Gene Summary

Gene:EXT1; exostosin glycosyltransferase 1
Summary: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]
Databases:OMIM, HGNC, GeneCard, Gene
Source:NCBIAccessed: 27 February, 2015


What does this gene/protein do?
Show (32)
Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

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.

Research Indicators

Publications Per Year (1990-2015)
Graph generated 27 February 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Cancer DNA
  • Genotype
  • Restriction Mapping
  • Childhood Cancer
  • Chromosome 8
  • FISH
  • Osteosarcoma
  • Adolescents
  • Single-Stranded Conformational Polymorphism
  • Loss of Heterozygosity
  • Mutation
  • Amino Acid Sequence
  • Asian Continental Ancestry Group
  • DNA Mutational Analysis
  • exostosin-1
  • Messenger RNA
  • N-Acetylglucosaminyltransferases
  • Chondrosarcoma
  • Genetic Predisposition
  • DNA Primers
  • Heterozygote
  • Exons
  • Chromosome Mapping
  • Gene Deletion
  • Genetic Testing
  • Syndecan-1
  • Base Sequence
  • Gene Expression Profiling
  • Bone Cancer
  • Polymerase Chain Reaction
  • China
  • Frameshift Mutation
  • Wnt1 Protein
  • Exostoses, Multiple Hereditary
  • Chromosome 11
  • Osteochondroma
  • Heparitin Sulfate
  • Genetic Linkage
  • Tumor Suppressor Gene
  • Chromatography, High Pressure Liquid
  • Cloning, Molecular
Tag cloud generated 27 February, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Entity Topic PubMed Papers
Multiple Hereditary ExostosesEXT1 and Multiple Hereditary Exostoses View Publications128
ChondrosarcomaEXT1 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.
View Publications32
OsteosarcomaSecondary Osteosarcoma following Osteochondroma
In rare cases osteosarcoma has been reported following malignant transformation of osteochondroma / multiple hereditary exostoses.
View Publications2

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: EXT1 (cancer-related)

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.

Ryckx A, Somers JF, Allaert L
Hereditary multiple exostosis.
Acta Orthop Belg. 2013; 79(6):597-607 [PubMed] Related Publications
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.

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.

Zhang F, Liang J, Guo X, et al.
Exome sequencing and functional analysis identifies a novel mutation in EXT1 gene that causes multiple osteochondromas.
PLoS One. 2013; 8(8):e72316 [PubMed] Free Access to Full Article Related Publications
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.

Huegel J, Sgariglia F, Enomoto-Iwamoto M, et al.
Heparan sulfate in skeletal development, growth, and pathology: the case of hereditary multiple exostoses.
Dev Dyn. 2013; 242(9):1021-32 [PubMed] Free Access to Full Article Related Publications
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.

Anower-E-Khuda MF, Matsumoto K, Habuchi H, et al.
Glycosaminoglycans in the blood of hereditary multiple exostoses patients: Half reduction of heparan sulfate to chondroitin sulfate ratio and the possible diagnostic application.
Glycobiology. 2013; 23(7):865-76 [PubMed] Related Publications
Hereditary multiple exostoses (HME) is an autosomal dominant skeletal disorder with wide variation in clinical phenotype and is caused by heterogeneous germline mutations in two of the Ext genes, EXT-1 and EXT-2, which encode ubiquitously expressed glycosyltransferases involved in the polymerization of heparan sulfate (HS) chains. To examine whether the Ext mutation could affect HS structures and amounts in HME patients being heterozygous for the Ext genes, we collected blood from patients and healthy individuals, separated it into plasma and cellular fractions and then isolated glycosaminoglycans (GAGs) from those fractions. A newly established method consisting of a combination of selective ethanol precipitation of GAGs, digestion of GAGs recovered on the filter-cup by direct addition of heparitinase or chondroitinase reaction solution and subsequent high-performance liquid chromatography of the unsaturated disaccharide products enabled the analysis using the least amount of blood (200 µL). We found that HS structures of HME patients were almost similar to those of controls in both plasma and cellular fractions. However, interestingly, although both the amounts of HS and chondroitin sulfate (CS) varied depending on the different individuals, the amounts of HS in both the plasma and cellular fractions of HME patient samples were decreased and the ratios of HS to CS (HS/CS) of HME patient samples were almost half those of healthy individuals. The results suggest that HME patients' blood exhibited reduced HS amounts and HS/CS ratios, which could be used as a diagnostic biomarker for HME.

Sakabe T, Tsuchiya H, Kanki K, et al.
Identification of the genes chemosensitizing hepatocellular carcinoma cells to interferon-α/5-fluorouracil and their clinical significance.
PLoS One. 2013; 8(2):e56197 [PubMed] Free Access to Full Article Related Publications
The incidence of advanced hepatocellular carcinoma (HCC) is increasing worldwide, and its prognosis is extremely poor. Interferon-alpha (IFN-α)/5-fluorouracil (5-FU) therapy is reportedly effective in some HCC patients. In the present study, to improve HCC prognosis, we identified the genes that are sensitizing to these agents. The screening strategy was dependent on the concentration of ribozymes that rendered HepG2 cells resistant to 5-FU by the repeated transfection of ribozymes into the cells. After 10 cycles of transfection, which was initiated by 5,902,875 sequences of a ribozyme library, three genes including protein kinase, adenosine monophosphate (AMP)-activated, gamma 2 non-catalytic subunit (PRKAG2); transforming growth factor-beta receptor II (TGFBR2); and exostosin 1 (EXT1) were identified as 5-FU-sensitizing genes. Adenovirus-mediated transfer of TGFBR2 and EXT1 enhanced IFN-α/5-FU-induced cytotoxicity as well as 5-FU, although the overexpression of these genes in the absence of IFN-α/5-FU did not induce cell death. This effect was also observed in a tumor xenograft model. The mechanisms of TGFBR2 and EXT1 include activation of the TGF-β signal and induction of endoplasmic reticulum stress, resulting in apoptosis. In HCC patients treated with IFN-α/5-FU therapy, the PRKAG2 mRNA level in HCC tissues was positively correlated with survival period, suggesting that PRKAG2 enhances the effect of IFN-α/5-FU and serves as a prognostic marker for IFN-α/5-FU therapy. In conclusion, we identified three genes that chemosensitize the effects of 5-FU and IFN-α/5-FU on HCC cells and demonstrated that PRKAG2 mRNA can serve as a prognostic marker for IFN-α/5-FU therapy.

Zhou YA, Ma YX, Zhang YH, et al.
[Screening for EXT1 and EXT2 gene mutations in a ethnic Han Chinese family from Shanxi with hereditary multiple exostoses].
Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2013; 30(1):95-8 [PubMed] Related Publications
OBJECTIVE: To screen for potential mutations in an ethnic Han Chinese family from Shanxi with hereditary multiple exostoses.
METHODS: Polymerase chain reaction and DNA sequencing were used to screen potential mutations in EXT1 and EXT2 genes.
RESULTS: For EXT1 gene, two synonymous mutations (P477P and E587E), three intronic mutations (c.1537 -48A>G, c.1721 +203A>G and c.1722 -103C>G) were detected. For EXT2 gene, five intronic mutations (c.-29 -148A>T, c.1080 -18T>A, c.1336 -93C>T, c.1526 -166C>T, and c.1526 -195C>T) were identified. Among these, EXT1 P477P, EXT1 E587E and EXT2 c.1080 -18T>A are polymorphisms listed by Multiple Osteochondroma Mutation Database, whilst the other 7 sites have not been reported.
CONCLUSION: No mutations have been found among all exons of the EXT1 and EXT2 genes in this family. Linkage analysis is necessary for identifying the cause of this disease.

Sarrión P, Sangorrin A, Urreizti R, et al.
Mutations in the EXT1 and EXT2 genes in Spanish patients with multiple osteochondromas.
Sci Rep. 2013; 3:1346 [PubMed] Free Access to Full Article Related Publications
Multiple osteochondromas is an autosomal dominant skeletal disorder characterized by the formation of multiple cartilage-capped tumours. Two causal genes have been identified, EXT1 and EXT2, which account for 65% and 30% of cases, respectively. We have undertaken a mutation analysis of the EXT1 and EXT2 genes in 39 unrelated Spanish patients, most of them with moderate phenotype, and looked for genotype-phenotype correlations. We found the mutant allele in 37 patients, 29 in EXT1 and 8 in EXT2. Five of the EXT1 mutations were deletions identified by MLPA. Two cases of mosaicism were documented. We detected a lower number of exostoses in patients with missense mutation versus other kinds of mutations. In conclusion, we found a mutation in EXT1 or in EXT2 in 95% of the Spanish patients. Eighteen of the mutations were novel.

Waaijer CJ, Winter MG, Reijnders CM, et al.
Intronic deletion and duplication proximal of the EXT1 gene: a novel causative mechanism for multiple osteochondromas.
Genes Chromosomes Cancer. 2013; 52(4):431-6 [PubMed] Related Publications
Multiple osteochondromas (MO) is a syndrome in which benign cartilage-capped neoplasms develop at the surface of the long bones. Most cases are caused by exonic changes in EXT1 or EXT2, but 15% are negative for these changes. Here we report for the first time a family of MO patients with germline genomic alterations at the EXT1 locus without detectable mutations or copy number alterations of EXT exonic sequences. Array-CGH showed an 80.7 kb deletion of Intron 1 of EXT1 and a 68.9 kb duplication proximal of EXT1. We identified a breakpoint between the distal end of the duplicated region and a sequence distal of the deleted region in the first intron. This breakpoint was absent in non-affected family members. The configuration of the breakpoint indicates a direct insertion of the duplicated region into the deletion. However, no other breakpoint was found, which suggests a more complex genomic rearrangement has occurred within the duplicated region. Our results reveal intronic deletion and duplication as a new causative mechanism for MO not detected by conventional diagnostic methods.

Ciavarella M, Coco M, Baorda F, et al.
20 novel point mutations and one large deletion in EXT1 and EXT2 genes: report of diagnostic screening in a large Italian cohort of patients affected by hereditary multiple exostosis.
Gene. 2013; 515(2):339-48 [PubMed] Related Publications
BACKGROUND: Hereditary multiple exostosis represents the most frequent bone tumor disease in humans. It consists of cartilage deformities affecting the juxta-ephyseal region of long bones. Usually benign, exostosis could degenerate in malignant chondrosarcoma form in less than 5% of the cases. Being caused by mutations in the predicted tumor suppressor genes, EXT1 (chr 8q23-q24) and EXT2 (chr 11p11-p12) genes, HMEs are usually inherited with an autosomal dominant pattern, although "de novo" cases are not infrequent.
AIM: Here we present our genetic diagnostic report on the largest Southern Italy cohort of HME patients consisting of 90 subjects recruited over the last 5years.
RESULTS: Molecular screening performed by direct sequencing of both EXT1 and EXT2 genes, by MLPA and Array CGH analyses led to the identification of 66 mutations (56 different occurrences) and one large EXT2 deletion out of 90 patients (74.4%). The total of 21 mutations (20 different occurrences, 33.3%) and the EXT2 gene deletion were novel. In agreement with literature data, EXT1 gene mutations were scattered along all the protein sequence, while EXT2 lesions fell in the first part of the protein. Conservation, damaging prediction and 3-D modeling, in-silico, analyses, performed on three novel missense variants, confirmed that at least in two cases the novel aminoacidic changes could alter the structure stability causing a strong protein misfolding.
CONCLUSIONS: Here we present 20 novel EXT1/EXT2 mutations and one large EXT2 deletion identified in the largest Southern Italy cohort of patients affected by hereditary multiple exostosis.

Jones KB, Datar M, Ravichandran S, et al.
Toward an understanding of the short bone phenotype associated with multiple osteochondromas.
J Orthop Res. 2013; 31(4):651-7 [PubMed] Free Access to Full Article Related Publications
Individuals with multiple osteochondromas (MO) demonstrate shortened long bones. Ext1 or Ext2 haploinsufficiency cannot recapitulate the phenotype in mice. Loss of heterozygosity for Ext1 may induce shortening by steal of longitudinal growth into osteochondromas or by a general derangement of physeal signaling. We induced osteochondromagenesis at different time points during skeletal growth in a mouse genetic model, then analyzed femora and tibiae at 12 weeks using micro-CT and a point-distribution-based shape analysis. Bone lengths and volumes were compared. Metaphyseal volume deviations from normal, as a measure of phenotypic widening, were tested for correlation with length deviations. Mice with osteochondromas had shorter femora and tibiae than controls, more consistently when osteochondromagenesis was induced earlier during skeletal growth. Volumetric metaphyseal widening did not correlate with longitudinal shortening, although some of the most severe shortening was in bones with abundant osteochondromas. Loss of heterozygosity for Ext1 was sufficient to drive bone shortening in a mouse model of MO, but shortening did not correlate with osteochondroma volumetric growth. While a steal phenomenon seems apparent in individual cases, some other mechanism must also be capable of contributing to the short bone phenotype, independent of osteochondroma formation. Clones of chondrocytes lacking functional heparan sulfate must blunt physeal signaling generally, rather than stealing growth potential focally.

Kang Z, Peng F, Ling T
Mutation screening of EXT genes in Chinese patients with multiple osteochondromas.
Gene. 2012; 506(2):298-300 [PubMed] Related Publications
Multiple osteochondromas (MO), a dominantly inherited genetic disorder, is characterized by the presence of multiple osteochondromas in the long bones. EXT1 and EXT2 are the causative genes in most MO patients. We have characterized 9 MO families and 1 sporadic case involving a total of 25 patients. The coding exons of EXT1 and EXT2 were screened in 10 probands affected with MO. In five of the 10 probands novel pathogenic mutations have been identified: two in EXT1 and three in EXT2. Four probands carried recurrent mutations and one proband had no detectable mutation. Our study extends the mutational spectrum in EXT1 and EXT2 and will facilitate the deep understanding of the pathophysiology of the disease.

Wang X, Li L, Li J, et al.
Pathogenic gene screening and mutation detection in a Chinese family with multiple osteochondroma.
Genet Test Mol Biomarkers. 2012; 16(7):827-32 [PubMed] Free Access to Full Article Related Publications
Multiple osteochondroma (MO) is an autosomal dominant disease characterized by abnormal skeleton development: one or more exostoses localized mainly at the end of long bones. Three pathogenic gene loci have been identified and cloned: EXT1, 2, and 3. Only EXT1 and 2 mutations were reported to cause MO. Here, we report on a large Chinese family with MO and a disease-causing mutation in EXT. We extracted DNA from peripheral blood samples of 25 family members, 9 with MO. Polymerase chain reaction and direct DNA sequencing of the entire coding regions of EXT1 and 2 for the nine patients revealed a novel pathogenic mutation, insertion of a T in exon 2 (c.72-73 insT) of EXT2. Our results extend the mutational spectrum of MO and can help with genetic counseling and prenatal diagnosis for this family.

Delgado MA, Sarrión P, Azar N, et al.
A novel nonsense mutation of the EXT1 gene in an Argentinian patient with multiple hereditary exostoses: a case report.
J Bone Joint Surg Am. 2012; 94(11):e76 [PubMed] Related Publications

Kyriazoglou AI, Dimitriadis E, Arnogiannaki N, et al.
Similar cytogenetic findings in two synchronous secondary peripheral chondrosarcomas in a patient with multiple osteochondromas.
Cancer Genet. 2011; 204(12):677-81 [PubMed] Related Publications
Secondary peripheral chondrosarcoma is a malignant chondroid tumor arising in a benign precursor, either an osteochondroma or an enchondroma. Multiple osteochondromas syndrome (MO) is an autosomal dominant skeletal disorder associated with bony growths in the form of osteochondromas that occasionally undergo malignant transformation to secondary peripheral chondrosarcomas. We describe the genetic examination of three secondary peripheral chondrosarcomas that had arisen synchronously from osteochondromas in a patient with MO by chromosome banding, high resolution chromosomal comparative genomic hybridization, and mutation analysis of the EXT1 and EXT2 genes. In two of the tumors (the third was not genetically informative), very similar chromosome abnormalities were found, indicating that they must somehow be part of the same neoplastic process in spite of being anatomically distinct.

Pedrini E, Jennes I, Tremosini M, et al.
Genotype-phenotype correlation study in 529 patients with multiple hereditary exostoses: identification of "protective" and "risk" factors.
J Bone Joint Surg Am. 2011; 93(24):2294-302 [PubMed] Related Publications
BACKGROUND: Multiple hereditary exostoses is an autosomal dominant skeletal disorder characterized by wide variation in clinical phenotype. The aim of this study was to evaluate whether the severity of the disease is linked with a specific genetic background.
METHODS: Five hundred and twenty-nine patients with multiple hereditary exostoses from two different European referral centers participated in the study. According to a new clinical classification based on the presence or absence of deformities and functional limitations, the phenotype of the patients was assessed as mild (the absence of both aspects), intermediate, or severe (the concurrent presence of both aspects). An identical molecular screening protocol with denaturing high-performance liquid chromatography and multiplex ligation-dependent probe amplification was performed in both institutions.
RESULTS: In our cohort of patients, variables such as female sex (odds ratio = 1.840; 95% confidence interval, 1.223 to 2.766), fewer than five skeletal sites with exostoses (odds ratio = 7.588; 95% confidence interval, 3.479 to 16.553), EXT2 mutations (odds ratio = 2.652; 95% confidence interval, 1.665 to 4.223), and absence of EXT1/2 mutations (odds ratio = 1.975; 95% confidence interval, 1.051 to 3.713) described patients with a mild phenotype; in contrast, a severe phenotype was associated with male sex (odds ratio = 2.431; 95% confidence interval, 1.544 to 3.826), EXT1 mutations (odds ratio = 6.817; 95% confidence interval, 1.003 to 46.348), and more than twenty affected skeletal sites (odds ratio = 2.413; 95% confidence interval, 1.144 to 5.091). Malignant transformation was observed in 5% of patients, and no evidence of association between chondrosarcoma onset and EXT mutation, sex, severity of disease, or number of lesions was detected.
CONCLUSIONS: The identified "protective" and "risk" factors, as well as the proposed classification system, represent helpful tools for clinical management and follow-up of patients with multiple hereditary exostoses; moreover, homogeneous cohorts of patients, useful for studies on the pathogenesis of multiple hereditary exostoses, have been identified.

Zhu HY, Hu YL, Yang Y, et al.
Mutation analysis and prenatal diagnosis of EXT1 gene mutations in Chinese patients with multiple osteochondromas.
Chin Med J (Engl). 2011; 124(19):3054-7 [PubMed] Related Publications
BACKGROUND: Multiple osteochondromas (MO), an inherited autosomal dominant disorder, is characterized by the presence of multiple exostoses on the long bones. MO is caused by mutations in the EXT1 or EXT2 genes which encode glycosyltransferases implicated in heparin sulfate biosynthesis.
METHODS: In this study, efforts were made to identify the underlying disease-causing mutations in patients from two MO families in China.
RESULTS: Two novel EXT1 gene mutations were identified and no mutation was found in EXT2 gene. The mutation c.497T > A in exon 1 of the EXT1 gene was cosegregated with the disease phenotype in family 1 and formed a stop codon at amino acid site 166. The fetus of the proband was diagnosed negative. In family 2, the mutation c.1430-1431delCC in exon 6 of the EXT1 gene would cause frameshift and introduce a premature stop codon after the reading frame being open for 42 amino acids. The fetus of this family inherited this mutation from the father.
CONCLUSIONS: Mutation analysis of two MO families in this study demonstrates its further application in MO genetic counseling and prenatal diagnosis.

Jennes I, Zuntini M, Mees K, et al.
Identification and functional characterization of the human EXT1 promoter region.
Gene. 2012; 492(1):148-59 [PubMed] Related Publications
BACKGROUND: Mutations in Exostosin-1 (EXT1) or Exostosin-2 (EXT2) cause the autosomal dominant disorder multiple osteochondromas (MO). This disease is mainly characterized by the appearance of multiple cartilage-capped protuberances arising from children's metaphyses and is known to display clinical inter- and intrafamilial variations. EXT1 and EXT2 are both tumor suppressor genes encoding proteins that function as glycosyltransferases, catalyzing the biosynthesis of heparan sulfate. At present, however, very little is known about the regulation of these genes. Two of the most intriguing questions concerning the pathogenesis of MO are how disruption of a ubiquitously expressed gene causes this cartilage-specific disease and how the clinical intrafamilial variation can be explained. Since mutations in the EXT1 gene are responsible for ~65% of the MO families with known causal mutation, our aim was to isolate and characterize the EXT1 promoter region to elucidate the transcriptional regulation of this tumor suppressor gene.
METHODS: In the present study, luciferase reporter gene assays were used to experimentally confirm the in silico predicted EXT1 core promoter region. Subsequently, we evaluated the effect of single nucleotide polymorphisms (SNP's) on EXT1 promoter activity and transcription factor binding using luciferase assays, electrophoretic mobility shift assays (EMSA), and enzyme-linked immunosorbent assays (ELISA). Finally, a genotype-phenotype study was performed with the aim to identify one or more genetic modifiers influencing the clinical expression of MO.
RESULTS: Transient transfection of HEK293 cells with a series of luciferase reporter constructs mapped the EXT1 core promoter at approximately -917 bp upstream of the EXT1 start codon, within a 123 bp region. This region is conserved in mammals and located within a CpG-island containing a CAAT- and a GT-box. A polymorphic G/C-SNP at -1158 bp (rs34016643) was demonstrated to be located in a USF1 transcription factor binding site, which is lost with the presence of the C-allele resulting in a ~56% increase in EXT1 promoter activity. A genotype-phenotype study was suggestive for association of the C-allele with shorter stature, but also with a smaller number of osteochondromas.
CONCLUSIONS: We provide for the first time insight into the molecular regulation of EXT1. Although a larger patient population will be necessary for statistical significance, our data suggest the polymorphism rs34016643, in close proximity of the EXT1 promoter, to be a potential regulatory SNP, which could be a primary modifier that might explain part of the clinical variation observed in MO patients.

Julien S, Ivetic A, Grigoriadis A, et al.
Selectin ligand sialyl-Lewis x antigen drives metastasis of hormone-dependent breast cancers.
Cancer Res. 2011; 71(24):7683-93 [PubMed] Related Publications
The glycome acts as an essential interface between cells and the surrounding microenvironment. However, changes in glycosylation occur in nearly all breast cancers, which can alter this interaction. Here, we report that profiles of glycosylation vary between ER-positive and ER-negative breast cancers. We found that genes involved in the synthesis of sialyl-Lewis x (sLe(x); FUT3, FUT4, and ST3GAL6) are significantly increased in estrogen receptor alpha-negative (ER-negative) tumors compared with ER-positive ones. SLe(x) expression had no influence on the survival of patients whether they had ER-negative or ER-positive tumors. However, high expression of sLe(x) in ER-positive tumors was correlated with metastasis to the bone where sLe(x) receptor E-selectin is constitutively expressed. The ER-positive ZR-75-1 and the ER-negative BT20 cell lines both express sLe(x) but only ZR-75-1 cells could adhere to activated endothelial cells under dynamic flow conditions in a sLe(x) and E-selectin-dependent manner. Moreover, L/P-selectins bound strongly to ER-negative MDA-MB-231 and BT-20 cell lines in a heparan sulfate (HS)-dependent manner that was independent of sLe(x) expression. Expression of glycosylation genes involved in heparan biosynthesis (EXT1 and HS3ST1) was increased in ER-negative tumors. Taken together, our results suggest that the context of sLe(x) expression is important in determining its functional significance and that selectins may promote metastasis in breast cancer through protein-associated sLe(x) and HS glycosaminoglycans.

de Andrea CE, Hogendoorn PC
Epiphyseal growth plate and secondary peripheral chondrosarcoma: the neighbours matter.
J Pathol. 2012; 226(2):219-28 [PubMed] Related Publications
Chondrocytes interact with their neighbours through their cartilaginous extracellular matrix (ECM). Chondrocyte-matrix interactions compensate the lack of cell-cell contact and are modulated by proteoglycans and other molecules. The epiphyseal growth plate is a highly organized tissue responsible for long bone elongation. The growth plate is regulated by gradients of morphogens that are established by proteoglycans. Morphogens diffuse across the ECM, creating short- and long-range signalling that lead to the formation of a polarized tissue. Mutations affecting genes that modulate cell-matrix interactions are linked to several human disorders. Homozygous mutations of EXT1/EXT2 result in reduced synthesis and shortened heparan sulphate chains on both cell surface and matrix proteoglycans. This disrupts the diffusion gradients of morphogens and signal transduction in the epiphyseal growth plate, contributing to loss of cell polarity and osteochondroma formation. Osteochondromas are cartilage-capped bony projections arising from the metaphyses of endochondral bones adjacent to the growth plate. The osteochondroma cap is formed by cells with homozygous mutation of EXT1/EXT2 and committed stem cells/wild-type chondrocytes. Osteochondroma serves as a niche (a permissive environment), which facilitates the committed stem cells/wild-type chondrocytes to acquire secondary genetic changes to form a secondary peripheral chondrosarcoma. In such a scenario, the micro-environment is the site of the initiating processes that ultimately lead to cancer.

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 Article Related 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) [2]/46,XY [18]. Records from additional cases will help determine the parameters that define these rare secondary bone lesions.

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