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1.  High-Dosage Ascorbic Acid Treatment in Charcot-Marie-Tooth Disease Type 1A: Results of a Randomized, Double-Masked, Controlled Trial 
JAMA neurology  2013;70(8):981-987.
Importance
No current medications improve neuropathy in subjects with Charcot-Marie-Tooth disease type 1A (CMT1A). Ascorbic acid (AA) treatment improved the neuropathy of a transgenic mouse model of CMT1A and is a potential therapy. A lower dosage (1.5 g/d) did not cause improvement in humans. It is unknown whether a higher dosage would prove more effective.
Objective
To determine whether 4-g/d AA improves the neuropathy of subjects with CMT1A.
Design
A futility design to determine whether AA was unable to reduce worsening on the CMT Neuropathy Score (CMTNS) by at least 50% over a 2-year period relative to a natural history control group.
Setting
Three referral centers with peripheral nerve clinics (Wayne State University, Johns Hopkins University, and University of Rochester).
Participants
One hundred seventy-four subjects with CMT1A were assessed for eligibility; 48 did not meet eligibility criteria and 16 declined to participate. The remaining 110 subjects, aged 13 to 70 years, were randomly assigned in a double-masked fashion with 4:1 allocation to oral AA (87 subjects) or matching placebo (23 subjects). Sixty-nine subjects from the treatment group and 16 from the placebo group completed the study. Two subjects from the treatment group and 1 from the placebo group withdrew because of adverse effects.
Interventions
Oral AA (4 g/d) or matching placebo.
Main Outcomes and Measures
Change from baseline to year 2 in the CMTNS, a validated composite impairment score for CMT.
Results
The mean 2-year change in the CMTNS was −0.21 for the AA group and −0.92 for the placebo group, both better than natural history (+1.33). This was well below 50% reduction of CMTNS worsening from natural history, so futility could not be declared (P > .99).
Conclusions and Relevance
Both treated patients and those receiving placebo performed better than natural history. It seems unlikely that our results support undertaking a larger trial of 4-g/d AA treatment in subjects with CMT1A.
Trial Registration
clinicaltrials.gov Identifier: NCT00484510
doi:10.1001/jamaneurol.2013.3178
PMCID: PMC3752369  PMID: 23797954
2.  Dynein mutations associated with hereditary motor neuropathies impair mitochondrial morphology and function with age 
Neurobiology of disease  2013;58:220-230.
Mutations in the tail domain of dynein heavy chain (DYNC1H1) cause two closely related human motor neuropathies, dominant spinal muscular atrophy with lower extremity predominance (SMA-LED) and axonal Charcot-Marie-Tooth (CMT) disease, and lead to sensory neuropathy and striatal atrophy in mutant mice. Dynein is the molecular motor carrying mitochondria retrogradely on microtubules, yet the consequences of dynein mutations on mitochondrial physiology have not been explored. Here, we show that mouse fibroblasts bearing heterozygous or homozygous point mutation in the tail domain of dynein, similar to human mutations, show profoundly abnormal mitochondrial morphology associated with loss of mitofusin 1. Furthermore, heterozygous dynein mutant mice display mitochondrial dysfunction in multiple tissues and mitochondria progressively increase in size and invade sarcomeres in muscles. As a likely consequence of systemic mitochondrial dysfunction, dynein mutant mice develop hyperinsulinemia and hyperglycemia and progress to glucose intolerance with age. Last, similar defects in mitochondrial morphology and mitofusin levels are observed in fibroblasts from patients with SMA-LED. Our results show that dynein function is required for the maintenance of mitochondrial morphology and function with ageing and suggest that mitochondrial dysfunction contributes to dyneindependent neurological diseases, such as SMA-LED.
doi:10.1016/j.nbd.2013.05.015
PMCID: PMC3748180  PMID: 23742762
3.  INHERITED NEUROPATHIES: CLINICAL OVERVIEW AND UPDATE 
Muscle & nerve  2013;48(4):604-622.
Inherited neuropathy is a group of common neurologic disorders with heterogeneous clinical presentations and genetic causes. Detailed neuromuscular evaluations, including nerve conduction studies, laboratory testing, and histopathologic examination, can assist in identification of the inherited component beyond family history. Genetic testing increasingly enables definitive diagnosis of specific inherited neuropathies. Diagnosis, however, is often complex, and neurologic disability may have both genetic and acquired components in individual patients. The decision of which genetic test to order or whether to order genetic tests is often complicated, and the strategies to maximize the value of testing are evolving. Apart from rare inherited metabolic neuropathies, treatment approaches remain largely supportive. We provide a clinical update of the various types of inherited neuropathies, their differential diagnoses, and distinguishing clinical features (where available). A framework is provided for clinical evaluations, including the inheritance assessment, electrophysiologic examinations, and specific genetic tests.
doi:10.1002/mus.23775
PMCID: PMC3918879  PMID: 23801417
ataxia; neuropathy; spinocerebellar; cerebellum; triplet repeats
4.  Curcumin derivatives promote Schwann cell differentiation and improve neuropathy in R98C CMT1B mice 
Brain  2012;135(12):3551-3566.
Charcot–Marie–Tooth disease type 1B is caused by mutations in myelin protein zero. R98C mice, an authentic model of early onset Charcot–Marie–Tooth disease type 1B, develop neuropathy in part because the misfolded mutant myelin protein zero is retained in the endoplasmic reticulum where it activates the unfolded protein response. Because oral curcumin, a component of the spice turmeric, has been shown to relieve endoplasmic reticulum stress and decrease the activation of the unfolded protein response, we treated R98C mutant mice with daily gastric lavage of curcumin or curcumin derivatives starting at 4 days of age and analysed them for clinical disability, electrophysiological parameters and peripheral nerve morphology. Heterozygous R98C mice treated with curcumin dissolved in sesame oil or phosphatidylcholine curcumin performed as well as wild-type littermates on a rotarod test and had increased numbers of large-diameter axons in their sciatic nerves. Treatment with the latter two compounds also increased compound muscle action potential amplitudes and the innervation of neuromuscular junctions in both heterozygous and homozygous R98C animals, but it did not improve nerve conduction velocity, myelin thickness, G-ratios or myelin period. The expression of c-Jun and suppressed cAMP-inducible POU (SCIP)—transcription factors that inhibit myelination when overexpressed—was also decreased by treatment. Consistent with its role in reducing endoplasmic reticulum stress, treatment with curcumin dissolved in sesame oil or phosphatidylcholine curcumin was associated with decreased X-box binding protein (XBP1) splicing. Taken together, these data demonstrate that treatment with curcumin dissolved in sesame oil or phosphatidylcholine curcumin improves the peripheral neuropathy of R98C mice by alleviating endoplasmic reticulum stress, by reducing the activation of unfolded protein response and by promoting Schwann cell differentiation.
doi:10.1093/brain/aws299
PMCID: PMC3577101  PMID: 23250879
Charcot-Marie-Tooth disease 1B; curcumin; myelin protein zero; peripheral neuropathy; unfolded protein response
5.  CASE REPORT: 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.
doi:10.1111/j.1529-8027.2012.00398.x
PMCID: PMC3731745  PMID: 22734905
6.  Lessons from London 
doi:10.1136/jnnp-2012-302858
PMCID: PMC3721145  PMID: 22696588
7.  Transitioning outcome measures: relationship between the CMTPedS and CMTNSv2 in children, adolescents and young adults with Charcot-Marie-Tooth disease 
Long term studies of Charcot-Marie-Tooth disease (CMT) across the entire lifespan require stable endpoints that measure the same underlying construct (e.g., disability). The aim of this study was to assess the relationship between the CMT Pediatric Scale (CMTPedS) and the adult CMT Neuropathy Score (CMTNSv2) in 203 children, adolescents and young adults with CMT. There was a moderate curvilinear correlation between the CMTPedS and the CMTNSv2 (Spearman’s rho ρ=0.716, p<0.0001), although there appears to be a floor effect of the CMTNSv2 in patients with a milder CMT phenotype. Univariate analyses indicate that the relationship between the CMTPedS and CMTNSv2 scores improves with worsening disease severity and advancing age. Although one universal scale throughout life would be ideal, our data supports the transition from the CMTPedS in childhood to the CMTNSv2 in adulthood as a continuum of measuring lifelong disability in patients with CMT.
doi:10.1111/jns5.12024
PMCID: PMC3714225  PMID: 23781965
8.  MpzR98C arrests Schwann cell development in a mouse model of early-onset Charcot–Marie–Tooth disease type 1B 
Brain  2012;135(7):2032-2047.
Mutations in myelin protein zero (MPZ) cause Charcot–Marie–Tooth disease type 1B. Many dominant MPZ mutations, including R98C, present as infantile onset dysmyelinating neuropathies. We have generated an R98C ‘knock-in’ mouse model of Charcot–Marie–Tooth type 1B, where a mutation encoding R98C was targeted to the mouse Mpz gene. Both heterozygous (R98C/+) and homozygous (R98C/R98C) mice develop weakness, abnormal nerve conduction velocities and morphologically abnormal myelin; R98C/R98C mice are more severely affected. MpzR98C is retained in the endoplasmic reticulum of Schwann cells and provokes a transitory, canonical unfolded protein response. Ablation of Chop, a mediator of the protein kinase RNA-like endoplasmic reticulum kinase unfolded protein response pathway restores compound muscle action potential amplitudes of R98C/+ mice but does not alter the reduced conduction velocities, reduced axonal diameters or clinical behaviour of these animals. R98C/R98C Schwann cells are developmentally arrested in the promyelinating stage, whereas development is delayed in R98C/+ mice. The proportion of cells expressing c-Jun, an inhibitor of myelination, is elevated in mutant nerves, whereas the proportion of cells expressing the promyelinating transcription factor Krox-20 is decreased, particularly in R98C/R98C mice. Our results provide a potential link between the accumulation of MpzR98C in the endoplasmic reticulum and a developmental delay in myelination. These mice provide a model by which we can begin to understand the early onset dysmyelination seen in patients with R98C and similar mutations.
doi:10.1093/brain/aws140
PMCID: PMC3381724  PMID: 22689911
Charcot–Marie–Tooth type 1B; demyelination; neuromuscular disorders; glial cells; neuropathy
9.  Inherited Peripheral Neuropathies 
Neurologic clinics  2013;31(2):597-619.
SYNOPSIS
Charcot Marie Tooth disease (CMT) is a heterogeneous group of inherited peripheral neuropathies in which the neuropathy is the sole or primary component of the disorder, as opposed to diseases in which the neuropathy is part of a more generalized neurological or multisystem syndrome. Due to the great genetic heterogeneity of this condition, it can be challenging for the general neurologist to diagnose patients with specific types of CMT. Here, we review the biology of the inherited peripheral neuropathies, delineate major phenotypic features of the CMT subtypes and suggest strategies for focusing genetic testing.
doi:10.1016/j.ncl.2013.01.009
PMCID: PMC3646296  PMID: 23642725
Charcot Marie Tooth; Inherited Neuropathy; Genetic Testing
10.  Anterior Tibialis CMAP Amplitude Correlations with Impairment in CMT1A 
Muscle & nerve  2013;47(4):493-496.
Introduction
CMT1A is a slowly progressive neuropathy in which impairment is length dependent. Fibular nerve conduction studies to the anterior tibialis muscle (AT) may serve as a physiological marker of disease progression in patients with CMT1A.
Objective
Determine whether the AT compound muscle action potential (CMAP) amplitude correlates with impairment in patients with CMT1A.
Methods
We correlated AT CMAP amplitudes and impairment measured by the CMT Neuropathy Score (CMTNS) in a cross-section of 121 patients with CMT1A and a subset of 27 patients with longitudinal data.
Results
AT CMAP amplitudes correlated with impairment as measured by the CMTNS in cross sectional analysis. Longitudinal changes in the AT CMAP showed a strong inverse correlation with leg strength but not other components of the CMTNS.
Discussion
AT CMAP amplitude may serve as a useful outcome measure for physiological changes in natural history studies and clinical trials for patients with CMT1A.
doi:10.1002/mus.23614
PMCID: PMC3608739  PMID: 23456782
Neuropathy; Charcot-Marie-Tooth Disease (CMT); Outcome measure; Charcot-Marie-Tooth Neuropathy Score (CMTNS); Nerve Conduction Studies (NCS)
11.  Unfolded protein response, treatment and CMT1B 
Rare Diseases  2013;1:e24049.
CMT1B is the second most frequent autosomal dominant inherited neuropathy and is caused by assorted mutations of the myelin protein zero (MPZ) gene. MPZ mutations cause neuropathy gain of function mechanisms that are largely independent MPZs normal role of mediating myelin compaction. Whether there are only a few or multiple pathogenic mechanisms that cause CMT1B is unknown. Arg98Cys and Ser63Del MPZ are two CMT1B causing mutations that have been shown to cause neuropathy in mice at least in part by activating the unfolded protein response (UPR). We have recently treated Arg98Cys mice with derivatives of curcumin that improved the neuropathy and reduced UPR activation.1 Future studies will address whether manipulating the UPR will be a common or rare strategy for treating CMT1B or other forms of inherited neuropathies.
doi:10.4161/rdis.24049
PMCID: PMC3915562  PMID: 25002989
Charcot Marie Tooth disease 1B (CMT1B); Unfolded Protein Response (UPR); curcumin; myelin; peripheral nerve; genetics
12.  Charcot Marie Tooth (CMT) Subtypes and Genetic Testing Strategies 
Annals of neurology  2011;69(1):22-33.
Background
Charcot Marie Tooth disease (CMT) affects one in 2500 people and is caused by mutations in more than 30 genes. Identifying the genetic cause of CMT is often necessary for family planning, natural history studies and for entry into clinical trials. However genetic testing can be both expensive and confusing to patients and physicians.
Methods
We analyzed data from 1024 of our patients to determine the percentage and features of each CMT subtype within this clinic population. We identified distinguishing clinical and physiological features of the subtypes that could be used to direct genetic testing for patients with CMT.
Findings
Of 1024 patients evaluated, 787 received CMT diagnoses. Five hundred twenty-seven patients with CMT (67%) received a genetic subtype, while 260 did not have a mutation identified. The most common CMT subtypes were CMT1A, CMT1X, HNPP, CMT1B, and CMT2A. All other subtypes accounted for less than 1% each. Eleven patients had more than one genetically identified subtype of CMT. Patients with genetically identified CMT were separable into specific groups based on age of onset and the degree of slowing of motor nerve conduction velocities.
Interpretation
Combining features of the phenotypic and physiology groups allowed us to identify patients who were highly likely to have specific subtypes of CMT. Based on these results, we propose a strategy of focused genetic testing for CMT illustrated in a series of flow diagrams created as testing guides.
doi:10.1002/ana.22166
PMCID: PMC3058597  PMID: 21280073
CMT; Charcot Marie Tooth disease; Autosomal Dominant; Autosomal Recessive
13.  Reliability of the CMT neuropathy score (second version) in Charcot-Marie-Tooth disease 
The Charcot-Marie-Tooth neuropathy score (CMTNS) is a reliable and valid composite score comprising symptoms, signs, and neurophysiological tests, which has been used in natural history studies of CMT1A and CMT1X and as an outcome measure in treatment trials of CMT1A. Following an international workshop on outcome measures in Charcot-Marie-Tooth disease (CMT), the CMTNS was modified to attempt to reduce floor and ceiling effects and to standardize patient assessment, aiming to improve its sensitivity for detecting change over time and the effect of an intervention. After agreeing on the modifications made to the CMTNS (CMTNS2), three examiners evaluated 16 patients to determine inter-rater reliability; one examiner evaluated 18 patients twice within 8 weeks to determine intra-rater reliability. Three examiners evaluated 63 patients using the CMTNS and the CMTNS2 to determine how the modifications altered scoring. For inter- and intra-rater reliability, intra-class correlation coefficients (ICCs) were ≥0.96 for the CMT symptom score and the CMT examination score. There were small but significant differences in some of the individual components of the CMTNS compared with the CMTNS2, mainly in the components that had been modified the most. A longitudinal study is in progress to determine whether the CMTNS2 is more sensitive than the CMTNS for detecting change over time.
doi:10.1111/j.1529-8027.2011.00350.x
PMCID: PMC3754828  PMID: 22003934
Charcot-Marie-Tooth disease; CMT neuropathy score; reliability
14.  Symmetry of foot alignment and ankle flexibility in paediatric Charcot-Marie-Tooth disease 
Background
Charcot-Marie-Tooth disease is the most common inherited nerve disorder and typically presents with pes cavus foot deformity and ankle equinus during childhood. Level in the variation of symmetry of musculoskeletal lower limb involvement across the clinical population is unknown, despite early reports describing gross asymmetry.
Methods
We measured foot alignment and ankle flexibility of the left and right limbs using accurate and reliable standardised paediatric outcome measures in 172 patients aged 3–20 years with a variety of disease subtypes recruited from the United States, United Kingdom, Italy and Australia.
Findings
While a large range of differences existed between left and right feet for a small proportion of children, there was no overall significant difference between limbs.
Interpretation
There are two important implications of these findings. Children with Charcot-Marie-Tooth disease generally exhibit symmetrical foot alignment and ankle flexibility between limbs. As such, analysing one limb only for biomechanical-related research is appropriate and satisfies the independence requirements for statistical analysis. However, because there are large differences between feet for a small proportion of children, an individualised limb-focused approach to clinical care is required.
doi:10.1016/j.clinbiomech.2012.02.006
PMCID: PMC3389135  PMID: 22424781
Foot; ankle; Charcot-Marie-Tooth disease; Foot Posture Index; children; pes cavus
15.  Neuropathy in Human and Mice with PMP22 null 
Archives of neurology  2011;68(6):814-821.
Background/Objective
Haploinsufficiency of PMP22 causes hereditary neuropathy with liability to pressure palsies (HNPP). However, the biological functions of PMP22 in humans are largely unexplored due to the absence of patients with PMP22 null mutations.
Design, Setting and Participants
We have evaluated a 7-year-old boy with PMP22 null. Findings were compared with those from nerves of Pmp22 null mice.
Results
Motor and sensory deficits in the proband were non-length dependent. Weakness was found in cranial muscles, but not in the limbs. Large fiber sensory modalities were profoundly abnormal, which started prior to the maturation of myelin. This is in line with the temporal pattern of PMP22 expression predominantly in cranial motor neurons and DRG during embryonic development, becoming undetectable in adulthood. Moreover, there were conspicuous maturation defects of myelinating Schwann cells that were more significant in motor nerve fibers than in sensory nerve fibers.
Conclusions
Taken together, these data suggest that PMP22 is important for the normal function of neurons that express PMP22 during early development, such as cranial motor neurons and spinal sensory neurons. Moreover, PMP22 deficiency differentially affects myelination between motor and sensory nerves, which may have contributed to the unique clinical phenotype in the patient with absence of PMP22.
doi:10.1001/archneurol.2011.110
PMCID: PMC3711535  PMID: 21670407
16.  Update on Charcot-Marie-Tooth Disease 
Charcot-Marie-Tooth disease (CMT) disease encompasses a genetically heterogeneous group of inherited neuropathies, also known as hereditary motor and sensory neuropathies. CMT results from mutations in more than 40 genes expressed in Schwann cells and neurons causing overlapping phenotypes. The classic CMT phenotype reflects length-dependent axonal degeneration characterized by distal sensory loss and weakness, deep tendon reflex abnormalities, and skeletal deformities. Recent articles have provided insight into the molecular pathogenesis of CMT, which, for the first time, suggest potential therapeutic targets. Although there are currently no effective medications for CMT, multiple clinical trials are ongoing or being planned. This review will focus on the underlying pathomechanisms and diagnostic approaches of CMT and discuss the emerging therapeutic strategies.
doi:10.1007/s11910-010-0158-7
PMCID: PMC3685483  PMID: 21080241
Charcot-Marie-Tooth; Hereditary; Neuropathy; Genetics; Therapy; Disease pathomechanism
17.  Conduction Block in PMP22 Deficiency 
Patients with PMP22 deficiency present with focal sensory and motor deficits when peripheral nerves are stressed by mechanical force. It has been hypothesized that these focal deficits are due to mechanically induced conduction block (CB). To test this hypothesis, we induced 60-70% CB (defined by electrophysiological criteria) by nerve compression in an authentic mouse model of HNPP with an inactivation of one of the two pmp22 alleles (pmp22+/−). Induction time for the CB was significantly shorter in pmp22+/− mice than that in pmp22+/+ mice. This shortened induction was not found in the mice with deficiency of myelin protein zero (MPZ), a major structural protein of compact myelin. Pmp22+/− nerves showed intact tomacula with no segmental demyelination in both non-compressed and compressed conditions, normal molecular architecture, and normal concentration of voltage-gated sodium channels by H3-saxitoxin binding assay. However, focal constrictions were observed in the axonal segments enclosed by tomacula, a pathological hallmark of HNPP. The constricted axons increase axial-resistance to action potential propagation, which should hasten the induction of CB in pmp22 deficiency. Taken together, these results demonstrate that a function of Pmp22 is to protect the nerve from mechanical injury.
doi:10.1523/JNEUROSCI.4264-09.2010
PMCID: PMC3676309  PMID: 20071523
PMP22; conduction block; paranode; tomacula; hereditary neuropathy with liability to pressure palsies (HNPP); Schwann cell; myelin; Charcot-Marie-Tooth disease; axonal constriction
18.  Validation of the CMT Pediatric Scale as an outcome measure of disability 
Annals of Neurology  2012;71(5):642-652.
Objective
Charcot-Marie-Tooth disease (CMT) is a common heritable peripheral neuropathy. There is no treatment for any form of CMT although clinical trials are increasingly occurring. Patients usually develop symptoms during the first two decades of life but there are no established outcome measures of disease severity or response to treatment. We identified a set of items that represent a range of impairment levels and conducted a series of validation studies to build a patient-centered multi-item rating scale of disability for children with CMT.
Methods
As part of the Inherited Neuropathies Consortium, patients aged 3–20 years with a variety of CMT types were recruited from the USA, UK, Italy and Australia. Initial development stages involved: definition of the construct, item pool generation, peer review and pilot testing. Based on data from 172 patients, a series of validation studies were conducted, including: item and factor analysis, reliability testing, Rasch modeling and sensitivity analysis.
Results
Seven areas for measurement were identified (strength, dexterity, sensation, gait, balance, power, endurance), and a psychometrically robust 11-item scale constructed (Charcot-Marie-Tooth disease Pediatric Scale: CMTPedS). Rasch analysis supported the viability of the CMTPedS as a unidimensional measure of disability in children with CMT. It showed good overall model fit, no evidence of misfitting items, no person misfit and it was well targeted for children with CMT.
Interpretation
The CMTPedS is a well-tolerated outcome measure that can be completed in 25-minutes. It is a reliable, valid and sensitive global measure of disability for children with CMT from the age of 3 years.
doi:10.1002/ana.23572
PMCID: PMC3335189  PMID: 22522479
19.  X inactivation in females with X-linked Charcot–Marie–Tooth disease 
Neuromuscular Disorders  2012;22(7):617-621.
X-linked Charcot–Marie–Tooth disease (CMT1X) is the second most common inherited neuropathy, caused by mutations in gap junction beta-1 (GJB1). Males have a uniformly moderately severe phenotype while females have a variable phenotype, suggested to be due to X inactivation. We aimed to assess X inactivation pattern in females with CMT1X and correlate this with phenotype using the CMT examination score to determine whether the X inactivation pattern accounted for the variable phenotype in females with CMT1X. We determined X inactivation pattern in 67 females with CMT1X and 24 controls using the androgen receptor assay. We were able to determine which X chromosome carried the GJB1 mutation in 30 females. There was no difference in X inactivation pattern between patients and controls. In addition, there was no correlation between X inactivation pattern in blood and phenotype. A possible explanation for these findings is that the X inactivation pattern in Schwann cells rather than in blood may explain the variable phenotype in females with CMT1X.
doi:10.1016/j.nmd.2012.02.009
PMCID: PMC3657177  PMID: 22483671
Charcot–Marie–Tooth disease; GJB1; Connexin32; X inactivation
20.  Shortened internodal length of dermal myelinated nerve fibres in Charcot–Marie-Tooth disease type 1A 
Brain  2009;132(12):3263-3273.
Charcot–Marie-Tooth disease type 1A is the most common inherited neuropathy and is caused by duplication of chromosome 17p11.2 containing the peripheral myelin protein-22 gene. This disease is characterized by uniform slowing of conduction velocities and secondary axonal loss, which are in contrast with non-uniform slowing of conduction velocities in acquired demyelinating disorders, such as chronic inflammatory demyelinating polyradiculoneuropathy. Mechanisms responsible for the slowed conduction velocities and axonal loss in Charcot–Marie-Tooth disease type 1A are poorly understood, in part because of the difficulty in obtaining nerve samples from patients, due to the invasive nature of nerve biopsies. We have utilized glabrous skin biopsies, a minimally invasive procedure, to evaluate these issues systematically in patients with Charcot–Marie-Tooth disease type 1A (n = 32), chronic inflammatory demyelinating polyradiculoneuropathy (n = 4) and healthy controls (n = 12). Morphology and molecular architecture of dermal myelinated nerve fibres were examined using immunohistochemistry and electron microscopy. Internodal length was uniformly shortened in patients with Charcot–Marie-Tooth disease type 1A, compared with those in normal controls (P < 0.0001). Segmental demyelination was absent in the Charcot–Marie-Tooth disease type 1A group, but identifiable in all patients with chronic inflammatory demyelinating polyradiculoneuropathy. Axonal loss was measurable using the density of Meissner corpuscles and associated with an accumulation of intra-axonal mitochondria. Our study demonstrates that skin biopsy can reveal pathological and molecular architectural changes that distinguish inherited from acquired demyelinating neuropathies. Uniformly shortened internodal length in Charcot–Marie-Tooth disease type 1A suggests a potential developmental defect of internodal lengthening. Intra-axonal accumulation of mitochondria provides new insights into the pathogenesis of axonal degeneration in Charcot–Marie-Tooth disease type 1A.
doi:10.1093/brain/awp274
PMCID: PMC2800385  PMID: 19923170
CMT1A; internodal length; Schwann cell; skin biopsy; Charcot–Marie-Tooth disease
21.  PMP22 expression in dermal nerve myelin from patients with CMT1A 
Brain  2009;132(7):1734-1740.
Charcot-Marie-Tooth disease type 1A (CMT1A) is caused by a 1.4 Mb duplication on chromosome 17p11.2, which contains the peripheral myelin protein-22 (PMP22) gene. Increased levels of PMP22 in compact myelin of peripheral nerves have been demonstrated and presumed to cause the phenotype of CMT1A. The objective of the present study was to determine whether an extra copy of the PMP22 gene in CMT1A disrupts the normally coordinated expression of PMP22 protein in peripheral nerve myelin and to evaluate PMP22 over-expression in patients with CMT1A and determine whether levels of PMP22 are molecular markers of disease severity. PMP22 expression was measured by taking skin biopsies from patients with CMT1A (n = 20) and both healthy controls (n = 7) and patients with Hereditary Neuropathy with liability to Pressure Palsies (HNPP) (n = 6), in which patients have only a single copy of PMP22. Immunological electron microscopy was performed on the skin biopsies to quantify PMP22 expression in compact myelin. Similar biopsies were analysed by real time PCR to measure PMP22 mRNA levels. Results were also correlated with impairment in CMT1A, as measured by the validated CMT Neuropathy Score. Most, but not all patients with CMT1A, had elevated PMP22 levels in myelin compared with the controls. The levels of PMP22 in CMT1A were highly variable, but not in HNPP or the controls. However, there was no correlation between neurological disabilities and the level of over-expression of PMP22 protein or mRNA in patients with CMT1A. The extra copy of PMP22 in CMT1A results in disruption of the tightly regulated expression of PMP22. Thus, variability of PMP22 levels, rather than absolute level of PMP22, may play an important role in the pathogenesis of CMT1A.
doi:10.1093/brain/awp113
PMCID: PMC2724915  PMID: 19447823
PMP22; CMT1A; CMTNS; HNPP; Schwann cell; myelin; Charcot-Marie-Tooth disease
22.  Copy number variations are a rare cause of non-CMT1A Charcot-Marie-Tooth disease 
Journal of neurology  2009;257(5):735-741.
Hereditary peripheral neuropathies present a group of clinically and genetically heterogeneous entities. All known forms, including the various forms of Charcot-Marie-Tooth disease (CMT) are characterized as Mendelian traits and over 35 genes have been identified thus far. The mutational mechanism of the most common CMT type, CMT1A, is a 1.5 Mb chromosomal duplication at 17p12 that contains the gene PMP22. Only recently it has been realized that such copy number variants (CNV) are a widespread phenomenon and important for disease. However, it is not known whether CNVs play a wider role in hereditary peripheral neuropathies outside of CMT1A. In a phenotypically heterogeneous sample of 97 patients, we performed the first high-density CNV study of 34 genomic regions harboring known genes for hereditary peripheral neuropathies including the 17p12 duplication region, with comparative genomic hybridization (CGH) microarrays. We identified three CNVs that affected coding exons. A novel shorter form of a PMP22 duplication was detected in a CMT1A family previously tested negative in a commercial test. Two other CNVs in MTMR2 and ARHGEF10 are likely not disease associated. Our results indicate that CNVs are a rare cause for non-CMT1A CMT. Their potential relevance as disease modifiers remains to be evaluated. The present study design cannot rule out that specific CMT forms exist where CNVs play a larger role.
doi:10.1007/s00415-009-5401-2
PMCID: PMC2865568  PMID: 19949810
Copy number variation; Charcot-Marie-Tooth disease; CMT1A; Peripheral neuropathies
23.  Mutation of FIG4 causes a rapidly progressive, asymmetric neuronal degeneration 
Brain  2008;131(8):1990-2001.
Recessive Charcot-Marie-Tooth disease type-4J (CMT4J) and its animal model, the pale tremor mouse (plt), are caused by mutations of the FIG4 gene encoding a PI(3,5)P2 5-phosphatase. We describe the 9-year clinical course of CMT4J, including asymmetric, rapidly progressive paralysis, in two siblings. Sensory symptoms were absent despite reduced numbers of sensory axons. Thus, the phenotypic presentation of CMT4J clinically resembles motor neuron disease. Time-lapse imaging of fibroblasts from CMT4J patients demonstrates impaired trafficking of intracellular organelles because of obstruction by vacuoles. Further characterization of plt mice identified axonal degeneration in motor and sensory neurons, limited segmental demyelination, lack of TUNEL staining and lack of accumulation of ubiquitinated protein in vacuoles of motor and sensory neurons. This study represents the first documentation of the natural history of CMT4J. Physical obstruction of organelle trafficking by vacuoles is a potential novel cellular mechanism of neurodegeneration.
doi:10.1093/brain/awn114
PMCID: PMC2724900  PMID: 18556664
FIG4 or SAC3 gene; PI(3,5)P2-5-phosphatase; neuronopathy; axonal degeneration; vacuoles; amyotrophic lateral sclerosis; motor neuron disease; segmental demyelination; Schwann cells
24.  Mutation of FIG4 causes neurodegeneration in the pale tremor mouse and patients with CMT4J 
Nature  2007;448(7149):68-72.
Membrane-bound phosphoinositides are signalling molecules that have a key role in vesicle trafficking in eukaryotic cells1. Proteins that bind specific phosphoinositides mediate interactions between membrane-bounded compartments whose identity is partially encoded by cytoplasmic phospholipid tags. Little is known about the localization and regulation of mammalian phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P2), a phospholipid present in small quantities that regulates membrane trafficking in the endosome–lysosome axis in yeast2. Here we describe a multi-organ disorder with neuronal degeneration in the central nervous system, peripheral neuronopathy and diluted pigmentation in the ‘pale tremor’ mouse. Positional cloning identified insertion of ETn2β (early transposon 2β)3 into intron 18 of Fig4 (A530089I17Rik), the homologue of a yeast SAC (suppressor of actin) domain PtdIns(3,5)P2 5-phosphatase located in the vacuolar membrane. The abnormal concentration of PtdIns(3,5)P2 in cultured fibroblasts from pale tremor mice demonstrates the conserved biochemical function of mammalian Fig4. The cytoplasm of fibroblasts from pale tremor mice is filled with large vacuoles that are immunoreactive for LAMP-2 (lysosomal-associated membrane protein 2), consistent with dysfunction of the late endosome–lysosome axis. Neonatal neurodegeneration in sensory and autonomic ganglia is followed by loss of neurons from layers four and five of the cortex, deep cerebellar nuclei and other localized brain regions. The sciatic nerve exhibits reduced numbers of large-diameter myelinated axons, slowed nerve conduction velocity and reduced amplitude of compound muscle action potentials. We identified pathogenic mutations of human FIG4 (KIAA0274) on chromosome 6q21 in four unrelated patients with hereditary motor and sensory neuropathy. This novel form of autosomal recessive Charcot–Marie–Tooth disorder is designated CMT4J.
doi:10.1038/nature05876
PMCID: PMC2271033  PMID: 17572665

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