MPZ Mutations Research Articles

Underestimated associated features in CMT neuropathies: clinical indicators for the causative gene?

IntroductionCharcot–Marie–Tooth neuropathy (CMT) is a genetically heterogeneous group of peripheral neuropathies. In addition to the classical clinical phenotype, additional features can occur.MethodsWe studied a wide range of additional features in a cohort of 49 genetically confirmed CMT patients and performed a systematic literature revision.ResultsPatients harbored a PMP22 gene alteration (n = 28) or a mutation in MPZ (n = 11), GJB1 (n = 4), LITAF (n = 2), MFN2 (n = 2), INF2 (n = 1), NEFL (n = 1). We identified four novel mutations (3 MPZ, 1 GJB1). A total of 88% presented at least one additional feature. In MPZ patients, we detected hypertrophic nerve roots in 3/4 cases that underwent spinal MRI, and pupillary abnormalities in 27%. In our cohort, restless legs syndrome (RLS) was present in 18%. We describe for the first time RLS associated with LITAF or MFN2 and predominant upper limb involvement with LITAF. Cold‐induced hand cramps occurred in 10% (PMP22,MPZ,MFN2), and autonomous nervous system involvement in 18% (PMP22,MPZ, LITAF,MFN2). RLS and respiratory insufficiency were mostly associated with severe neuropathy, and pupillary abnormalities with mild to moderate neuropathy.ConclusionsIn CMT patients, additional features occur frequently. Some of them might be helpful in orienting genetic diagnosis. Our data broaden the clinical spectrum and genotype–phenotype associations with CMT.

Clinical and genetic spectra in a series of Chinese patients with Charcot–Marie–Tooth disease

The aim of this study was to determine the clinical features and frequencies of genetic subtypes in a series of patients with Charcot-Marie-Tooth (CMT) disease from Eastern China. Patients were divided into three subtypes, CMT1, CMT2 and hereditary neuropathy with liability to pressure palsy (HNPP), according to their electrophysiological manifestations. Multiplex ligation-dependent probe analysis (MLPA) was performed to detect duplications/deletions in the PMP22 gene. The coding regions and splice sites of the GJB1, MPZ, MFN2 and GDAP-1 genes were determined by direct sequencing. Among the 148 patients in the study, 37.2% of the cases had mutations in genes assessed. The mutation detection rate was higher in patients with family histories than in spontaneous cases. PMP22 duplication (13.5%) was predominant in this group of patients, followed by PMP22 deletion (11.5%), and point mutations in GJB1 (8.8%), MPZ (2.0%) and MFN2 (0.7%). Three novel mutations (c.151T>C and c.310 A>G in GJB1 and c.1516 C>G in MFN2) were detected. A small deletion in PMP22 exon 4 was detected in a patient with severe CMT1. Genetic tests have great value in CMT patients with family histories. The frequency of PMP22 duplications was lower in Asian patients than in others. We suggest that genetic testing strategies in CMT patients should be primarily based on electromyography data.

Wide Spectrum of Neuropathy in Homozygous and Heterozygous Novel Frameshift MPZ Mutation in a Tunisian Family (P2.062)

Wide Spectrum of Neuropathy in Homozygous and Heterozygous Novel Frameshift MPZ Mutation in a Tunisian Family (P2.062)

Diagnostic laboratory testing for Charcot Marie Tooth disease (CMT): the spectrum of gene defects in Norwegian patients with CMT and its implications for future genetic test strategies

BackgroundCurrent genetic test algorithms for Charcot Marie Tooth (CMT) disease are based on family details and comprehensive clinical and neurophysiological data gathered under ideal conditions for clinical assessment. However, in a diagnostic laboratory setting relying on external test requisitions and patient samples, such conditions are not always met. Our objective was therefore to perform a retrospective evaluation of the data given in laboratory request forms and to assess their quality and applicability with regard to the recommended algorithms for CMT diagnostics. As we are the main test centre for CMT in Norway our results also provide an overview of the spectrum of gene defects in the Norwegian CMT population.MethodsGenetic testing was performed according to polyneuropathy type; demyelinating/mixed: PMP22 duplication, MPZ, EGR2, LITAF, NEFL, PMP22, GJB1, axonal: MFN2, MPZ, NEFL, and GJB1.ResultsDiagnostic testing of index patients was requested in 435 of the 549 cases. Seventy-two (16.6%) positive molecular genetic findings were made. The majority (94.6%) of mutation positive cases showed disease onset before 50 years of age. PMP22 (duplication), MPZ, GJB1 and MFN2 mutations constituted 95.8% of the positive findings. Within the nerve conduction study groups, mutation detection rates were; demyelinating 33.8%; mixed 29.0%; axonal 8.8%; unspecified 16.5%.ConclusionWe suggest a simplified algorithm intended for referral centres, dealing with DNA/blood samples, which involves the assessment of age at onset and neurophysiological data followed by testing of four genes; PMP22 (duplication), MPZ, GJB1 and MFN2. Patients negative for mutations in those four genes should be subjected to evaluation at an interdisciplinary inherited neuropathy clinic with the capacity for extended molecular genetic analysis by next generation sequencing.

Charcot-Marie-Tooth disease: Frequency of genetic subtypes in a German neuromuscular center population

Charcot-Marie-Tooth (CMT) neuropathies belong to the most common neurogenetic disorders. To date, mutations in more than 40 genes are known to be able to cause CMT. This genetic heterogeneity is a challenge for genetic diagnostics. Data on frequencies of mutations in CMT genes from large patient cohorts are needed to develop strategies for efficient genetic testing. In this study we have analysed patient histories, electrophysiological and genetic testing data in our cohort of 776 patients. In electrophysiologically demyelinating CMT, PMP22 duplication was the most common genetic cause, followed by mutations in GJB1 and MPZ. In axonal CMT, GJB1 was the most commonly affected gene, followed by MFN2 and MPZ. In CMT1, the clearance rate was 66%, in CMT2 it was 35%. Overall, the genetic clearance rate in our patient cohort was 58%. We found a higher rate of genetic diagnosis in patients seen in our neuromuscular center compared to out-of-clinic patients whose DNA was tested in our laboratory. This study provides further data on frequencies of CMT genes and subtypes and points to the importance of a thorough clinical and electrophysiological work-up for the direction of genetic testing.

Early-onset CMT1B due to the MPZ mutation c.320A>T associated with collateral inclusion body myopathy and Deafness

Early-onset CMT1B due to the MPZ mutation c.320A>T associated with collateral inclusion body myopathy and Deafness

Early-onset CMT1B due to the MPZ mutation c.320A>T associated with collateral inclusion body myopathy and Deafness

Aims: To present the case of a patient with early-onset demyelinating neuropathy due to a MPZ-mutation, associated with deafness and inclusion-body-myopathy. Methods: Nerve conduction studies, electromyography, muscle biopsy, genetic testing. Results and Discussion: In a 46yo male with slowly progressive weakness and wasting since childhood initially of the lower and later also of the distal upper-limbs, ptosis, recurrent hyper-CK-emia, and progressive hearing impairment, nerve conduction studies revealed mixed demyelinating and axonal polyneuropathy and electromyography revealed neurogenic motor unit architecture. Nerve biopsy disclosed diffuse loss of myelinated fibers, reduced diameter of non-myelinated fibers, and fibers with hypomyelination and variable internodal myelination. Muscle biopsy revealed classical features of inclusion-body-myopathy. Upon genetic diagnostic work-up the MPZ-mutation c.320A>T, p.Glu107Val was detected. Since his son presented with a similar phenotype, inclusion-body-myopathy was interpreted as secondary to the neuropathy. Conclusions: CMT1B may show secondary axonal loss and mild clinical manifestations Research Article British Journal of Medicine & Medical Research, 3(4): 832-840, 2013 833 despite early onset. CMT1B may be associated with severe hearing impairment and collateral inclusion-body-myopathy.

G.P.88 Peripheral neuropathies caused by mutations in the myelin protein zero

Abstract Charcot–Marie–Tooth disease (CMT), is a group of clinically and genetically heterogeneous neuropathies divided into demyelinating (CMT1) and axonal forms (CMT2). Mutations in the myelin protein zero (MPZ/P0) gene are the third most frequent cause of CMT. This gene is a member of the immunoglobulin gene superfamily that encodes the most abundant protein of the peripheral myelin, necessary for myelin compaction. There are many mutations in MPZ, most of them cause the CMT1B phenotype with normal early development but disability appears during the first two decades of life; and others, are responsible for severe neuropathies of infancy designated as Dejerine–Sottas syndrome. MPZ mutations have also been shown also in axonal type of CMT2. Hereby, we report the clinical and electrophysiological features of eight patients belonging to eight families affected by CMT 1B. The mean age of the patients is 13 years (range: 4–29). In five patients, the symptoms appeared between 2 and 3 years of age, showing motor clumsiness, difficulty to rise from the floor and for climbing stairs. In two cases, debuted before age of two, with a delay to develop an autonomous gait. The other one, presented an atypical phenotype at the age of seven, with hand tremor and episodes of muscular pain after exercising, with an intermittent increase of the CPK. Most of the patients had a stable evolution; five of them developed scoliosis and had affected their upper extremities. Only one of the patients developed a proximal weakness, and required scoliosis surgery at the age of 13. The electrophysiological study, showed a demyelinating neuropathy in all of the cases. Two patients with the same mutation, C241A, had different clinical evolution. There is a wide clinical spectrum in patients with MPZ gene mutation, which makes difficult to establish a genotype-phenotype correlation. We recommend the study on MPZ gene in patients with demyelinating neuropathy (once mutations in the PMP22 gene have been ruled out).

Nerve conduction studies in Charcot–Marie–Tooth disease in a cohort from Turkey

In the demyelinating form of Charcot-Marie-Tooth disease, median motor conduction velocity (MCV) was noted to be around 20 m/s in peripheral myelin protein 22 (PMP22) duplications, in contrast to higher MCVs in connexin 32 gene (Cx32) mutations and lower MCVs in the demyelinating form of myelin protein zero gene (MPZ) mutations.Nerve conduction studies were performed in 64 families with both common and rare mutations.Mean MCV of the median nerve was 20 ± 5 m/s in PMP22 duplications, 34 ± 6 m/s in Cx32 mutations, 20 ± 9 m/s in KIAA1985 (SH3TC2) mutations, and 11 ± 8 m/s in MPZ mutations. Conduction was generally uniform; however, conduction blocks were present in 1 patient each with the MPZ mutation and PMP22 duplication, both with unusual phenotypes.Our results confirm those of the other investigators. Electrophysiological results of the rare KIAA1985 (SH3TC2) mutation reveal that their MCVs span a broad range and that conduction is uniform.

A Novel MPZ Gene Mutation in Exon 2 Causing Late-Onset Demyelinating Charcot–Marie–Tooth Disease

The myelin protein zero gene (MPZ) encodes the major structural protein component of myelin in the peripheral nervous system. More than 120 mutations in MPZ have been detected so far. Clinical phenotypes include CMT1B, CMT2, Dejerine-Sottas syndrome, and congenital hypomyelination neuropathy. We report a new previously unreported mutation in the MPZ gene causing a demyelinating peripheral neuropathy. The initial apparent absence of a family history resulted in the patient being treated for an inflammatory neuropathy with some subjective improvement. We subsequently identified another affected member of the same family with the same genotype leading to the correct diagnosis. Both the affected individuals had an 8-base pair deletion, c.160_167delTCCCGGGT in MPZ exon 2.

Phenotypic presentation of the Ser63Del MPZ mutation

Mutations in MPZ cause CMT1B, the second most frequent cause of CMT1. Elegant studies with Ser63del mice suggest that Ser63del MPZ is retained in the ER where it activates the unfolded protein response (UPR) that contributes to the neuropathy. Clinical information about patients with this mutation is limited. We present clinical and electrophysiological data on a large multigenerational family with CMT1B caused by Ser63del MPZ. The patients have a classical CMT1 phenotype that is much less severe than that of patients with Arg98Cys MPZ that also activates the UPR. These results suggest that clinical presentation along cannot predict which MPZ mutations will be retained in the ER and activate the UPR.

MPZ Mutation in an Early-Onset Charcot-Marie-Tooth Disease Type 1B Family by Genome-Wide Linkage Analysis (P05.148)

MPZ Mutation in an Early-Onset Charcot-Marie-Tooth Disease Type 1B Family by Genome-Wide Linkage Analysis (P05.148)

Gain of glycosylation: A new pathomechanism of myelin protein zero mutations

We report the first case of a missense mutation in MPZ causing a gain of glycosylation in myelin protein zero, the main protein of peripheral nervous system myelin. The patient was affected by a severe demyelinating neuropathy caused by a missense mutation, D32N, that created a new glycosylation sequence. We confirmed that the mutant protein is hyperglycosylated, is partially retained into the Golgi apparatus in vitro, and disrupts intercellular adhesion. By sequential experiments, we demonstrated that hyperglycosylation is the main mechanism of this mutation. Gain of glycosylation is a new mechanism in Charcot-Marie-Tooth type 1B.

Novel peripheral myelin protein 22 (PMP22) micromutations associated with variable phenotypes in Greek patients with Charcot-Marie-Tooth disease

ARTICLE Sir, We read with interest the paper by Taioli et al . (2011) reporting eight different micromutations of PMP22 in patients with inherited demyelinating neuropathies. Small frameshift insertions/deletions (indels), nonsense nucleotide substitutions and splice-site mutations led to phenotypically and pathologically variable neuropathies. Patients with mutations causing a premature or delayed stop codon had a phenotype within the hereditary neuropathy with liability to pressure palsies (HNPP) spectrum. One patient with a splice-site mutation causing an in-frame skipping of exon 4 had a CMT1 phenotype. As the authors state, micromutations of PMP22 are considered very rare causes of Charcot–Marie–Tooth (CMT) in most populations and this certainly includes our experience of PMP22 analysis in cases with CMT from the UK. We presently report three novel PMP22 micromutations identified in a Greek cohort of patients with CMT that were associated with variable clinical phenotypes, ranging from severe CMT1 of the Dejerine–Sottas disease spectrum to HNPP. These novel cases, taken together with the findings of Taioli et al . (2011) illustrate that, despite some exceptions, in-frame indels in PMP22 usually lead to CMT1 of varying severity, whereas frameshift changes more often cause HNPP. DNA was extracted from peripheral blood following standard procedures. Patients were previously found negative for the common duplication/deletion in chromosome 17 and for mutations in GJB1 and MPZ . The four coding exons (exons 2–5) of PMP22 with adjacent intronic sequences were amplified by polymerase chain reaction and sequenced on an Applied Biosystems 3730XL genetic analyser. Fragment analysis was performed with GeneMapper® software after running fragments on the 3730XL with a LIZ500 standard. RNA was obtained from peripheral blood using the Qiagen/PreAnalytix™ blood RNA system. Complementary DNA was synthesized using the Applied Biosystems high capacity complementary DNA reverse transcription kit. A 391 bp fragment of complementary DNA spanning the regions of interest …

A novel mutation of myelin protein zero associated with late-onset predominantly axonal Charcot-Marie-Tooth disease

We report a case of late-onset predominantly axonal Charcot-Marie-Tooth disease resulting from a novel mutation in the MPZ gene encoding myelin protein zero (P0). Neurological examination, electrophysiological examination and genetic testing were performed on three members of a Finnish family (family A) and one member of a German family (family B). Three other members of the Finnish family were interviewed and genetically tested. Genetic testing was also performed on 95 healthy Finnish controls. Three members in two generations of family A and the member of family B were affected with late-onset axonal more than demyelinating, motor and sensory polyneuropathy. Heterozygous c.316C>T mutation in MPZ leading to p.Arg106Cys in P0 was found in all the affected subjects, but not in the three unaffected members of the Finnish family. None of 95 healthy Finnish controls harbored the mutation. The findings of this study indicate that p.Arg106Cys allele in MPZ causes late-onset predominantly axonal sensory and motor neuropathy.

INF2Mutations in Charcot–Marie–Tooth Disease with Glomerulopathy

Charcot-Marie-Tooth neuropathy has been reported to be associated with renal diseases, mostly focal segmental glomerulosclerosis (FSGS). However, the common mechanisms underlying the neuropathy and FSGS remain unknown. Mutations in INF2 were recently identified in patients with autosomal dominant FSGS. INF2 encodes a formin protein that interacts with the Rho-GTPase CDC42 and myelin and lymphocyte protein (MAL) that are implicated in essential steps of myelination and myelin maintenance. We therefore hypothesized that INF2 may be responsible for cases of Charcot-Marie-Tooth neuropathy associated with FSGS. We performed direct genotyping of INF2 in 16 index patients with Charcot-Marie-Tooth neuropathy and FSGS who did not have a mutation in PMP22 or MPZ, encoding peripheral myelin protein 22 and myelin protein zero, respectively. Histologic and functional studies were also conducted. We identified nine new heterozygous mutations in 12 of the 16 index patients (75%), all located in exons 2 and 3, encoding the diaphanous-inhibitory domain of INF2. Patients presented with an intermediate form of Charcot-Marie-Tooth neuropathy as well as a glomerulopathy with FSGS on kidney biopsy. Immunohistochemical analysis revealed strong INF2 expression in Schwann-cell cytoplasm and podocytes. Moreover, we demonstrated that INF2 colocalizes and interacts with MAL in Schwann cells. The INF2 mutants perturbed the INF2-MAL-CDC42 pathway, resulting in cytoskeleton disorganization, enhanced INF2 binding to CDC42 and mislocalization of INF2, MAL, and CDC42. INF2 mutations appear to cause many cases of FSGS-associated Charcot-Marie-Tooth neuropathy, showing that INF2 is involved in a disease affecting both the kidney glomerulus and the peripheral nervous system. These findings provide new insights into the pathophysiological mechanisms linking formin proteins to podocyte and Schwann-cell function. (Funded by the Agence Nationale de la Recherche and others.).

Congenital hypomyelinating neuropathy due to a novel MPZ mutation

Congenital hypomyelinating neuropathy (CHN) is a severe inherited neuropathy with neonatal or early infancy onset, reduced nerve conduction velocity, and pathological evidence of hypomyelination. We describe a case of CHN that presented with neonatal hypotonia and a progressive downhill clinical course, developing cranial nerve dysfunction, and respiratory failure. The nerve conduction velocities were severely slowed and sural nerve biopsy revealed non-myelinated and poorly myelinated axons, with no typical onion bulbs. The mutational screening showed that our proband harbored a novel missense mutation, p.S121F, in the MPZ gene. In silico analyses and molecular modeling predicted that the replacement of a serine by a phenylalanine is a non-tolerated change and may affect the folding and the stability of the protein. Subcellular location studies were performed and revealed that the mutant protein loses its correct location on the cell membrane surface and is mainly expressed in the cytosol, reducing its adhesive properties. This case illustrates the clinical heterogeneity that exists in neuropathies associated with MPZ mutations and highlights that in patients with mild hypotonia in the first months that develop a very severe demyelinating neuropathy, the MPZ gene must be taken into account.

Clinical and cellular characterization of two novel MPZ mutations, p.I135M and p.Q187PfsX63

ObjectivesWe report the clinical and cellular phenotypes of two novel MPZ mutations associated with CMT1B. MethodsThe two families were evaluated clinically, electrophysiologically, and genetically. The wild-type and mutant P0 fused with fluorescent proteins were expressed in vitro to monitor their intracellular trafficking. Adhesion assay was also performed to evaluate the adhesiveness of cells. ResultsThe two novel heterozygous MPZ mutations, p.I135M and p.Q187PfsX63, are associated with a childhood-onset demyelinating polyneuropathy. The median motor nerve conduction velocities of the two index patients carrying each mutation were 12.9 and 13.6m/s, respectively. Fluorescence analysis demonstrated that the P0 I135M protein was located on the cell membrane, but the P0 Q187PfsX63 protein was retained ectopically in the endoplasmic reticulum and Golgi apparatus. Adhesion assay demonstrated a defective adhesiveness of cells expressing either mutant P0 protein, and P0 Q187PfsX63 had a more prominent defect of self-adhesive ability than P0 I135M. ConclusionsThis study expanded the spectrum of the MPZ mutations and revealed two disparate mechanisms of MPZ mutations associated with a typical CMT1B phenotype. Other modifying genetic, epigenetic, or environmental factors on CMT1B may exist to explain the discrepancy between the cellular phenotypes.

Genetic spectrum of hereditary neuropathies with onset in the first year of life

Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine–Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot–Marie–Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot–Marie–Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot–Marie–Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset.

MPZ mutation in an early-onset Charcot-Marie-Tooth disease type 1B family by genome-wide linkage analysis

Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous peripheral neuropathy. The objective of this study was to find the causative mutation(s) in a demyelinating autosomal dominant CMT family. A high density SNP-based genome-wide linkage scan was performed, and causative mutations were determined by sequencing of candidate genes in the linkage disequilibrium region. Linkage analysis mapped the underlying gene to a region on chromosome 1q22-q23 with a maximum two-point LOD score of 2.036. Sequencing analysis revealed a novel c.243C>G (His81Gln) mutation in the MPZ gene, which encodes the major integral membrane protein of the peripheral nerve system. MPZ is well known as a CMT-causative gene with wide phenotypic spectrum. The clinical symptoms were more similar to those of patients with the His81Arg than patients with the His81Tyr mutation. The novel mutation completely co-segregated with affected members, and was not found in controls. Therefore, we suggest that the identified mutation in MPZ is the underlying cause of CMT in the family. In addition, this study demonstrated that the clinical phenotypes may be variable with different mutations at the same site in the MPZ gene.