Familial, demyelinating sensory and motor polyneuropathy with conduction block

New evidence for secondary axonal degeneration in demyelinating neuropathies

Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.

The LITAF/SIMPLE I92V sequence variant results in an earlier age of onset of CMT1A/HNPP diseases

Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) represent the most common heritable neuromuscular disorders. Molecular diagnostics of CMT1A/HNPP diseases confirm clinical diagnosis, but their value is limited to the clinical course and prognosis. However, no biomarkers of CMT1A/HNPP have been identified. We decided to explore if the LITAF/SIMPLE gene shared a functional link to the PMP22 gene, whose duplication or deletion results in CMT1A and HNPP, respectively. By studying a large cohort of CMT1A/HNPP-affected patients, we found that the LITAF I92V sequence variant predisposes patients to an earlier age of onset of both the CMT1A and HNPP diseases. Using cell transfection experiments, we showed that the LITAF I92V sequence variant partially mislocalizes to the mitochondria in contrast to wild-type LITAF which localizes to the late endosome/lysosomes and is associated with a tendency for PMP22 to accumulate in the cells. Overall, this study shows that the I92V LITAF sequence variant would be a good candidate for a biomarker in the case of the CMT1A/HNPP disorders.

Electrophysiological evaluation of chronic inflammatory demyelinating polyneuropathy and charcot-marie-tooth type 1: dispersion and correlation analysis

[Purpose] The purpose of this study was to analyze and compare electrophysiological characteristics observed in nerve conduction studies (NCS) of chronic inflammatory demyelinating polyneuropathy (CIDP) and Charcot-Marie-Tooth disease type 1 (CMT 1). [Subjects] A differential diagnosis of acquired and congenital demyelinating neuropathies was based on a study of 35 patients with NCS-confirmed CIDP and 30 patients with CMT 1 genetically proven by peripheral myelin protein-22 (PMP-22) gene analysis, pulsed-field gel electrophoresis (PFGE), and Southern blot analysis. [Methods] We analyzed values collected in motor nerve conduction studies. We conducted dispersion analysis of the amplitudes of the compound muscle action potential (CMAP) of various nerve types and correlation coefficient analysis of the motor nerve conduction velocity (MNCV). [Results] We found that CIDP and CMT 1 were clearly attributable to severe polyneuropathy. In dispersion analysis, CIDP showed greater differences in proximal-to-distal amplitude ratios. Moreover, CMT 1 showed relatively high correlations compared to CIDP based on correlation coefficient analysis of MNCV. [Conclusion] The results of this study suggest that CIDP showed greater asymmetry than CMT 1 in MNCV and CMAP amplitudes.