Hereditary chronic polyneuropathy. Electrophysiological and pathological studies in an affected family

Molecular genetics and neuropathology of Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth (CMT) syndrome describes a genetically and clinically heterogeneous group of polyneuropathies. Electrophysiologically, at least two types of CMT can be distinguished; CMT1 which has decreased nerve conduction velocities (NCV) and CMT2 which has normal or near normal NCV with decreased amplitudes. For CMT1, three gene loci (on chromosomes 1, 17 and the X chromosome) have been mapped. The locus on chromosome 17, CMT type 1A (CMT1A), is responsible for the most common form of CMT which has recently been shown to be associated with a large DNA duplication. Recent data demonstrates that the CMT1A phenotype results from an inherited DNA rearrangement and a gene dosage effect. The trembler (Tr) and allelic tremblerJ (TrJ) mice have been proposed as animal models for CMT. Tr has similar electrophysiological and neuropathological features to CMT1 patients and maps to mouse chromosome 11 in a region of conserved synteny with human chromosome 17p. Tr and TrJ have recently been shown to have different point mutations in regions encoding putative transmembrane domains of the myelin specific protein PMP-22. The human peripheral nerve-specific PMP-22 gene maps within the CMT1A duplication. PMP-22 is thus a candidate gene for CMT1A. This paper describes the molecular genetics of CMT1A and sural nerve pathology in CMT1A patients with the CMT1A duplication.

Localization of a locus for Charcot-Marie-Tooth neuropathy type Ia (CMT1A) to chromosome 17

Phenotypic data for 71 genetic markers for members of five Caucasian kindreds were tested for linkage with the autosomal dominant mutations causing Charcot-Marie-Tooth (hereditary motor sensory) neuropathy type I, characterized by markedly reduced nerve conduction velocities. Lod score analysis gave no evidence of linkage to the closely linked chromosome 1 loci SPTA1-FY-F5-AT3 and APOA2. In contrast, these mutations were found to map closely (zeta = 10.828, theta = 0.0) to D17S58, an anonymous segment of DNA from 17p11.2-p11.1, and thus define the CMT1A locus. Segregation information data for an inferred recombinant offspring indicated that the CMT1A locus is probably proximal to MYH2, the locus encoding adult skeletal muscle myosin heavy polypeptide 2, which maps to 17p13. Analysis of the lod scores on a per kindred basis gave no evidence of genetic heterogeneity.

Focal neuropathy preceding chronic inflammatory demyelinating polyradiculoneuropathy by several years

We report three patients who exhibited an unusual clinical course of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) in which mononeuropathic limb weakness developed 2, 11 and 23 years, respectively, before the development of generalized polyradiculoneuropathy. The eventual diagnosis remained uncertain until other causes of neuropathy were excluded, and the clinical disorder progressed to involve the other limbs. Focal or regional variants of CIDP suggest that the pathologic, and perhaps the immunologic, abnormalities can be localized and selective for prolonged periods of time. Although this clinical variant seems to account for a small number of CIDP cases, its recognition may aid in making an early diagnosis.

Dominantly inherited motor and sensory neuropathy type I. Genetic, clinical, electrophysiological and pathological features in four families

This report describes the genetic, clinical, electrophysiological and sural nerve biopsy features in 26 affected members and 21 unaffected relatives from 4 families with autosomal dominant inherited motor and sensory neuropathy (HMSN), Type I. In all age categories, the proportion of affected to unaffected individuals at risk did not significantly differ from the expected 50%. The peak age of onset was in the first decade. There was a complete concordance between nerve conduction velocity in the propositi and that in their affected relatives within each family. Marked slowing of conduction velocities was present as early as the age of 2.5 years, while precocious clinical signs and symptoms were quite subtle. Determination of conduction velocity is a valuable aid aid to the early diagnosis of the disease.

Quantitative studies of the abnormal axon-Schwann cell relationship in the peripheral motor and sensory nerves of the dystrophic mouse

The nature and extent of abnormal axon-Schwann cell relationships in peripheral portions of dystrophic motor and sensory nerves were quantitatively evaluated between 1 and 9 months of age using teased fibres and electron micrographs. The results show that in the dystrophic (dy/dy) common peroneal (CPN) and tibial nerves (TN), and less in the dy/dy sural nerve (SN): (1) the number of Schwann cell nuclei associated with myelinated axons is increased with respect to normal; (2) the average internodal length is correspondingly reduced; (3) the average dystrophic internode elongates roughly in parallel with the average normal internode, and with the dystrophic limb; the longitudinal growth of the dystrophic limb is normal; (4) the variation of internodal length is greater than normal; it does not increase with age; (5) the incidence of the nodes of Ranvier which are wider than the normal 3 micrometers limit does not increase with age; and (6) the number of myelinated axons is reduced in the dy/dy CPN and TN but not in the dy/dy SN; it shows no change with age. These data indicate that: (1) in the dy/dy peripheral nerves (PNS) the abnormal axon-Schwann cell relationships and the reduced number of myelinated axons have been established prior to 1 month of age, thereafter progressive degenerative processes do not appear to take place, and (2) the dy/dy sensory nerves are less affected than the motor ones.

The peroneal muscular atrophy syndrome. Clinical, genetic, electrophysiological and nerve biopsy studies. Part 2. Observations on pathological changes in sural nerve biopsies

The light-and electron-microscopic, single teased nerve and morphometric studies of a series of 17 sural nerve biopsies from patients with personeal muscular atrophy are presented. The cases are divided into the following groups according to the criteria of Davis, Bradley and Madrid (1977): Hypertrophic Neuropathy Group; Intermediate Group; Neuronal Sensorimotor Group; Neuronal Motor Group. The Hypertrophic Neuropathy Group had nerve hypertrophy and marked segmental demyelination and onion bulb formation. The Intermediate Group also had segmental demyelilination and onion bulb formation, but nerve hypertrophy was not seen, and axonal degeneration and regeneration were prominent. The Neuronal Sensorimotor Group cases were all sporadic, and showed some onion bulbs, paranodal demyelination and evidence of axonal degeneration and regeneration. The sensory nerve biopsy in the Neuronal Motor Group showed no major abnormality apart from some cluster formation indicating axonal regeneration. The data tend to support the classification of peroneal muscular atrophy proposed by Davis et al. (1977), though there was overlap between the groups in individual pathological parameters.

Charcot-Marie-Tooth disease associated with "essential tremor": Report of 7 cases and a review of the literature

A study of 7 cases of Charcot-Marie-Tooth disease associated with a dyskinesia resembling benign essential tremor is presented. In 4 patients, the family history strongly suggested an autosomal mode of transmission, 2 cases were sporadic without an established genetic pattern and 1 was probably recessive. The distal parts of the upper and lower limbs showed imparied muscle strength with slight or no atrophy in 4 patients and conspicuous weakness and wasting in another 2. One patient was a chairbound. Although essential tremor and the tremor seen in these patients are clinically (phenotypically) similar it seems possible that they result from two different genotypes. Further, it seems that cases with Charcot-Marie-Tooth disease and "essential tremor" are not the result of the association of two separate dominant characteristics which are generally inherited as mendelian dominant traits. In spite of the diversity of the clinical manifestations of the peripheral neuropathy, the semiologically different types of essential tremor and the electrophysiological data, it is concluded that patients who develop a peripheral neuropathy on a familial basis and who exhibit clinical features of similar character, suffer from a common type of pathological disorder. Stress is laid upon the fact that Friedreich's ataxia and Charcot-Marie-Tooth disease share many clinical features. It is suggested that when Friedreich's ataxia and Charcot-Marie-Tooth disease seem to be present in the same individual and/or alternate in different members of the same family, the process is likely to be one of Charcot-Marie-Tooth disease. The value of the type of inheritance, natural history, clinical examination and electrophysiological data in differentiating Charcot-Marie-Tooth disease (with or without essential tremor) from other degenerative disorders is analyzed.