Charcot-Marie-Tooth disease type 2 associated with mutation of the myelin protein zero gene.
ABSTRACT Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), is a clinically and genetically heterogeneous condition. Mutations of the myelin protein zero (MPZ) gene have been associated with CMT1B, Dejerine-Sottas disease, and congenital hypomyelination, which are inherited demyelinating neuropathies characterized by different clinical severity. HMSN type II (HMSN II) or CMT2, the axonal form of CMT, is genetically heterogeneous. Linkage to 1p35-p36 (CMT2A), 3q (CMT2B), and 7p (CMT2D) chromosomes has been reported in the disease; however, most HMSN II families do not link to any of the reported loci. In a large HMSN II Sardinian family, we found a missense mutation in the chromosome 1q MPZ gene. This Ser44Phe mutation was located in exon 2 and was present in the heterozygous state in all affected individuals. This is the first example of an HMSN II family showing an MPZ point mutation. The MPZ gene Ser44Phe mutation found in the HMSN II family presented in this study suggests that genetic analysis of HMSN II families should also include the MPZ gene, previously not considered to be involved in the axonal form of HMSN.
- [show abstract] [hide abstract]
ABSTRACT: Myelin protein zero mutations were found to produce Charcot-Marie-Tooth disease phenotypes with various degrees of myelin impairment and axonal loss, ranging from the mild 'demyelinating' adult form to severe and early onset forms. Protein zero deficient homozygous mice ( ) show a severe and progressive dysmyelinating neuropathy from birth with compromised myelin compaction, hypomyelination and distal axonal degeneration. A previous study using immunofluorescence showed that motor nerves deficient of myelin protein zero upregulate the Na(V)1.8 voltage gated sodium channel isoform, which is normally present only in restricted populations of sensory axons. The aim of this study was to investigate the function of motor axons in protein zero-deficient mice with particular emphasis on ectopic Na(V)1.8 voltage gated sodium channel. We combined 'threshold tracking' excitability studies with conventional nerve conduction studies, behavioural studies using rotor-rod measurements, and histological measures to assess membrane dysfunction and its progression in protein zero deficient homozygous mutants as compared with age-matched wild-type controls. The involvement of Na(V)1.8 was investigated by pharmacologic block using the subtype-selective Na(V)1.8 blocker A-803467 and chronically in Na(V)1.8 knock-outs. We found that in the context of dysmyelination, abnormal potassium ion currents and membrane depolarization, the ectopic Na(V)1.8 channels further impair the motor axon excitability in protein zero deficient homozygous mutants to an extent that precipitates conduction failure in severely affected axons. Our data suggest that a Na(V)1.8 channelopathy contributed to the poor motor function of protein zero deficient homozygous mutants, and that the conduction failure was associated with partially reversible reduction of the electrically evoked muscle response and of the clinical function as indicated by the partial recovery of function at rotor-rod measurements. As a consequence of these findings of partially reversible dysfunction, we propose that the Na(V)1.8 voltage gated sodium channel should be considered as a novel therapeutic target for Charcot-Marie-Tooth disease.Brain 02/2011; 134(Pt 2):585-601. · 9.92 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Charcot-Marie-Tooth disease (CMT) is a heterogeneous group of disorders of the peripheral nervous system, mainly characterized by distal muscle weakness and atrophy leading to motor handicap. With an estimated prevalence of 1 in 2,500, this condition is one of the most commonly inherited neurological disorders. Mutations in more than 30 genes affecting glial and/or neuronal functions have been associated with different forms of CMT leading to a substantial improvement in diagnostics of the disease and in the understanding of implicated pathophysiological mechanisms. However, recent data from systematic genetic screening performed in large cohorts of CMT patients indicated that molecular diagnosis could be established only in ∼50-70% of them, suggesting that additional genes are involved in this disease. In addition to providing an overview of genetic and functional data concerning various CMT forms, this review focuses on recent data generated through the use of highly parallel genetic technologies (SNP chips, sequence capture and next-generation DNA sequencing) in CMT families, and the current and future impact of these technologies on gene discovery and diagnostics of CMTs.Molecular syndromology 11/2012; 3(5):204-14.
- [show abstract] [hide abstract]
ABSTRACT: The relationship between dysmyelination and the progression of neuropathy in Charcot-Marie-Tooth (CMT) hereditary polyneuropathy is unclear. Mice heterozygously deficient for the myelin protein P0 gene (P0+/-) are indistinguishable from wild-type (WT) at birth and then develop a slowly progressing demyelinating neuropathy reminiscent of CMT Type 1b. Accumulating evidence suggests that impulse conduction can become lethal to acutely demyelinated central and peripheral axons. Here we investigated the vulnerability of motor axons to long-lasting, high-frequency repetitive stimulation (RS) in P0+/- mice as compared to WT littermates at 7, 12, and 20months of age. RS was carried out in interrupted trains of 200Hz trains for 3h. Tibial nerves were stimulated at the ankle while the evoked compound muscle action potentials (CMAPs) and the ascending compound nerve action potentials (CNAPs) were recorded from plantar muscles and the sciatic nerve, respectively. In 7-month mice, there was recovery of CMAP and CNAP following RS. When mice were about one year old, electrophysiological recovery following RS was incomplete and in P0+/- also associated with morphological signs of partial Wallerian degeneration. The effect of RS was larger in P0+/- as compared to age-matched WT. When mice were about 2years old, the effect was stronger and became similar between WT and P0+/-. RS was followed by a transient hyperpolarization, which decreased with age and was smaller in P0+/- than in WT. Our data suggest that both aging and the dysmyelinating disease process may contribute to the susceptibility to activity-induced axonal degeneration. It is possible that in aging mice and in P0+/- there is inadequate energy-dependent Na+/K+ pumping, as indicated by the reduced post-stimulation hyperpolarization, which may lead to a lethal Na+ overload in some axons.Experimental Neurology 02/2013; · 4.65 Impact Factor