Reduced neurofilament expression in cutaneous nerve fibers of patients with CMT2E

Abstract

Objective: To investigate the effects of NEFL Glu396Lys mutation on the expression and assembly of neurofilaments (NFs) in cutaneous nerve fibers of patients with Charcot-Marie-Tooth disease type 2E (CMT2E).Methods: A large family with CMT2E underwent clinical, electrophysiologic, and skin biopsy studies. Biopsies were processed by indirect immunofluorescence (IF), electron microscopy (EM), and Western blot analysis. Results:The clinical features demonstrated intrafamilial phenotypic variability, and the electrophysiologic findings revealed nerve conductions that were either slow or in the intermediate range. All patients had reduced or absent compound muscular action potential amplitudes. Skin biopsies showed axons labeled with the axonal markers protein gene product 9.5 and a-tubulin, but not with NFs. The results of Western blot analysis were consistent with those of IF, showing reduced or absent NFs and normal expression of a-tubulin. EM revealed clusters of regenerated fibers, in absence of myelin sheath abnormalities. Both IF and EM failed to show NF aggregates in dermal axons. The morphometric analysis showed a smaller axonal caliber in patients than in controls. The study of the nodal/paranodal architecture demonstrated that sodium channels and Caspr were correctly localized in patients with CMT2E.Conclusions: Decrease in NF abundance may be a pathologic marker of CMT2E. The lack of NF aggregates, consistent with prior studies, suggests that they occur proximally leading to subsequent alterations in the axonal cytoskeleton. The small axonal caliber, along with the normal molecular architecture of nodes and paranodes, explain the reduced velocities detected in patients with CMT2E. Our results also demonstrate that skin biopsy can provide evidence of pathologic and pathogenic abnormalities in patients with CMT2E. Charcot-Marie-Tooth disease (CMT) is a group of peripheral neuropathies associated with mutations in more than 80 distinct genes. CMT is divided into different forms based on the pattern of inheritance and neurophysiology. Electrophysiologic studies allow for classification of CMT into demyelinating (CMT1) and axonal (CMT2) forms.1 The classification of CMT has been further divided into subtypes, identified by letters, as defined by the mutated gene.2 CMT2E refers to autosomal dominant CMT2 caused by mutations in the neurofilament light chain (NEFL) gene. Some patients with NEFL mutations have slow conduction velocities, in the "demyelinating" range, and are characterized as having CMT1F. Patients with CMT2E and CMT1F are clinically heterogeneous and the age at onset ranges from infancy, typically with severe impairment, to adulthood with milder impairment. Usually those with slowed conductions present early either in infancy with delayed motor milestones or in late childhood/early adolescence.

Absence of Dystrophin Related Protein-2 disrupts Cajal bands in a patient with Charcot–Marie–Tooth disease

“…Whereas segmental demyelination, a hallmark of chronic inflammatory demyelinating polyneuropathy, is absent in the dermal myelinated nerve fibres of CMT1A patients [20]. More recently our group has observed a reduction in neurofilament expression in dermal nerve fibres in patients with CMT2E that is caused by mutations in the neurofilament light chain gene [27]. Once again skin biopsy has proven useful in the evaluation of inherited neuropathy.…”

Schwann cell transcript biomarkers for hereditary neuropathy skin biopsies

“…12,13,[24][25][26] Total RNA isolated from samples were prepared for RNA-seq using NuGEN ovation library prep kits, and the libraries were loaded on the Illumina HiSeq 2500 (Illumina, San Diego, CA) at the UW Biotechnology Center. 12,13,[24][25][26] Total RNA isolated from samples were prepared for RNA-seq using NuGEN ovation library prep kits, and the libraries were loaded on the Illumina HiSeq 2500 (Illumina, San Diego, CA) at the UW Biotechnology Center.…”

NEFL N98S mutation: another cause of dominant intermediate Charcot–Marie–Tooth disease with heterogeneous early-onset phenotype

“…NEFL mutations have occasionally been associated with intermediately slowed MCV [16,20,21], just one pedigree having been reported under the rubric of DI-CMT [8]. As a whole, NEFL mutations represent between 0.8 and 2 % of all patients with CMT [15,18,[22][23][24][25].…”