Hereditary neuropathy with liability to pressure palsies in children

The clinical and neurophysiologic findings of two children presenting with focal weakness and atrophy in unusual nerve distributions and no apparent antecedent injuries are reported. Patient 1 presented with a droopy left shoulder that was initially attributed to scoliosis. Patient 2 presented with right biceps brachii atrophy that was first brought to his parent's attention during a routine physical examination. In addition to documenting focal spinal accessory and musculocutaneous mononeuropathies as the cause of weakness in Patients 1 and 2, respectively, nerve conduction studies also revealed evidence of superimposed diffuse demyelinating polyneuropathy in both children. The latter findings suggested the diagnosis of hereditary neuropathy with liability to pressure palsies and led to definitive DNA diagnoses.

Variability of presentation in hereditary neuropathy with liability to pressure palsy results in underrecognition

The genetic defect responsible for hereditary neuropathy with liability to pressure palsy (HNPP) is located in the same segment that is duplicated in Charcot-Marie-Tooth type 1A (CMT1A). HNPP had been presumed to be rare until an epidemiological study found a much higher incidence than was expected; the researchers suggested that HNPP was underrecognized because many affected persons have mild symptoms. We believe that another reason for underdiagnosis of HNPP is the marked phenotypic variability of the disease. We recommend, therefore, that DNA analysis for the 17p11.2 deletion be considered in patients with unexplained demyelinating neuropathy regardless of family history.

Distal hereditary motor neuronopathy of the Jerash type

A novel form of autosomal recessive distal hereditary motor neuronopathy (distal HMN) is reported. The presence of pyramidal signs within the early stages of the disease with persistence of knee hyperreflexia form distinctive clinical features. We have mapped the HMN-J gene to chromosome 9p21.1-p12, within an estimated interval of 1.2-Mb.

Facial nerve dysfunction in hereditary motor and sensory neuropathy type I and III

Facial nerve function was studied in 19 patients with hereditary motor and sensory neuropathy type I (HMSN I) and 2 patients with hereditary motor and sensory neuropathy type III (HMSN III, Déjérine-Sottas), and compared to that in 24 patients with Guillain-Barré syndrome (GBS). The facial nerve was stimulated electrically at the stylomastoid fossa, and magnetically in its proximal intracanalicular segment. Additionally, the face-associated motor cortex was stimulated magnetically. The facial nerve motor neurography was abnormal in 17 of 19 HMSN I patients and in both HMSN III patients, revealing moderate to marked conduction slowing in both the extracranial and intracranial nerve segments, along with variable reductions of compound muscle action potential (CMAP) amplitudes. The facial nerve conduction slowing paralleled that of limb nerves, but was not associated with clinical dysfunction of facial muscles, because none of the HMSN I patients had facial palsy. Conduction slowing was most severe in the HMSN III patients, but only slight facial weakness was present. In GBS, conduction slowing was less marked, but facial weakness exceeded that in HMSN patients in all cases. We conclude that involvement of the facial nerve is common in HMSN I and HMSN III. It affects the intra- and extracranial part of the facial nerve and is mostly subclinical.

Autonomic function in patients with hereditary motor and sensory neuropathy type I and Lambert-Eaton myasthenic syndrome

Noninvasive tests of four autonomic organ systems (vasomotor control, baroreceptor reflexes, sudomotor function and pupillary reflexes) were performed on nine patients with hereditary motor and sensory neuropathy (HMSN) type I and three patients with Lambert-Eaton myasthenic syndrome (LEMS). The results were compared with those of 33 control subjects. Autonomic dysfunction was considered present when at least two of the four organ system tests were abnormal. The three patients with LEMS had abnormal results in two or more different systems, whereas only one of the nine patients with HMSN type I had two abnormal test results. This study demonstrates that autonomic dysfunction is not a common finding in patients with HMSN type I and its presence should alert us to find the cause of this autonomic disorder.

Peripheral late waves in patients with hereditary motor sensory neuropathy

Patents with different forms of hereditary motor sensory neuropathy (HMSN) were investigated. Peripheral late waves (PLWs) were recorded when determining F wave at supramaximal stimulation. We registered them most frequently in patients with demyelinating neuropathies (HMSN1--58% and HMSN3--100%) and in patients with HMSN2--24% and HMN--13%. In patients with HMSN1 and HMSN3 the peripheral late waves sometimes were more than one--two or three. They had a consistent appearance above a maximal threshold of stimulation, an invariable latency, amplitude and wave-form. Their latency times were in parallel with the M-response latency. These PLWs can be explained by collateral regeneration in case of axonal neuropathy. The ephaptic transmission might be taken in consideration when interpreting data from patients with demyelinating processes.

Central motor conduction in hereditary motor and sensory neuropathy and hereditary spastic paraplegia

Conduction of the central motor pathways (CMCT) by magnetic stimulation of the motor cortex (TMS) was performed in 17 patients with hereditary motor sensory neuropathy (HMSN) and 2 siblings with hereditary spastic paraplegia (HSP). CMCT was prolonged in two patients with HMSN I with associated pyramidal features and in two subjects with HMSN II without clinical pyramidal signs. CMCT may be abnormal in HMSN due to central motor pathways involvement or altered spinal excitability with increased synaptic delay. CMCT was normal in the upper limbs in patients with HSP but increased in the legs. Diagnostic yield of TMS increased in less disabled cases with HSP when selective conduction at the spinal level (C7-S1) was calculated. Abnormal spinal conduction in HSP is consistent with degeneration of the crossed corticospinal tracts at the thoracic level found in neuropathologic observations.

Varying occurrence of vocal cord paralysis in a family with autosomal dominant hereditary motor and sensory neuropathy

A white British family with the axonal form of hereditary motor and sensory neuropathy (HMSN, type II) contained one member who developed a recurrent laryngeal nerve palsy at the age of 41 years, in addition to 4 years of symptomatic polyneuropathy and an abducens nerve palsy. Neither of the other family members (the mother and sister) with electrophysiologically confirmed polyneuropathy had any neuropathic symptoms in the limbs or laryngeal or respiratory muscle involvement. An autosomal dominant pattern of inheritance is likely. This is a second report of this rare form of HMSN (type IIC) in which there is associated laryngeal or respiratory muscle weakness. This family differs from the two previously reported pedigrees in which laryngeal or diaphragm weakness had commenced within the first two decades. The discovery of asymptomatic family members attests to the diagnostic value of clinical and electrophysiological study of first-degree relatives when laryngeal or bulbar symptoms develop in the context of chronic axonal polyneuropathy. HMSN type IIC should be distinguished from the more common forms of HMSN - type IIA, in which axonal polyneuropathy is restricted to the limbs, and type IIB, which is of early onset and associated with foot ulceration.

Hereditary auditory, vestibular, motor, and sensory neuropathy in a Slovenian Roma (Gypsy) kindred

Members of a Roma (Gypsy) family with hereditary motor and sensory peripheral neuropathy (HMSN) and concomitant auditory and vestibular cranial neuropathies were identified in Kocevje, Slovenia. The illness begins in childhood with a severe and progressive motor disability and the deafness is delayed until the second decade. There are no symptoms of vestibular dysfunction. The family structure is consistent with an autosomal recessive pattern of inheritance and the genetic locus for the disorder is linked to the same region of chromosome 8q24 as other Roma families with HMSN and deafness from Lom, Bulgaria (HMSN-Lom). The present study shows that the deafness is caused by a neuropathy of the auditory nerve with preserved measures of cochlear outer hair cell function (otoacoustic emissions and cochlear microphonics) but absent neural components of auditory brainstem potentials. The hearing loss affects speech comprehension out of proportion to the pure tone loss. Vestibular testing showed absence of caloric responses. Physiological and neuropathological studies of peripheral nerves were compatible with the nerve disorder contemporaneously affecting Schwann cells and axons resulting in both slowed nerve conduction and axonal loss. Genetic linkage studies suggest a refinement of the 8q24 critical region containing the HMSN-Lom locus that affects peripheral motor and sensory nerves as well as the cranial auditory and vestibular nerves.

[X-linked recessive bulbospinal neuronopathy--Kennedy's syndrome]

Kennedy's syndrome is an inherited disease which was probably first described 100 years ago. Although rare, a recent report suggests that the prevalence may show considerable regional differences. A review of 30 different names of the disease is given. Originally, the disorder was regarded as a spinal and bulbar muscular atrophy but it is now obvious that there is severe axonal degeneration, also of the sensory fibres with the pattern of a central-peripheral distal axonal neuropathy. This was also present in the two recognized cases presented here. The sensory symptoms develop slowly and it is suggested that a peripheral sprouting compensates for the loss not only of motor, but also sensory fibres. It is important to distinguish the disease from motor neuron diseases since the progression is slow and the expected life span is normal. The clinical presentation with facial palsy and perioral contraction-fasciculations is pathognomonic. However, demonstration of increased (CAG)n repeat size in the androgen receptor gene is diagnostic. A normal (CAG)n repeat size excludes the diagnosis, since the abnormal expansion is the only mutation associated with the disease. Other types of mutations in the androgen receptor gene lead to a different clinical presentation, testicular feminization.

Spectrum of clinical and electrophysiologic features in HNPP patients with the 17p11.2 deletion

OBJECTIVE

To study the clinical and electrophysiologic features of a large series of carriers of the 17p11.2 deletion.

BACKGROUND

The 17p11.2 deletion is associated in most patients with recurrent acute nerve palsies, which is the typical presentation of hereditary neuropathy with liability to pressure palsies (HNPP). Nevertheless, a few other phenotypes have been reported.

METHODS

On the basis of clinical and electrophysiologic data, the authors conducted a retrospective study of 99 individuals with the 17p11.2 deletion referred to their neurogenetic department between 1993 and 1997.

RESULTS

In addition to the typical presentation of HNPP, they describe five other phenotypes in 15 patients: recurrent positional short-term sensory symptoms, progressive mononeuropathy, Charcot-Marie-Tooth disease-like polyneuropathy, chronic sensory polyneuropathy, and chronic inflammatory demyelinating polyneuropathy-like, recurrent subacute polyneuropathy; and 14 asymptomatic patients. In all the deletion carriers, regardless of their phenotype and by the second decade, the authors found a characteristic, multifocal electrophysiologic neuropathy consisting of a diffuse increase in distal motor latencies contrasting with normal or moderately reduced motor nerve conduction velocities, a diffuse reduction in sensory nerve action potential, and multiple focal slowing of nerve conduction at the usual sites of entrapment. The key diagnostic criterion is a bilateral slowing of sensory and motor nerve conduction at the carpal tunnel with at least one abnormal parameter for motor conduction in one peroneal nerve.

CONCLUSION

The authors confirm the clinical phenotypic heterogeneity of the 17p11.2 deletion and suggest that electrophysiologic examination is a reliable tool for screening suspected HNPP patients in its various clinical presentations.

Inherited neuropathies: from gene to disease

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A), another to chromosome 3p (CMT2B) and another to 7p (CMT2D). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.

Diagnosis of chronic neuropathy

Chronic neuropathy is the most frequent condition affecting the peripheral nervous system. It includes symmetrical polyneuropathies, multifocal mononeuropathies, mononeuropathies and radiculopathies. Mononeuropathies are mainly due to compression or entrapment and are not discussed in this review, which focuses on polyneuropathies and multifocal mononeuropathies with a chronic course, lasting for more than 2 months. Their diagnosis requires a systematic approach including clinical, electrophysiological, biological, and sometimes pathological investigations. The search for an etiological diagnosis may involve a very wide panel of hereditary and acquired diseases. Despite progress in the understanding and diagnosis of many chronic neuropathies, some of them remain unresolved.

[A case of hereditary motor and sensory neuropathy with pyramidal tract sign, optic nerve atrophy and mental retardation]

The patient was a 61-year-old man who suffered from gait disturbance since childhood. He also had mental retardation. Gait disturbance was slowly progressive. His mother, sister, brother and son of his sister suffered from gait disturbance. On neurological examination, he showed mental retardation, optic nerve atrophy and neural deafness. He also showed severe muscle atrophy and weakness of bilateral lower limbs associated with pes cavus. Muscle tonus of lower limbs and patellar tendon reflex were increased bilaterally. Achilles tendon reflex was absent. Babinski and Chaddock signs were positive. Superficial and deep sensations were almost normal. There were no cerebellar signs. Blood chemistry was normal. On nerve conduction studies, motor nerve conduction velocity of the upper limbs was normal and that of the posterior tibial nerve was decreased; right 36.0m/sec, left 29.7m/sec. Sensory nerve conduction velocity of the median nerve was slightly decreased; right 36.5m/sec, left 45.2m/sec and sural nerve did not respond to electric stimuli. On sural nerve biopsy, the density of myelinated fibers was severely decreased. Onion bulb formation was not observed. We classified this case as hereditary motor and sensory neuropathy (HMSN) type II based on nerve conduction studies and findings from sural nerve biopsy. HMSN with pyramidal tract sign has been classified as type V and HMSN with optic nerve atrophy as type VI. This case had characteristic symptoms as type V and VI. Histopathological findings of HMSN type V and VI have not been established yet. This case might provide an important clue for classification of HMSN.

Correlation between denervation activity and compound muscle action potential amplitude in hereditary motor and sensory neuropathy I and II

Studying the electrophysiological characteristics of the various types of Charcot-Marie-Tooth disease is important in the understanding of its pathophysiology. The purpose of this study was to identify the frequency of fibrillation potentials and positive sharp waves (FP/PWs) in HMSN I and II and, since they are indices of denervation, to elucidate whether they are correlated with the amplitude of compound muscle action potentials (CMAP). We reviewed the electrophysiological findings of 47 patients who have been studied in our hospital and found to suffer from Charcot-Marie-Tooth polyneuropathy. FP/PW were graded according to a 4-grade scale and the 38 m/sec criterion for motor conduction velocity (MCV) was used for distinction between HMSN I and II subgroups. Seventy percent of HMSN II patients and 81% of HMSN I patients showed fibrillation potentials in the upper or lower limbs. There was no difference in the frequency of FP/PW appearance between the two groups. In the HMSN II group the FP/PW grade correlated with CMAP amplitude in the upper limbs. In both groups there was no correlation between FP/PW grade and MCV. Our findings might indicate that in HMSN I there is a considerable axonal destruction that occurs concurrently with myelin loss.

Hereditary neuropathy with liability to pressure palsies. Phenotypic differences between patients with the common deletion and a PMP22 frame shift mutation

In six families with hereditary neuropathy with liability to pressure palsies (HNPP) the 17p11.2 deletion was absent, but single strand conformation-analysis and subsequent sequencing demonstrated a heterozygous G-insertion in a stretch of six Gs at nt 276281 of the PMP22 gene, resulting in a frame shift after Gly94. Haplotype comparison of the six families revealed common ancestry. We compared the phenotype of 23 patients from these six families with the phenotype of 63 patients of 17 families with the common deletion. The patients with the G-insertion showed the clinical, electrophysiological and morphological characteristics of common HNPP, but in addition they had significantly more neuropathic features, mimicking hereditary motor and sensory neuropathy type I (HMSN I) or Charcot-Marie-Tooth disease type 1 (CMT1). To explain this distinct phenotype we suggest that, by translation of the mutated gene, a markedly changed polypeptide is formed without the normal cytoplasmic C-terminal of the native protein, resulting in a loss of function similar to that with the common deletion, but exerting an extra disturbance of Schwann cell functions, probably by hampering normal myelin formation or maintenance.

Many facets of the peripheral myelin protein PMP22 in myelination and disease

Peripheral myelin protein 22 (PMP22) is a small, hydrophobic glycoprotein, which is most prominently expressed by Schwann cells as a component of compact myelin of the peripheral nervous system (PNS). Recent progress in molecular genetics revealed that mutations affecting the PMP22 gene including duplications, deletions, and point mutations are responsible for the most common forms of hereditary peripheral neuropathies including Charcot-Marie-Tooth disease type 1A (CMT1A), hereditary neuropathy with liability to pressure palsies (HNPP), and a subtype of Dejerine-Sottas Syndrome (DSS). Functionally, PMP22 is involved in correct myelination during development of peripheral nerves, the stability of myelin, and the maintenance of axons. While most of these functions relate to a role of PMP22 as a structural component of myelin, PMP22 has also been proposed as a regulator of Schwann cell proliferation and differentiation. In this review, we will discuss our current knowledge of PMP22 and its related proteins in the normal organism as well as in disease. In particular, we will focus on how the function of PMP22 and its regulation may be relevant to particular disease mechanisms.

Electrophysiological findings in hereditary motor and sensory neuropathy type I and II--a conduction velocity study

We performed clinical and electrophysiological studies in 42 children with hereditary motor and sensory neuropathy type I and II (HMSN I and HMSN II) and in 103 members of their families. In 24 families with HMSN I the conduction velocity and the latency were markedly changed in the nerves innervating the distal muscles (median, peroneal nerves), as well as proximal muscles (facial, axillary, and musculocutaneous nerves). The changes were uniform in all motor and sensory nerves studied in the particular patient. No nerve conduction worsening with age has been found in cross-sectional analysis. In patients with HMSN I the conduction velocity was impaired even when the clinical abnormalities were minimal. The degree of the conduction velocity slowing was uniform within majority of the families. Homogeneity of conduction velocity slowing in individuals with HMSN I regardless of clinical expression suggests a primary myelin defect as an underlying cause. In patients from 18 families with HMSN II slight changes in conduction velocity were found only in the nerves innervating the distal muscles, the latency of axillary and facial nerves was within normal range. We recommend examining conduction time in facial and axillary nerves as a useful procedure for differentiation between HMSN I and II, especially in families with borderline conduction values in the long nerves.

Hereditary motor and sensory neuropathy--Lom, a novel demyelinating neuropathy associated with deafness in gypsies. Clinical, electrophysiological and nerve biopsy findings

A previously unrecognized neuropathy was identified in Bulgarian gypsies, and was designated hereditary motor and sensory neuropathy-Lom (HMSNL) after the town where the initial cases were found. It was subsequently identified in other gypsy communities. The disorder, which is of autosomal recessive inheritance, was mapped to chromosome 8q24. It begins consistently in the first decade of life with gait disorder followed by upper limb weakness in the second decade and, in most subjects, by deafness which is most often first noticed in the third decade. Sensory loss affecting all modalities is present, both this and the motor involvement predominating distally in the limbs. Skeletal deformity, particularly foot deformity, is frequent. Severely reduced motor nerve conduction velocity indicates a demyelinating basis, which was confirmed by nerve biopsy. The three younger patients biopsied showed a hypertrophic 'onion bulb' neuropathy. The hypertrophic changes were not evident in the oldest individual biopsied and it is likely that they had regressed secondarily to axon loss. In the eight cases in which brainstem auditory evoked potentials could be recorded, the results suggested demyelination in the eighth cranial nerve and also abnormal conduction in the central auditory pathways in the brainstem. As no myelin genes are known to be located at chromosome 8q24, the disorder may involve a gene for a novel myelin protein or be due to an abnormality of axon-Schwann cell signalling.

Absence of mutations in peripheral myelin protein-22, myelin protein zero, and connexin 32 in autosomal recessive Dejerine-Sottas syndrome

Motor and sensory neuropathies with the clinical features of HMSN III (Dejerine-Sottas syndrome, DSS) are etiologically related to heterozygous mutations in either peripheral myelin protein-22 (PMP22) or myelin protein zero (MPZ). Heterozygous mutations in either of these two genes are also responsible for other hereditary peripheral neuropathies (HNPP, CMT1A, CMT1B or CH). In two families DSS was related to the homozygous presence of a MPZ mutation while heterozygosity showed a much milder phenotype. It has therefore been suggested that the clinical phenotype in peripheral neuropathies is related to the mutated gene, the type of mutation and confounding effects from other sources. In this study we describe a family with recessive DSS in which mutations were absent from the PMP22, MPZ, and connexin 32 (Cx32) genes. We conclude that DSS also exists as a distinct genetic entity with autosomal recessive inheritance as originally defined by Dejerine and Sottas in 1893.

[Nerve circuit disorders: determination of polyneuropathy]

So many conditions, both hereditary and acquired, can lead to polyneuropathy that a systematic approach is needed to identify the cause. Finding a cause is necessary to inform the patient about prognosis, handicap and chances of treatment. Three patients with polyneuropathy are described. The first was a man aged 34 with a predominantly motor neuropathy who appeared to have a duplication in the pmp-22 gene on chromosome 17PII.2. The diagnosis was hereditary sensorimotor neuropathy type IA (hypertrophic form of Charcot-Marie-Tooth disease). The second was a woman of 58 years; she had a sensory polyneuropathy as the first manifestation of Hodgkin's disease. The last patient, a 67-year-old man, had polyneuropathy due to vasculitis. He showed a prompt response to treatment.