X-LINKED DOMINANT CHARCOT-MARIE-TOOTH NEUROPATHY: ANALYSIS OF A PEDIGREE WITH A NOVEL MUTATION OF CONNEXIN 32

Objective: To report a family with X-linked Charcot-Marie-Tooth neuropathy (CMTX) with a novel mutation of connexin 32 (Cx32).
Background: Cx32, a gap-junction protein, is expressed in various neural and non-neural tissues. In the peripheral nervous system (PNS), Cx32 is expressed by the Schwann cell and it is believed to form reflexive gap-junctions at the Schmidt-Lantermann incisures and paranodes; in the central nervous system, Cx32 is expressed by neurons and oligodendrocytes. Mutations of Cx32 causes an apparently tissue-specific disorder of PNS: CMTX.
Methods: We examined, clinically and electrophysiologically, 2 brothers with CMT and their asymptomatic mother. We performed a sural nerve biopsy in the 29-year-old proband and analysed the Cx32 gene (GJB1) by direct nucleotide sequencing.
Results: We detected a novel GTA→GAA of GJB1 that is predicted to cause a Val23Glu substitution in the first transmembrane domain of Cx32. NCV studies disclosed features of a demyelinating neuropathy in the severely-affected hemizygous brother, and slowing of the sensory conduction velocity in the sural nerve in the mother who showed pes cavus and areflexia. In all three examined patients, BAEPs showed both delayed wave 1 and prolonged interpeak-latency-time (IPL I-V); central motor conduction time by MEPs was normal. The nerve biopsy in the proband was consistent with a primary axonal degeneration.
Conclusions: Cx32 mutations may lead also to a dysfunction of the CNS. Electrophysiological abnormalities of the CNS pathways may orientate the diagnosis of CMT towards Cx32.     

X连锁腓骨肌萎缩症Cx32基因的突变、临床和电生理特点

目的 分析X连锁腓骨肌萎缩症（CMTX）患者Cx32基凶的突变及其临床表现和电生理特点、方法应用多聚酶链反应一单链构象多态性分析结合DNA直接测序的方法,对24例无周围髓鞘蛋白（PMP）22基因大片段重复突变,家系中无男传男的腓骨肌萎缩症（CMT）先证者进行Cx32基因的突变分析;对先证者及其家系内患者进行临床和电生理检查。结果 在6个X连锁遗传家系和1例散发患者中发现了7个不同的Cx32基因突变,其中4个家系临床分型为CMTI型,2个家系为CMT中间型,散发病例为CMT1型检测到有Cx32基因突变的家系成员共38例,其巾男性20例,全部为CMTX患者;女性18例,其中6例为CMTX患者,12例为无临床症状的携带者;26例患者均为周围神经轻、中度受累。结论 CMTX的遗传方式可为X连锁显性、X连锁隐性遗传,也可为散发。根据临床和电生理特点分为CMTI型或CMT中间型,多为周围神经轻、中度受累,男性患者的症状通常较女性重。在没有检测到PMP22基因大片段重复突变和无男传男的CMT家系中应首先进行Cx32基因突变分析。     

Phenotypic expression of a Pro 87 to Leu mutation in the connexin 32 gene in a large Swiss family with Charcot-Marie-Tooth neuropathy

BACKGROUND: The clinical manifestations of CMTX have been well described but the natural history has not yet been studied in detail. We studied phenotype variability in a family with a Pro 87 to Leu mutation of the connexin 32 (Cx32) gene. METHODS: A total of 32 family members, of which 19 patients were affected, underwent clinical, electrophysiological, and genetic studies. RESULTS: Onset was in the second decade. Clinical features were similar in both sexes when quantitative scores were compared, but more males had a steppage gait and skeletal deformities. All adult patients had a predominant involvement of the thenar muscles. The median values of nerve conduction velocities (NCVs) were not statistically different in men and in women. The correlation coefficients were low between motor NCVs within the same extremities, indicating nonuniform slowing between nerves, the ulnar nerve being the least affected. When disability was rated, a strong correlation was seen in male patients between severity of motor axonal loss and duration of the disease. The main pathological features were axonal loss, clusters of regenerating fibers and paranodal demyelination, the hallmark of a Schwann cell pathology. CONCLUSIONS: Our data support the hypothesis that clinical disability in CMTX is caused by loss of large myelinated axons in men. Furthermore, this study shows that the nerves are not uniformly affected in terms of axonal loss. Preventing axonal degeneration and promoting axonal regeneration in the most affected nerves might be the best therapeutic approaches to ameliorate disability in CMTX.     

A NOVEL MUTATION OF CONNEXIN-32 GENE IN A CMTX ITALIAN FAMILY

X-linked Charcot-Marie-Tooth is an inherited motor and sensory neuropathy associated with mutations in GJB1, a gene on chromosome X coding for the gap junction protein "connexin 32" (Cx32). Cx 32 gene is expressed in both peripheral and central nervous system myelin.
We describe a family affected by X-linked CMT neuropathy with a novel point mutation in Cx32 gene, in which the mother, the putative carrier, and three affected sons were examined. The affected sons (32, 35, 38 yrs) presented a motor-sensory slowly progressive neuropathy mainly involving lower limbs. Nerve conduction study showed both axonal and demyelinating pattern of denervation. Evoked potentials indicated visual and brainstem auditory pathway involvement. The mother showed subclinical electrophysiological abnormalities in nerve conduction velocities.
By mutational analysis of GJB1 using SSCP and sequencing of candidate regions, a previously undescribed missense mutation in the exon 2, codon 151, was found. This mutation was due to a transversion (TAT-> TCT) leading to a Tyr->Ser substitution in the 2nd extracellular domain.
Our findings further stress the wide variability in the spectrum of Cx32 mutations associated to CMTX, making it worthwhile to deepen knowledge about genotypic–phenotypic interrelationship in this disease.     

腓骨肌萎缩症X型临床、电生理及Connexin 32新突变一例

目的报告1例X连锁型腓骨肌萎缩症(CMTX),探讨其临床表现、电生理特点和连接蛋白32(Cx32)基因突变特点。方法对1例临床诊断CMT患者进行详细的病史采集和临床查体,分析其电生理和神经活检检查结果,同时进行周围髓鞘结构蛋白22(PMP22)基因重复和Connexin32(Cx32)基因突变检测。结果患者临床表现为经典的遗传性感觉运动神经病,肌电图检查提示脱髓鞘损害伴轴索损害,同时出现传导阻滞;神经活检示脱髓鞘性周围神经损害;基因检测发现Cx32基因编码序列第414位碱基发生单碱基错义突变(414C>G),造成其编码的第138位的氨基酸由丝氨酸突变为精氨酸(Ser138Arg)。结论 414C>G突变为Cx32基因新突变,国内外文献未见报道。该基因型没有产生特殊的临床表现,但电生理表现为脱髓鞘为主的混合性周围神经病变,且具有传导阻滞的特点。Cx32基因不同的突变位点和形式可能是导致CMTX临床异质性的原因之一。     

Six novel connexin32 (GJB1) mutations in X-linked Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMTX) is a clinically heterogeneous hereditary motor and sensory neuropathy with X-linked transmission. Common clinical manifestations of CMTX, as in other forms of Charcot-Marie-Tooth disease (CMT), are distal muscle wasting and weakness, hyporeflexia, distal sensory disturbance, and foot deformities. Motor nerve conduction velocity is reduced. In male patients it is often less than 38 m/s in the median nerve (a value often used to distinguish between "demyelinating" and "axonal" forms of CMT), but in female patients conduction velocity may be faster than this or normal. Mutations in the connexin32 (gap junction protein beta 1 (GJB1)) gene are responsible for the majority of CMTX cases. This report describes six British CMTX families with six novel mutations (four missense, one nonsense, and one frame shift) of the GJB1 gene. Affected members in these six families had typical signs of CMT but in some affected members of three families there was additional central nervous system involvement or deafness in the absence of any other explanation other than CMT.     

A novel mutation in PRPS1 causes X‐linked Charcot‐Marie‐Tooth disease‐5

X‐linked Charcot‐Marie‐Tooth disease‐5 (CMTX5) is a rare hereditary disorder caused by mutations in the gene for phosphoribosyl pyrophosphate synthetase‐1 (PRPS1). We investigated a boy with a novel PRPS1 mutation (c.334G>C, p.V112L) via genetic, neuropathological and enzymatic tests. The proband was a 13‐year‐old boy with congenital non‐syndromic sensorineural deafness. At 3 year old, he developed progressive distal weakness of all limbs with muscle atrophy of both hands and shanks. Nerve conduction study revealed the loss of sensory nerve action potentials, and slowing down of motor nerve conduction velocities with a decrease of amplitudes of compound motor action potentials. Visual evoked potentials and brainstem auditory evoked potentials were not bilaterally evocable. Sural biopsy proved the loss of myelinated nerve fibers, with axonal degeneration, regenerating clusters and onion bulbs. Enzymatically, PRPS1 activity was close to zero in the proband and mildly reduced in his mother, compared with controls. To our knowledge, this is the first report of CMTX5 in a Chinese population. The genetic finding has expanded the genotypic spectrum of PRPS1 mutations.     

腓骨肌萎缩症伴神经性耳聋一家系临床和分子遗传学分析

目的探讨一个X连锁腓骨肌萎缩症(CMTX)伴常染色体隐性遗传的神经性耳聋家系的临床特点并研究其分子遗传学病因。方法对9名家系成员进行详细的临床检查，先证者进行了神经肌电图、听觉诱发电位和神经活检，3名耳聋患者进行电测听检查。运用聚合酶链反应一单链构象多态性分析技术(PCR-SSCP)结合直接测序法进行间隙连接蛋白32(eonnexin32)的突变分析，直接测序法进行间隙连接蛋白26(connexin26)的突变分析。结果家系中3名腓骨肌萎缩症患者为X连锁显性遗传，3名神经性耳聋患者为常染色体隐性遗传，其中1名患者同时出现腓骨肌萎缩症和神经性耳聋的临床症状。CMTX由connexin32错义突变C223T(Arg75Trp)引起。耳聋症状与connexin32点突变无共分离现象，对connexin26直接测序亦未发现突变，耳聋的致病基因有待进一步探讨。结论该家系腓骨肌萎缩症和耳聋分别由不同基因突变引起，这种在一个家系中同时出现两种不同遗传方式，不同致病基因的遗传病罕有报道。     

Inter-nerves and intra-nerve conduction heterogeneity in CMTX with Arg(15)Gln mutation.

OBJECTIVE: In X-linked Charcot-Marie-Tooth disease (CMTX), electrophysiological and histopathological studies have suggested either a demyelinating or an axonal polyneuropathy. We report a CMTX family with a striking heterogeneity of nerve conductions between and within nerves. METHODS: Two men and one woman have been studied by conduction velocities, sural nerve biopsy with morphometry (one man) and DNA analysis. RESULTS: In both men motor conduction velocities were slowed in the demyelinating range, conduction velocity differences among nerves in the same subject varied from 13 to 24 m/s, and distal median compound muscle action potential (CMAP) amplitudes were 3-5 times reduced compared to ulnar CMAPs. Abnormal area reduction or excessive temporal dispersion of proximal CMAP was present in at least two nerves in all patients. Sural nerve biopsy showed reduction of large myelinated fibres, cluster formations, occasional onion bulbs. Teased fibres study revealed short internodes for fibre diameter, enlarged Ranvier nodes but no evidence of segmental demyelination and remyelination. DNA analysis showed an Arg(15)Gln mutation in connexin32 gene in all patients. CONCLUSIONS: In this family conduction slowing and segmental conduction abnormalities, in absence of morphological evidence of de-remyelination, may be related to short internodes, widened Ranvier nodes and the specific effect of the mutation. The occurrence in some CMTX patients of a non uniform involvement between and within nerves, as in acquired demyelinating neuropathies, should be kept in mind to avoid misdiagnoses.     

Central visual, acoustic, and motor pathway involvement in a Charcot-Marie-Tooth family with an Asn205Ser mutation in the connexin 32 gene

BACKGROUND: X linked dominant Charcot-Marie-Tooth disease (CMT1X) is an inherited motor and sensory neuropathy that mainly affects the peripheral nervous system. CMT1X is associated with mutations in the gap junction protein connexin 32 (Cx32). Cx32 is expressed in Schwann cells and oligodendrocytes in the peripheral (PNS) and in the (CNS) respectively. METHODS: A CMT1X family with a Cx32 mutation was examined clinically and electrophysiologically to determine whether PNS, or CNS, or both pathways were affected. RESULTS: In a CMT1X family a novel mutation (Asn205Ser) was found in the fourth transmembrane domain of Cx32. The patients showed typical clinical and electrophysiological abnormalities in the PNS, but in addition visual, acoustic, and motor pathways of the CNS were affected subclinically. This was indicated by pathological changes in visually evoked potentials (VEPs), brainstem auditory evoked potentials (BAEPs), and central motor evoked potentials (CMEPs). CONCLUSIONS: These findings underscore the necessity of a careful analysis of CNS pathways in patients with CMT and Cx32 mutations. Abnormal electrophysiological findings in CNS pathway examinations should raise the suspicion of CMTX and a search for gene mutations towards Cx32 should be considered.     

腓骨肌萎缩症X型伴有可逆性中枢神统系统受累

目的探讨的腓骨肌萎缩症X型的临床特点和引起中枢神经系统受累可能的发病机制。方法报道1例国内未报道过的CMTX可引起中枢神经系统受累Cx32基因突变,分析该例患者的临床、电生理及病理改变特点。结果该患者为基因检查确诊Arg424Trp(R142W)突变的CMTX。临床存在可逆性眼震,电生理提示感觉运动神经受累均受累,轴索髓鞘均损害。肌肉活检提示慢性神经源性病理改变。周围神经活检示周围神经髓鞘损害为主。BAEP提示可逆性中枢性损害。结论 R142W突变的CMTX可以在应激条件下出现可逆性中枢神经系统损害。     

X连锁Charcot-Marie-Tooth病1型六个家系的病理和基因突变特点

目的 报道6个X连锁Charcot-Marie-Tooth病1型(CMTX1)家系的神经病理和基因型改变特点.方法 6个CMTX1家系的先证者均为男性,发病年龄11 ～24岁,出现下肢远端为主的肌无力、腱反射减低和轻度感觉减退.先证者1伴随发作性白质脑病,先证者5伴随小脑性共济失调.12名家系成员也出现周围神经损害症状,另7名存在高弓足或腱反射减低.对6例先证者行腓肠神经活体组织检查,并对6例先证者、8名受累家庭成员和10名无症状家系成员及50名健康女性进行缝隙连接蛋白32( Cx32)基因测序.结果 6例先证者有髓神经纤维出现轻-中度减少伴轴索再生变性,5例出现薄髓鞘神经纤维,其中3例伴洋葱球样结构,2例伴炎细胞浸润.6个家系的Cx32基因存在5种新突变和1种同义突变,即L20T、I127F、D178G、A197V错义突变,403_404T insT插入突变和L10L沉默突变,10名无症状家系成员中有4名女性为携带者,6名男性和健康对照均没有这些基因突变.结论 该组CMTX1患者的周围神经病理改变以慢性轴索损害为主,Cx32基因较多新突变的出现提示我国CMTX1患者具有个体突变特点.     

腓骨肌萎缩症X1型1个家系的临床、电生理和Connexin32基因突变分析

目的观察腓骨肌萎缩症(CMT)X1型的临床、电生理特点和Connexin32(Cx32)基因突变情况.方法对1个无基因重复的临床可疑的CMTX1家系中的3例患者进行详尽的临床和神经电生理检查,并应用变性高效液相色谱结合混和样品池法和DNA序列测定对包括先证者在内的3名成员的Cx32基因进行突变检测.结果 该家系中的病人发生了Gly12Ser,50名正常人中未发现上述改变,提示该突变为致病性突变.家系中男性病人临床症状重于女性;电生理特点为脱髓鞘改变;同一病人的不同神经间存在异质性.结论 Gly12Ser突变可能导致原发性脱髓鞘性神经病,不伴有特殊的临床表现.     

CNS involvement in CMTX1 caused by a novel connexin 32 mutation: a 6-year follow-up in neuroimaging and nerve conduction

X-linked Charcot-Marie-Tooth disease, type 1 (CMTX1) is one of the most common inherited neurological disorders. Obvious CNS involvement is relatively rare in CMTX1 patients. A 24-year-old male with CMTX1 presented with three transient stroke-like attacks, and was followed up regularly for 6 years with brain MRI and electrophysiological examination. Transient symmetrical high signals on T2 imaging and restricted diffusion were found in bilateral deep white matter. Electrophysiological measurement revealed a sensorimotor peripheral neuropathy with slightly reduced nerve conduction velocities. A novel thymine to cytosine mutation at nucleotide position 445 in the connexin 32 allele of the GJB1 gene was identified. During the 6-year longitudinal study, patient’s motor and sensory function did not worsen; radiological abnormalities correlated with episodes of CNS dysfunction and resolved after clinical recovery; electrophysiological records showed no obvious change. Little change in the patient’s clinical, radiological and electrophysiological results over the follow-up reflected a slow disease progression.     

Unusual electrophysiological findings in X-linked dominant Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMTX) is the second most common form of Charcot-Marie-Tooth disease. Variable histopathological and nerve conduction velocity (NCV) results have suggested either a primary demyelinating or axonal polyneuropathy. We identified five individuals across three generations in a family with CMTX associated with a mutation in the gene coding for connexin 32. All individuals were studied by clinical neurological examination, DNA analysis, and nerve conduction studies. The proband (1174/KD) also underwent a sural nerve biopsy. As expected, all the affected males were more clinically affected than the females. All affected males and obligate female carriers exhibited some electrophysiological characteristics of demyelination. However, striking heterogeneity of nerve conduction velocities was seen. This family shows that CMTX is a heterogeneous and distinctly nonuniform demyelinating polyneuropathy, the severity of which varies with sex and age. Such electrophysiological variability is unique among hereditary neuropathies.     

Case report of transient splenium abnormality in Charcot-Marie-Tooth disease]

We report a patient of Charcot-Marie-Tooth disease (CMT) accompanied by transient splenium abnormality in brain MRI. A 34-year-old man suffered from chronic progressive unsteadiness and sensory disturbance of all limbs. Neurological examination showed muscle weakness and atrophy in the distal extremities with pes cavus, mild sensory disturbance of four extremities and generalized decreased reflexes. The nerve conduction study described the presence of sensory-motor polyneuropathy. We could not investigate his GJB1 gene. However, we suspected that he was X-linked CMT (CMTX), because his electrophysiological findings showed intermediate slowing of MCV, and auditory brain-stem response (ABR) demonstrated central conduction slowing. Brain MRI revealed the abnormal high signal intensity in the splenium of the corpus callosum on T2-weighted image. This lesion diminished two months later without any treatment. Recently, there had been reported transient splenium abnormality in CMTX cases, and there were clinical similarities between the cases of these reports and our case. We considered that the pathophysiology of this case was the disruption of gap junction communications expressed between oligodendrocyte and astrocytes induced by connexin 32 (Cx32) mutations. Furthermore, the transient functional disturbance of astrocytes would be another pathophysiologic mechanism of splenium abnormality.     

Transient,recurrent, white matter lesions in X-linked Charcot-Marie-Tooth disease with novel connexin 32 mutation

BACKGROUND: X-linked hereditary demyelinating neuropathies (Charcot-Marie-Tooth Disease [CMTX]) caused by mutations in the connexin 32 (Cx32) gene account for approximately 10% to 20% of all hereditary demyelinating neuropathies. Mild subclinical central nervous system (CNS) involvement has been previously described, and CMTX patients with transient white matter lesions allied to CNS symptoms have very recently been described. This is of potential interest, as Cx32 is widely expressed in both peripheral nerve and the brain. PATIENTS: We describe a family with hereditary demyelinating neuropathy and transient CNS symptoms. For this study, family members underwent genotyping and detailed clinical, electrophysiological, and magnetic resonance imaging examination. RESULTS: We present a CMTX family with a novel mutation in the Cx32 gene. Affected family members show, in addition to the classic polyneuropathy, transient and reversible white matter lesions on magnetic resonance imaging scans, correlating similarly transient CNS symptoms. CONCLUSION: Patients with CMTX can present with transient CNS symptoms and marked white matter lesions on magnetic resonance imaging scans.     

Charcot‐Marie‐Tooth type X: unusual phenotype of a novel CX32 mutation

Background: X‐linked Charcot‐Marie‐Tooth disease (CMTX), caused by mutations in the gene encoding connexin32, is the second most common form of inherited demyelinating neuropathy, next to CMT 1A, and accounts for 10–20% of all hereditary demyelinating neuropathies. Aims of the study: To describe clinical and electrophysiological data of an Italian family carrying a novel mutation in the Cx32 gene. Patients and methods: Clinical, electrophysiological, and genetic findings of three patients carrying the Ser128Leu mutation in the intracellular domain of the Cx32 gene were reported. Brain MRI studies were also performed. Results: In our family the disease was characterized by a moderate‐to‐severe polyneuropathy affecting similarly males as well females. In the proband the phenotype was quite unusual in terms of late‐onset, rapidity of evolution and severity. Abnormal brain MRI in association with CNS symptoms were also observed. Both sons had also clinical evidence of CNS involvement. Conclusions: The Ser128Leu mutation in the Cx‐32 gene is a novel substitution, which has not been reported so far. This novel mutation could be added to the group of Cx‐32 mutations with CNS phenotypes. The identification of new CMTX causing mutations is a crucial step for carrier detection and pre‐symptomatic diagnosis.     

A novel mutation of gap junction protein β 1 gene in X-linked Charcot-Marie-Tooth disease

Introduction: In this study we report a novel mutation in the gap junction protein beta 1 (GJB1) gene of a Chinese X‐linked Charcot–Marie–Tooth disease (CMTX1) family, which has specific electrophysiological characteristics. Methods: Twenty members in the family were studied by clinical neurological examination and GJB1 gene mutation analysis, and 3 patients were studied electrophysiologically. The proband and his mother also underwent sural nerve biopsy. Results: All patients have the CMT phenotype, except for 2 asymptomatic carriers. Electrophysiological examinations showed non‐uniform slowing of motor conduction velocities and partial motor conduction blocks and temporal dispersion. Sural nerve biopsy confirmed a predominantly demyelinating neuropathy, and an Asn2Lys mutation in the amino‐terminal domain was found in 9 members of this family, but not in 25 normal controls in the family. Conclusions: This family represents a novel mutation in the GJB1 form of CMTX1. The mutation in the amino‐terminus has an impact on the electrophysiological characteristics of the disease. Muscle Nerve, 2011     

远端型遗传性运动神经病Ⅴ型一家系

目的 报道1个远端型遗传性运动神经病Ⅴ型(dHMN-Ⅴ)家系的临床、病理和基因改变特点.方法 该家系中连续4代有9例(4例男性,5例女性)在13～40岁之间发病,其中6例出现下肢无力;有2例女性患者仅出现双手肌肉无力和萎缩,其中1例出现锥体束征.先证者为20岁女性,13岁时发现双手肌肉萎缩和无力,15岁后出现下肢无力;肌电图提示神经源性损伤,神经传导速度检查显示运动神经复合肌肉动作电位波幅显著降低,伴随传导速度轻度减慢,感觉神经传导速度和动作电位波幅均正常.对先证者进行腓肠神经活体组织病理检查,并对先证者和其他4例发病者进行血Berardinelli-Seip先天性脂肪营养不良基因2(BSCL2)基因检查.结果 病理检查显示腓肠神经的有髓神经纤维数量轻度减少,伴随个别有髓神经纤维再生簇以及洋葱球样改变.基因检查显示BSCL2基因的第3号外显子存在263A→G杂合突变.结论 临床和基因检查证实该家系为dHMN-Ⅴ,其发病年龄和临床表现在同一家系中存在异质性,可以伴随轻微锥体束征和感觉神经损害.