一个遗传性多发性骨软骨瘤家系的基因突变检测

目的 确定一个遗传性多发性骨软骨瘤(hereditary multiple exostoses,HME)家系的致病基因.方法 应用与EXT1、EXT2紧密连锁的短串联重复序列(short tandem repeat,STR)对该家系进行连锁分析,确定候选基因,然后对候选基因的编码区及外显子与内含子交界处进行PCR-测序法突变分析.结果 该家系致病基因被定位在EXT2基因区,测序发现EXT2基因536G>A无义突变,该突变位于EXT2基因第3外显子,导致编码第180位氨基酸的密码子成为终止密码,突变与疾病共分离,其余外显子未发现突变.另发现1例外显不全.结论 EXT2基因536G>A突变是导致这个家系发生骨软骨瘤的原因.     

Tricho-rhino-phalangeal syndrome without exostoses, with an interstitial deletion of 8q23

We report on a patient with the Tricho-Rhino-Phalangeal syndrome (TRPS) with normal mentation, without exostoses and with a partial microdeletion of 8q23. Although she had the phenotypic characteristics of TRPS Type I, karyotypic analysis demonstrated the 8q-microdeletion usually associated with TRPS Type II, in which exostoses are present. Our patient represents the second reported instance of this phenotypic chromosomal association and provides further evidence for homogeneity of the TRPS.     

Forearm deformities in multiple cartilaginous exostoses

Sixteen patients with 20 forearm deformities were reviewed. The deformities were classified into three types. The degree of ulnar tilt of the radius, ulnar displacement of the carpus, and relative ulnar shortening were determined. The severity of the deformity correlated with these measurements. Metacarpal lengths were also measured. Significant metacarpal shortening without exostoses was seen in 10 of 11 patients and with exostoses remote from the metaphysis in 10 of 13 patients. Metacarpal shortening correlated with the type and severity of deformity.     

Heparan sulfate in skeletal development,growth, and pathology: The case of hereditary multiple exostoses

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. Developmental Dynamics 242:1021–1032, 2013. © 2013 Wiley Periodicals, Inc.     

Autism-like socio-communicative deficits and stereotypies in mice lacking heparan sulfate

Heparan sulfate regulates diverse cell-surface signaling events, and its roles in the development of the nervous system recently have been increasingly uncovered by studies using genetic models carrying mutations of genes encoding enzymes for its synthesis. On the other hand, the role of heparan sulfate in the physiological function of the adult brain has been poorly characterized, despite several pieces of evidence suggesting its role in the regulation of synaptic function. To address this issue, we eliminated heparan sulfate from postnatal neurons by conditionally inactivating Ext1, the gene encoding an enzyme essential for heparan sulfate synthesis. Resultant conditional mutant mice show no detectable morphological defects in the cytoarchitecture of the brain. Remarkably, these mutant mice recapitulate almost the full range of autistic symptoms, including impairments in social interaction, expression of stereotyped, repetitive behavior, and impairments in ultrasonic vocalization, as well as some associated features. Mapping of neuronal activation by c-Fos immunohistochemistry demonstrates that neuronal activation in response to social stimulation is attenuated in the amygdala in these mice. Electrophysiology in amygdala pyramidal neurons shows an attenuation of excitatory synaptic transmission, presumably because of the reduction in the level of synaptically localized AMPA-type glutamate receptors. Our results demonstrate that heparan sulfate is critical for normal functioning of glutamatergic synapses and that its deficiency mediates socio-communicative deficits and stereotypies characteristic for autism.     

Multiple hereditary exostoses and enchondromatosis

Multiple hereditary exostoses (MHE) and enchondromatosis are rare multifocal benign disorders usually causing skeletal deformities appearing already in childhood. MHE is a dominant autosomal inherited disorder characterized by multiple osteochondromas (exostoses) growing outward from the metaphyses of long bones as well as from flat bones. They may cause reduced joint motion and pain due to tendon, muscle, and nerve compression.Enchondromatosis (or Ollier's disease) is a noninherited disorder characterized by the presence of multiple intraosseous enchondromas located asymmetrically in the skeleton and with a wide variation regarding location, size, and number ranging from the involvement of a single hand to the involvement of the entire skeleton. It can occur together with soft-tissue hemangiomas in Maffucci's syndrome. Clinical problems caused by the enchondromas are mainly related to skeletal deformities causing malalignment and restricted motion of joint.In both disorders, there is a risk of malignant transformation as well as secondary degenerative joint changes.     

1例遗传性多发性骨软骨瘤家系EXT1基因分析

目的 遗传性多发性骨软骨瘤（HME）是一种常染色体单基因显性遗传骨发育异常疾病,超过70% 为EXT1、EXT2 突变所致。该文目的是分析一HME 家系（3 代24 名成员,6 名HME 患者）临床特征及致病基因与突变;并通过文献复习统计分析中国人种基因突变情况。方法 收集、整理、分析该家系临床资料;应用PCR 及直接测序进行EXT1 基因分析;应用Pubmed 及万方数据库检索中国人种HME 基因突变文献。结果 （1）该家系起病年龄逐代变早,骨软骨瘤发作部位及数量逐代增多,身体变形逐代严重。（2）患者均发现EXT1 基因杂合剪切突变IVS5+1G>A,该突变在中国人中首次发现。（3）至今中国HME 家庭（含该家系）基因突变构成比为EXT1 为29%（26/90）,EXT2 为43%（39/90）。结论 （1）该HME 家系呈现病情逐代加重情况。（2）该家系由EXT1 基因剪切突变IVS5+1G>A 导致发病。（3）中国人种EXT1、EXT2 突变构成比与西方人不一致。     

The molecular and cellular basis of exostosis formation in hereditary multiple exostoses

The different clinical entities of osteochondromas, hereditary multiple exostoses (HME) and non-familial solitary exostosis, are known to express localized exostoses in their joint metaphyseal cartilage. In the current study biopsies of osteochondromas patients were screened with respect to a number of cellular and molecular parameters. Specifically, cartilaginous biopsy samples of nine HME patients, 10 solitary exostosis patients and 10 articular cartilages of control subjects were collected and cell cultures were established. Results obtained showed that one of the two HME samples that underwent DNA sequencing analysis (HME-1) had a novel mutation for an early stop codon, which led to an aberrant protein, migrating at a lower molecular weight position. The EXT-1 mRNA and protein levels in chondrocyte cultures derived from all nine HME patients were elevated, compared with solitary exostosis patients or control subjects. Furthermore, cell cultures of HME patients had significantly decreased pericellular heparan sulphate (HS) in comparison with cultures of solitary exostosis patients or control subjects. Immunohistochemical staining of tissue sections and Western blotting of cell cultures derived from HME patients revealed higher levels of heparanase compared with solitary exostosis patients and of control subjects. Further investigations are needed to determine whether the low pericellular HS levels in HME patients stem from decreased biosynthesis of HS, increased degradation or a combination of both. In conclusion, it appears that due to a mutated glycosyltransferase, the low content of pericellular HS in HME patients leads to the anatomical deformations with exostoses formation. Hence, elevation of HS content in the pericellular regions should be a potential molecular target for correction.     

Identification of a novel EXT2 frameshift mutation in a family with hereditary multiple exostoses by whole‐exome sequencing

BackgroundHereditary multiple exostoses (HME), also referred to as multiple osteochondromas, is an autosomal dominant skeletal disease characterized by the development of multiple overgrown benign bony tumors capped by cartilage and is associated with bone deformity, joint limitation, and short stature. Mutations in exostosin glycosyltransferase (EXT)1 and EXT2 genes, which are located on chromosomes 8q24.1 and 11p13, contribute to the pathogenesis of HME.MethodsIn the present study, a genetic analysis of a four‐generation Chinese family with HME was conducted using whole‐exome sequencing (WES), followed by validation using Sanger sequencing.ResultsA novel heterozygous frameshift mutation in exon 5 of EXT2 (c.944dupT, p.Leu316fs) was identified in all affected individuals but was not detected in any unaffected individuals. This mutation results in a frameshift that introduces a premature termination codon at position 318 (p.Leu316fs) with the ability to produce a truncated EXT2 protein that lacks the last 433 amino acids at its C‐terminal to indicate a defective exostosin domain and the absence of the glycosyltransferase family 64 domain, or to lead to the degradation of mRNAs by nonsense‐mediated mRNA decay, which is critical for the function of EXT2.ConclusionOur results indicate that WES is effective in extending the EXT mutational spectra and is advantageous for genetic counseling and the subsequent prenatal diagnosis.