgical removal of symptomatic exostoses. No definitive treatments have been established to inhibit further formation and growth of exostoses, prevent transition to malignancy, or address other medical problems experienced by MHE patients, including chronic pain. Thus, the goals of the Conference were to assess our current understanding of MHE pathogenesis, identify key gaps in information, envision future therapeutic strategies and discuss ways to test and implement them. This report provides an assessment of the exciting and promising findings in MHE and related fields presented at the Conference and a discussion of the future MHE research directions. The Conference underlined the critical usefulness of gathering experts in several research fields to forge new alliances and identify cross-fertilization areas to benefit both basic and translational biomedical research on the skeleton.
Jochmann K, Bachvarova V, Vortkamp A Heparan sulfate as a regulator of endochondral ossification and osteochondroma development. Matrix Biol. 2014; 34:55-63 [PubMed] Related Publications
Most elements of the vertebrate skeleton are formed by endochondral ossification. This process is initiated with mesenchymal cells that condense and differentiate into chondrocytes. These undergo several steps of differentiation from proliferating into hypertrophic chondrocytes, which are subsequently replaced by bone. Chondrocyte proliferation and differentiation are tightly controlled by a complex network of signaling molecules. During recent years, it has become increasingly clear that heparan sulfate (HS) carrying proteoglycans play a critical role in controlling the distribution and activity of these secreted factors. In this review we summarize the current understanding of the role of HS in regulating bone formation. In human, mutations in the HS synthetizing enzymes Ext1 and Ext2 induce the Multiple Osteochondroma syndrome, a skeletal disorder characterized by short stature and the formation of benign cartilage-capped tumors. We review the current insight into the origin of the disease and discuss its possible molecular basis. In addition, we summarize the existing insight into the role of HS as a regulator of signal propagation and signaling strength in the developing skeleton.
Tang Y, Zheng DZ, Guo XY, et al. [Molecular diagnosis and prenatal diagnosis in a hereditary multiple osteochondromas family]. Beijing Da Xue Xue Bao. 2013; 45(6):906-9 [PubMed] Related Publications
OBJECTIVE: To identify the mutation in the disease gene and provide prenatal diagnosis for a hereditary multiple osteochondromas (HMO) family. METHODS: The exons of EXT1 gene in the proband with HMO and his family members were amplified by PCR. The products were analyzed by direct sequencing. Prenatal genetic diagnosis was performed by amniocentesis sampling after genotyping the proband. RESULTS: In the family, the affected proband was heterozygous of the mutation of 1476_1477delTC in the EXT1 gene, and the proband's father carried the same mutation in part of his somatic cells. No mutation was found in the EXT1 gene of the proband's mother and other 11 siblings of his father. CONCLUSION: METHODS for molecular diagnosis and prenatal diagnosis of HMO were established and applied to a family of HMO.
Huang XS, Liu JS, Jiang HO, et al. [Genetic diagnosis for a Chinese Han family with hereditary multiple osteochondromas]. Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2013; 30(6):645-8 [PubMed] Related Publications
OBJECTIVE: To identify the genetic cause for a Chinese Han family affected with hereditary multiple osteochondromas. METHODS: Two patients, five unaffected relatives of the family and 100 unrelated healthy controls were collected. The coding sequences and intron/exon boundaries of EXT1 gene were amplified with polymerase chain reaction (PCR) and sequenced. RESULTS: A heterozygous c.600G>A (p.Trp200X) mutation in exon 1 of the EXT1 gene was detected in the patients. The same mutation was not found in unaffected family members and 100 healthy controls. CONCLUSION: The hereditary multiple osteochondromas in the family is caused by a nonsense mutation (p.Trp200X) in the EXT1 gene.
Cao L, Liu F, Kong M, et al. Novel EXT1 mutation identified in a pedigree with hereditary multiple exostoses. Oncol Rep. 2014; 31(2):713-8 [PubMed] Related Publications
Hereditary multiple exostoses (HME) is an autosomal dominant bone disorder characterized by the presence of multiple benign cartilage-capped tumors. EXT1 located on chromosome 8q23-q24 and EXT2 located on 11p11-p12 are the main disease-causing genes which are responsible for ~90% of HME cases. Mutations of EXT1 or EXT2 result in insufficient heparan sulfate biosynthesis, which facilitates chondrocyte proliferation, boosts abnormal bone growth of neighboring regions, causes multiple exostoses, and ultimately leads to possible malignant transformation. A family who displayed typical features of HME was enrolled in the present study. Mutation screening by Sanger sequencing identified a novel heterozygous nonsense mutation c.1902C>A (p.Tyr634X) in the EXT1 gene exclusively in all 3 patients, which is located in the glycosyltransferase domain and results in the truncation of 112 amino acids at the C-terminus of the EXT1 protein. Thus, the present study identified a novel disease-causing EXT1 mutation in a pedigree with HME, which provides additional evidence for developing quick and accurate genetic tools for HME diagnosis.
Busse-Wicher M, Wicher KB, Kusche-Gullberg M The exostosin family: proteins with many functions. Matrix Biol. 2014; 35:25-33 [PubMed] Related Publications
Heparan sulfates are complex sulfated molecules found in abundance at cell surfaces and in the extracellular matrix. They bind to and influence the activity of a variety of molecules like growth factors, proteases and morphogens and are thus involved in various cell-cell and cell-matrix interactions. The mammalian EXT proteins have glycosyltransferase activities relevant for HS chain polymerization, however their exact role in this process is still confusing. In this review, we summarize current knowledge about the biochemical activities and some proposed functions of the members of the EXT protein family and their roles in human disease.
Kang QL, Xu J, Zhang Z, et al. Mutation screening for the EXT1 and EXT2 genes in Chinese patients with multiple osteochondromas. Arch Med Res. 2013; 44(7):542-8 [PubMed] Related Publications
BACKGROUND AND AIMS: Multiple osteochondromas (MO), an autosomal dominant skeletal disease, is characterized by the presence of multiple cartilage-capped bone tumors (exostoses). Two genes with mutations that are most commonly associated with MO have been identified as EXT1 and EXT2, which are Exostosin-1 and Exostosin-2. In this study, a variety of EXT1 and EXT2 gene mutations were identified in ten Chinese families with MO. METHODS: We investigated ten unrelated Chinese families involving a total of 46 patients who exhibited typical features of MO. The coding exons of EXT1 and EXT2 were sequenced after PCR amplification in ten probands. Radiological investigation was conducted simultaneously. RESULTS: Nine mutations were identified, five in EXT1 and four in EXT2, of which three were de novo mutations and six were novel mutations. One proband carried mutations in both EXT1 and EXT2 simultaneously, and three probands, including one sporadic case and two familial cases, had no detectable mutations. CONCLUSIONS: Our findings are useful for extending the mutational spectrum in EXT1 and EXT2 and understanding the genetic basis of MO in Chinese patients.
Multiple osteochondromas (MO) is an inherited skeletal disorder, and the molecular mechanism of MO remains elusive. Exome sequencing has high chromosomal coverage and accuracy, and has recently been successfully used to identify pathogenic gene mutations. In this study, exome sequencing followed by Sanger sequencing validation was first used to screen gene mutations in two representative MO patients from a Chinese family. After filtering the data from the 1000 Genome Project and the dbSNP database (build 132), the detected candidate gene mutations were further validated via Sanger sequencing of four other members of the same MO family and 200 unrelated healthy subjects. Immunohistochemisty and multiple sequence alignment were performed to evaluate the importance of the identified causal mutation. A novel frameshift mutation, c.1457insG at codon 486 of exon 6 of EXT1 gene, was identified, which truncated the glycosyltransferase domain of EXT1 gene. Multiple sequence alignment showed that codon 486 of EXT1 gene was highly conserved across various vertebrates. Immunohistochemisty demonstrated that the chondrocytes with functional EXT1 in MO were less than those in extragenetic solitary chondromas. The novel c.1457insG deleterious mutation of EXT1 gene reported in this study expands the causal mutation spectrum of MO, and may be helpful for prenatal genetic screening and early diagnosis of MO.
Heparan sulfate (HS) is an essential component of cell surface and matrix-associated proteoglycans. Due to their sulfation patterns, the HS chains interact with numerous signaling proteins and regulate their distribution and activity on target cells. Many of these proteins, including bone morphogenetic protein family members, are expressed in the growth plate of developing skeletal elements, and several skeletal phenotypes are caused by mutations in those proteins as well as in HS-synthesizing and modifying enzymes. The disease we discuss here is hereditary multiple exostoses (HME), a disorder caused by mutations in HS synthesizing enzymes EXT1 and EXT2, leading to HS deficiency. The exostoses are benign cartilaginous-bony outgrowths, form next to growth plates, can cause growth retardation and deformities, chronic pain and impaired motion, and progress to malignancy in 2-5% of patients. We describe recent advancements on HME pathogenesis and exostosis formation deriving from studies that have determined distribution, activities and roles of signaling proteins in wild-type and HS-deficient cells and tissues. Aberrant distribution of signaling factors combined with aberrant responsiveness of target cells to those same factors appear to be a major culprit in exostosis formation. Insights from these studies suggest plausible and cogent ideas about how HME could be treated in the future.
Wu Y, Xing X, Xu S, et al. Novel and recurrent mutations in the EXT1 and EXT2 genes in Chinese kindreds with multiple osteochondromas. J Orthop Res. 2013; 31(9):1492-9 [PubMed] Related Publications
Multiple osteochondromas (MO) is an autosomal dominant hereditary disorder caused by heterozygous germline mutations in the exostonsin-1 (EXT1) or exostosin-2 (EXT2) genes. In this study, we screened mutations in the EXT1/EXT2 genes in four Chinese MO kindreds by direct sequencing. Three point mutations were detected, including a nonsense mutation in the EXT2 gene (c.544C > T) and two splice site mutations in the EXT1 and EXT2 genes, respectively (EXT1: c.1883 + 1G > A and EXT2: c.1173 + 1G > T). Although splice site mutations constitute at least 10% of all mutations that cause MO, there has been limited research on their pathogenic effect on RNA processing due to poor availability of patient RNA samples. In this study, ex vivo and in vivo splicing assays were used to investigate the effect of EXT1 and EXT2 mutations on aberrant splicing at the mRNA level. Our results indicate that identified splice site mutations can cause either cryptic splice site usage or exon skipping.
Bovée JV, Sakkers RJ, Geirnaerdt MJ, et al. Intermediate grade osteosarcoma and chondrosarcoma arising in an osteochondroma. A case report of a patient with hereditary multiple exostoses. J Clin Pathol. 2002; 55(3):226-9 [PubMed] Free Access to Full ArticleRelated Publications
A 40 year old man with hereditary multiple exostoses (HME), affecting predominantly his left proximal tibia, distal femur, and proximal femur, underwent resection of an osteochondroma near the trochanter major of his left proximal femur because of malignant transformation of the cartilaginous cap towards secondary peripheral chondrosarcoma. The patient had a history of a papillary thyroid carcinoma four years previously. At examination of the resected specimen, a third malignant tumour, an intermediate grade osteosarcoma (grade II/IV), was found in the osseous stalk of the osteochondroma. Although no mutations were found in the EXT1 and EXT2 genes, the genes involved in HME, or in exons 5-8 of the p53 gene, the development of three malignancies before the age of 40 suggests that this patient is genetically prone to malignant transformation.
Engel EE, Nogueira-Barbosa MH, Brassesco MS, et al. Osteosarcoma arising from osteochondroma of the tibia: case report and cytogenetic findings. Genet Mol Res. 2012; 11(1):448-54 [PubMed] Related Publications
Osteochondroma is a cartilage capped benign tumor developing mainly at the juxta-epiphyseal region of long bones. The rate of malignant transformation, mainly into chondrosarcoma, is estimated to be less than 1-3%. Transformation into osteosarcoma is very rare and has been reported only thirteen times. There is little information on treatment and outcome. We report the case of a secondary osteosarcoma arising in the left tibia of a 23-year-old male, 10 years after the initial diagnosis of osteochondroma and after two partial resections. Malignant transformation occurred at the stalk and not at the cartilage cap, as would normally be expected. Chromosome banding analysis revealed the karyotype: 46,XY, t(3;13)(q21;q34) /46,XY . Records from additional cases will help determine the parameters that define these rare secondary bone lesions.