腓骨肌萎缩症分子突变研究现状

腓骨肌萎缩症(charcot marie tooth disease,CMT)是一组高发病率的周围神经系统的单基因遗传病,具有临床和遗传异质性。可分为CMT1型,CMT2型,CMTX型和CMT4型。近些年随着分子遗传学和分子生物学的快速发展,已经发现了很多CMT的相关致病基因。主要包括外周髓鞘蛋白22基因、髓鞘蛋白零蛋白基因、间隙连接蛋白-32基因、驱动蛋白1B基因、Ras相关蛋白7基因、小分子热休克蛋白27基因等。本文就CMT相关致病基因研究现状作一综述。     

一个Charcot-Marie-Tooth病家系的分子遗传学分析

目的 鉴定一个Charcot-Marie-Tooth病(CMT)家系的致病突变.方法 根据家族史、临床表现和肌电图检查结果判断家系CMT分型.采集16名家系成员外周血,提取基因组DNA.针对CMT1的6个亚型,选择微卫星标记进行连锁分析.针对PMP22基因重复突变,采用实时定量PCR检测家系成员.结果 本家系疾病呈常染色体显性遗传.患者均有青少年发病、缓慢进展的下肢无力症状.部分患者经查体发现下肢腱反射减弱、痛触觉减弱,下肢神经传导速度均小于30 m/s,提示为CMT1型.通过连锁分析排除了CMT1A、CMT1E以外的其他4个亚型,证实患者基因组内PMP22基因存在重复突变.结论 此家系患者表型为CMT1A,其致病突变为染色体17p11.2区域内PMP22基因的重复.     

Golli蛋白在体内的分布与功能研究

髓鞘碱性蛋白(myelin basic protein,MBP),是一种单链多肽,相对分子质量(Mr)约为18500,主要分布位于神经系统的髓鞘与髓核中,在神经纤维的绝缘和快速传导中发挥重要作用.     

实时荧光定量PCR在周围髓鞘蛋白22基因重复或缺失检测中的应用

目的 应用实时荧光定量PCR在腓骨肌萎缩症和遗传性压力易感性神经病患者中检测周围髓鞘蛋白22基因（peripheral myelin protein 22，PMP22）重复或缺失。方法 采用实时荧光定量PCR检测113个腓骨肌萎缩症家系先证者、4个遗传性压力易感性神经病家系先证者和50名正常人PMP22基因重复或缺失突变。结果 113个腓骨肌萎缩症家系中发现有36个存在PMP22基因重复，4个遗传性压力易感性神经病先证者均存在PMP22基因缺失，50名正常人未发现异常。结论 我国PMP22基因重复突变的致病频率为31．9％（36／113），PMP22基因缺失突变是遗传性压力易感性神经病常见的致病原因。     

腓骨肌萎缩症1A亚型的发病机制及靶向药物研究进展

腓骨肌萎缩症(Charcot-Marie-Tooth disease,CMT)是一组常见的累及周围神经的单基因遗传病,其发病率约为1/2500。CMT1A是CMT最常见的亚型,约占确诊病例的50%。目前认为CMT1A的病因为外周髓鞘蛋白22基因重复突变,导致基因表达调控机制紊乱,与NRG1/ErbB通路失调、脂质代谢障碍等多种因素共同影响施旺细胞髓鞘形成。目前CMT1A患者的治疗以对症支持为主,针对上述可能的发病机制,CMT1A的靶向治疗药物正在研发中。本文就CMT1A的发病机制和靶向治疗药物的研究进展做一综述。     

遗传性运动感觉性周围神经病的研究进展

遗传性运动感觉性周围神经病又称夏科-马里-图思病（Charcot-Maric-Toothdisease，CMT病）及腓骨肌萎缩症，分别由Charcot、Marie及Tooth于1886年首次报道。该病代表了一组临床和遗传异质性的周围神经系统疾病。典型患者表现为遗传性慢性运动和感觉性多发性神经病。发病率约为1／2500。临床特点是上下肢远端肌肉进行性无力和萎缩，伴有轻到中度感觉减退，腱反射减弱和弓形足等。目前根据分子生物学研究结果将CMT分为CMT1、CMT2、CMT3、CMT4、CMTX等型，各型又再分为若干类型。不同类型有其相应的相关基因和特异的临床表现。目前通过遗传连锁研究已成功鉴定出至少22个基因位点和9个相关基因与该病有关。本文就近年来CMT病的致病基因、发病机制、遗传学特征、病理表现、临床症状及实验室检查等方面的研究进展进行阐述。希望明确CMT病基因型和表现型之间关系，从而为诊断及治疗该病提供新的依据，现作综述，     

丙烯酰胺暴露对幼鼠胼胝体PLP和MBP表达的影响

目的:检测断乳期幼鼠胼胝体髓鞘蛋白PLP和MBP的表达,探讨丙烯酰胺(acrylamide,ACR)染毒对幼鼠胼胝体部髓鞘发育的影响。方法:断乳期幼鼠随机分为对照组(0 mg/kg)、低(18 mg/kg)和高(36 mg/kg)剂量组,每组12只,从出生后第22~42 d进行灌胃染毒。观测幼鼠步态的变化,用免疫组化方法和免疫荧光双标记法检测幼鼠胼胝体髓鞘蛋白脂蛋白(myelin PLP,PLP)和髓鞘碱性蛋白(myelin basic protein,MBP)的表达。结果:ACR染毒后幼鼠的步态评分均增加,差异有统计学意义(P0.01),免疫组织化学检测结果显示,与对照组相比较,ACR高剂量组幼鼠大脑PLP和MBP表达减少,差异有统计学意义(P0.05)。免疫荧光双标技术检测结果与免疫组织化学检测结果一致,即ACR染毒后胼胝体PLP和MBP均表达减少。结论:ACR染毒可能会通过减少PLP和MBP的表达,抑制胼胝体髓鞘的形成而影响神经系统发育。     

Pelizaeus-Merzbacher病的分子遗传学研究进展

Pelizaeus-Merzbacher病(PMD)是罕见的遗传性脑白质营养不良病,是由于蛋白脂蛋白(poteolipid protein 1,PLP1)基因的突变导致髓鞘不能正常形成所致,其中以PLP1基因的重复突变最多见.PLP1基因不同的突变可导致特定的疾病类型,且基因型和表型之间总体上存在对应关系.本文对PMD的分子遗传学特点及近期对该病分子、细胞机制的认识进行综述.     

髓鞘形成不良变异鼠shi~(mld):在位与体外培养观察下与等位基因鼠shi之比较

Shi~(mld)鼠系一种中枢神经髓鞘形成发生障碍的变异鼠,它与另一种变异鼠Shi具有共同的遗传学上的等位基因。除了髓鞘碱性蛋白(MBP myelin basic protein)外,两者极为相似。我们用遗传学方法,将Shi~(mld)鼠的基因转移到正常B_6C_3H鼠,并与Shi鼠及其它髓鞘形成不良变异诸鼠进行比较。我们采用的B_6C_3H鼠是在Shi~(mld)基因转移持续四代以后的变异鼠,这样,其特殊基因转移获得之可能性在93％以上。     

小热休克蛋白22基因在腓骨肌萎缩症中的突变分析

目的 探讨小热休克蛋白22（small heat-shock protein 22，HSP22）基因在中国人腓骨肌萎缩症（Charcot-Marie-Tooth disease，CMT）中的突变特点。方法 应用聚合酶链反应和DNA直接测序方法，对1个发现HSP22基因423（G→T）突变的CMT2L家系外的114个CMT家系先证者进行了且HSP22基因的突变分析。结果 114个先证者中有2例患者在且HSP22基因的第3外显子发生了582（C→T）碱基改变，由于编码的氨基酸未改变，均为色氨酸（Thr），为一种同义突变。结论 HSP22基因突变在中国人的腓骨肌萎缩症患者中少见，突变率为0.87％（1／115）。     

Charcot–Marie–Tooth 1B caused by expansion of a familial myelin protein zero (MPZ) gene duplication

Charcot–Marie–Tooth (CMT) disease is a group of hereditary disorders affecting the motor and sensory nerves of the peripheral nervous system. CMT patterns of inheritance include dominant, recessive, and X-linked disorders. Charcot–Marie–Tooth disease, type 1B (CMT1B, OMIM 118200) is an autosomal dominant neuropathy caused by mutations in myelin protein zero (MPZ, OMIM 159440), a structural protein of peripheral myelin. Most causative MPZ mutations are missense sequence variants; however, recent clinical reports have described cases of CMT1B caused by increased dosage of the MPZ gene, with over-expression of the MPZ protein suspected to be causative of the disorder. We report an unusual case of early onset de novo CMT1B, caused by amplification of a familial, apparently benign, MPZ duplication.     

Mutations in the myelin protein zero gene associated with Charcot-Marie-Tooth disease type 1B

Charcot-Marie-Tooth type 1 (CMT1) disease is an autosomal dominant neuropathy of the peripheral nerve. The majority of CMT 1 cases are due to a duplication of an 1.5-Mb DNA fragment on chromosome 17pl1.2 (CMT la). Micromutations were found in the gene for peripheral myelin protein 22 (PMp22) located in the duplicated region of CMT la, and in the peripheral myelin protein zero (PO) located on chromosome lq21-23 (CMT Ib). We have characterized two new mutations in the PO gene in two french families presenting CMT disease. Both mutations occur in the extracellular domain of the PO protein. One mutation is a de novo mutation and is from paternal origin. © 1995 Wiley-Liss, Inc.     

Mutation analysis of the nerve specific promoter of the peripheral myelin protein 22 gene in CMT1 disease and HNPP.

We analysed the nerve specific promoter of the peripheral myelin protein 22 gene (PMP22) in a set of 15 unrelated patients with Charcot-Marie-Tooth type 1 disease (CMT1) and 16 unrelated patients with hereditary neuropathy with liability to pressure palsies (HNPP). In these patients no duplication/deletion nor a mutation in the coding region of the CMT1/ HNPP genes was detected. In one autosomal dominant CMT1 patient, we identified a base change in the non-coding exon 1A of PMP22 which, however, did not cosegregate with the disease in the family. This study indicates that mutations in the nerve specific PMP22 promoter and 5' untranslated exon will not be a common genetic cause of CMT1A and HNPP.     

Novel mutations in the Charcot-Marie-Tooth disease genes PMP22, MPZ,and GJB1

Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous disorder of the peripheral nervous system. CMT type 1 is most frequently caused by a 1.4 Mb tandem duplication in chromosome 17p11.2 comprising the peripheral myelin protein 22 (PMP22) gene. Furthermore sequence variations of PMP22, myelin protein zero (MPZ) and the gap junction protein b 1 gene (GJB1 or Connexin 32) may cause a variety of distinct CMT phenotypes. In this study we screened DNA from 42 unrelated patients for mutations in the PMP22, MPZ and GJB1 genes. Four novel mutations were identified. A Val65Phe amino acid exchange in PMP22 causes CMT type 1 associated with deafness, in GJB1 Tyr7_Thr8delinsSer, Pro172Ala and Ser138Asn are causes of CMTX neuropathies".     

Molecular analysis in Japanese patients with Charcot-Marie-Tooth disease: DGGE analysis for PMP22, MPZ,and Cx32/GJB1 mutations

Charcot-Marie-Tooth disease (CMT) is a heterogeneous disorder and is traditionally classified into two major types, CMT type 1 (CMT1) and CMT type 2 (CMT2). Most CMT1 patients are associated with the duplication of 17p11.2-p12 (CMT1A duplication) and small numbers of patients have mutations of the peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ), connexin 32 (Cx32/GJB1), and early growth response 2 (EGR2) genes. Some mutations of MPZ and Cx32 were also associated with the clinical CMT2 phenotype. We constructed denaturing gradient gel electrophoresis (DGGE) analysis as a screening method for PMP22, MPZ, and Cx32 mutations and studied 161 CMT patients without CMT1A duplication. We detected 27 mutations of three genes including 15 novel mutations; six of PMP22, three of MPZ, and six of Cx32. We finally identified 21 causative mutations in 22 unrelated patients and five polymorphic mutations. Eighteen of 22 patients carrying PMP22, MPZ, or Cx32 mutations presented with CMT1 and four of them with MPZ or Cx32 mutations presented with the CMT2 phenotype. DGGE analysis was sensitive for screening for those gene mutations, but causative gene mutation was not identified in many of the Japanese patients with CMT, especially with CMT1. Other candidate genes should be studied to elucidate the genetic basis of Japanese CMT patients.     

Mtmr13/Sbf2-deficient mice: an animal model for CMT4B2

Charcot-Marie-Tooth (CMT) disease denotes a large group of genetically heterogeneous hereditary motor and sensory neuropathies and ranks among the most common inherited neurological disorders. Mutations in the Myotubularin-Related Protein-2 (MTMR2) or MTMR13/Set-Binding Factor-2 (SBF2) genes are associated with the autosomal recessive disease subtypes CMT4B1 or CMT4B2. Both forms of CMT share similar features including a demyelinating neuropathy associated with reduced nerve conduction velocity (NCV) and focally folded myelin. Consistent with a common disease mechanism, the homodimeric MTMR2 acts as a phosphoinositide D3-phosphatase with phosphatidylinositol (PtdIns) 3-phosphate and PtdIns 3,5-bisphosphate as substrates while MTMR13/SBF2 is catalytically inactive but can form a tetrameric complex with MTMR2, resulting in a strong increase of the enzymatic activity of complexed MTMR2. To prove that MTMR13/SBF2 is the disease-causing gene in CMT4B2 and to provide a suitable animal model, we have generated Mtmr13/Sbf2-deficient mice. These animals reproduced myelin outfoldings and infoldings in motor and sensory peripheral nerves as the pathological hallmarks of CMT4B2, concomitant with decreased motor performance. The number and complexity of myelin misfoldings increased with age, associated with axonal degeneration, and decreased compound motor action potential amplitude. Prolonged F-wave latency indicated a mild NCV impairment. Loss of Mtmr13/Sbf2 did not affect the levels of its binding partner Mtmr2 and the Mtmr2-binding Dlg1/Sap97 in peripheral nerves. Mice deficient in Mtmr13/Sbf2 together with known Mtmr2-deficient animals will be of major value to unravel the disease mechanism in CMT4B and to elucidate the critical functions of protein complexes that are involved in phosphoinositide-controlled processes in peripheral nerves.     

Inherited neuropathies: from gene to disease

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A), another to chromosome 3p (CMT2B) and another to 7p (CMT2D). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.     

Localization of a gene responsible for autosomal recessive demyelinating neuropathy with focally folded myelin sheaths to chromosome 11q23 by homozygosity mapping and haplotype sharing

Hereditary motor and sensory neuropathy (HMSN) with focally folded myelin sheaths, or Charcot-Marie-Tooth type 4B (CMT4B), is a distinct clinical entity belonging to the heterogeneous group of autosomal recessive demyelinating neuropathies. We first described a large pedigree with CMT4B, which showed a high consanguinity level and an autosomal recessive pattern of inheritance. Through conventional linkage analysis, we excluded linkage of the locus segregating in this pedigree to any of the known genes responsible for other HMSNs. Using homozygosity mapping and haplotype sharing analysis, we were able to localize the disease gene in a 4 cM interval on chromosome 11q23, between the D11S1332 and D11S917 loci. On the basis of the clinical characteristics of the disease, we propose that this locus corresponds to the CMT4B gene.      

Genetic basis of inherited peripheral neuropathies

Progress in the elucidation of the genetic basis for inherited peripheral neuropathies has been remarkable over the last years. In particular, the molecular mechanisms underlying the autosomal dominantly inherited disorders Charcot–Marie–Tooth disease type 1A (CMT1 A), Charcot–Marie–Tooth disease type 1B (CMT1B), and hereditary neuropathy with liability to pressure palsies (HNPP) have been determined. While mutation in the gene encoding the major myelin protein, P_o has been associated with CMT1B, CMT1A and HNPP have been shown to be associated with reciprocal recombination events leading either to a large submicroscopic duplication in CMT1 A, or the corresponding DNA deletion in HNPP. Available evidence is consistent with the hypothesis that one or more genes within the relevant rearranged segment of 1.5 Mb on chromosome 17 is sensitive to gene dosage providing a novel mechanism for inherited human disorders. It is likely that the gene encoding the peripheral myelin protein PMP22 is at least one of the genes involved since the PMP22 gene maps within the CMT1A duplication (or HNPP deletion), and point mutations within it have been shown to cause a CMT phenotype in humans and comparable neuropathies in rodents (trembler and trembler^J). The mechanism(s) by which gene dosage and point mutations affecting the same gene might lead to a similar phenotype are currently unknown but recent transgenic mouse experiments suggest that similar mechanisms may also underlie other genetic diseases. © 1994 Wiley-Liss, Inc.