EXT1 Gene Mutations Research Articles

A patient with novel mutations causing MEN1 and hereditary multiple osteochondroma.

SummaryWe report of a male patient aged 32 years who presented with primary hyperparathyroidism. Three parathyroid glands were resected. At the age of 46 years, nervus facialis irritation was noted, and an MRI scan incidentally revealed a non-functioning pituitary adenoma with affection of the chiasma opticum. The patient underwent transsphenoidal operation resulting in pituitary insufficiency postoperatively. At the same time, primary hyperparathyroidism reoccurred and a parathyroid adenoma located at the thymus was resected. The mother of the patient died early due to multiple tumors. The patient was suspected to have multiple endocrine neoplasia type 1 (MEN1) and genetic analysis was performed. In addition, on clinical examination, multiple exostoses were noticed and an additional genetic analysis was performed. His father was reported to have multiple osteochondromas too. MEN1 was diagnosed in the patient showing a novel heterozygote mutation c.2T>A in exon 2, codon 1 (start codon ATG>AAG;p.Met1?) of the MEN1 gene. In genetic mutational analysis of the EXT1 gene, another not yet known mutation c.1418-2A>C was found in intron 5 of the EXT1 gene (heterozygotic). In conclusion, we report novel mutations of the EXT1 and the MEN1 genes causing hereditary multiple osteochondromas and MEN1 in one patient.Learning points It is important to ask for the patient's family history in detail.Patients with MEN1 are characterized by the occurrence of tumors in multiple endocrine tissues and nonendocrine tissues, most frequently parathyroid (95%), enteropancreatic neuroendocrine (50%), and anterior pituitary (40%) tissues.Familiar MEN1 has a high degree of penetrance (80–95%) by the age over 50; however, combinations of the tumors may be different in members of the same family.Patients with EXT1 gene mutations should be monitored for possible transformation of bone lesions into osteochondrosarcoma.

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

BackgroundHereditary 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. AimHere we present our genetic diagnostic report on the largest Southern Italy cohort of HME patients consisting of 90 subjects recruited over the last 5years. ResultsMolecular 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. ConclusionsHere 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.

Gene mutation screening and the genotype-phenotype correlation of hereditary multiple exostoses

Objective To establish the method of gene mutation screening for HME and investigate the relationship between genotype and clinical phenotype in HME patients. Methods Fifteen cases of HME probands were divided into the following four subgroups: mild (M) and severe ( Ⅰ S, Ⅱ S, Ⅲ S) according to the clinical diagnosis. DNA samples were obtained from the probands and family members. All of the EXT1 and EXT2 gene exons and their boundary sequences were amplified by PCR, and sequenced by directsequencing. Then the relationship between the genotypes and clinical phenotype was analyzed. Results Among the fifteen cases of HME probands, nine harbored EXT1 gene mutation, while the other 6 were positive for EXT2 gene mutation. Moreover, six novel mutations in EXT1 gene, including I8 + 2T ＞ G, c. 1182delG,c. 1108G ＞T(p. E370X) ,c. 335delA,c. 361C ＞T(p. Q121X) and c. 1879_1881delCAC were identified. In 9 patients with EXT1 gene mutation, 2 (22. 2% ) were M-type, 2 (22. 2% ) were Ⅰ S -type, 4 (44. 4% )were Ⅱ S-type,and 1 ( 11.1% ) was ⅢS-type. Whereas, 5 cases (83.3%) were M-type and only one case was Ⅱ S-type( 16. 7% ) in 6 patients with EXT2 gene mutation. Conclusions An accurate and simple gene diagnostic method for HME was established. Six novel EXT1 gene mutations, including I8 + 2T ＞ G,c. 1182delG, c. 1108G ＞T(p. E370X), c. 335delA, c. 361C ＞T(p. Q121X)and c. 1879_1881delCAC were identified as well. The clinical phenotype of the patients with EXT1 gene mutation was more severe compared to those with EXT2 gene mutations. Key words: Exostoses, multiple hereditary; N-Acetylglucosaminyltransferase; Genes, tumor suppressor; Mutation; Genotype; Phenotype

Osteopoikilosis and multiple exostoses caused by novel mutations in LEMD3 and EXT1 genes respectively - coincidence within one family

BackgroundOsteopoikilosis is a rare autosomal dominant genetic disorder, characterised by the occurrence of the hyperostotic spots preferentially localized in the epiphyses and metaphyses of the long bones, and in the carpal and tarsal bones [1]. Heterozygous LEMD3 gene mutations were shown to be the primary cause of the disease [2]. Association of the primarily asymptomatic osteopokilosis with connective tissue nevi of the skin is categorized as Buschke-Ollendorff syndrome (BOS) [3]. Additionally, osteopoikilosis can coincide with melorheostosis (MRO), a more severe bone disease characterised by the ectopic bone formation on the periosteal and endosteal surface of the long bones [4-6]. However, not all MRO affected individuals carry germ-line LEMD3 mutations [7]. Thus, the genetic cause of MRO remains unknown. Here we describe a familial case of osteopoikilosis in which a novel heterozygous LEMD3 mutation coincides with a novel mutation in EXT1, a gene involved in aetiology of multiple exostosis syndrome. The patients affected with both LEMD3 and EXT1 gene mutations displayed typical features of the osteopoikilosis. There were no additional skeletal manifestations detected however, various non-skeletal pathologies coincided in this group.MethodsWe investigated LEMD3 and EXT1 in the three-generation family from Poland, with 5 patients affected with osteopoikilosis and one child affected with multiple exostoses.ResultsWe found a novel c.2203C > T (p.R735X) mutation in exon 9 of LEMD3, resulting in a premature stop codon at amino acid position 735. The mutation co-segregates with the osteopoikilosis phenotype and was not found in 200 ethnically matched controls. Another new substitution G > A was found in EXT1 gene at position 1732 (cDNA) in Exon 9 (p.A578T) in three out of five osteopoikilosis affected family members. Evolutionary conservation of the affected amino acid suggested possible functional relevance, however no additional skeletal manifestations were observed other then those specific for osteopoikilosis. Finally in one member of the family we found a splice site mutation in the EXT1 gene intron 5 (IVS5-2 A > G) resulting in the deletion of 9 bp of cDNA encoding three evolutionarily conserved amino acid residues. This child patient suffered from a severe form of exostoses, thus a causal relationship can be postulated.ConclusionsWe identified a new mutation in LEMD3 gene, accounting for the familial case of osteopoikilosis. In the same family we identified two novel EXT1 gene mutations. One of them A598T co-incided with the LEMD3 mutation. Co-incidence of LEMD3 and EXT1 gene mutations was not associated with a more severe skeletal phenotype in those patients.

Identification of Four NovelEXT1andEXT2Mutations in Five Chinese Pedigrees with Hereditary Multiple Exostoses

Hereditary multiple exostoses (HME) is an autosomal dominant skeletal disorder most frequently caused by the EXT1 and EXT2 gene mutations resulting in reduction or absence of heparan sulfate (HS) in the exostotic cartilage cap. In this study, we investigated the molecular defects in five Chinese pedigrees with HME by direct sequencing analysis. Two novel EXT1 gene mutations and two novel EXT2 gene mutations were identified in two and three pedigrees, respectively. Of the four mutations identified, the c.651-664delinsTTT and c.680delG mutations in the exon 1 of EXT1 gene would cause frameshift (K218fs and R227fs) and introduce premature stop codon at amino acid site 220 and 251, respectively. The two missense mutations of c.398T > G in exon 2 and c.1016G > A in exon 6 of EXT2 gene result in the Leu133Arg and Cys339Tyr substitution, respectively. As HME is caused by defects in HS synthesis that is a complex process and not fully understood, these naturally occurring EXT mutations may provide important clues to future studies elucidating how EXT proteins contribute to HS biosynthesis.