This gene encodes one of two glycosyltransferases involved in the chain elongation step of heparan sulfate biosynthesis. Mutations in this gene cause the type II form of multiple exostoses. Alternatively spliced transcript variants encoding different isoforms have been noted for this gene. [provided by RefSeq, Jul 2008]
EXT2 mutations in Secondary 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.
Genetics Home Reference - NLM Information about the EXT2 gene including normal function and role in hereditary conditions.
EXT2 OMIM, Johns Hopkin University Referenced article focusing on the relationship between phenotype and genotype.
EXT2 International Cancer Genome Consortium. Summary of gene and mutations by cancer type from ICGC
EXT2 Cancer Genome Anatomy Project, NCI Gene Summary
EXT2 COSMIC, Sanger Institute Somatic mutation information and related details
EXT2 GEO Profiles, NCBI Search the gene expression profiles from curated DataSets in the Gene Expression Omnibus (GEO) repository.
Latest Publications: EXT2 (cancer-related)
Long X, Li Z, Huang Y, et al. Identification of pathogenic mutations in 6 Chinese families with multiple exostoses by whole-exome sequencing and multiplex ligation-dependent probe amplification: Case series. Medicine (Baltimore). 2019; 98(20):e15692 [PubMed] Free Access to Full ArticleRelated Publications
RATIONALE: Hereditary multiple exostoses (HMEs) is an autosomal dominant skeletal disorder. PATIENT CONCERNS: Six probands of the 6 unrelated Han Chinese families were identified as having HME. These patients had exostoses at multiple sites and significantly affected joints malformation and movement. DIAGNOSES: Hereditary multiple exostoses. INTERVENTIONS: To detect the genetic mechanism of HME in 6 unrelated Chinese families, whole-exome sequencing (WES) and multiplex ligation-dependent probe amplification (MLPA) were used after genomic DNA was isolated from peripheral blood leucocytes. Point mutations identified by these methods were verified by Sanger sequencing after PCR amplification. OUTCOMES: Six mutations in the EXT1 and EXT2 genes were identified, including a heterozygous deletion mutation from exon 2 to exon 8 (Family 1), a c.448C>T, p.(Gln150X) heterozygous nonsense mutation (Family 4), a c.1057-2A>T heterozygous splicing substitution (Family 5), and a c.1468dupC, p.(Leu490fs519X) (Family 6) heterozygous duplication mutation in the EXT1 gene in addition to a heterozygous deletion mutation from exon 2 to exon 3 (Family 2) and a c.1197C>G, p.(Tyr399X) heterozygous nonsense mutation (Family 3) in the EXT2 gene. LESSONS: Overall, we identified 5 novel mutations and 1 recurrent mutation in the EXT1 and EXT2 genes in 6 Chinese families with HME. Our findings expand the mutational spectrum of the EXT1 and EXT2 genes and are useful for genetic counseling and prenatal diagnosis.
The molecular mechanism of hereditary multiple exostoses (HME) remains ambiguous and a limited number of studies have investigated the pathogenic mechanism of mutations in patients with HME. In the present study, a novel heterozygous splice mutation (c.1284+2del) in exostosin glycosyltransferase 1 (EXT1) gene was identified in a three‑generation family with HME. Bioinformatics and TA clone‑sequencing indicated that the splice site mutation would result in exon 4 skipping. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) revealed that the expression levels of wild‑type EXT1/EXT2 mRNA in patients with HME were significantly decreased, compared with normal control participants (P<0.05). Abnormal EXT1 transcript lacking exon 4 (EXT1‑DEL) and full‑length EXT1 mRNA (EXT1‑FL) were overexpressed in 293‑T cells and Cos‑7 cells using lentivirus infection. RT‑qPCR demonstrated that the expression level of EXT1‑DEL was significantly increased, compared with EXT1‑FL (17.032 vs. 6.309, respectively; P<0.05). The protein encoded by EXT1‑DEL was detected by western blot analysis, and the level was increased, compared with EXT1‑FL protein expression. Immunofluorescence indicated that the protein encoded by EXT1‑DEL was located in the cytoplasm of Cos‑7 cells, which was consistent with the localization of the EXT1‑FL protein. In conclusion, the present study identified a novel splice mutation that causes exon 4 skipping during mRNA splicing and causes reduced expression of EXT1/EXT2. The mutation in EXT1‑DEL generated a unique peptide that is located in the cytoplasm in vitro, and it expands the mutation spectrum and provides molecular genetic evidence for a novel pathogenic mechanism of HME.
Oliver GR, Blackburn PR, Ellingson MS, et al. RNA-Seq detects a SAMD12-EXT1 fusion transcript and leads to the discovery of an EXT1 deletion in a child with multiple osteochondromas. Mol Genet Genomic Med. 2019; 7(3):e00560 [PubMed] Free Access to Full ArticleRelated Publications
BACKGROUND: We describe a patient presenting with pachygyria, epilepsy, developmental delay, short stature, failure to thrive, facial dysmorphisms, and multiple osteochondromas. METHODS: The patient underwent extensive genetic testing and analysis in an attempt to diagnose the cause of his condition. Clinical testing included metaphase karyotyping, array comparative genomic hybridization, direct sequencing and multiplex ligation-dependent probe amplification and trio-based exome sequencing. Subsequently, research-based whole transcriptome sequencing was conducted to determine whether it might shed light on the undiagnosed phenotype. RESULTS: Clinical exome sequencing of patient and parent samples revealed a maternally inherited splice-site variant in the doublecortin (DCX) gene that was classified as likely pathogenic and diagnostic of the patient's neurological phenotype. Clinical array comparative genome hybridization analysis revealed a 16p13.3 deletion that could not be linked to the patient phenotype based on affected genes. Further clinical testing to determine the cause of the patient's multiple osteochondromas was unrevealing despite extensive profiling of the most likely causative genes, EXT1 and EXT2, including mutation screening by direct sequence analysis and multiplex ligation-dependent probe amplification. Whole transcriptome sequencing identified a SAMD12-EXT1 fusion transcript that could have resulted from a chromosomal deletion, leading to the loss of EXT1 function. Re-review of the clinical array comparative genomic hybridization results indicated a possible unreported mosaic deletion affecting the SAMD12 and EXT1 genes that corresponded precisely to the introns predicted to be affected by a fusion-causing deletion. The existence of the mosaic deletion was subsequently confirmed clinically by an increased density copy number array and orthogonal methodologies CONCLUSIONS: While mosaic mutations and deletions of EXT1 and EXT2 have been reported in the context of multiple osteochondromas, to our knowledge, this is the first time that transcriptomics technologies have been used to diagnose a patient via fusion transcript analysis in the congenital disease setting.
Hamanaka K, Sugawara Y, Shimoji T, et al. De novo truncating variants in PHF21A cause intellectual disability and craniofacial anomalies. Eur J Hum Genet. 2019; 27(3):378-383 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Potocki-Shaffer syndrome (PSS) is a contiguous gene syndrome caused by 11p11.2 deletions. PSS is clinically characterized by intellectual disability, craniofacial anomalies, enlarged parietal foramina, and multiple exostoses. PSS occasionally shows autism spectrum disorder, epilepsy, and overgrowth. Some of the clinical features are thought to be associated with haploinsufficiency of two genes in the 11p11.2 region; variants affecting the function of ALX4 cause enlarged parietal foramina and EXT2 lead to multiple exostoses. However, the remaining clinical features were still yet to be linked to specific genetic alterations. In this study, we identified de novo truncating variants in an 11p11.2 gene, PHF21A, in three cases with intellectual disability and craniofacial anomalies. Among these three cases, autism spectrum disorder was recognized in one case, epilepsy in one case, and overgrowth in two cases. This study shows that PHF21A haploinsufficiency results in intellectual disability and craniofacial anomalies and possibly contributes to susceptibility to autism spectrum disorder, epilepsy, and overgrowth, all of which are PSS features.
Li Y, Wang J, Tang J, et al. Heterogeneous spectrum of EXT gene mutations in Chinese patients with hereditary multiple osteochondromas. Medicine (Baltimore). 2018; 97(42):e12855 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Hereditary multiple osteochondroma (HMO) is one of the most common genetic skeletal disorders. It is caused by mutations in either EXT1 or EXT2 resulting in abnormal skeletal growth and morphogenesis. However, the spectrum and frequency of EXT1 and EXT2 mutations in Chinese patients with HMO was not previously investigated.Mutations were identified by performing Sanger sequencing analysis of the complete coding regions and flanking intronic sequences of EXT1 and EXT2, followed by multiplex ligation-dependent probe amplification (MLPA) analysis to detect gene deletions or duplications that could not be identified by the Sanger sequencing method.The present study identified pathogenic mutations in 93% (68/73) of unrelated HMO probands from 73 pedigrees. Mutations in EXT1 and EXT2 were identified in 53% (39/73) and 40% (29/73) of families. We identified 58 distinct mutations in EXT1 and EXT2, including 20 frameshift mutations, 16 nonsense mutations, 7 missense mutations, 9 splice site mutations, 5 large deletions, and 1 in-frame deletion mutation. Twenty-six of these mutations were novel and 32 were previously reported. Most of the mutations in EXT1 were base deletions or insertions (21/33), whereas the majority of those in EXT2 were single base substitution (18/25).Complete sequencing of both the EXT1 and EXT2 followed by MLPA analysis is recommended for genetic analysis of Chinese patients with HMO. This study provides a comprehensive characterization of the genetic aberrations found in Chinese patients with HMO and highlights the diagnostic value of molecular genetic analysis in this particular disease.
Wu ZY, Wang Y, Wang JW, et al. The role of EXT1 gene mutation and its high expression of calcitonin gene-related peptide in the development of multiple exostosis. Biochem Biophys Res Commun. 2018; 505(4):959-965 [PubMed] Related Publications
OBJECTIVE: Screening and identifying the gene mutation of EXT1, EXT2 and EXT3 associated with multiple exostosis (ME) and the expression in tumor tissues. METHODS: Nine patients with multiple exostosis were collected and genomic DNA was extracted. Polymerase chain reaction (PCR) amplification and direct sequencing techniques were used to screen all exons, 5' and 3' ends of the EXT1, EXT2 and EXT3 related causative genes. EXT1, EXT2 and EXT3 gene were screened and quantified by RNA-SEQ and RT-qPCR. The concentration of calcitonin gene-related peptide (CGRP) in peripheral blood of tumor patients and normal controls was detected by ELISA. RESULTS: Between the two patients with ME, the EXT1 gene was found in one patient to have c.79 T>A mutation, which caused the change of p.M27T, the non polar methionine was replaced by the high frequency mutation of polar threonine, and the rest of patients was found the splicing mutation c.1284 + 8 delAT of the heterozygosity of the EXT1 gene. The serum CGRP concentration of ME patients (623 + 49 pg/ml) was significantly higher than that of normal controls (196 + 68 pg/ml), and EXT1 mutation patients were also higher than non mutation patients.
Gironi LC, Colombo E, Pasini B, et al. Melanoma-prone families: new evidence of distinctive clinical and histological features of melanomas in CDKN2A mutation carriers. Arch Dermatol Res. 2018; 310(10):769-784 [PubMed] Related Publications
Germline mutations on the CDKN2A gene, the most important known genetic factors associated with cutaneous melanomas (CMs), predispose carriers to multiple primary CMs (MPMs) with higher frequency and younger onset compared to non-carriers. Most of the largest published studies concerning clinical and histological characteristics of CMs with CDKN2A mutation carriers did not specify if the described CMs are first or subsequent to the first, and they used sporadic CMs from non-genotyped patients as controls. We conducted a single-centre observational study to compare clinical and histological CM features of 32 unrelated carriers (MUT) of 5 germline CDKN2A mutations (one of which was never previously described) compared to 100 genotyped wild-type (WT) patients. We stratified the data based on time of diagnosis, anatomical site and histological subtype of CMs, demonstrating several significant unreported differences between the two groups. MUT developed a higher number of dysplastic nevi and MPMs. We proved for the first time that anatomical distribution of CMs in MUT was independent of gender, unlike WTs. MUTs developed in situ and superficial spreading melanomas (SSMs) more frequently, with significantly higher number of SSMs on the head/neck. In MUTs, Breslow thickness was significantly lower for all invasive CMs. When CMs were stratified on the basis of the time of occurrence, statistical significance was maintained only for SSMs subsequent to the first. In WTs, Clark level was significantly higher, and ulceration was more prevalent than in MUTs. Significant differences in ulceration were observed only in SSMs. In nodular CMs, we did not find differences in terms of Breslow thickness or ulceration between WTs and MUTs. In situ CMs developed 10 years earlier in MUTs with respect to WTs, whereas no significant differences were observed in invasive CMs. In contrast to those reported previously by other authors, we did not find a difference in skin phototype.
Sembajwe LF, Katta K, Grønning M, Kusche-Gullberg M The exostosin family of glycosyltransferases: mRNA expression profiles and heparan sulphate structure in human breast carcinoma cell lines. Biosci Rep. 2018; 38(4) [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Breast cancer remains a leading cause of cancer-related mortality in women. In recent years, regulation of genes involved in heparan sulphate (HS) biosynthesis have received increased interest as regulators of breast cancer cell adhesion and invasion. The exostosin (EXT) proteins are glycosyltransferases involved in elongation of HS, a regulator of intracellular signaling, cell-cell interactions, and tissue morphogenesis. The EXT family contains five members: EXT1, EXT2, and three EXT-like (EXTL) members: EXTL1, EXTL2, and EXTL3. While the expression levels of these enzymes change in tumor cells, little is known how this changes the structure and function of HS. In the present study, we investigated gene expression profiles of the EXT family members, their glycosyltransferase activities and HS structure in the estrogen receptor (ER), and progesterone receptor (PR) positive MCF7 cells, and the ER, PR, and human epidermal growth factor receptor-2 (HER2) negative MDA-MB-231 and HCC38 epithelial breast carcinoma cell lines. The gene expression profiles for MDA-MB-231 and HCC38 cells were very similar. In both cell lines
Chen Z, Bi Q, Kong M, Chen Y A Novel EXT1 Mutation Identified in a Family with Multiple Osteochondromas. Genet Test Mol Biomarkers. 2019; 23(4):251-254 [PubMed] Related Publications
AIMS: Multiple exostoses (MO), also referred to as hereditary multiple exostoses (HME), is an autosomal dominant inherited skeletal disorder that has been found to be associated with mutations in the EXT1 and EXT2 genes. In the present study, we report a Chinese family with HME and our mutational analyses of the EXT1 and EXT2 genes in affected and unaffected individuals. METHODS: All exons of the EXT1 and EXT2 genes in seven family members were polymerase chain reaction amplified from blood and sequenced. RESULTS: A heterozygous mutation (c.1056G>T) was identified in exon 2 of the EXT1 gene in the proband and other affected family members; this mutation was not found in the unaffected family members. DISCUSSION: This c.1056G>T mutation is located in the exostosin domain of the EXT1 protein and leads to an amino acid change of Glutamine (Gln) to Histidine (His) at position 352. Homology searches reveal that Gln352 is highly conserved in many species and may play an essential role in the normal function of the EXT1 protein. CONCLUSIONS: This study contributes to a better understanding of the genetic basis of HME, expands the known mutational spectrum of EXT1, and provides a reference for genetic counseling and prenatal diagnosis of this family.
Santos SCL, Rizzo IMPO, Takata RI, et al. Analysis of mutations in EXT1 and EXT2 in Brazilian patients with multiple osteochondromas. Mol Genet Genomic Med. 2018; 6(3):382-392 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
BACKGROUND: Multiple osteochondromas is a dysplasia characterized by growth of two or more osteochondromas. It is genetically heterogeneous, caused by pathogenic variants in EXT1 or EXT2 genes in 70%-90% of patients. The EXT1 is more often mutated than EXT2 gene, with a variable prevalence between populations. There are no data about EXT1 and EXT2 pathogenic variants in patients with multiple osteochondromas in Brazilian population. The aim of this survey is to characterize these to determine the genotype profile of this population. METHODS: DNA sequencing (Sanger Method) and MLPA analysis were performed to identify point mutations and deletions/duplications in the sample of 153 patients in 114 families. RESULTS: Germline variants were identified in 83% of families in which EXT2 variants were detected in 46% and EXT1 in 37% of cases. No variants were detected in 17% of them. We identified 50 different variants, 33 (13 frameshift, 11 nonsense, 5 missense, 2 splice site mutation, and 2 large deletions) in EXT1 and 17 (6 frameshift, 6 splice site mutation, 3 nonsense, 1 missense, and 1 large deletion) in EXT2. Of all 50 variants, 31 (62%) were novel, including 20 out of 33 (60,6%) EXT1 and 11 out of 17 (64.7%) EXT2 alleles. The vast majority of variants (88%) were "loss-of-function" and two novel hotspots in EXT2 gene were observed in our study. CONCLUSION: The prevalence of variants detected in the EXT2 gene differs from other researches from Latin America, European, and Asian population. This uncommon prevalence could be related with the newly characterized variant hotspot sites detected in EXT2 gene (p.Ala409Profs*26 and p.Ser290*). A high number of novel variants were also identified indicating that Brazilian population has a unique genetic profile. Characterizing this population and establishing its genotype is essential to understand the molecular pathogenesis of this disease in Brazil.
Li Y, Wang J, Wang Z, et al. A genotype-phenotype study of hereditary multiple exostoses in forty-six Chinese patients. BMC Med Genet. 2017; 18(1):126 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
BACKGROUND: Hereditary multiple exostoses (HME) is a rare autosomal dominant skeletal disorder that can cause a variety of clinical manifestations. We aimed to evaluate the general clinical phenotypic severity of HME by using a scoring system and correlate the genotypes with different clinical phenotypes in Chinese patients. METHODS: Forty-six patients from different families were prospectively enrolled. The mutations were identified by direct sequencing of PCR-amplified genomic DNA or by multiplex ligation-dependent probe amplification (MLPA). Patients' demographic data, height, age of onset, number of anatomical sites, forearm deformity, and lower extremity alignment were analysed according to genotype and gender. A scoring system was used to assess the severity of the clinical phenotype. RESULTS: Thirty (60%) patients presented mutations in the EXT1 gene, and 16 (32%) presented mutations in the EXT2 gene. The mean age of onset was 2.96 years. The mean number of involved anatomic sites was 15.35. Male patients had more lesion sites than female patients (15.97 vs. 13.77, p = 0.046). The height evaluation illustrated that 67% of the patients (31 of 46) were below the 50th percentile, and the patients with EXT1 mutations were shorter than those with EXT2 mutations (p = 0.005). Forearm deformity showed a significant correlation with the number of involved anatomical sites (r = 0.382, p = 0.009). Moreover, a higher total score was found in patients with EXT1 mutations (p = 0.001). CONCLUSIONS: The clinical manifestations of 46 Chinese HME patients were similar to those in previous reports of Western populations. Patients with EXT1 mutations have a more severe clinical phenotype than patients with EXT2 mutations.
Hurst LD, Batada NN Depletion of somatic mutations in splicing-associated sequences in cancer genomes. Genome Biol. 2017; 18(1):213 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
BACKGROUND: An important goal of cancer genomics is to identify systematically cancer-causing mutations. A common approach is to identify sites with high ratios of non-synonymous to synonymous mutations; however, if synonymous mutations are under purifying selection, this methodology leads to identification of false-positive mutations. Here, using synonymous somatic mutations (SSMs) identified in over 4000 tumours across 15 different cancer types, we sought to test this assumption by focusing on coding regions required for splicing. RESULTS: Exon flanks, which are enriched for sequences required for splicing fidelity, have ~ 17% lower SSM density compared to exonic cores, even after excluding canonical splice sites. While it is impossible to eliminate a mutation bias of unknown cause, multiple lines of evidence support a purifying selection model above a mutational bias explanation. The flank/core difference is not explained by skewed nucleotide content, replication timing, nucleosome occupancy or deficiency in mismatch repair. The depletion is not seen in tumour suppressors, consistent with their role in positive tumour selection, but is otherwise observed in cancer-associated and non-cancer genes, both essential and non-essential. Consistent with a role in splicing modulation, exonic splice enhancers have a lower SSM density before and after controlling for nucleotide composition; moreover, flanks at the 5' end of the exons have significantly lower SSM density than at the 3' end. CONCLUSIONS: These results suggest that the observable mutational spectrum of cancer genomes is not simply a product of various mutational processes and positive selection, but might also be shaped by negative selection.
Ushakov VS, Tsidulko AY, de La Bourdonnaye G, et al. Heparan Sulfate Biosynthetic System Is Inhibited in Human Glioma Due to EXT1/2 and HS6ST1/2 Down-Regulation. Int J Mol Sci. 2017; 18(11) [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Heparan sulfate (HS) is an important component of the extracellular matrix and cell surface, which plays a key role in cell-cell and cell-matrix interactions. Functional activity of HS directly depends on its structure, which determined by a complex system of HS biosynthetic enzymes. During malignant transformation, the system can undergo significant changes, but for glioma, HS biosynthesis has not been studied in detail. In this study, we performed a comparative analysis of the HS biosynthetic system in human gliomas of different grades. RT-PCR analysis showed that the overall transcriptional activity of the main HS biosynthesis-involved genes (
Medek K, Zeman J, Honzík T, et al. Hereditary Multiple Exostoses: Clinical, Molecular and Radiologic Survey in 9 Families. Prague Med Rep. 2017; 118(2-3):87-94 [PubMed] Related Publications
Hereditary multiple exostoses (HME) represents a heterogeneous group of diseases often associated with progressive skeletal deformities. Most frequently, mutations in EXT1 and EXT2 genes with autosomal dominant inheritance are responsible for HME. In our group of 9 families with HME we evaluated the clinical course of the disease and analysed molecular background using Sanger sequencing and MLPA in EXT1 and EXT2 genes. The mean age in our group of patients, when the first exostosis was recognised was 4.5 years (range 2-10 years) and the number of exostoses per one patient documented on X-ray ranged from 2 to 54. Most of the exostoses developed before the growth was completed and they were dominantly localised in the distal femurs, proximal tibia, proximal humerus and distal radius. In all patients, at least one to 8 surgeries were necessary due to complaints and local complications, but neither patient developed malignant transformation. In half of the patients, the disease resulted in short stature. DNA analyses were positive in 7 families. In five probands, different EXT1 gene mutations resulting in premature stop-codon (p.Gly124Argfs*65, p.Leu191*, p.Trp364Lysfs*11, p.Val371Glyfs*10, p.Leu490Profs*31) were found. In two probands, nonsense mutations were found in EXT2 gene (p.Val187Profs*115, p.Cys319fs*46). Five mutations have been novel and two mutations have occurred de novo in probands. Although the risk for malignant transformation is usually low, especially in patients with low number of exostoses, early diagnostics and longitudinal follow up of patients is of a big importance, because early surgery can prevent progression of secondary bone deformities.
Xu Y, Kang Q, Zhang Z Identification of mutations in EXT1 and EXT2 genes in six Chinese families with multiple osteochondromas. Mol Med Rep. 2017; 16(4):5599-5605 [PubMed] Related Publications
The aim of the present study was to identify mutations of major causative genes in six unrelated Chinese families with multiple osteochondromas (MO). Radiographic examinations and genetic analyses were performed in 8 patients exhibiting typical features of MO. Analysis was also performed on unaffected members of the six families and 250 healthy volunteers. Radiographies of the patients revealed multiple exostoses in the cartilage of long bones. A total of five different mutations were identified, one in exostosin‑1 (EXT1) and four in exostosin‑2 (EXT2). Two novel mutations were detected in EXT2: A missense mutation, c.1385G>A, in exon 8, resulting in p.Trp462X; and a splice site mutation, c.725+1G>C, which consisted of a heterozygous guanine‑to‑cytosine transition at nucleotide 725+1 in intron 3. Three common EXT mutations were also detected: c.1036C>T in exon 5 of EXT2 resulting in p.Gln346X; c.1299C>A in exon 8 of EXT2 resulting in p.Phe433Leu; and c.1038A>T in exon 2 of EXT1 resulting in p.Arg346Ser. In conclusion, the present study identified a novel missense mutation (c.1385G>A) in exon 8 and a splicing mutation (c.725+1G>C) in intron 3 of the EXT2 gene, which are responsible for MO in certain Chinese patients. The findings are useful for expanding the database of known EXT2 mutations and understanding the genetic basis of MO in Chinese patients, which may improve genetic counseling and the prenatal diagnosis of MO.
Sinha S, Mundy C, Bechtold T, et al. Unsuspected osteochondroma-like outgrowths in the cranial base of Hereditary Multiple Exostoses patients and modeling and treatment with a BMP antagonist in mice. PLoS Genet. 2017; 13(4):e1006742 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Hereditary Multiple Exostoses (HME) is a rare pediatric disorder caused by loss-of-function mutations in the genes encoding the heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2. HME is characterized by formation of cartilaginous outgrowths-called osteochondromas- next to the growth plates of many axial and appendicular skeletal elements. Surprisingly, it is not known whether such tumors also form in endochondral elements of the craniofacial skeleton. Here, we carried out a retrospective analysis of cervical spine MRI and CT scans from 50 consecutive HME patients that included cranial skeletal images. Interestingly, nearly half of the patients displayed moderate defects or osteochondroma-like outgrowths in the cranial base and specifically in the clivus. In good correlation, osteochondromas developed in the cranial base of mutant Ext1f/f;Col2-CreER or Ext1f/f;Aggrecan-CreER mouse models of HME along the synchondrosis growth plates. Osteochondroma formation was preceded by phenotypic alteration of cells at the chondro-perichondrial boundary and was accompanied by ectopic expression of major cartilage matrix genes -collagen 2 and collagen X- within the growing ectopic masses. Because chondrogenesis requires bone morphogenetic protein (BMP) signaling, we asked whether osteochondroma formation could be blocked by a BMP signaling antagonist. Systemic administration with LDN-193189 effectively inhibited osteochondroma growth in conditional Ext1-mutant mice. In vitro studies with mouse embryo chondrogenic cells clarified the mechanisms of LDN-193189 action that turned out to include decreases in canonical BMP signaling pSMAD1/5/8 effectors but interestingly, concurrent increases in such anti-chondrogenic mechanisms as pERK1/2 and Chordin, Fgf9 and Fgf18 expression. Our study is the first to reveal that the cranial base can be affected in patients with HME and that osteochondroma formation is amenable to therapeutic drug intervention.
McCool C, Spinks-Franklin A, Noroski LM, Potocki L Potocki-Shaffer syndrome in a child without intellectual disability-The role of PHF21A in cognitive function. Am J Med Genet A. 2017; 173(3):716-720 [PubMed] Related Publications
Chen XJ, Zhang H, Tan ZP, et al. Novel mutation of EXT2 identified in a large family with multiple osteochondromas. Mol Med Rep. 2016; 14(5):4687-4691 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Multiple osteochondromas (MO), also known as hereditary multiple exostoses, is an autosomal dominant bone disorder. Mutations in exostosin glycosyl transferase‑1 (EXT1) and exostosin glycosyl transferase‑2 (EXT2), including missense, nonsense, frameshift and splice‑site mutations, account for up to 80% of reported cases. The proteins EXT1 and EXT2 form a hetero‑oligomeric complex that functions in heparan sulfate proteoglycan biosynthesis. A heterozygous EXT2 mutation, c.939+1G>T, was identified in a five‑generation 33‑member MO family, and was present in all 13 affected members. The mutation results in deletion of exon 5 in the mRNA, producing a frameshift that leads to a premature termination codon. The present study extends the mutational spectrum of EXT2.
Cousminer DL, Arkader A, Voight BF, et al. Assessing the general population frequency of rare coding variants in the EXT1 and EXT2 genes previously implicated in hereditary multiple exostoses. Bone. 2016; 92:196-200 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Hereditary multiple exostoses (HME) is a rare childhood-onset skeletal disease linked to mutations in exostosin glycosyltransferase 1 (EXT1) or 2 (EXT2). Patients are heterozygous for either an EXT1 or EXT2 mutation, and it is widely assumed that exostosis formation and associated defects, such as growth retardation and skeletal deformities, require loss-of-heterozygosity or a second hit in affected cells. However, the relevance and phenotypic impact of many presumed pathogenic EXT variants remain uncertain. We extracted all amino acid-altering (missense) and loss of function (LoF; nonsense, frameshift, or splice-site) variants from the Exome Aggregation Consortium (ExAC), a large population-based repository of exome sequence data from diverse ancestries that has screened out severe pediatric disease, to assess the overall mutation spectrum of predicted protein-damaging variants across these two genes in the general population. We then determined whether clinically-identified, presumably pathogenic variants implicated in HME exist among healthy individuals. We found six EXT1 and four EXT2 missense mutations in ExAC, suggesting that these mutations have either been misclassified as pathogenic or are not fully penetrant. Furthermore, EXT1 is heavily selectively constrained, while EXT2 is more tolerant to protein-damaging variants, especially at its C-terminus, possibly explaining the genotype-phenotype correlation that EXT1 variants usually result in more severe disease. In conclusion, population-based exome data is a useful filter for determining whether clinically detected variants are likely pathogenic, as well as revealing biological insight into rare disease genes such as EXT1 and EXT2.
Pitt SC, Hernandez RA, Nehs MA, et al. Identification of Novel Oncogenic Mutations in Thyroid Cancer. J Am Coll Surg. 2016; 222(6):1036-1043.e2 [PubMed] Related Publications
BACKGROUND: Thyroid cancer patients frequently have favorable outcomes. However, a small subset develops aggressive disease refractory to traditional treatments. Therefore, we sought to characterize oncogenic mutations in thyroid cancers to identify novel therapeutic targets that may benefit patients with advanced, refractory disease. STUDY DESIGN: Data on 239 thyroid cancer specimens collected between January 2009 and September 2014 were obtained from the Dana Farber/Brigham and Women's Cancer Center. The tumors were analyzed with the OncoMap-4 or OncoPanel high-throughput genotyping platforms that survey up to 275 cancer genes and 91 introns for DNA rearrangement. RESULTS: Of the 239 thyroid cancer specimens, 128 (54%) had oncogenic mutations detected. These 128 tumors had 351 different mutations detected in 129 oncogenes or tumor suppressors. Examination of the 128 specimens demonstrated that 55% (n = 70) had 1 oncogenic mutation, and 45% (n = 48) had more than 1 mutation. The 351 oncogenic mutations were in papillary (85%), follicular (4%), medullary (7%), and anaplastic (4%) thyroid cancers. Analysis revealed that 2.3% (n = 3 genes) of the somatic gene mutations were novel. These included AR (n = 1), MPL (n = 2), and EXT2 (n = 1), which were present in 4 different papillary thyroid cancer specimens. New mutations were found in an additional 13 genes known to have altered protein expression in thyroid cancer: BLM, CBL, CIITA, EP300, GSTM5, LMO2, PRAME, SBDS, SF1, TET2, TNFAIP3, XPO1, and ZRSR2. CONCLUSIONS: This analysis revealed that several previously unreported oncogenic gene mutations exist in thyroid cancers and may be targets for the development of future therapies. Further investigation into the role of these genes is warranted.
Ishimaru D, Gotoh M, Takayama S, et al. Large-scale mutational analysis in the EXT1 and EXT2 genes for Japanese patients with multiple osteochondromas. BMC Genet. 2016; 17:52 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
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.
Labonne JD, Vogt J, Reali L, et al. A microdeletion encompassing PHF21A in an individual with global developmental delay and craniofacial anomalies. Am J Med Genet A. 2015; 167A(12):3011-8 [PubMed] Related Publications
In Potocki-Shaffer syndrome (PSS), the full phenotypic spectrum is manifested when deletions are at least 2.1 Mb in size at 11p11.2. The PSS-associated genes EXT2 and ALX4, together with PHF21A, all map to this region flanked by markers D11S1393 and D11S1319. Being proximal to EXT2 and ALX4, a 1.1 Mb region containing 12 annotated genes had been identified by deletion mapping to explain PSS phenotypes except multiple exostoses and parietal foramina. Here, we report a male patient with partial PSS phenotypes including global developmental delay, craniofacial anomalies, minor limb anomalies, and micropenis. Using microarray, qPCR, RT-qPCR, and Western blot analyses, we refined the candidate gene region, which harbors five genes, by excluding two genes, SLC35C1 and CRY2, which resulted in a corroborating role of PHF21A in developmental delay and craniofacial anomalies. This microdeletion contains the least number of genes at 11p11.2 reported to date. Additionally, we also discuss the phenotypes observed in our patient with respect to those of published cases of microdeletions across the Potocki-Shaffer interval.
Huegel J, Enomoto-Iwamoto M, Sgariglia F, et al. Heparanase stimulates chondrogenesis and is up-regulated in human ectopic cartilage: a mechanism possibly involved in hereditary multiple exostoses. Am J Pathol. 2015; 185(6):1676-85 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
Hereditary multiple exostoses is a pediatric skeletal disorder characterized by benign cartilaginous tumors called exostoses that form next to growing skeletal elements. Hereditary multiple exostoses patients carry heterozygous mutations in the heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2, but studies suggest that EXT haploinsufficiency and ensuing partial HS deficiency are insufficient for exostosis formation. Searching for additional pathways, we analyzed presence and distribution of heparanase in human exostoses. Heparanase was readily detectable in most chondrocytes, particularly in cell clusters. In control growth plates from unaffected persons, however, heparanase was detectable only in hypertrophic zone. Treatment of mouse embryo limb mesenchymal micromass cultures with exogenous heparanase greatly stimulated chondrogenesis and bone morphogenetic protein signaling as revealed by Smad1/5/8 phosphorylation. It also stimulated cell migration and proliferation. Interfering with HS function both with the chemical antagonist Surfen or treatment with bacterial heparitinase up-regulated endogenous heparanase gene expression, suggesting a counterintuitive feedback mechanism that would result in further HS reduction and increased signaling. Thus, we tested a potent heparanase inhibitor (SST0001), which strongly inhibited chondrogenesis. Our data clearly indicate that heparanase is able to stimulate chondrogenesis, bone morphogenetic protein signaling, cell migration, and cell proliferation in chondrogenic cells. These properties may allow heparanase to play a role in exostosis genesis and pathogenesis, thus making it a conceivable therapeutic target in hereditary multiple exostoses.
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.
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] Article available free on PMC after 01/03/2020 Related 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] Article available free on PMC after 01/03/2020 Related 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.
Delgado MA, Martinez-Domenech G, Sarrión P, et al. A broad spectrum of genomic changes in latinamerican patients with EXT1/EXT2-CDG. Sci Rep. 2014; 4:6407 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
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.
Tian C, Yan R, Wen S, et al. A splice mutation and mRNA decay of EXT2 provoke hereditary multiple exostoses. PLoS One. 2014; 9(4):e94848 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
BACKGROUND: Hereditary multiple exostoses (HME) is an autosomal dominant disease. The classical paradigm of mutation screening seeks to relate alterations in the exostosin glycosyltransferase genes, EXT1 and EXT2, which are responsible for over 70% of HME cases. However, the pathological significance of the majority of these mutations is often unclear. METHODS: In a Chinese family with HME, EXT1 and EXT2 genes were screened by direct sequencing. The consequence of a detected mutant was predicted by in silico analysis and confirmed by mRNA analysis. The EXT1 and EXT2 mRNA and protein levels and the HS patterns in the HME patients were compared with those in healthy controls. RESULTS: A heterozygous transition (c.743+1G>A) in the EXT2 gene, which co-segregated with the HME phenotype in this family, was identified. The G residue at position +1 in intron 4 of EXT2 was predicted to be a 5' donor splice site. The mRNA analysis revealed an alternative transcript with a cryptic splice site 5 bp downstream of the wild-type site, which harbored a premature stop codon. However, the predicted truncated protein was not detected by western blot analysis. Decay of the mutant mRNA was shown by clone sequencing and quantification analysis. The corresponding downregulation of the EXT2 mRNA will contribute to the abnormal EXT1/EXT2 ratio and HS pattern that were detected in the patients with HME. CONCLUSION: The heterozygous mutation c.743+1G>A in the EXT2 gene causes HME as a result of abnormal splicing, mRNA decay, and the resulting haploinsufficiency of EXT2.
Jamsheer A, Socha M, Sowińska-Seidler A, et al. Mutational screening of EXT1 and EXT2 genes in Polish patients with hereditary multiple exostoses. J Appl Genet. 2014; 55(2):183-8 [PubMed] Article available free on PMC after 01/03/2020 Related Publications
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.