Intraparenchymal injections of acid sphingomyelinase results in regional correction of lysosomal storage pathology in the Niemann-Pick A mouse

Niemann-Pick A disease (NPD-A) is caused by a deficiency of acid sphingomyelinase (ASM) leading to the intracellular accumulation of sphingomyelin and cholesterol in lysosomes. We evaluated the effects of direct intraparenchymal brain injections of purified recombinant human ASM (hASM) at correcting the storage pathology in a mouse model of NPD-A (ASMKO). Different doses (0.1 ng to 10 mug of hASM) were injected into the right hemisphere of the hippocampus and thalamus of 12- to 14-week-old ASMKO mice. Immunohistochemical analysis after 1 week indicated that animals treated with greater than 1 mug hASM/site showed detectable levels of enzyme around the injected regions. However, localized clearance of sphingomyelin and cholesterol storage were observed in animals administered lower doses of enzyme, starting at 100 ng hASM/site. Areas of correction were also noted at distal sites such as in the contralateral hemispheres. Indications of storage re-accumulation were seen after 2 weeks post-injection. Injections of hASM did not cause any significant cell infiltration, astrogliosis, or microglial activation. These results indicate that intraparenchymal injection of hASM is associated with minimal toxicity and can lead to regional reductions in storage pathology in the ASMKO mouse.     

Neuropathology of the acid sphingomyelinase knockout mouse model of Niemann-Pick A disease including structure-function studies associated with cerebellar Purkinje cell degeneration

Niemann-Pick A (NP-A) is an inherited metabolic (lysosomal storage) disease characterized by neurovisceral accumulation of sphingomyelin due to deficiency of acid sphingomyelinase (ASM). An ASM knockout (ASMKO) mouse model of NP-A is available through targeted disruption of the parent gene. This study presents the pattern and time course of lysosomal pathology and neurodegeneration in the ASMKO mouse nervous system. Cells throughout the nervous system developed the classic foamy appearance associated with lysosomal storage disorders. Despite this, neurons were capable of retrogradely transporting dyes within established brain pathways comparable to control animals. A silver degeneration staining method demonstrated widespread damage in the form of ‘classic’ impregnation of cells, fibers and synaptic terminals. Of particular interest was the degeneration of Purkinje cells (PC) within the cerebellum, beginning by 7 weeks of age in parasagittal bands and culminating with near complete degeneration of this cell type by 20 weeks. In parallel, ASMKO mice had progressively deteriorating motor performance on two versions of the rotating rod test (accelerating and rocking). ASMKO mice at 5–7 weeks of age performed similarly to controls on both rotating rod tests, but performance sharply deteriorated between 7 and 20 weeks of age. This study further characterized the neuropathology associated with ASM deficiency, and identifies quantitative histological and behavioral endpoints for evaluation of therapeutic intervention in this authentic NP-A mouse model.     

Motion analysis of a child with Niemann–Pick disease type C treated with miglustat

Niemann–Pick disease type C (NPC) is a progressive neurodegenerative disorder for which there is no effective treatment other than supportive therapy. Recently, the oral medication miglustat has been offered as a possible therapy aimed at reducing pathological substrate accumulation. This article describes the use of computerized three‐dimensional motion analysis to evaluate a 3‐year‐old child with NPC treated with miglustat for 12 months. Motion analysis provided quantitative data on the patient's gait. However, dementia and motor dysfunction progressed despite the treatment, and the patient lost the ability to walk between 9 and 12 months of the study. Motion analysis should be considered among the tools for measuring functional outcomes in future therapeutical trials of patients with neurodegenerative diseases. It is not possible to draw conclusions about miglustat therapy in NPC from a single patient experience. © 2007 Movement Disorder Society     

Decreased purinergic inhibition of synaptic activity in a mouse model of Niemann‐Pick disease type C

Niemann‐Pick disease type C (NPC) is a progressive neurodegenerative disorder characterized by accumulation of free cholesterol in lysosomes, mainly due to a mutation in the NPC1 gene. The pathophysiological basis of the neural disorders in NPC, however, is not well understood. We found that the hippocampal field excitatory postsynaptic potential (fEPSP) was enhanced in NPC1 mutant mice. A1‐receptor antagonist or adenosine degrading enzyme enhanced the fEPSP in both types of mice, but had a much weaker effect in the mutant mice, suggesting less tonic inhibition of synaptic transmission by endogenous adenosine in the mutant. Further evidence showed impaired hippocampal long term potentiation (LTP) in mutant mice. Supplement of A1 agonist N6‐Cyclopentyladenosine (CPA) partially rescued the impaired LTP in mutant mice. Moreover, adenosine release from hippocampal slices was significantly decreased in the mutant. The enhanced excitatory synaptic transmission and the decreased synaptic plasticity due to the decreased adenosine release in NPC brain may partially contribute to the neural disorders of NPC disease, such as seizures, neurodegeneration, and dementia. © 2010 Wiley‐Liss, Inc.     

Reduced cerebellar neurodegeneration after combined therapy with cyclodextrin/allopregnanolone and miglustat in NPC1: A mouse model of Niemann‐Pick type C1 disease

Niemann‐Pick type C1 (NPC1) disease is a lysosomal storage disease characterized by a deficiency of NPC1 gene function. The malfunction of protein results in a progressive accumulation of lipids in many organs. A combined approach with substrate‐reduction therapy (SRT) and byproduct therapy (BPT) has been shown to ameliorate the disease course in a mutant mouse model (NPC1^–/–). The present study examines the morphological parameters underlying these changes. For the combined SRT/BPT treatment, NPC1^–/– mutant mice (NPC1^{–/–SRT/BPT}) were injected with allopregnanolone/cyclodextrin weekly, starting at postnatal day (P) 7. Starting at P10, a miglustat injection was administered daily until P23. Thereafter, miglustat was added to the powdered chow. For the sham treatment, both mutant NPC1^–/– (NPC1^–/–sham) and wild‐type (NPC1^+/+sham) mice received an NaCl injection and were fed powdered chow without miglustat. Analysis was performed on cerebellar slices by histology and immunohistochemistry. The volumes and cell counts of cerebellar structures were quantified. Additionally, ultrastructural analysis was performed with transmission electron microscopy. In agreement with previous studies, the current study demonstrates Purkinje cell degeneration in the mutant mice, which was partially abrogated by SRT/BPT. The volumes of cerebellar white matter and molecular layer were reduced as well. Also, the number of neurons was reduced in granular and molecular layers. However, only the molecular layer benefited from the therapy, as shown by an increase in the volume and the amount of neurons. The volume and number of neurons of the deep cerebellar nuclei were significantly decreased in mutant mice; an appreciable therapeutic benefit could be demonstrated for the nucleus interpositus. © 2014 Wiley Periodicals, Inc.     

Severe demyelination in a patient with a late infantile form of Niemann‐Pick disease type C

Niemann‐Pick disease type C (NPC) is a cholesterol storage disease caused by defective cellular cholesterol transportation. The onset and progression of NPC are variable, and autopsy findings have mainly been reported for the adult and juvenile forms of this disease. Here we report the clinical and pathological findings from a 9‐year‐old female patient with the late infantile form of NPC due to NPC1 gene mutation. She had notable splenomegaly at 4 months of age. She lost the ability to speak at 18 months of age. She learned to walk, but often fell and could no longer walk after 30 months. At 3 years of age, she was diagnosed with NPC. Sequence analysis of the NPC1 gene revealed compound heterozygous mutation of T2108C (F703S) and C2348G (S813X) (both novel). Thereafter, the patient suffered repeated respiratory infections and died of respiratory failure at 9 years of age. Pathological findings included cerebral atrophy (particularly of white matter), severe demyelination, and the loss of neurons from the cerebrum and from the nuclei of the brain stem. Remnant neuronal cells and microglia in the cerebrum, cerebellum, and brain stem had become swollen and foamy. Neurons of the hippocampal CA1 and Purkinje cells were relatively spared, and senile plaques and axonal spheroids were not present. Foamy cells were also observed in other organs, especially the spleen and bone marrow. The F703S mutation in this patient was localized in a sterol‐sensing domain (SSD). Severe neurological phenotypes have been previously reported in patients with missense mutations in an SSD. It is considered that the combination of a nonsense mutation and missense mutation in an SSD was responsible for the severe neurological phenotype of our present patient. While pathological findings of adult/juvenile forms of NPC have included swollen neurons and glia, neuronal cell loss, and NFTs, demyelination may be a predominant finding in the infantile form of NPC.     

Amelioration of enteric neuropathology in a mouse model of Niemann‐Pick C by Npc1 expression in enteric glia

Niemann‐Pick C (NPC) disease is an autosomal recessive, lethal, neurodegenerative disorder caused by mutations in NPC1. By using the glial fibrillary acidic protein (GFAP) promoter, we demonstrated previously that astrocyte‐specific expression of Npc1 decreased neuronal storage of cholesterol in Npc1^?/? mice; reduced numbers of axonal spheroids; and produced less degeneration of neurons, reactive astrocytes, and loss of myelin tracts in the central nervous system. GFAP‐Npc1, Npc1^?/? mice exhibited markedly enhanced survival, and death was not associated with the severe terminal weight loss observed in Npc1^?/? mice. Intestinal transit is delayed in Npc1^?/? mice but is normal in GFAP‐NPC1, Npc1^?/? until late in the course of their disease. Because glia play an important role in the enteric nervous system, we studied morphology and cholesterol content of intestines from Npc1^?/? mice and examined the effect of GFAP‐promoted restoration of Npc1 in enteric glia. Although the number of neurons was not altered, the total amount of cholesterol stored in the small intestine was decreased, as were the number of neurons with inclusions and the number of inclusions per neuron. We conclude that expression of Npc1 by enteric glial cells can ameliorate the enteric neuropathology, and we speculate that dysfunction of the enteric nervous system contributes to the retarded intestinal transit, weight loss, and demise of Npc1^?/? mice. © 2009 Wiley‐Liss, Inc.     

Cathepsin S contributes to microglia‐mediated olfactory dysfunction through the regulation of Cx3cl1–Cx3cr1 axis in a Niemann–Pick disease type C1 model

Microglia can aggravate olfactory dysfunction by mediating neuronal death in the olfactory bulb (OB) of a murine model of Niemann–Pick disease type C1 (NPC1), a fatal neurodegenerative disorder accompanied by lipid trafficking defects. In this study, we focused on the crosstalk between neurons and microglia to elucidate the mechanisms underlying extensive microgliosis in the NPC1‐affected brain. Microglia in the OB of NPC1 mice strongly expressed CX3C chemokine receptor 1 (Cx3cr1), a specific receptor for the neural chemokine C‐X3‐C motif ligand 1 (Cx3cl1). In addition, a high level of Cx3cl1 was detected in NPC1 mouse‐derived CSF due to enhanced catalytic activity of Cathepsin S (Ctss), which is responsible for Cx3cl1 secretion. Notably, nasal delivery of Cx3cl1 neutralizing antibody or Ctss inhibitor could inhibit the Cx3cl1–Cx3cr1 interaction and support neuronal survival through the suppression of microglial activation, leading to an improvement in the olfactory function in NPC1 mice. Relevant in vitro experiments revealed that intracellular cholesterol accumulation could act as a strong inducer of abnormal Ctss activation and, in turn, stimulated the Cx3cl1–Cx3cr1 axis in microglia via p38 mitogen‐activated protein kinase signaling. Our data address the significance of Cx3cl1–Cx3cr1 interaction in the development of microglial neurotoxicity and suggest that Ctss is a key upstream regulator. Therefore, this study contributes to a better understanding of the crosstalk between neurons and microglia in the development of the neurodegeneration and provides a new perspective for the management of olfactory deficits and other microglia‐dependent neuropathies. GLIA 2016;64:2291–2305     

Long-term memory for aversive training is impaired in Idua(-/-) mice, a genetic model of mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease that leads to neurodegeneration and neurological deficits, among other pathological and clinical consequences. The aim of the present study was to evaluate neurobehavioral parameters in a genetic mouse model of mucopolysaccharidosis type I (MPS I). During exploration of an open field, adult MPS I (Idua(-/-)) mice showed normal locomotion and anxiety but reduced number of rearings. Idua(-/-) mice performed normally in a novel object recognition memory task and showed normal short-term retention of inhibitory avoidance training. By contrast, long-term retention of inhibitory avoidance was impaired in Idua(-/-) mice. The deficit in inhibitory avoidance memory could not be attributed to reduced footshock reactivity. The results indicate that Idua(-/-) mice present deficits in long-term memory for aversive training and reduced exploratory behavior.     

Thalamocortical neuron loss and localized astrocytosis in the Cln3 knock-in mouse model of Batten disease

Juvenile neuronal ceroid lipofuscinosis (JNCL) is the result of mutations in the Cln3 gene. The Cln3 knock-in mouse (Cln3Deltaex7/8) reproduces the most common Cln3 mutation and we have now characterized the CNS of these mice at 12 months of age. With the exception of the thalamus, Cln3Deltaex7/8 homozygotes displayed no significant regional atrophy, but a range of changes in individual laminar thickness that resulted in variable cortical thinning across subfields. Stereological analysis revealed a pronounced loss of neurons within individual laminae of somatosensory cortex of affected mice and the novel finding of a loss of sensory relay thalamic neurons. These affected mice also exhibited profound astrocytic reactions that were most pronounced in the neocortex and thalamus, but diminished in other brain regions. These data provide the first direct evidence for neurodegenerative and reactive changes in the thalamocortical system in JNCL and emphasize the localized nature of these events.     

Distribution of acid sphingomyelinase in rodent and non-human primate brain after intracerebroventricular infusion

One treatment approach for lysosomal storage diseases (LSDs) is the systemic infusion of recombinant enzyme. Although this enzyme replacement is therapeutic for the viscera, many LSDs have central nervous system (CNS) components that are not adequately treated by systemic enzyme infusion. Direct intracerebroventricular (ICV) infusion of a high concentration of recombinant human acid sphingomyelinase (rhASM) into the CNS over a prolonged time frame (hours) has shown therapeutic efficacy in a mouse model of Niemann–Pick A (NP/A) disease. To evaluate whether such an approach would translate to a larger brain, rhASM was infused into the lateral ventricles of both rats and Rhesus macaques, and the resulting distribution of enzyme characterized qualitatively and quantitatively. In both species, ICV infusion of rhASM resulted in parenchymal distribution of enzyme at levels that were therapeutic in the NP/A mouse model. Enzyme distribution was global in nature and exhibited a relatively steep gradient from the cerebrospinal fluid compartment to the inner parenchyma. Additional optimization of an ICV delivery approach may provide a therapeutic option for LSDs with neurologic involvement.     

A therapeutic trial of gangliosides and thymosin in the Wobbler mouse model of motor neuron disease

Mixed bovine gangliosides have been reported to enhance neuronal regeneration and sprouting. The Wobbler mouse model of motor neuron disease was used to test the clinical effects of long-term ganglioside administration on the course of the disease. Mixed gangliosides were injected subcutaneously into a group of 5 Wobbler mice and compared to a control group of 5 Wobbler mice which received saline. Because of several reports implicating involvement of the immune system in ALS, a 3rd group of 5 Wobbler mice received thymosin. All mice were 4 weeks old at commencement of injections. The 3 groups were examined weekly and graded with respect to front leg power, ability to climb a vertical grating, and walking posture. After 4 months of treatment, no significant difference between either experimental group and the controls was found.     

Lysosomal storage results in impaired survival but normal neurite outgrowth in dorsal root ganglion neurones from a mouse model of Sandhoff disease

Sandhoff disease is a heritable lysosomal storage disease resulting from impaired degradation of GM2 ganglioside and related substrates. A mouse model of Sandhoff disease created by gene targeting displays progressive neurological manifestations, similar to patients with the disease. In the present in vivo and in vitro studies, we examined morphological and functional abnormalities of dorsal root ganglion (DRG) neurones in Sandhoff disease mice at an asymptomatic stage (approximately 1 month of age). Light microscopic studies with Nissl staining and immunocytochemistry suggested extensive intracytoplasmic storage of GM2 ganglioside in the Sandhoff mouse DRG neurones. These findings were consistent with the results of electron microscopy, in which a huge number of pleomorphic inclusion bodies immunoreactive for GM2 ganglioside were present in the cytoplasm of the neurones. The inclusion bodies were also identified in satellite cells and Schwann cells in the Sandhoff mouse DRG. The survival ratios of DRG neurones after 1, 2, 4 and 6 days in culture were significantly lower in the Sandhoff mice than in the age-matched heterozygous mice. The ratio of neurite-bearing cells on poly-l-lysine-coated dishes after 2 days in culture was also lower by approximately 10% in the Sandhoff mice compared to the heterozygotes, but additional coating of laminin onto poly-l-lysine dramatically enhanced the neurite extension from the neurones in both groups of mice. These results indicate that accumulation of GM2 ganglioside in DRG neurones impairs the capability of the neurones to survive in vitro, although viable neurones from the Sandhoff mice in culture can regenerate neurites nearly as well as unaffected neurones.     

Astrocyte reactivity in related brain regions in a mouse model of MPTP-induced Parkinson's disease

BACKGROUND: Severe injury to dopaminergic neuronal cell bodies and their axon terminals in the substantia nigra pars compacta (SNC) has been observed in both Parkinson's disease (PD) patients or in 1-methy-4-phenyl-1,2,3,6-tetrahydropyrindine(MPTP)-induced PD animal models, but only slight injury occurs in the adjacent ventral tegmental area (VTA). The mechanisms underlying this selective injury remain poorly understood.OBJECTIVE: To comparatively observe astrocyte reactivity in the SNC, caudate putamen (Cpu), VTA, and frontal association cortex (FrA).DESIGN, TIME AND SETTING: A cellular and molecular biology, randomized, controlled experiment was performed at the Institute of Neurobiology, Department of Human Anatomy, Medical School of Nantong University, between December 2006 and September 2008.MATERIALS: A total of 80 healthy adult male C57BL/6 mice were included in this study. MPTP was purchased from Sigma, USA.METHODS: Mice were randomly divided into a model group (n = 64) and a sham-operated group (n = 16). PD was induced in the mice from the model group by intraperitoneal injection of 20 mg/kg MPTP, once every three hours, for a total of 4 times.MAIN OUTCOME MEASURES: Tyrosine hydroxylase (TH)-immunoreactive neurons and glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were examined by dual immunofluorescence labeling. GFAP-immunoreactive astrocytes in the Cpu and FrA were determined by immunofluorescent staining. GFAP mRNA expression in the SNC, Cpu, VTA, and FrA was detected using real-time polymerase chain reaction. TH protein levels in the TH-immunoreactive axon terminals of the Cpu and FrA were detected by Western blotting.RESULTS: Numbers of TH-immunoreactive neurons in the SNC, and TH protein level in the Cpu, markedly decreased (by approximately 68%) 1 day after MPTP injection, and gradually increased at 3 days. Simultaneously, astrocyte reactivity was strengthened, in particular at 7 days. However, after MPTP injection, decreases in the numbers of TH-immunoreactive neurons in the VTA, and TH protein levels in the FrA, were less apparent (approximately 15%). Also, no obvious astrocyte reactivity was observed.CONCLUSION: In a mouse model of PD, astrocyte reactivity was apparent in the SNC and Cpu, but not the VTA or FrA. In addition, astrocyte reactivity was greater in regions where injury to dopaminergic neurons was more severe.     

姜黄素对阿尔茨海默病模型小鼠脑内胶质细胞介导的炎症反应的抑制作用

目的探讨姜黄素对AD模型小鼠学习记忆能力的影响。方法将80小鼠按随机原则分四组,对照组、Alcl3组、溶剂组及姜黄素组。Alcl3制作小鼠AD模型,之后给予腹腔注射姜黄素3 d,给药后14 d水迷宫测试学习记忆能力。免疫染色及western blot方法检测Aβ42、GFAP和Iba-1β蛋白水平。ELISA方法检测海马区炎症因子IL-1β,IL-6和TNF-α的水平。结果与对照组比,Alcl3能够导致逃避潜伏期延长和记忆下降更明显,说明AD模型成功建立。与Alcl3组和溶剂治疗组相比,姜黄素组明显减少潜伏期及增加穿越次数,而且显著减少Aβ42表达。相比Alcl3组,姜黄素组的GFAP和Iba-1β以及海马区IL-1β、IL-6及TNF-α的指标下降有显著意义。结论研究表明姜黄素有潜在治疗AD的可能,通过下调Alcl致胶质细胞过度活化引起炎症反应,而提高学习记忆能力。     

Intracerebroventricular delivery of glucocerebrosidase reduces substrates and increases lifespan in a mouse model of neuronopathic Gaucher disease

Gaucher disease is caused by a deficit in the enzyme glucocerebrosidase. As a consequence, degradation of the glycolipids glucosylceramide (GluCer) and glucosylsphingosine (GluSph) is impaired, and their subsequent buildup can lead to significant pathology and early death. Type 1 Gaucher patients can be treated successfully with intravenous replacement enzyme, but this enzyme does not reach the CNS and thus does not ameliorate the neurological involvement in types 2 and 3 Gaucher disease. As one potential approach to treating these latter patients, we have evaluated intracerebroventricular (ICV) administration of recombinant human glucocerebrosidase (rhGC) in a mouse model of neuronopathic Gaucher disease. ICV administration resulted in enzyme distribution throughout the brain and alleviated neuropathology in multiple brain regions of this mouse model. Treatment also resulted in dose-dependent decreases in GluCer and GluSph and significantly extended survival. To evaluate the potential of continuous enzyme delivery, a group of animals was treated ICV with an adeno-associated viral vector encoding hGC and resulted in a further extension of survival. These data suggest that ICV administration of rhGC may represent a potential therapeutic approach for type 2/3 Gaucher patients. Preclinical evaluation in larger animals will be needed to ascertain the translatability of this approach to the clinic.     

APP/PS1双转基因小鼠早期记忆功能障碍与胆碱能系统的关系研究

目的观察转APP/PS1基因阿尔茨海默病小鼠(APP/PS1小鼠)早期空间学习记忆功能及乙酰胆碱能系统的变化以及两者之间的相关性,探讨阿尔茨海默病早期学习记忆障碍的发病机制。方法应用Morris水迷宫法评定3月龄APP/PS1小鼠及相应野生型(WT)小鼠的空间学习记忆功能;采用免疫组织化学及组织化学染色方法检测脑组织中β-淀粉样蛋白(Aβ)斑块沉积情况;采用ELISA法检测脑组织中乙酰胆碱(ACh)含量以及胆碱乙酰转移酶(ChAT)和乙酰胆碱酯酶(AChE)活性,并探讨小鼠脑组织中ACh含量与其空间记忆能力、ChAT活性的相关性。结果水迷宫评定结果显示两组小鼠到达平台的潜伏期无统计学差异(P>0.05);APP/PS1小鼠在目标象限的游泳时间百分比〔(29.02±4.27)%〕和距离百分比〔(28.85±3.77)%〕较WT小鼠均下降(P<0.05)。APP/PS1小鼠脑组织中尚无Aβ斑块的沉积。APP/PS1小鼠脑组织中ACh含量〔(45.23±1.40)ng/g prot〕和ChAT活性〔(279.53±12.13)U/g组织湿重〕均较WT小鼠〔分别为(54.08±4.84)ng/gprot、(315.84±11.32)U/g组织湿重〕显著降低(P<0.05),两组小鼠脑组织中AChE活性无统计学差异(P>0.05)。小鼠脑组织中ACh含量与其空间记忆功能(目标象限航行时间百分比、目标象限航行路程百分比)呈正相关(r=0.861、r=0.874,P<0.05),ACh含量与ChAT活性呈正相关(r=0.926,P<0.05)。结论 APP/PS1小鼠空间记忆功能障碍、ACh含量减少和ChAT活性降低可发生于Aβ斑块沉积之前。脑组织中ACh含量减少和ChAT活性降低可能与APP/PS1小鼠记忆功能损害密切相关。     

Normal nerve striations are altered in the trembler‐J mouse,a model of charcot–marie–tooth disease

Introduction: This study was initiated because it was noted that the peripheral nerves of Trembler‐J mice (a model of human Charcot–Marie–Tooth disease) appear to lack normal striations. Methods: We performed confocal microscopy of whole sciatic nerves and tested the effect of axial stress on impulse conduction. Results: We found that the axons of mutant mice were longer than those of the wild‐type (1.55 mm of axon/mm length of nerve vs. 1.28 mm/mm respectively). This axonal elongation altered the helical nerve striations (bands of Fontana). As nerves were stretched axially, the conduction distance became correspondingly shorter. The effect on latency was significantly greater in the more coiled nerves of Trembler‐J mice (P = 0.038). Conclusions: The finding that mice with a mutated peripheral myelin protein 22 (PMP22) possess excessively long axons may be related to the excess Schwann cell numbers found in this disorder. Muscle Nerve 51 : 246–252, 2015