Charcot-Marie-Tooth disease: New insights from skin biopsy

Abstract

Objective: To evaluate, by skin biopsy, dermal nerve fibers in 31 patients with 3 common Charcot-Marie-Tooth (CMT) genotypes (CMT1A, late-onset CMT1B, and CMTX1), and rarer forms of CMT caused by mutations in RAB7 (CMT2B), TRPV4 (CMT2C), and GDAP1 (AR-CMT2K) genes.

Methods: We investigated axonal loss by quantifying Meissner corpuscles and intrapapillary myelinated endings and evaluated morphometric changes in myelinated dermal nerve fibers by measuring fiber caliber, internodal, and nodal gap length.

Results: The density of both Meissner corpuscles and intrapapillary myelinated endings was reduced in skin samples from patients with CMT1A and all the other CMT genotypes. Nodal gaps were larger in all the CMT genotypes though widening was greater in CMT1A. Perhaps an altered communication between axons and glia may be a common feature for multiple forms of CMT. Internodal lengths were shorter in all the CMT genotypes, and patients with CMT1A had the shortest internodes of all our patients. The uniformly shortened internodes in all the CMT genotypes suggest that mutations in both myelin and axon genes may developmentally impede internode formation. The extent of internodal shortening and nodal gap widening are likely both important in determining nerve conduction velocities in CMT.

Conclusions: This study extends the information gained from skin biopsies on morphologic abnormalities in various forms of CMT and provides insights into potential pathomechanisms of axonal and demyelinating CMT.

Figure 1. Confocal images show morphometric analysis methods

(A, B) Protein gene product (PGP)/myelin basic protein (MBP) double-stained images exemplify the procedures used to measure node (B.b), internode (B.c), and fiber diameter (B.d), calculated as the mean value of 4 random measures along the internode. Measurements were performed on MBP channel, as shown by arrowheads, while PGP staining (arrow in B.a) was necessary to check on axonal continuity. (C) The nodal region on an image double-stained with neurofascin (NF) and MBP: branching originates always from nodes (arrowhead). (D.a, D.b) The same image at higher magnification after splitting the 2 channels. Scale bar: 50 μm (A); 100 μm (C).

Figure 2. Boxplots of internodal length in each Charcot-Marie-Tooth genotype and controls

Dark horizontal lines represent the median value, with the box representing the 25th and 75th percentiles, the whiskers the lower and upper adjacent values, and outside values represented by dots.

Figure 3. Confocal images of glabrous skin in patients with Charcot-Marie-Tooth disease and controls

A moderate loss of Meissner corpuscles is observed in a patient with CMT1A (B) and a severe loss of Meissner corpuscles is present in a patient with RAB7 mutation (C), compared to a control (A). (D–F) Abnormalities of myelinated fibers such as fragmentation (D) and swellings (arrowheads in E and F). (G–I) Disruption of nodal/paranodal architecture with elongation and asymmetry of the paranodes with expansion of neurofascin aggregation along the internode (arrows in H and I) compared to control (G). Scale bar: 200 μm (A, B, C); 30 μm (D, E, F); 50 μm (G, H, I). MBP = myelin basic protein; NF = neurofascin; PGP = protein gene product.