A-waves in patients with novel hereditary motor and sensory neuropathy Lom

OBJECTIVES

To determine A-waves of a family with autosomal recessive form of demyelinatig hereditary motor and sensory neuropathy Lom (HMSNL).

METHODS

A-waves were investigated during conventional F-wave study of family members with HMSNL which had genetic testing.

RESULTS

During routine F-wave studies A-waves were observed in all tested nerves. They appeared between M-responses and F-wave. The A-waves were with low amplitude, shorter duration and constant shape and latency than F-waves. They appeared independently of F-waves. A-waves were more often recorded as multiple waves in lower and upper extremities. More than three A-waves per nerve were found mostly in ulnar and facial nerves. In 16 cases A-waves were found in the absence of F-waves.

CONCLUSION

It is assumed that the A-waves could be seen as additional signs of pathology because they were not observed in unaffected members of the family and in healthy subjects.

The range of chronic demyelinating neuropathy of infancy: a clinico-pathological and genetic study of 15 unrelated cases

The concept of Dejerine-Sottas disease, which corresponds to presumed recessive demyelinating neuropathies with onset in infancy, remains controversial. To learn more on the subject, we performed a clinico-pathological and molecular genetic study in 15 unrelated patients with the Dejerine-Sottas phenotype seen over a 16 year period. There were 12 females and 3 males, born to asymptomatic parents. Study of the PMP22, P0 and Egr2 genes was performed in all cases and 14 underwent a nerve biopsy. First manifestations of neuropathy occurred before 3 years of age in all patients. An inherited disorder was suspected in 10 patients, because of their family history and/or disclosure of a molecular genetic defect in 4 of them. One patient had a recessively transmitted homozygous point mutation (Arg157Trp) of the PMP22 gene. A heterozygous duplication of the 17p11.2-12 segment was detected in one offspring of a consanguineous marriage. One patient carried a "de novo" heterozygous Ser72Leu substitution in the PMP22. A heterozygous double mutation of the P0 gene including a "de novo" Val42 deletion and an Ala221Thr substitution, maternally inherited, were found in an apparently sporadic case. No mutation of the Egr2 gene was identified. A neuropathy with focally folded myelin sheaths (CMT4B) was diagnosed in the nerve biopsy specimens of two patients. In five patients, the clinico-pathological findings along with the absence of an identified mutation suggested the diagnosis of chronic inflammatory demyelinating polyneuropathy of infantile onset. Our findings illustrate the genetic heterogeneity of cases with identified mutations, the scarcity of cases with "demonstrated" recessive transmission and the likelihood of early acquired chronic inflammatory demyelinating polyneuropathy in several patients.

EGR2 mutation R359W causes a spectrum of Dejerine-Sottas neuropathy

Heterozygous mutations in the early growth response gene 2 (EGR2), which encodes a zinc-finger transcription factor that regulates the late stages of myelination, cause myelinopathies including congenital hypomyelinating neuropathy, Dejerine-Sottas neuropathy (DSN), and Charcot-Marie-Tooth disease type 1. We screened 170 unrelated neuropathy patients without mutations involving the peripheral myelin protein 22 gene (PMP22), the myelin protein zero gene (MPZ), or the gap junction protein beta1 gene (GJB1) and identified two DSN patients with the heterozygous mutation R359W in the alpha-helix domain of the first zinc-finger of EGR2. We now report that this mutation is a recurrent cause of DSN, and that expressivity ranges from that typical for DSN to a more rapidly progressive neuropathy that can cause death by age 6 years. Furthermore, in contrast to patients with typical DSN, patients with the EGR2 R359W mutation have more respiratory compromise and cranial nerve involvement.

Intermediate CAG repeat lengths (53,54) for MJD/SCA3 are associated with an abnormal phenotype

We report on a Dutch family in which 4 members in 2 generations have intermediate repeat lengths (53 and 54) for Machado-Joseph Disease/Spinocerebellar Ataxia (MJD/SCA3). All but the youngest have a restless legs syndrome with fasciculations and a sensorimotor axonal polyneuropathy. Central neurological abnormalities are only present in 2. This family shows that intermediate repeat lengths can be pathogenic and may predispose for restless legs and peripheral nerve disorder.

A novel 3′-splice site mutation in peripheral myelin protein 22 causing hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant, demyelinating peripheral neuropathy. Clinical hallmarks are recurrent painless focal neuropathies mostly preceded by minor trauma or compression at entrapment sites of peripheral nerves. In the majority of the patients, HNPP is caused by a 1.5 Mb deletion on chromosome 17p11.2-p12 containing the peripheral myelin protein 22 (PMP22) gene. Point mutations within this gene are reported in only a few families. We report a novel mutation in the PMP22 gene in a Spanish family with HNPP. The mutation is a 3' splice-site mutation, preceding coding exon 3 (c.179-1 G>C), causing a mild HNPP phenotype.

Phe 84 deletion of the PMP22 gene associated with hereditary motor and sensory neuropathy HMSN III with multiple cranial neuropathy: clinical, neurophysiological and magnetic resonance imaging findings

Hereditary motor and sensory neuropathy (HMSN) is a heterogeneous group of peripheral neuropathies which are diagnosed on the basis of clinical, electrophysiological and neuropathological findings. Among the hypertrophic demyelinating neuropathies, HMSN III is the most severe. It is often associated with de novo mutations in the genes encoding for peripheral myelin proteins. While peripheral nerve hypertrophy is an expected finding in HMSN III, cranial nerve hypertrophy is exceptional. Here we describe a mutation in the PMP22 gene in a 19-year-old man with infantile onset of sensory motor polyneuropathy without family history and multiple cranial nerve hypertrophy shown by cranial magnetic resonance imaging.

Hereditary motor and sensory neuropathy-Lom (HMSNL) in a Spanish family: clinical, electrophysiological, pathological and genetic studies

The clinical, electrophysiological, pathological and genetic findings are described in the first Spanish family diagnosed with hereditary motor and sensory neuropathy type Lom (HMSNL) initially identified by Kalaydjeva et al. in 1996. The three affected patients belong to a non-consanguineous family with Gypsy background that were followed up over 10 years. Serial clinical and neurophysiological examinations and genetic analysis were undertaken in every patient. Sural nerve biopsy was performed in the oldest patient. The clinical features are similar to those previously described in HMSNL and all of them showed abnormal brain auditory evoked potentials. The oldest brother developed sensorineural deafness at the age of 20. Conduction velocities were unobtainable in all patients and nerves tested except for the median nerve in the youngest child in whom conduction was severely slowed. Neuropathological examination revealed a severely depleted nerve with very few surviving myelinated fibers which possessed thin myelin sheaths. Schwann cell processes were arranged in circular configurations without typical onion bulb configuration. Genetic analysis showed that the maternal chromosome inherited by all three affected siblings displayed a very unusual haplotype. Our patients show the characteristic clinical, electrophysiological and pathological findings described in HMSNL and represent the first reported Spanish family affected from the disease. The genetic findings in this family have contributed to refine the HMSNL critical linkage region.

A novel form of distal hereditary motor neuronopathy maps to chromosome 9p21.1-p12

Distal hereditary motor neuronopathies (dHMNs) form a heterogeneous group of rare disorders characterized by distal weakness and wasting in the limbs with no significant sensory involvement. Harding has classified dHMNs into seven categories based on clinical and genetic criteria. We report a novel form of autosomal recessive dHMN in 7 consanguineous families located in the Jerash region of Jordan. Onset of the disease is between 6 and 10 years of age and is characterized by weakness and atrophy of the lower limbs associated with pyramidal features. Within 2 years, symptoms progress to the upper limbs. Neurophysiological studies typically show normal conduction velocities, reduced compound motor action potential amplitudes, normal sensory nerve action potentials, and chronic neurogenic changes on needle electromyography. No significant abnormalities are seen on sural nerve biopsy. We call this novel form of dHMN Jerash hereditary motor neuronopathy. We studied the families at the molecular genetic level and mapped the Jerash hereditary motor neuronopathy gene to an approximately 0.54-cM region on chromosome 9p21.1-p12, flanked by microsatellite polymorphic marker loci D9S1845 and D9S1791. A maximum LOD score of 19.80 at theta = 0.001 was obtained between the disease and locus D9S1878.

Mouse genetics in cell biology

Genetic methodologies have provided powerful means for investigating the cellular and molecular mechanisms of biological functions. Cell-cell and cell-extracellular matrix interactions in particular have been studied in different functional systems with genetically modified animals. In the peripheral and central nervous system, many aspects of specific processes based on such interactions, including myelination, synaptic transmission and plasticity, have been elucidated at the cellular and molecular level. Importantly, genetic approaches have greatly advanced the understanding of pathologies resulting from impaired cellular interactions in the brain and the periphery. In this review, some of the most relevant genetic mouse models in cell biology and the methodologies employed for their production will be described. In addition their usefulness for studies of the mechanisms of hereditary neuropathies, learning and memory, and tumorigenesis will be illustrated.

[Hereditary neuropathy with liability to pressure palsies (tomaculous neuropathy). Clinical, electrophysical and molecular study of two affected families]

INTRODUCTION

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal-dominant disorder of peripheral myelin characterized by episodes of recurrent mononeuropathies usually involving nerves at common sites of entrapment and compression. Additional features include evidence of a diffuse demyelinating sensorimotor polyneuropathy on nerve conduction studies, focal myelin thickening (tomacula) on sural nerve biopsy, and a 1.5 Mb deletion on 17p11.2 encompassing the peripheral myelin protein 22 (PMP22) gene in most families.

PATIENTS AND METHODS

Two girls, aged 10 and 12 years, presented with peroneal nerve palsy and peroneal nerve palsy plus tibial nerve palsy, respectively. In none case, a clear causal factor was recognizable. Neurophysiological studies: both cases showed diffuse sensory and motor nerve conduction velocity slowing and prolongation of distal motor latencies. In addition, features of focal entrapment neuropathy were obtained at proximal peroneal nerve level. Sural nerve biopsy: large axons demyelination, redundant myelin and intraaxonal looping (case 1) and tomaculas (case 2). Molecular genetics: 17p12-p11 deletion was demonstrated in both affected girls, the mother and two maternal uncles of case 1 and in the father, paternal grandfather and two paternal uncles of case 2.

CONCLUSIONS

NHPP should be suspected in cases of peripheral neuropathy without clearly recognizable cause. Electrophysiological and molecular studies permit both delineation of the condition and identification of otherwise clinically normal family members.

Correlation between quantitative EMG and muscle MRI in patients with axonal neuropathy

The aim of the study was to investigate whether there are correlations between electromyography (EMG) data and findings in muscle magnetic resonance imaging (MRI). Quantitative EMG data and the amount of pathologic spontaneous activity (PSA) were compared with MRI signal intensities of the tibialis anterior muscles of 20 patients with axonal polyneuropathy and 14 healthy subjects. Using hierarchical regression analysis, the mean motor unit action potential (MUAP) size index (SI) and the amount of PSA were accurate predictors of T1-weighted signal intensity in MRI, an expression of fatty degeneration. The MUAP SI was superior to MUAP amplitude in explaining the variance of T1 signal intensity. Age was not a relevant factor. A high correlation was found between the amount of PSA and the T2-weighted signal intensity in short tau inversion recovery sequence. Magnetic resonance imaging demonstrates the structural changes and thus visualizes the outcome of the functional changes of denervation and reinnervation detected by EMG.

Progressive infantile axonal polyneuropathy

Polyneuropathies are relatively uncommon in early infancy and the majority of affected children are found to have hypomyelinating neuropathies. Axonal sensorimotor neuropathies have been described in childhood but the majority of affected children present at or after 6 months of age, have nonprogressive courses, and achieve the ability to walk, albeit late. Here we present three infants with infantile progressive axonal polyneuropathy from two families with nonconsanguineous parents. Each child presented shortly after the neonatal period and with rapid progression to quadriplegia. Involvement of the lower cranial nerves, phrenic nerves, or both was present in each child. Electrophysiology was diagnostic in each child. While the diagnosis of spinal muscular atrophy was considered in each case, clinical presentation, biopsies, and genetic testing were inconsistent with this diagnosis. Recognition of this early form of progressive axonal neuropathy is important as respiratory compromise occurred early and the condition showed familial inheritance in two of our patients.

Neuromyotonia in mice with hereditary myelinopathies

The purpose of this study was to further characterize neuromyotonia in mice with deletions and point mutations of myelin protein genes. Clinical observation showed irregular stretching of the hindlimbs, tremor and generalized myokymia in mice with targeted deletions of the genes encoding myelin protein zero (P0-/-) or peripheral myelin protein 22 (Pmp22-/-), and Trembler mice, which carry a point mutation of Pmp22. By electromyography (EMG), we found irregular high-frequency bursts of spontaneous motor unit activity and rhythmic doublet or multiplet discharges of motor units in these mouse models of human hereditary neuropathies. The EMG signs are typical for neuromyotonia and myokymia, respectively. The activity persisted after a proximal nerve section in many cases, localizing the generator to the peripheral nerve or the muscle. We now show that blocking neuromuscular transmission with suxamethonium abolished the spontaneous activity, ruling out a muscle origin. Phenytoin ameliorated the motor behavior. Taken together, our study shows that neuromyotonia develops in different mouse models of hereditary myelinopathies. This indicates that spontaneous motor unit activity may underlie neuromyotonia, which is occasionally observed in Charcot-Marie-Tooth disease. These animal models will be useful to study the pathogenesis of neuromyotonia.

Dejerine-sottas disease with a novel de novo dominant mutation, Ser 149 Arg, of the peripheral myelin protein 22

The Ser149Arg mutation of peripheral myelin protein 22 (PMP22) was found in a 19-year-old woman with a sporadic case of Dejerine-Sottas disease. The patient showed delayed motor development. She walked for the first time with support at the age of 2 years. Scoliosis developed at age 4 years. Her walking ability was best at age 11. Thereafter, she showed progressive muscle weakness and sensory disturbances in the distal extremities. At the age of 18 years, the use of a wheelchair became necessary. Motor and sensory nerve conduction studies showed absent motor and sensory responses on electrical stimulation of the limb nerves. A sural nerve biopsy specimen showed marked decreases in the numbers of both large and small myelinated fibers, abundant onion-bulb formation, and hypomyelination. Electron microscopic observation revealed the presence of demyelinated axons and myelin sheaths disproportionately thin relative to axon diameter. That this was a de novo mutation was established by parentage testing and PMP22 gene analysis of the parents. The mutation seems to be novel and dominant.

Hereditary motor and sensory neuropathy associated with auditory neuropathy in a Gypsy family

In a Slovene Gypsy family of 19 subjects from four generations three patients with clinical characteristics compatible with hereditary motor and sensory neuropathy - Lom (HMSNL). were found They had severe distal and milder proximal muscle atrophy and weakness with areflexia of myotatic jerks. Two had facial weakness at the time when already wheelchair bound. All sensory modalities were affected distally in the limbs. Sluggish pupillary responses to light and convergence were found. They had skeletal abnormalities. One patient had polydactily on the hand. Nerve conduction studies were compatible with demyelinative polyneuropathy. Nerve biopsy showed mainly axonal loss without hypertrophic changes. Auditory neuropathy was diagnosed in all of them. None of the patients had duplication of 17p1.2-12 or point mutations in the Protein zero. Peripheral myelin protein and Connexin32 genes. Similar disorder that mapped to 8q24 was previously described in some Bulgarian and Italian Gypsy families. Members of our family may suffer from the same hereditary disease and may carry the same ancestor mutation, which was in the past spread in European Gypsy populations.

Sensory involvement in spinal-bulbar muscular atrophy (Kennedy's disease)

Spinal-bulbar muscular atrophy (SBMA) is a rare X-linked neuronopathy associated with an abnormal representation of androgen receptors in the nervous system. Standard nerve conduction and histopathological studies have disclosed the involvement of large myelinated sensory fibers in the spinal nerves of SBMA patients. Little is known about the involvement of small sensory neurons and trigeminal nerves. Laser evoked potentials (LEPs) were studied in 6 unrelated patients with SBMA; 5 of these patients also underwent trigeminal reflex recordings, and 3 a sural nerve biopsy. LEPs were markedly abnormal, indicating a dysfunction in pain pathways. Given the sparing of small fibers in the sural nerve specimens, we hypothesize a dysfunction in spinothalamic cells, possibly due to an abnormal representation of the androgen receptors. Except for the jaw-jerk, all the trigeminal reflexes were markedly abnormal. Since the afferents for the jaw-jerk have their cell body within the central nervous system instead of the ganglion, the selective sparing of the jaw-jerk indicates a trigeminal ganglionopathy.

Electrodiagnostic features of hereditary neuropathy with liability to pressure palsies

OBJECTIVE

Because diagnosis of hereditary neuropathy with liability to pressure palsies (HNPP) frequently is missed or delayed, we looked for electrodiagnostic features that raise suspicion of the disorder by making comparisons with two more common diseases that mimic it electrophysiologically: chronic inflammatory demyelinating polyneuropathy (CIDP) and diabetic polyneuropathy.

METHODS

A retrospective review of the neuromuscular laboratory database was performed.

RESULTS

Nine HNPP subjects, 22 with CIDP and 49 with diabetic polyneuropathy. Of all the HNPP nerves studied, abnormally slow sensory nerve conduction velocity (SNCV) was found in 93%, prolonged distal motor latencies (DML) in 78%, slow motor nerve conduction velocity in 31%, and prolonged F-wave latencies in 90%. Mean SNCV for HNPP was 85.6%+/-10.6% of the lower limit of normal and significantly slower than for CIDP (114.3%+/-20.1%; p<0.0001) or diabetes (108.1%+/-14.8%; p<0.0001). Excluding the carpal tunnel site from the analysis did not alter this observation: Mean DML were more prolonged in HNPP, even without median nerve data in the analysis (118.5%+/-31.0% of the upper limit of normal), than in CIDP (103.2%+/-31.6%; p<0.05) or diabetes (86.3%+/-18.3%; p<0.0001). Mean HNPP motor nerve conduction velocity was within normal limits.

CONCLUSIONS

According to findings, hereditary neuropathy with liability to pressure palsies (HNPP) has a distinctive background polyneuropathy independent of superimposed entrapment neuropathy. It is characterized by diffuse sensory nerve conduction velocity (SNCV) slowing and prolongation of distal motor latencies with relatively infrequent and minor reduction of motor nerve conduction velocities. This indicates disproportionate distal conduction slowing in the disorder.

Clinical and pathological observations in men lacking the gap junction protein connexin 32

The X-linked form of Charcot-Marie-Tooth disease has been associated with mutations in the connexin 32 (Cx 32) gene, which encodes a gap junction protein. The majority of identified mutations are missense, but a few nonsense mutations or frame-shifting microdeletions have been encountered. Functional assessments of the mutated gap junction protein have demonstrated altered or simple losses of function. Mutations segregate with a typical clinical phenotype, which is the result of an age-related, progressive neuropathy. The mechanisms that cause the nerve damage are unknown. This report describes the consequences of a unique deletion mutation that eliminates the entire coding sequence of Cx 32, resulting in the absence of the Cx 32 gap junction protein in affected, hemizygous men. The clinical expression of this unique mutation was studied by the clinical, electrophysiological, and pathological evaluation of this kinship of five generations. The resulting severe neuropathy combines features of demyelination, notably in paranodal distribution, and distal accentuated axonal degeneration. The predicted absence of Cx 32 gap junctions is shown to be associated with a severe dysfunction of the axon-Schwann cell unit. Observed changes resemble those of Cx 32-null mice. No central nervous system changes were demonstrated.

Autosomal recessive hereditary neuropathy with focally folded myelin sheaths and linked to chromosome 11q23: a distinct and homogeneous entity

We describe a six generation Saudi kindred, with a recessive hereditary motor and sensory neuropathy (HMSN). Four individuals were affected including two children (a boy and a girl) and a 23-year-old man. The fourth (a female) died at the age of 14 years. Onset of the disease was early (< 2 years) and the clinical and neurophysiological features were, generally, quite similar to those of an Italian family linked to chromosome 11q23. The peculiar pathologic pattern was irregular and redundant loops associated with folding of the myelin sheaths. The genetic study confirmed linkage to chromosome 11q23 and refined the location of the gene between D11S1311 and D11S917, a 3.3 cM region. These findings support the existence of a homogeneous and distinct entity within the form of HMSN associated with focally folded myelin sheaths.

Altered molecular architecture of peripheral nerves in mice lacking the peripheral myelin protein 22 or connexin32

Peripheral nerves of mutant mice deficient for peripheral myelin protein 22 (PMP22) or connexin32 (Cx32) display similar pathologies as observed in hereditary human peripheral neuropathies. Mice lacking PMP22 develop focal hypermyelination followed by myelin degeneration and axonal atrophy. Cx32-deficient mice form normal myelin initially but develop demyelination and remyelination at older ages. We have examined the lack of PMP22 or Cx32 on the distribution of other components of the myelin sheath including myelin basic protein (MBP), E-cadherin, and myelin-associated glycoprotein (MAG), as well as the delayed rectifying potassium channel Kv1.1 as an intrinsic membrane protein of axons. In peripheral nerves of wild-type mice, Kv1.1 is present as a pair of juxtaparanodal clusters and a focal line extending longitudinally into the internode, branching parallel and adjacent to Schmidt-Lanterman incisures. Myelinated peripheral nerve fibers of 3-week-old PMP22(0/0) mice show tomacula and abnormally short internodes of variable lengths with minor effects on the localization of E-cadherin and Kv1.1. In older PMP22(0/0) mice, hypomyelinated fibers contain supernumerary Schwann cells and loose focally restricted E-cadherin and Kv1.1 expression. In contrast, remyelinated fibers in adult Cx32(0/0) mice exhibit a correct localization of these marker proteins, except that juxtaparanodal Kv1.1 clusters are aligned in abnormally short intervals of regular distances accompanied by an increased number of Schwann cells. Thus, different degrees of demyelination and remyelination in demyelinating mouse models have variable effects on the confinement of specific proteins to structural and functional internodal domains.