A novel deletion mutation of the EXT2 gene in a large Chinese pedigree with hereditary multiple exostosis

EXT2: a novel prognostic and predictive biomarker for head and neck squamous cell carcinoma

OBJECTIVE

This study focused on EXT2, a member of the EXT family involved in heparan sulfate synthesis, to evaluate its potential as a prognostic and predictive biomarker in head-neck squamous cell carcinoma (HNSCC).

MATERIALS AND METHODS

The present study used the cancer genome atlas head-neck squamous cell carcinoma (TCGA-HNSC) dataset-based UALCAN database to analyze the EXT2 expression and its clinicopathological features. In addition, we recruited 51 oral squamous cell carcinoma patients (OSCC), the most common HNSCC subtype, to validate the EXT2 mRNA expression analysis. In addition, we identified the role of EXT2 in prognosis using a Kaplan-Meier plot and immune signature using the tumor infiltration level. Furthermore, functional roles were analyzed using the EXT2 gene and protein networks.

RESULTS

The expression of EXT2 mRNA was significantly upregulated in OSCC tumors, which is consistent with the UALCAN-based results. EXT2 protein was also significantly overexpressed in HNSCC samples and was correlated with clinicopathological features. High EXT2 expression is associated with poor survival outcomes in HNSCC patients. Functional analysis of EXT2 using in silico tools revealed its involvement in critical pathways, including Wnt signaling, proteoglycans in cancer, and cellular responses to fibroblast growth and inflammation.

CONCLUSION

These findings highlight the potential of EXT2 as a prognostic and predictive biomarker of HNSCC.

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

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

The role of EXT1 gene mutation and its high expression of calcitonin gene-related peptide in the development of multiple exostosis

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.

Identification of a new mutation in an Iranian family with hereditary multiple osteochondromas

BACKGROUND

Hereditary multiple osteochondromas (HMO), previously named hereditary multiple exostoses (HME), is an autosomal dominant skeletal disorder characterized by the growth of multiple osteochondromas and is associated with bony deformity, skeletal growth reduction, nerve compression, restriction of joint motion, and premature osteoarthrosis. HMO is genetically heterogeneous, localized on at least three chromosomal loci including 8q24.1 (EXT1), 11p11-p13 (EXT2), and 19p (EXT3). The median age of diagnosis is 3 years; almost all affected individuals are diagnosed by age 12. The risk for malignant degeneration to osteochondrosarcoma increases with age, although the lifetime risk of malignant degeneration is low (~1%).

METHODS AND RESULTS

This study was performed on an Iranian family with nine affected individuals from three consecutive generations. Here, the proband was an affected woman who received genetic counseling prior to pregnancy. All exons of the three genes were examined in the proband using polymerase chain reaction and sequencing methods (the last member of this family is a male with severe deformities and lesions, especially around his large joints). Exon 4 of EXT1 (c.1235 G>A) was changed in affected individuals. This mutation alters tryptophan to a premature stop codon on amino acid position 412 (p.Trp412x).

CONCLUSION

The outcome of this study has extended the genotypic spectrum of Iranian patients with HMO, revealing a way for improving detection and genetic counseling in carriers.

A splice mutation and mRNA decay of EXT2 provoke hereditary multiple exostoses

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.

Novel mutations of EXT1 and EXT2 genes among families and sporadic cases with multiple exostoses

Hereditary multiple exostoses (HME) is an autosomal dominantly inherited disorder characterized by multiple benign cartilage-capped exostoses. Clinical manifestation of the disease is heterogenous. Overriding toes, scoliosis, spinal cord compression, and brachydactyly caused by shortening of metatarsals are rare findings. EXT1 and EXT2 are the genes responsible in most HME patients. We have characterized 11 HME families and 6 sporadic cases involving a total of 37 patients and performed mutational analysis of EXT1 and EXT2. Structural modeling of the wild and mutant proteins was also performed. Thirteen mutations were identified, including 8 that are novel. Among the novel mutations in EXT1, c.1004T>G-associated HME exhibited overriding toes and scoliosis, c.1883+2T>A-associated HME exhibited brachydactyly, and c.459_460delCT-associated exostosis arising from vertebra T4 caused spinal cord compression. Our structural predictions revealed four domains in the proteins encoded by EXT1 and EXT2: signalP, transmembrane regions, exostosin, and glyco_transf-64. The mutations truncated either part or whole of the exostosin domain and/or the C terminus of the glyco_transf-64 domain, or occurred within one of the domains. Our results provide new data for genetic diagnosis, identification of presymptomatic carriers, phenotype-genotype correlation, and understanding of the mechanisms of disease.

Multiple osteochondromas: mutation update and description of the multiple osteochondromas mutation database (MOdb)

Multiple osteochondromas (MO) is an autosomal dominant skeletal disease characterized by the formation of multiple cartilage-capped bone tumors growing outward from the metaphyses of long tubular bones. MO is genetically heterogeneous, and is associated with mutations in Exostosin-1 (EXT1) or Exostosin-2 (EXT2), both tumor-suppressor genes of the EXT gene family. All members of this multigene family encode glycosyltransferases involved in the adhesion and/or polymerization of heparin sulfate (HS) chains at HS proteoglycans (HSPGs). HSPGs have been shown to play a role in the diffusion of Ihh, thereby regulating chondrocyte proliferation and differentiation. EXT1 is located at 8q24.11-q24.13, and comprises 11 exons, whereas the 16 exon EXT2 is located at 11p12-p11. To date, an EXT1 or EXT2 mutation is detected in 70-95% of affected individuals. EXT1 mutations are detected in +/-65% of cases, versus +/-35% EXT2 mutations in MO patient cohorts. Inactivating mutations (nonsense, frame shift, and splice-site mutations) represent the majority of MO causing mutations (75-80%). In this article, the clinical aspects and molecular genetics of EXT1 and EXT2 are reviewed together with 895 variants in MO patients. An overview of the reported variants is provided by the online Multiple Osteochondromas Mutation Database (http://medgen.ua.ac.be/LOVD).

Therapeutic value of glycosaminoglycans in cancer

Glycosaminoglycans are unbranched polysaccharides composed of repeating units of alternating uronic acids and amino sugars. Most glycosaminoglycans are covalently attached to core proteins to form proteoglycans. Posttranslational modifications result in specific motifs that bind to a large variety of ligands, thus regulating growth factor signaling, cellular behavior, inflammation, angiogenesis, and the proteolytic environment. Dysregulated expression of glycosaminoglycans is present in cancer and reported to correlate with clinical prognosis in several malignant neoplasms. Recent knowledge on the biological roles of these molecules in cancer biology, tumor angiogenesis, and metastasis has promoted the development of drugs targeting them. Pharmaceutical approaches include the use of chemically modified heparins and glycosaminoglycans with defined structures, combination of inhibitors of glycosaminoglycan biosynthesis and polyamine depletion, and biologically active glycosaminoglycan-binding peptides. In addition, glycosaminoglycans are used as tumor-specific delivery and targeting vehicles for toxins and chemotherapeutics. Encouraging results in animal studies and clinical trials show the clinical relevance of glycosaminoglycan-based drugs and the use of glycosaminoglycans as therapeutic targets.