Correlation between PMP-22 messenger RNA expression and phenotype in hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is associated with a deletion in chromosome 17p11.2, which includes the gene for the peripheral myelin protein 22 (PMP-22). A "gene dosage" effect is probably the mechanism underlying HNPP, but the amount of PMP-22 mRNA in sural nerves of HNPP patients is highly variable and the role of PMP-22 underexpression in impairing myelination has yet to be clarified. We have studied 6 genetically proven HNPP patients, to evaluate the relationship between PMP-22 mRNA levels, and clinical, neurophysiological, and neuropathological findings. Underexpression of PMP-22 mRNA correlates with disease severity and with mean axon diameter and g ratio, but not with myelin thickness, number of "tomacula," or nerve conduction parameters. Our findings further confirm that underexpression of PMP-22 is the main pathogenetic mechanism underlying the severity of clinical symptoms and signs in HNPP. Smaller axons in sural nerves of HNPP patients with lower PMP-22 levels suggests that underexpression of PMP-22 may also affect axon development.     

A case of hereditary neuropathy with liability to pressure palsies (HNPP) with diabetes mellitus

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant neuropathy recently reported to be associated with deletion of the peripheral myelin protein-22 (PMP-22) gene. We report a 39-year-old man with recurrent brachial plexopathy and foot drop complicated by uncontrolled diabetes mellitus (DM). Right foot drop occurred at 31 years of the age and the patient subsequently experienced difficulty in raising his right arm. Neurological examination revealed weakness of the right deltoid, biceps muscles and tibialis anterior muscles. Deep tendon reflexes were generally absent. Sensory nerve conduction velocities in th ulnar, median and sural nerves were prolonged. Serum glucose and HB Alc levels were elevated to 468 mg/dl and 12.5%, respectively. Initially, it was difficult to diagnose the neuropathy as HNPP because the patient had poorly controlled diabetes mellitus and was unaware of similar disease in his family. In addition, focal asymmetric motor neuropathy and good recovery can develop in diabetes mellitus, occasionally with recurrence. We were able to make a final diagnosis of HNPP by detecting deletion of the PMP-22 gene region. After the diagnosis was confirmed, we examined the patient's family and found that his father experienced recurrent episodes of bilateral foot drop. This case suggests that gene analysis is sometimes essential in the differential diagnosis of hereditary peripheral neuropathies.     

Molecular basis of Charcot-Marie-Tooth neuropathy

Charcot-Marie-Tooth neuropathy (CMT) is the most common inherited peripheral neuropathy. CMT is classified into type types on the basis of pathological and electrophysiological findings: type 1(CMT1), characterized by decreased nerve conduction velocities and by "onion bulb" formation: type 2(CMT2), in which nerve conduction velocities are normal and "onion bulb" formations are rarely seen. CMT1 loci map to chromosome 17 (CMT1A), chromosome 1(CMT1B), another unknown autosome (CMT1C) and the X chromosome (CMTX). Recent work has identified the gene products corresponding to CMT1A, CMT1B and CMTX as peripheral myelin protein-22(PMP22), Po and connexin 32, respectively. Dejerine-Sottas disease has been identified as being caused by the mutation of PMP-22 or Po gene.     

Genetics and pathophysiology of hereditary motor and sensory neuropathy type 1

Hereditary motor and sensory neuropathy type 1 (HMSN1) is the most common, but genetically heterogenous demyelinating peripheral neuropathy. HMSN1A is caused in most cases by a 1.5-Mb tandem duplication in chromosome 17p11.2. Hereditary neuropathy with liability to pressure palsies is caused by the reciprocal deletion of the 1.5-Mb HMSN1A region. The peripheral myelin protein22 (PMP-22) gene is located within the HMSN1A region and has a point mutation in non-duplicated HMSN1A patients. HMSN1B patients have a mutation in the protein zero (P0) gene located on chromosome 1q22-23 Point mutation in PMP-22 or P0 is also reported in patients with Dejerine-Sottas disease. In X-linked HMSN1 patients (HMSNX1) a mutation occurs in the connexin 32 gene located on chromosome Xq13. The morphological phenotype is different among the genotypes of HMSN1.     

Subacute multifocal painful neuropathy with spontaneous remission

We present the cases of two patients with subacute onset of multifocal painful neuropathy with spontaneous remission and no relapse. The distribution of pain in patient 1 was hands (median > ulnar nerve region) and feet (peroneal and terminal tibial nerve regions), and in patient 2, hands (ulnar nerve region) and feet, left worse than in right. Both patients experienced facial numbness. Deep tendon reflexes were intact except for absent ankle jerks in patient 2. Motor nerve conduction studies demonstrated a marked prolongation of the distal motor latencies with normal proximal segment conduction velocities, suggesting distal demyelination. Cerebrospinal fluid protein concentration was elevated in patient 2, but no definite abnormality was found on sural nerve biopsy. A demyelinating neuropathy with a monophasic self-limited course may be consistent with Guillain-Barre syndrome (GBS). However, the multifocal painful sensory symptoms with facial numbness and the marked distal nerve conduction slowing in our cases are not consistent with GBS.     

Potential of Schwann cells from unmyelinated nerves to produce myelin: a quantitative ultrastructural and radiographic study

In adult mice, most fibres in the cervical sympathetic trunk (CST) are unmyelinated whereas a large proportion of sural nerve fibres are myelinated. This study of nerve grafts in syngeneic mice was designed to determine if Schwann cells originating from the unmyelinated CST would produce myelin when in contact with regenerating axons of the sural nerve. Quantitative microscopy of triated thymidine-labelled CST segments grafted to unlabelled sural nerve stumps revealed that, one month after grafting, previously unmyelinated grafts contained many myelinated fibres. By phase and electron microscope radioautography, nearly 40% of the myelin-producing cells in the reinnervated graft were shown to have originated in the unmyelinated CST. These findings indicate that Schwann cells originating from unmyelinated fibres are able to differentiate into myelin producing cells.     

Mutation analysis of the nerve specific promoter of the peripheral myelin protein 22 gene in CMT1 disease and HNPP

We analysed the nerve specific promoter of the peripheral myelin protein 22 gene (PMP22) in a set of 15 unrelated patients with Charcot-Marie-Tooth type 1 disease (CMT1) and 16 unrelated patients with hereditary neuropathy with liability to pressure palsies (HNPP). In these patients no duplication/deletion nor a mutation in the coding region of the CMT1/ HNPP genes was detected. In one autosomal dominant CMT1 patient, we identified a base change in the non-coding exon 1A of PMP22 which, however, did not cosegregate with the disease in the family. This study indicates that mutations in the nerve specific PMP22 promoter and 5' untranslated exon will not be a common genetic cause of CMT1A and HNPP.     

Gene dosage effects in hereditary peripheral neuropathy. Expression of peripheral myelin protein 22 in Charcot-Marie-Tooth disease type 1A and hereditary neuropathy with liability to pressure palsies nerve biopsies

A duplication of a 1.5-Megabase genomic region encompassing the gene for the peripheral myelin protein 22 (PMP22) is found on chromosome 17p11.2-12 in Charcot-Marie-Tooth disease type 1A (CMT1A), whereas the reciprocal deletion is associated with hereditary neuropathy with liability to pressure palsies (HNPP). Since most CMT1A patients harbor three copies of the PMP22 gene, and most HNPP patients carry only a single copy, a gene dosage effect has been proposed as a mechanism for both diseases. We have analyzed the steady-state expression of PMP22 protein in sural nerve biopsies from three CMT1A and four HNPP patients. Quantitative immunohistochemical determination showed that PMP22 protein expression relative to that of myelin protein zero and myelin basic protein was increased in all CMT1A patients and reduced in all HNPP patients, as compared with biopsy samples of patients with normal PMP22 gene expression. These data demonstrate that both neuropathies result from an imbalance of PMP22 protein expression.     

Use of pulsating high-frequency electromagnetic fields in patients with diabetic neuropathies and angiopathies

High-frequency pulsating electromagnetic field therapy was carried out in 22 patients with diabetic polyneuropathy and angiopathy manifested on lower extremities (18 men, 4 women, aged 48.2 +/- 6.3 years; 10 insulin-dependent persons, and 12 on oral antidiabetic treatment). The aim of the study was to verify the effect of this therapy on symptoms, neurophysiological findings and peripheral circulation. The diagnose of diabetic polyneuropathy was based on the electromyographic examination of foot and calf muscles, measurement of motor nerve conduction velocity of peroneal and tibial nerve, and sensory nerve conduction velocity of sural nerve. Diagnosis of diabetic polyneuropathy was based on electromyographic examination of the foot and calf muscles, measurement of the motor nerve conduction velocity of peroneal and tibial nerves, and the sensory nerve conduction velocity of the sural nerve. Diagnosis of diabetic angiopathy was established by oscillometric examination, measurement of skin temperature and claudication distance. The same methods were used for the evaluation of the therapeutical effect of electromagnetic field. Significant improvement of symptoms, and of all registered parameters of peripheral circulation was established after the therapy, but there were no significant changes of neurophysiological parameters. Therefore, high-frequency pulsating electromagnetic field is recommended for the treatment of diabetic angiopathy. In patients with neuropathic changes it can be used as an introduction procedure, or as an additional procedure to physical agents which are commonly used in the treatment of peripheral nerve lesion.     

Body mass index effect on common nerve conduction study measurements

This study was performed to determine whether there is a difference in nerve conduction study (NCS) measures based on body fat (body mass index; BMI). Two hundred fifty-three subjects had the following NCS tests performed on them: median, ulnar, peroneal, and tibial motor studies; median, ulnar, radial, and sural sensory studies; median and ulnar mixed nerve studies; and H-reflex studies. BMI was calculated as weight (kg) divided by height (m) squared. A repeated measures analysis of variance was run adjusting for age, sex, and height and using BMI as both a continuous variable and by dividing BMI into upper, middle, and lower thirds. The sensory and mixed nerve amplitudes correlated significantly (P < or = 0.01) with BMI for all nerves tested, with means being approximately 20-40% lower in the obese than in the thin subjects. No correlation was noted between BMI and nerve conduction velocity, H-reflex latency, or most of the other motor/sensory/mixed measures. The correlation between increased BMI and lower sensory/mixed nerve amplitudes should be taken into account in clinical practice.     

Thermal comfort and fever or research on how to feel better

OBJECTIVE: To verify if GAA expansion size in Friedreich's ataxia could account for the severity of sensory neuropathy. METHODS: Retrospective study of 56 patients with Friedreich's ataxia selected according to homozygosity for GAA expansion and availability of electrophysiological findings. Orthodromic sensory conduction velocity in the median nerve was available in all patients and that of the tibial nerve in 46 of them. Data of sural nerve biopsy and of a morphometric analysis were available in 12 of the selected patients. The sensory action potential amplitude at the wrist (wSAP) and at the medial malleolus (m mal SAP) and the percentage of myelinated fibres with diameter larger than 7, 9, and 11 microm in the sural nerve were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) expanded allele in each pair. Pearson's correlation test and stepwise multiple regression were used for statistical analysis. RESULTS: A significant inverse correlation between GAA1 size and wSAP, m mal SAP, and percentage of myelinated fibres was found. Stepwise multiple regression showed that GAA1 size significantly affects electrophysiological and morphometric data, whereas duration of disease has no effect. CONCLUSION: The data suggest that the severity of the sensory neuropathy is probably genetically determined and that it is not progressive.     

Comparison of a neurothesiometer and vibration in measuring vibration perception thresholds and relationship to nerve conduction studies

OBJECTIVE: To compare vibration perception thresholds (VPTs) obtained with two different instruments, a neurothesiometer and a vibratron, and to characterize variability of repeat measures and correlation with sural nerve conduction parameters. RESEARCH DESIGN AND METHODS: A total of 152 patients with diabetic peripheral neuropathy received electrodiagnostic evaluation and quantitative VPT testing with the Vibratron II and the Horwell Neurothesiometer. Of the patients, 42 returned for repeat nerve conduction studies and VPT testing with both types of equipment on three separate occasions. RESULTS: The variability of repeat testing for the vibratron was 34 and 31% in the right and left first toes, respectively. Variability for neurothesiometer was 8 and 6% for the right and left toes. This variability compares with that of sural nerve conduction velocity of 2% and that of sural nerve amplitude of 8% in this series of patients. CONCLUSIONS: We conclude that VPT determined with the neurothesiometer is less variable than with the vibratron and more reflective of peripheral nerve function. Our results indicate that the neurothesiometer can be used reliably in clinical research trials.     

Clinical and pathological correlations in Charcot-Marie-Tooth neuropathy type 1A with the 17p11.2p12 duplication: a cross-sectional morphometric and immunohistochemical study in twenty cases

In a cross-sectional, clinical, and morphometric analysis we assessed the correlation between the clinical and pathological evolution of disease in 20 unrelated patients of various ages affected by Charcot-Marie-Tooth neuropathy type 1A (CMT1A) with the 17p11.2p12 (peripheral myelin protein 22, PMP22) duplication. The severity of neurologic deficits and slowing of motor conduction velocity at the median nerve did not vary significantly with the patients' age. The amount of demyelination was significantly higher below 15 years than in older age groups; in contrast, myelinated fiber and onion bulb densities were similar at all ages. The results indicate that in duplicated CMT1A, the pathological process develops early in life and progresses little during the course of the disease. Younger patients had lower g-ratio values, suggesting that the trigger of demyelination in early years could be a hypermyelination, resulting from PMP22 overexpression. Yet none of the 20 patients examined had immunohistochemical evidence of altered PMP22 expression. The early onset and development of the disorder make it difficult to detect PMP22 overdosage in nerve biopsies.     

A novel PMP22 point mutation causing HNPP phenotype: studies on nerve xenografts

BACKGROUND: Hereditary neuropathy with liability to pressure palsies (HNPP) in most cases is caused by a deletion in chromosome 17p11.2-12 or, rarely, mutations resulting in a functional loss of one copy of the peripheral myelin protein 22 (PMP22) gene. Point mutations that lie deep within transmembrane (TM) domains causing major structural changes in PMP22 are associated with severe neuropathy. METHODS: A 25-year-old asymptomatic woman with a normal neurologic examination volunteered as a control subject. Electrophysiologic studies showed multiple entrapment neuropathies, prompting a search for a genetic defect. In addition, sural nerve fascicles from the subject were grafted into the cut ends of the sciatic nerve of nude mice and studied at 2, 6, and 8 weeks and compared with controls. RESULTS: Direct sequencing of the PMP22 gene revealed a G-->A transition at position 202 in axon 3 of the PMP22 gene. To determine if this was a causative mutation rather than a polymorphism, 102 DNA samples from controls were studied; none showed a similar base pair change. In the nerve xenografts, there was a marked delay at the onset of myelination and an impairment in the regenerative capacity of the nude mice axons engulfed by the mutant human Schwann cells. The axon tips were enlarged and demonstrated neurofilament density increase. Neurofilament density distribution histograms were bimodal in xenografts as well as in the subject's sural nerve. CONCLUSION: This study provides unequivocal evidence that a base pair change causing a Val30Met substitution at the junction of the first TM domain and the extracellular loop of PMP22 results in the HNPP phenotype.     

Effects found in a one-year oral toxicity study in Sprague-Dawley rats of a novel 5-HT1A receptor partial agonist for the treatment of anxiety in humans

Regeneration of motor axons is enhanced if they have sprouted prior to nerve injury. We examined whether sensory axon regeneration and recovery of pain response was affected by previous collateral sprouting. In the experimental group of rats, the right saphenous, tibial, and sural nerves were transected and ligated. The peroneal nerve was left to sprout into the adjacent denervated skin. Two months later, the axons of the peroneal nerve were crushed in the sciatic nerve. In the control group, the right sciatic nerve was crushed at the same time that the saphenous, tibial, and sural nerves were transected. Recovery of pain response in the foot was determined by the skin pinch test. Sensory axon elongation rate was measured by the nerve pinch test. The number of myelinated axons was determined in nerve cross sections stained by Azur blue. Recovery of pain sensitivity in the animals of the experimental group was delayed for 2-3 weeks in comparison to the control group. Moreover, the spatial pattern of pain response in the experimental group was irregular, displaying residual regions of insensitive skin which were not present in controls. The elongation rate of regenerating sensory axons in the experimental group was not decreased, and the number of myelinated axons in the peroneal nerves was even about 10% higher than in the control group. Therefore, we assume that the terminal arborization of the neurilemmal tubes pertaining to the former axon sprouts delayed regrowth of sensory axon terminals in the skin.     

The prevalence of Helicobacter pylori-positive serology in asymptomatic children

Surgeons frequently perform sural nerve biopsy as part of the work-up of patients with peripheral neuropathy. The indications for the procedure, therapeutic value, and complications associated with the procedure have received little attention in the surgical literature. A retrospective chart review of 60 patients with the suspected diagnosis of peripheral neuropathy undergoing sural nerve biopsy was performed. Vasculitis was suspected in 29 (48%) patients undergoing biopsy. This diagnosis was confirmed in 6 of the 29 patients and resulted in the alteration of therapy in 31% of patients with this suspected diagnosis. In 27 (45%) patients, the etiology of their peripheral neuropathy was unknown. Twelve (44%) patients in this group had sural nerve pathology; however, no change in therapy was required. Ten patients in our series had associated malignant tumors; some of these patients were diagnosed after referral for sural nerve biopsy. Twenty-five (42%) patients remained undiagnosed after biopsy. Nerve conduction studies were performed in 14 (22%) patients. Thirteen patients with abnormal lower extremity nerve conduction studies had 6 normal and 7 abnormal biopsy results. The one patient with a normal study had a normal nerve biopsy result. There were six (10%) patients with wound infections, seven (12%) patients with delayed wound healing, and three (5%) patients with new onset of chronic pain in the distribution of the sural nerve, for an overall complication rate of 27%. There was no correlation between the preoperative use of antibiotics, type of local anesthetic used, or length of nerve excised and complication rate. We conclude that the complication rate after sural nerve biopsy is significant. Strict criteria should be employed in selecting patients for sural nerve biopsy including a careful neurologic history and physical examination, nerve conduction studies, appropriate work-up for vasculitis if suspected, and implementation of a search for malignancy if this is not apparent. If the diagnosis is still in question, then sural nerve biopsy would seem appropriate, especially in patients with suspected vasculitis.     

Immunoreactivity of PMP-22, P0, and other 19 to 28 kDa glycoproteins in peripheral nerve myelin of mammals and fish with HNK1 and related antibodies

Mammalian peripheral nervous system (PNS) myelin contains several glycoproteins with molecular weights of 19 to 28 kDa, including the major 28 kDa P0 glycoprotein and a recently cloned protein called PMP-22. Some glycoproteins in this M(r) range in humans, cats and some other mammals react with HNK1, a mouse monoclonal antibody that identifies a carbohydrate epitope shared between the immune system and a number of adhesion proteins in the nervous system. A variety of antibodies to P0, PMP-22, and the carbohydrate determinants reacting with HNK1 were used to characterize immunochemically these 19 to 28 kDa glycoproteins of cat PNS myelin. The HNK1-reactive components include P0 and two slightly smaller 23 to 26 kDa proteins that are immunologically related to P0. However, HNK1 reacts most strongly with a lower molecular weight glycoprotein that does not react with the antibodies to P0 and was identified as PMP-22. Since the carbohydrate structure reacting with HNK1 is generally expressed on adhesion molecules, this result suggests that PMP-22 may function in cell-cell or membrane-membrane interactions. Furthermore, the related human anti-MAG monoclonal IgM antibodies from patients with neuropathy also react strongly with PMP-22, suggesting that it may be a target antigen in the pathogenesis of this disease. Purified PNS and CNS myelin from bony fish (toadfish and trout) were also shown to contain major glycoproteins, in the same 19 to 28 kDa M(r) range, that react very strongly with HNK1. It is shown that fish myelin has major proteins of this size that are immunologically and structurally related to mammalian P0, and it is demonstrated here that one of the strongly HNK1-positive proteins reacted well with an antiserum raised to bovine P0. The presence of high levels of the adhesion-related HNK1 epitope on these major myelin proteins of fish suggests that this carbohydrate structure may have played a role in the molecular evolution of myelin.     

Langerhans cell density in normal human oral mucosa and skin: relationship to age, smoking and alcohol consumption

Hyperthyroidism is a common endocrinologic disorder affecting many organ systems. Musculoskeletal and neurological involvement present themselves as fatigue, muscle weakness and paralysis. Electromyography (EMG) is essential for differential diagnosis of muscle weakness. Well defined neuropathy and myopathy have been described in these patients. In the present study 17 hyperthyroid patients were evaluated with electrophysiological tests in addition to physical and neurological examinations and biochemical laboratory studies. Needle EMG, motor and sensory conduction velocities, median and tibial somatosensory evoked potentials (SEP) were studied. For assessment of the activity of disease clinical status, neurological symptom and disability scores and serum T3, T4 and TSH levels were examined. Statistical analysis of neuroelectrophysiological findings of the patient and the control groups yielded meaningful difference in the needle EMG, sensory conduction velocity and evoked potential findings. Abnormalities were observed in 80% of the proximal muscles besides polyphasic potentials that were seen in 20% of the extensor digitorum brevis muscle. Median, ulnar and sural nerve sensory action potential amplitudes were found to be lower than that of the control group. Sural sensory nerve conduction velocity of patients was decreased in 35.5%, prolongation of median SEP latencies and increase in the amplitudes were not however statistically significant. Prolongation of Tibial SEP N1, P2 latencies were seen in 47%, amplitudes of N1 were increased in 88.2%, P2 in 58.8%, N2 in 47%. The thyroid clinical status score was correlated with Tibial SEPs amplitude. These findings suggest the presence of an initial axonal type of mild polyneuropathy. As a conclusion electrophysiological studies can be useful in the diagnosis of asymptomatic polyneuropathy in hyperthyroid patients.     

Regeneration across preserved peripheral nerve grafts

The potential to store nerve grafts for a prolonged period of time was assessed in a rat sciatic nerve model. Three-centimeter syngeneic nerve grafts were stored in Belzer/University of Wisconsin cold storage solution at different temperatures (5 degrees C, 22 degrees C, or 37 degrees C) for varying time periods (6 h, 24 h, or 3 weeks) prior to transplantation. Functional assessment using serial walking track analyses revealed no difference between storage times and temperatures. At 14 months postengraftment, the conduction velocities and the number of myelinated fibers that had regenerated across all grafts stored at 5 degrees C for all time periods tested were superior to grafts stored at either 22 degrees C or 37 degrees C. Nerve grafts stored for up to 3 weeks at 5 degrees C acted as effective conduits for proximal regenerating fibers and resulted in histologic, electrophysiologic, and functional results equivalent to fresh nerve grafts. Nerve graft storage may be applicable to nerve allografts and potentially provide allograft material that requires reduced or no associated host immunosuppression.     

Video-assisted thoracoscopic surgery for pneumothorax

A 28-year-old Japanese woman who suffered from mononeuritis multiplex was admitted to our hospital. Serological study revealed cryoglobulinemia (type III), hypocomplementemia, high titers of rheumatoid factor (RF), and positive antihepatitis C virus (HCV) antibody. Nerve conduction velocities were slower in sensory nerves than in motor nerves. Biopsied sural nerve showed a marked decrease of myelinated fibers but no evidence of angitis. She received plasma exchange and cryoglobulinpheresis over a period of 2 months with approximately 2.0 L (40 ml/kg) of plasma replaced in each procedure. Both plasma exchange and cryoglobulinpheresis alleviated clinical symptoms, and nerve conduction velocities were improved in several nerves. The serum cryoglobulin level was markedly reduced after the treatment together with the recovery of the C4 level. Thus, complements appeared to be consumed in large quantities in the presence of cryoglobulinemia in this patient. Efficacy of cryoglobulinpheresis indicates the possibility that cryoglobulins produced in association with HCV infection played a role in damaging the nerve directly through the activation of the complement system.