Expression of P0 protein in sural nerve of a patient with hereditary motor and sensory neuropathy type III

Genotype-phenotype characteristics and baseline natural history of heritable neuropathies caused by mutations in the MPZ gene

We aimed to characterize genotype-phenotype correlations and establish baseline clinical data for peripheral neuropathies caused by mutations in the myelin protein zero (MPZ) gene. MPZ mutations are the second leading cause of Charcot-Marie-Tooth disease type 1. Recent research makes clinical trials for patients with MPZ mutations a realistic possibility. However, the clinical severity varies with different mutations and natural history data on progression is sparse. We present cross-sectional data to begin to define the phenotypic spectrum and clinical baseline of patients with these mutations. A cohort of patients with MPZ gene mutations was identified in 13 centres of the Inherited Neuropathies Consortium - Rare Disease Clinical Research Consortium (INC-RDCRC) between 2009 and 2012 and at Wayne State University between 1996 and 2009. Patient phenotypes were quantified by the Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and the Charcot-Marie-Tooth disease paediatric scale outcome instruments. Genetic testing was performed in all patients and/or in first- or second-degree relatives to document mutation in MPZ gene indicating diagnosis of Charcot-Marie-Tooth disease type 1B. There were 103 patients from 71 families with 47 different MPZ mutations with a mean age of 40 years (range 3-84 years). Patients and mutations were separated into infantile, childhood and adult-onset groups. The infantile onset group had higher Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and slower nerve conductions than the other groups, and severity increased with age. Twenty-three patients had no family history of Charcot-Marie-Tooth disease. Sixty-one patients wore foot/ankle orthoses, 19 required walking assistance or support, and 10 required wheelchairs. There was hearing loss in 21 and scoliosis in 17. Forty-two patients did not begin walking until after 15 months of age. Half of the infantile onset patients then required ambulation aids or wheelchairs for ambulation. Our results demonstrate that virtually all MPZ mutations are associated with specific phenotypes. Early onset (infantile and childhood) phenotypes likely represent developmentally impaired myelination, whereas the adult-onset phenotype reflects axonal degeneration without antecedent demyelination. Data from this cohort of patients will provide the baseline data necessary for clinical trials of patients with Charcot-Marie-Tooth disease caused by MPZ gene mutations.

Neuropathology of Charcot-Marie-Tooth and related disorders

The peripheral nervous system (PNS), with all its branches and connections, is so complex that it is impossible to study all components at the light or electron microscopic level in any individual case; nevertheless, in certain diseases a simple nerve biopsy may suffice to arrive at a precise diagnosis. Structural changes of the PNS in neuropathies of the Charcot-Marie-Tooth (CMT) type and related disorders comprise various components of the PNS. These include peripheral motor, sensory, and autonomous neurons with their axons, Schwann cells, and myelin sheaths in the radicular and peripheral nerves as well as satellite cells in spinal and autonomous ganglia. Astrocytes, oligodendroglial cells, and microglial cells around motor neurons in the anterior horn and around sensory neurons in other areas of the spinal cord are also involved. In addition, connective tissue elements such as endoneurial, perineurial, and epineurial components including blood and lymph vessels play an important role. This review focuses on the cellular components and organelles involved, that is, myelin sheaths, axons with their micro-tubules and neurofilaments; nuclei, mitochondria, endoplasmic reticulum, and connective tissue including the perineurium and blood vessels. A major role is attributed to recent progress in the pathomorphology of various types of CMT1, 2,4, CMTX, and HMNSL, based on light and electron microscopic findings, morphometry, teased fiber studies, and new immunohisto-chemical results such as staining of certain periaxin domains in CMT4F.

Vincristine-induced neuropathy as the initial presentation of charcot-marie-tooth disease in acute lymphoblastic leukemia: a Pediatric Oncology Group study

PURPOSE

After profound peripheral neurotoxicity during induction chemotherapy for acute lymphoblastic leukemia (ALL) in the index patient with Charcot-Marie-Tooth hereditary neuropathy (CMT), study coordinators of the Pediatric Oncology Group (POG) front-line ALL protocols reviewed patient registrations to identify any other patients with possible CMT. The goal was to provide preliminary information about patients with undiagnosed CMT who develop ALL.

PATIENTS AND METHODS

Five children with ALL who were enrolled in POG B-precursor or T-cell ALL protocols from 1994 to 1999 subsequently were determined to have CMT hereditary neuropathy. Their clinical presentations and treatment records were reviewed in detail. Records of all patients entered on POG 9201 (lesser-risk ALL) were reviewed to identify all cases of significant vincristine toxicity noted in the first 6 months of treatment.

RESULTS

The five identified patients all had substantial peripheral neurotoxicity that required alteration in treatment and/or orthopedic/physical therapy evaluation and follow-up. The POG 9201 review identified 25 of 686 patients (3.6%) with significant peripheral neuropathy. Three of 25 were diagnosed with CMT; the others have had no testing reported.

CONCLUSIONS

A family history of CMT or other peripheral neuropathy should be sought at the time of diagnosis of ALL. Testing for CMT should be considered in any child with substantial vincristine-induced peripheral neurotoxicity. Treatment of such patients must be individualized. Testing of all patients with significant peripheral neuropathy would be necessary to determine the percentage of such neuropathy explained by underlying CMT.

Expression of peripheral myelin protein zero in sural nerve of patients with Charcot-Marie-Tooth disease 1B

A Charcot-Marie-Tooth disease 1B (CMT1B) family with a mutation of the Po gene is presented. A to G substitution of nucleotide 389 in exon 3 resulted in Lys 131 Arg substitution. Immunostaining for Po in biopsied sural nerve from one family member with CMT1B was expressed in a small number of myelinated fibers. Immunoblot analysis for Po revealed that it was of normal molecular weight (29 kDa) although significantly reduced in amount. This heterozygous mutation could lead to a reduction in the total amount of normal protein in peripheral nerves through a mechanism of loss of function.

Clinical and pathological phenotype of the original family with Charcot-Marie-Tooth type 1B: a 20-year study

Charcot-Marie-Tooth type 1B is an uncommon form of hereditary motor and sensory neuropathy caused by mutations in the P(0) myelin protein gene on chromosome 1. We report here a 20-year observation of 13 members of the first family with Charcot-Marie-Tooth disease to demonstrate linkage to chromosome 1 and now known to have a C270A mutation in the P(0) gene altering the extracellular domain of the protein. Affected individuals generally show an early age at onset, often indicated by delayed ability to walk. Proximal muscle weakness of the lower extremities is common and often marked, but the individuals remain ambulatory and there is no decrease in life span. Motor nerve conduction velocities of the fastest fibers are severely slowed (mean, 9-11 m/sec), even when compared with 3 families having Charcot-Marie Tooth type 1A (mean, 19-21 m/sec). Variability of disability between family members suggests that genetic and environmental factors in addition to the P(0) mutation play a role in the final phenotype. Nerve biopsy specimens demonstrate hypertrophy, onion bulb formation, loss of myelinated fibers, and occasional myelin thickening similar to that described in P(0) myelin knockout mice. Autopsy of the 92-year-old great-grandmother in this family demonstrated diffuse involvement of sensory and motor nerves, with loss of myelin in the posterior columns of the spinal cord and loss of anterior horn neurons but without other involvement of the central nervous system. This family demonstrates the long-term phenotypic consequences on the peripheral nervous system of a specific point mutation in the P(0) myelin gene.