New point mutations and deletions of the connexin 32 gene in X-linked Charcot-Marie-Tooth neuropathy

X-linked Charcot Marie Tooth mutations alter CO2 sensitivity of connexin32 hemichannels

Connexin32 (Cx32) is expressed in myelinating Schwann cells. It forms both reflexive gap junctions, to facilitate transfer of molecules from the outer to the inner myelin layers and hemichannels at the paranode to permit action potential-evoked release of ATP into the extracellular space. Loss of function mutations in Cx32 cause X-linked Charcot Marie Tooth disease (CMTX), a slowly developing peripheral neuropathy. The mechanistic links between Cx32 mutations and CMTX are not well understood. As Cx32 hemichannels can be opened by increases in PCO2, we have examined whether CMTX mutations alter this CO2 sensitivity. By using Ca2+ imaging, dye loading and genetically encoded ATP sensors to measure ATP release, we have found 5 CMTX mutations that abolish the CO2 sensitivity of Cx32 hemichannels (A88D, 111-116 Del, C179Y, E102G, V139M). Others cause a partial loss (L56F, R220Stop, and R15W). Some CMTX mutations have no apparent effect on CO2 sensitivity (R15Q, L9F, G12S, V13L, V84I, W133R). The mutation R15W alters multiple additional aspects of hemichannel function including Ca2+ and ATP permeability. The mutations that abolish CO2 sensitivity are transdominant and abolish CO2 sensitivity of co-expressed Cx32WT. We have shown that Schwannoma RT4 D6P2T cells can release ATP in response to elevated PCO2 via the opening of Cx32. This is consistent with the hypothesis that the CO2 sensitivity of Cx32 may be important for maintenance of healthy myelin. Our data, showing a transdominant effect of certain CMTX mutations on CO2 sensitivity, may need to be taken into account in any future gene therapies for this condition.

Whole exome sequencing establishes diagnosis of Charcot-Marie-Tooth 4J, 1C, and X1 subtypes

BACKGROUND

Charcot-Marie-Tooth (CMT) hereditary polyneuropathies pose a diagnostic challenge. Our aim here is to describe CMT patients diagnosed by whole exome sequencing (WES) following years of fruitless testing.

METHODS/RESULTS

Three patients with polyneuropathy suspected to be genetic in origin, but not harboring PMP22 gene deletion/duplication, were offered WES. The first patient, a 66-year-old man, had been suffering from progressive weakness and atrophies in the lower and upper extremities for 20 years. Due to ambiguous electrophysiological findings, immune therapies were administered to no avail. Twelve years after PMP22 deletion/duplication testing, WES revealed two pathogenic variants in the FIG4 gene (p.Ile41Thr and p.Phe598fs, respectively), as a cause of CMT 4J. The second patient, a 19-year-old man, had been suffering from hearing and gait impairment since at least his infancy, and recently presented with weakness and dystonia of the lower extremities. In this patient, WES identified the p.Leu122Val LITAF gene variant in heterozygous state, suggesting the diagnosis of CMT 1C, several years after initial genetic analyses. The third patient, a 44-year-old man, presented with progressive weakness and atrophies of the lower and upper extremities since the age of 17 years old. In this patient, WES identified the hemizygous p.Arg164Gln pathogenic variant in the GJB1 gene, establishing the diagnosis of CMT X1, 8 years after testing for PMP22 deletion/duplication.

CONCLUSION

Novel diagnostic techniques, such as WES, offer the possibility to decipher the cause of CMT subtypes, ending the diagnostic Odyssey of the patients and sparing them from unnecessary and potentially harmful treatments.

Gap junctions in inherited human disease

Gap junctions (GJ) provide direct intercellular communication. The structures underlying these cell junctions are membrane-associated channels composed of six integral membrane connexin (Cx) proteins, which can form communicating channels connecting the cytoplasms of adjacent cells. This provides coupled cells with a direct pathway for sharing ions, nutrients, or small metabolites to establish electrical coupling or balancing metabolites in various tissues. Genetic approaches have uncovered a still growing number of mutations in Cxs related to human diseases including deafness, skin disease, peripheral and central neuropathies, cataracts, or cardiovascular dysfunctions. The discovery of a growing number of inherited human disorders provides an unequivocal demonstration that gap junctional communication is crucial for diverse physiological processes.

Transgenic disruption of gap junctional intercellular communication enhances early but not late stage hepatocarcinogenesis in the rat

Much experimental evidence supports the conclusion that loss of gap junctional intercellular communication (GJIC) contributes to carcinogenesis. Transgenic rats featuring a dominant negative mutant of the connexin 32 gene under albumin promoter control (Cx32Delta Tg-High and Cx32Delta Tg-Low lines, respectively with high and low copy numbers of the transgene) have disrupted GJIC, as demonstrated by scrape dye-transfer assay in vivo as previous report by Asamoto et al. (2004). In the present study, we investigated the susceptibility of these transgenic rats to a single intraperitoneal administration of diethylnitrosamine (DEN), and found a significant increase in preneoplastic glutathione S-transferase placental form (GST-P) positive lesions in the livers of Cx32Delta Tg-High but not Cx32Delta Tg-Low rats. However, incidences of adenomas and hepatocellular carcinomas were not elevated at the end of the experiment (52 weeks). In addition, we investigated the promotional effect of phenobarbital (PB) on Cx32Delta Tg-High rats pretreated with DEN and found enhanced formation of GST-P positive lesions, in contrast to the lack of promoting effects reported for Cx32 deficient mice. The results indicate that although both high and low expression of the dominant negative connexin 32 mutant gene in our rats is able to inhibit gap junctional capacity, only high expression is effective at enhancing susceptibility to early stage DEN-induced liver carcinogenesis.

Connexin 32 dominant-negative mutant transgenic rats are resistant to hepatic damage by chemicals

Connexins are subunits of gap junction channels, which allow direct transfer of ions, secondary messenger molecules, and other metabolites between contacting cells. Gap junctions are believed to be involved in tissue homeostasis, embryonic development, and control of cell proliferation. Several studies have shown that cell damage signals are transmitted through gap junctions when cells are irradiated or when cells bearing the herpes simplex virus-thymidine kinase (HSV-TK) gene are treated with ganciclovir. We established 2 lines of transgenic rats with a dominant-negative mutant of connexin 32 gene under control of the albumin promoter. In the livers of transgenic rats, membrane localization of normal endogenous connexin 32 protein is disturbed, and gap junction capacity measured by scrape dye-transfer assay in vivo is markedly decreased when compared with wild-type rats. The present investigation concerned susceptibility to the liver-toxic substances D-galactosamine and carbon tetrachloride. These toxicants induced massive liver cell death and elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the wild-type rats; however, much fewer liver cells were damaged and serum enzyme elevation was much lower in the transgenic rats. In conclusion, gap junctional intercellular communication (GJIC) plays an important role in toxic effects of chemicals; damage or death signals may pass through gap junctions in the rat liver in vivo.

Gap junctions and neurological disorders of the central nervous system

Gap junctions are intercellular channels which directly connect the cytoplasm between neighboring cells. In the central nervous system (CNS) various kinds of cells are coupled by gap junctions, which play an important role in maintaining normal function. Neuronal gap junctions are involved in electrical coupling and may also contribute to the recovery of function after cell injury. Astrocytes are involved in the pathology of most neuronal disorders, including brain ischemia, Alzheimer's disease and epilepsy. In the pathology of brain tumors, gap junctions may be related to the degree of malignancy and metastasis. However, the role of connexins, gap junctions and hemichannels in the pathology of the diseases in the CNS is still ambiguous. Of increasing importance is the unraveling of the function of gap junctions in the neural cell network, involving neurons, astrocytes, microglia and oligodendrocytes. A better understanding of the role of gap junctions may contribute to the development of new therapeutic approaches to treating diseases of the CNS.

Functional analysis of connexin-32 mutants associated with X-linked dominant Charcot-Marie-Tooth disease

To investigate the pathogenic role of connexin-32 (Cx32) mutation in X-linked dominant Charcot-Marie-Tooth disease (CMTX), dual whole-cell voltage-clamp recordings and tracer coupling were performed to investigate functional properties of wild-type and 22 CMTX mutant Cx32 proteins expressed in N2A cells. Ten mutant Cx32 proteins either formed defective junctional channels (Y65C, V95M, R107W, L156R, R164W and G199R) or failed to form gap junctions (G12S, S182T, E208K and Y211stop). Except (G12S) and (E208K) mutants, other mutant Cx32 proteins were localized in the cell membrane despite their impaired ability to form functional gap junctions. Twelve CMTX mutations (V13L, R15Q, R22Q, I30N, V35M, V63I, R75Q, Q80R, W133R, P158A, P172S and N205S) did not affect the ability of Cx32 to form homotypic gap junctions in N2A cells. Our results indicate that 10 of 22 CMTX Cx32 mutations studied in the present investigation could lead to the assembly of defective Cx32 gap junctions, which in turn may result in peripheral neuropathy. However, further studies are required to elucidate the exact mechanism by which CMTX mutant Cx32 proteins, which retain the ability to form homotypic junctional channels, damage Schwann cells and cause demyelinating neuropathy.

Gap junction protein beta 1 (GJB1) mutations and central nervous system symptoms in X-linked Charcot-Marie-Tooth disease

OBJECTIVES

To clarify the clinical variability, including central nervous system (CNS) involvement, in X-linked Charcot-Marie-Tooth disease (CMTX) patients.

MATERIAL AND METHODS

We clinically, pathologically and genetically studied six CMTX patients with distinct symptoms and four different GJB1 mutations.

RESULTS

One patient with Val63Ile had deafness, low intelligence, saccadic eye movement, upper extremity distal dominant muscle weakness and normal sensation. Another patient with Glu186Lys had severe sensorineural deafness at the age of 6 years, but did not develop muscle weakness until the age of 20 years. Two patients with Arg22Gln had typical CMT1A-like clinical features, no CNS symptoms and obvious onion bulb formations. Two siblings with deletion of the entire GJB1 gene had mild to moderate lower extremity muscle weakness and sensory disturbance without CNS involvement.

CONCLUSION

These findings suggest that some gain of function mutations of GJB1 may be related to CNS symptoms because the patients with GJB1 deletion only had peripheral neuropathy, although other unknown associated factors may contribute to their clinical phenotypes.

A founder mutation in French-Canadian families with X-linked hereditary neuropathy

BACKGROUND

The aim of the present study was to identify the mutations in the connexin 32 gene in French-Canadian families with X-linked Charcot-Marie-Tooth disease (CMTX).

METHODS

Molecular analysis was performed by nonisotopic single strand conformation polymorphism (SSCP) analysis and sequencing. Clinical evaluation was carried out according to the scale defined by the European Hereditary Motor and Sensory Neuropathy Consortium.

RESULTS

In one family, the mutation Arg142Trp was located in the transmembrane domain III whereas, in four other families we identified a novel mutation (Ser26Trp) located in the transmembrane domain I of the connexin 32 gene. Haplotype analysis revealed that these four families are related and suggests a founder mutation. Sixteen patients from these four families were studied. As expected, all the affected males were more clinically affected than the females and all affected patients exhibited some electrophysiological characteristics of demyelination.

CONCLUSION

Our study suggests that the Ser26Trp mutation may cause a primary demyelinating neuropathy that is not associated with a specific clinical phenotype. We also find evidence that the majority of kindreds share a common ancestor.

Junctional communication between isolated pairs of canine atrial cells is mediated by homogeneous and heterogeneous gap junction channels

INTRODUCTION

The expression of multiple connexins (Cxs) in the canine right atria raises the possibility that heterogeneous gap junction channels might be formed.

METHODS AND RESULTS

We compared the unitary conductance (gamma(j)) of gap junction channels between isolated canine atrial cell pairs with those of homogeneous cardiac gap junction channels expressed in other systems. After partial uncoupling with halothane (2 mmol/L), the (gamma)j calculations for atrial isolated cardiocytes ranged from 30 to 220 pS and their distribution in event histograms was spread over the entire range, with a small peak at approximately 100 pS. This distribution deviates from the discrete peaks calculated from (gamma)j of homogeneous channels. All-points histograms of junctional current traces revealed distinct open-state levels. Some of these are related to the main open state of connexin43 (Cx43) (approximately 100 pS), observed between canine ventricular cells, or connexin40 (Cx40) (approximately 215 pS) observed between transfected N2A cells under similar recording conditions. Intermediate values for (gamma)j were not observed in recordings from ventricular cells, which express mostly Cx43, nor in those from N2A cells expressing Cx40, but were observed consistently between atrial cells. Because they were measured as first openings from the nonconductance state, these intermediate values most likely represent main conductance states of heterogeneous channels rather than subconductance states of homogeneous channels.

CONCLUSION

This suggests that regulation of cell-to-cell coupling in the heart depends not only on posttranslational modulation of preexisting Cxs, but also on the intracellular assembly mechanisms, and the way individual Cxs interact with others within a connexon and/or with other connexons from adjacent cells.

Abnormalities in the axonal cytoskeleton induced by a connexin32 mutation in nerve xenografts

The X-linked form of Charcot-Marie-Tooth neuropathy is associated with mutations in the connexin32 (Cx32) gene. The functional role of Cx32 in Schwann cells and the relationship of these mutations to the progressive axonal loss and distal limb weakness seen in this disease have not been elucidated. To investigate the local influence of Schwann cells bearing the Cx32 gene defect on axonal cytoskeleton and the myelination process, the nerve xenograft model was used to transfer a Cx32 missense mutation (Glu102Gly) from human to an in vivo myelination system in nude mice. Twelve nerve grafts from two family members with Cx32 mutations and 17 grafts from three healthy individuals were generated by end-to-end anastomosis of approximately 6-mm sural nerve fascicles into the cut ends of the sciatic nerve in nude mice. Specimens were examined at 2, 4, 8, 12, and 16 weeks. Ultrastructural morphometric analysis showed Schwann cells with Cx32 mutation have a profound effect on the nude mice axons, resulting in an increase in neurofilament density, a depletion of microtubules associated with fragmentation of smooth axonal reticulum, and increased vesicles and mitochondria. At 16 weeks, axonal enlargement was evident within the proximal part of the graft; axonal atrophy, degeneration, and fiber loss were seen in distal-graft and host segments. The myelination process was not affected. We conclude that Cx32 mutation impairs a modulatory function of Schwann cells on axons, resulting in profound cytoskeletal alterations leading to distal axonal degeneration. These observations emphasize the role of impaired Schwann cell-axon interactions in the pathogenesis of hereditary neuropathies.

Spectrum of mutations in Finnish patients with Charcot-Marie-Tooth disease and related neuropathies

Our patient material included families and sporadic patients of Finnish origin with the diagnosis of Charcot-Marie-Tooth (CMT) disease types 1 and 2, Dejerine-Sottas syndrome (DSS), and hereditary neuropathy with liability to pressure palsies (HNPP). We screened for mutations in the peripheral myelin protein genes connexin 32 (Cx32), myelin protein zero (P0) and peripheral myelin protein 22 (PMP22) by direct sequencing. All patients chosen for mutation screening were negative for the 1.5 Mb duplication/deletion at 17p11.2-p12. Eleven Cx32 mutations were found in 12 families, six with a CMT2 diagnosis, three with a CMT1 diagnosis and three with unclassified CMT. The total number of patients in these 12 CMTX families was 61, giving a minimum prevalence of 1.2/100,000 for CMTX in Finland. Four of the mutations, Pro58Arg, Pro172Leu, Asn175Asp and Leu204Phe, have not been previously reported. One male patient with an early onset CMT had a double Cx32 mutation, Arg22Gln and Val63Ile. The double de novo mutation was found to be of maternal grandpaternal origin. In the P0 gene a Ser78Leu mutation was found in one family with severe CMT1 and a de novo Tyr82Cys mutation was found in one DSS patient. Both mutations have been previously reported in other CMT1 families. A novel PMP22 mutation, deletion of Phe84, was found in one sporadic DSS patient. Our mutation screening results show the necessity of molecular diagnosis, in addition to clinical and electrophysiological evaluation, for proper subtyping of the disease and for accurate genetic counseling.

Changes in permeability caused by connexin 32 mutations underlie X-linked Charcot-Marie-Tooth disease

The relationship between the loss of connexin 32 function and clinical manifestations of X-linked Charcot-Marie-Tooth (CMTX) disease is unknown. Here, we report that eight of nine CMTX mutations investigated form channels with measurable electrical conductance. Single-channel studies of two mutations demonstrate reduced junctional permeability caused by a decrease in either pore size (S26L) or open channel probability (M34T) that favors residency in a low-conductance substate. Permeation of second messengers such as cAMP through reflexive gap junctions between adjacent cytoplasmic loops of myelinating Schwann cells is likely to be reduced or absent in these channels. We propose that CMTX mutations impair the transduction of signals arising from normal glial-neuronal interactions and thereby cause demyelination and axonal degeneration.

Connexin32 and X-linked Charcot-Marie-Tooth disease

Mutations in the gap junction gene connexin32 (Cx32) cause the X-linked form of Charcot-Marie-Tooth disease, an inherited demyelinating neuropathy. More than 130 different mutations have been described, affecting all portions of the Cx32 protein. In transfected cells, the mutant Cx32 proteins encoded by some Cx32 mutations fall to reach the cell surface; other mutant proteins reach the cell surface, but only one of these forms functional gap junctions. In peripheral nerve, Cx32 is localized to incisures and paranodes, regions of noncompact myelin within the myelin sheath. This localization suggests that Cx32 forms "reflexive" gap junctions that allow ions and small molecules to diffuse directly across the myelin sheath, which is a thousandfold shorter distance than the circumferential pathway through the Schwann cell cytoplasm. Cx32 mutations may interrupt this shorter pathway or have other toxic effects, thereby injuring myelinating Schwann cells and their axons.

Charcot-Marie-Tooth disease with intermediate motor nerve conduction velocities: characterization of 14 Cx32 mutations in 35 families

Charcot-Marie-Tooth disease can be inherited either autosomal dominantly or recessively or linked to the X chromosome. X-linked dominant Charcot-Marie-Tooth disease (CMTX) is a sensorimotor peripheral neuropathy in which males have usually more severe clinical symptoms and decreased nerve conduction velocities than do females. CMTX is usually associated with mutations in exon 2 of the connexin 32 (Cx32) gene. DNA from 35 unrelated CMT patients, without the 17p11.2 duplication, but with median nerve conduction between 30 and 40 m/s, were tested for the presence of Cx32 mutations. The entire coding sequence of the Cx32 gene was explored using a rapid nonradioactive technique to detect single-strand conformation polymorphisms (SSCP) on large PCR fragments. Thirteen abnormal SSCP profiles were detected and characterized by sequencing. In addition, systematic sequencing of the entire Cx32 coding region in the remaining index cases revealed another mutation that was not detected by SSCP. A total of 14 mutations were found, five of which were not previously reported. These results demonstrate the high frequency (40%) of mutations in the coding region of the Cx32 gene in CMT patients with intermediate MNCV, without 17p11.2 duplications. Most of these mutations (93%) can be detected by SSCP.

Myelin mutants: model systems for the study of normal and abnormal myelination

Spontaneous mutations that perturb myelination occur in a range of species including man, and together with engineered mutations have been used to study disease, normal myelination and axon/glial inter-relationships. Only a minority of the currently defined mutations have an apparently simple pathogenesis due to lack of a functional protein. Mutations in the myelin basic protein gene lead to a lack of protein, resulting in changes in the structure of myelin, which can be rescued by transgenic complementation. The pathogenesis of autosomal dominant and X-linked mutations affecting either oligodendrocytes or Schwann cells is more complex. Point mutations may act in a dominant negative manner and gene dosage is clearly linked to phenotypic change. Mutations in regulatory genes, such as those encoding transcription factors, can also disturb myelination by selected cell types. Other less-well studied and unexpected consequences of myelin mutations, such as seizures in mutations affecting genes expressed in Schwann cells and axonal changes associated with dysmyelination, are also considered. With the major developments in gene mapping and cloning it is now relevant to study mutations in a variety of species with the real prospect of defining their molecular basis. Examples are given of unusual, but potentially useful, uncharacterized mutations in dog and bovine.

Correlation between connexin 32 gene mutations and clinical phenotype in X-linked dominant Charcot-Marie-Tooth neuropathy

We studied the relationship between the genotype and clinical phenotype in 27 families with dominant X-linked Charcot-Marie-Tooth (CMTX1) neuropathy. Twenty-two families showed mutations in the coding region of the connexin32 (cx32) gene. The mutations include four nonsense mutations, eight missense mutations, two medium size deletions, and one insertion. Most missense mutations showed a mild clinical phenotype (five out of eight), whereas all nonsense mutations, the larger of the two deletions, and the insertion that produced frameshifts showed severe phenotypes. Five CMTX1 families with mild clinical phenotype showed no point mutations of the cx32 gene coding region. Three of these families showed positive genetic linkage with the markers of the Xq13.1 region. The genetic linkage of the remaining two families could not be evaluated because of their small size.

The human connexin32 gene is transcribed from two tissue-specific promoters

The connexin32 (cx32) gene codes for the gap junction protein found in liver, pancreas and nervous tissue. Recently mutations in the coding region of this gene have been associated with the dominant X-linked form of Charcot-Marie-Tooth (CMTX1) neuropathy. Since some CMTX1 patients show no mutations in their cx32 gene coding region, it was speculated that these patients carry mutations in the promoter region of the gene. This paper describes the organization of the human cx32 gene and its tissue-specific transcription. The gene consists of three exons that are alternatively spliced to produce mRNAs with different 5'-untranslated regions (UTRs). Transcription is initiated from two tissue-specific promoters. In liver and pancreas, promoter P1, located more than 8 kb upstream of the translation start codon, is used, and the transcript is processed to remove a large intron. In contrast, in nerve cells, transcription is initiated from promoter P2, located 497 bp upstream from the translation start codon, and the transcript is processed to remove a small 355-pb intron. The downstream exon, which includes the entire coding sequence, is shared by both mRNAs. CMTX1 patients with a normal cx32 coding region are expected to have mutations in this newly described promoter P2 rather than the known promoter P1.

Connexin 32 mutations from X-linked Charcot-Marie-Tooth disease patients: functional defects and dominant negative effects

We have characterized the function of connexin (Cx) 32 gene mutations found in X-linked dominant Charcot-Marie-Tooth disease with respect to their ability to form functional gap junctions among themselves and to inactivate wild-type Cx32 by a dominant negative mechanism. We prepared four types of Cx32 mutant cDNAs and transfected them into HeLa cells, which do not show detectable levels of gap junctional intercellular communication (GJIC), nor expression of any connexins examined. Cells transfected with the wild-type Cx32 gene, but not those transfected with three different base substitution mutations (i.e. Cys 60 to Phe, Val 139 to Met, and Arg 215 to Trp), restored GJIC. Unexpectedly, in cells transfected with a nonsense mutant at codon 220, there was also restored GJIC. When we double-transfected these mutant constructs into the HeLa cells that had already been transfected with the wild-type Cx32 gene and thus were GJIC proficient, three base substitution mutants inhibited GJIC, suggesting that these three mutants can eliminate the function of wild-type Cx32 in a dominant negative manner. The nonsense mutation at codon 220 did not show such a dominant negative effect. Since both mutant and wild-type Cx32 mRNAs were detected, but only poor Cx32 protein expression at cell-cell contact areas was observed in the double transfectants, it is suggested that certain mutants form nonfunctional chimeric connexons with wild-type connexins, which are not properly inserted into the cytoplasmic membrane.

Connections with connexins: the molecular basis of direct intercellular signaling

Adjacent cells share ions, second messengers and small metabolites through intercellular channels which are present in gap junctions. This type of intercellular communication permits coordinated cellular activity, a critical feature for organ homeostasis during development and adult life of multicellular organisms. Intercellular channels are structurally more complex than other ion channels, because a complete cell-to-cell channel spans two plasma membranes and results from the association of two half channels, or connexons, contributed separately by each of the two participating cells. Each connexon, in turn, is a multimeric assembly of protein subunits. The structural proteins comprising these channels, collectively called connexins, are members of a highly related multigene family consisting of at least 13 members. Since the cloning of the first connexin in 1986, considerable progress has been made in our understanding of the complex molecular switches that control the formation and permeability of intercellular channels. Analysis of the mechanisms of channel assembly has revealed the selectivity of inter-connexin interactions and uncovered novel characteristics of the channel permeability and gating behavior. Structure/function studies have begun to provide a molecular understanding of the significance of connexin diversity and demonstrated the unique regulation of connexins by tyrosine kinases and oncogenes. Finally, mutations in two connexin genes have been linked to human diseases. The development of more specific approaches (dominant negative mutants, knockouts, transgenes) to study the functional role of connexins in organ homeostasis is providing a new perception about the significance of connexin diversity and the regulation of intercellular communication.

Arginine-164-tryptophan substitution in connexin32 associated with X linked dominant Charcot-Marie-Tooth disease

A Spanish family with X linked dominant Charcot-Marie-Tooth (CMTX1) neuropathy was screened for point mutations in the connexin32 gene (GJ beta 1). The patients showed a C-T transition at position 552 which predicts arginine to tryptophan substitution at amino acid 164 (R164K). This mutation destroys an AciI restriction site at position 552 and creates a PflMI restriction site.