Demyelinating Peripheral Neuropathy Research Articles

Abstracts of the 8th Meeting of the Italian Peripheral Nerve Study Group: 51

We report a case of peripheral both demyelinating and axonal polyneuropathy in a patient affected from intestinal aganglionosis with high dose intermittent metronidazole therapy. Intestinal aganglionosis is a myenteric plexus disorder with lack of innervation concerning the whole digestive tract from the rectum to the esophagus. The familial incidence of this condition seems to be high and a recessive autosomal transmission is likely. In the pathogenesis of this disorder aberrant neural crest migration seems to be implicated: indeed frequent neurologic signs resembling dysautonomic ones, deafness and rare peripheral demyelinating or axonal neuropathies are associated. The patient was a 12 years old female child affected by intestinal aganglionosis and underwent to chronic intermittent Metronidazole treatment, with daily doses of 500 mg for 15 day every month. She was admitted to our Hospital for inability to walk, dysesthesias and pain at lower limbs, acutely started and progressively worsening. At the admission neurological examination showed ataxic gait with bilateral foot drop, severe distal weakness, bilateral tibialis anterior muscle atrophy, absent deep tendon reflexes, rapidly worsening. CSF was normal. Antibodies against to peripheral nerve (antigangliosides, sulfatide, MAG, glycosaminoglycans) resulted negative. Spinal cord MRI revealed increased roots size and increased epidural space. EMG showed denervation spontaneous activity with neurogenic MUAP modification on distal muscles. Nerve conduction study showed severe slowing of motor velocity on right and left peroneal nerves with reduced amplitude of CMAP. Sensory conduction was mild slowing on both sural nerves with reduced amplitude of SAP. Metronidazole therapy was discontinued; desametazone, high dose vitamin and intravenous immunoglobulin therapy was established in addition to rehydration and parenteral nutrition. Clinical conditions progressively improved and at two months follow up the girl was able to walk with mild ataxia. The authors emphasize in described case the difficulty to differentiate toxic or vitamin deficiency or autoimmune pathogenesis.

Abstracts of the 8th Meeting of the Italian Peripheral Nerve Study Group: 65

Mutations in a gene encoding a novel protein of unknown function, the ganglioside‐induced differentiation‐associated protein 1 gene (GDAP1), are associated with one of the autosomal recessive forms of Charcot‐Marie‐Tooth disease (CMT4A). Mutations in GDAP1 can cause both axonal and demyelinating inherited peripheral neuropathies. The GDAP1 gene maps on chromosome 8q21.1, encompassing 13.9 kb of genomic DNA. The coding sequence is comprised of six exons. Little is known about the function of GDAP1. The mouse homologue Gdap1 is highly expressed in brain. Northern‐blot analysis showed that GDAP1 is also expressed in peripheral nerves, both in neurons and in Schwann cells. A series of Italian patients with demyelinating (n = 42) and axonal (n = 39) peripheral neuropathy with possible recessive inheritance was screened for mutations in the GDAP1 gene. The entire coding region, including exon‐intron boundaries, was examined by single strand conformation polymorphism (SSCP) and direct sequencing. All patients were negative for the 17p11.2 duplication and for mutations in the MPZ, GJB1, PMP22 and EGR2 genes. SSCP analysis showed a few electrophoretic variants, in the exon 1, exon 3 and exon 4, respectively. Direct sequencing demonstrated the presence of a common single nucleotide polymorphism in the exon 4 (c.507T > G) and a nucleotide substitution in the exon 3. The latter was found in four patients, belonging to three families, and was not detected in a series of normal subjects. Further studies are in progress to evaluate the possible role of this variant in the pathophysiology of the disease. This work was partially supported by grants MURST 2000 to F.A. and Ministero della Sanità to P.M.

The function of the Periaxin gene during nerve repair in a model of CMT4F.

Mutations in the Periaxin (PRX) gene are known to cause autosomal recessive demyelinating Charcot-Marie-Tooth (CMT4F) and Dejerine-Sottas disease. The pathogenesis of these diseases is not fully understood. However, progress is being made by studying both the periaxin-null mouse, a mouse model of the disease, and the protein-protein interactions of periaxin. L-periaxin is a constituent of the dystroglycan-dystrophin-related protein-2 complex linking the Schwann cell cytoskeleton to the extracellular matrix. Although periaxin-null mice myelinate normally, they develop a demyelinating peripheral neuropathy later in life. This suggests that periaxin is required for the stable maintenance of a normal myelin sheath. We carried out sciatic nerve crushes in 6-week-old periaxin-null mice, and, 6 weeks later, found that although the number of myelinated axons had returned to normal, the axon diameters remained smaller than in the contralateral uncrushed nerve. Not only do periaxin-null mice have more hyper-myelinated axons than their wild-type counterparts but they also recapitulate this hypermyelination during regeneration. Therefore, periaxin-null mice can undergo peripheral nerve remyelination, but the regulation of peripheral myelin thickness is disrupted.

Inhibition of human squalene monooxygenase by selenium compounds

Selenosis in animals is characterized by a variety of neurological abnormalities, but the chemical species of selenium and the molecular targets that mediate this neurotoxicity are unknown. We have previously shown that selenite is a potent inhibitor of squalene monooxygenase, the second enzyme in the committed pathway for cholesterol biosynthesis; inhibition of this enzyme by dimethyltellurium leads to a peripheral demyelinating neuropathy similar to that seen in selenosis. To evaluate the role methylation plays in selenium toxicity, we examined the ability of three methylselenium compounds, methylselenol, dimethylselenide, and trimethylselenonium iodide, to inhibit purified recombinant human squalene monooxygenase. IC(50) values for methylselenol (95 microM) and dimethylselenide (680 microM) were greater than that previously obtained for selenite (37 microM), and inhibition by trimethylselenonium iodide was evident only at concentrations above 3 mM. Inhibition by methylselenol as well as by selenite was slow and irreversible, suggestive of covalent binding to the enzyme, and thiol-containing compounds could prevent and reverse this inhibition, indicating that these compounds were reacting with sulfhydryl groups on the protein. Monothiols such as glutathione and beta-mercaptoethanol provided better protection than did dithiols, suggesting that these selenium compounds bind to only one of the two proposed vicinal cysteines on squalene monooxygenase. Unexpectedly, the inhibition by selenite was significantly enhanced by dithiols, indicating that a more toxic species, possibly selenide, was formed in the presence of these dithiol reductants.

Inhibition of human squalene monooxygenase by selenium compounds

Selenosis in animals is characterized by a variety of neurological abnormalities, but the chemical species of selenium and the molecular targets that mediate this neurotoxicity are unknown. We have previously shown that selenite is a potent inhibitor of squalene monooxygenase, the second enzyme in the committed pathway for cholesterol biosynthesis; inhibition of this enzyme by dimethyltellurium leads to a peripheral demyelinating neuropathy similar to that seen in selenosis. To evaluate the role methylation plays in selenium toxicity, we examined the ability of three methylselenium compounds, methylselenol, dimethylselenide, and trimethylselenonium iodide, to inhibit purified recombinant human squalene monooxygenase. IC50 values for methylselenol (95 μM) and dimethylselenide (680 μM) were greater than that previously obtained for selenite (37 μM), and inhibition by trimethylselenonium iodide was evident only at concentrations above 3 mM. Inhibition by methylselenol as well as by selenite was slow and irreversible, suggestive of covalent binding to the enzyme, and thiol-containing compounds could prevent and reverse this inhibition, indicating that these compounds were reacting with sulfhydryl groups on the protein. Monothiols such as glutathione and β-mercaptoethanol provided better protection than did dithiols, suggesting that these selenium compounds bind to only one of the two proposed vicinal cysteines on squalene monooxygenase. Unexpectedly, the inhibition by selenite was significantly enhanced by dithiols, indicating that a more toxic species, possibly selenide, was formed in the presence of these dithiol reductants. © 2002 Wiley Periodicals, Inc. J Biochem Mol Toxicol 16:18–23, 2002; DOI 10.1002/jbt.10014

Mutation analysis in Chariot-Marie Tooth disease type 1: point mutations in the MPZ gene and the GJB1 gene cause comparable phenotypic heterogeneity.

Charcot-Marie-Tooth disease type 1 (CMT1) is a demyelinating peripheral neuropathy most commonly caused by a DNA duplication on chromosome 17p11.2 including the peripheral myelin protein 22 (PMP22). Point mutations in the myelin protein zero gene (MPZ) and gap junction protein, beta-1 gene (GJB1) are also found in association with CMT1 or the subclass of CMT type X (CMTX), respectively. Recently point mutations in these genes have been found in patients showing the axonal variant of CMT, CMT type 2 (CMT2). We here describe the clinical and electro-physiological findings caused by two novel and two recently described MPZ mutations and six GJB1 mutations. Different MPZ and GJB1 mutations were associated with different grades of severity in CMT1 and CMTX. The novel MPZ Glu141st op mutation was associated with the axonal CMT2. We conclude that the clinical and electrophysiological heterogeneity among CMT patients carrying point mutations in MPZ and GJB1 is similar. Thus for clinical purposes CMT1 and CMT2 patients should be screened for mutations in these two genes after duplication on chromosome 17p11.2 has been excluded as the disease causing mutation.

Periaxin Mutations Cause Recessive Dejerine-Sottas Neuropathy

The periaxin gene (PRX) encodes two PDZ-domain proteins, L- and S-periaxin, that are required for maintenance of peripheral nerve myelin. Prx(-/-) mice develop a severe demyelinating peripheral neuropathy, despite apparently normal initial formation of myelin sheaths. We hypothesized that mutations in PRX could cause human peripheral myelinopathies. In accordance with this, we identified three unrelated Dejerine-Sottas neuropathy patients with recessive PRX mutations-two with compound heterozygous nonsense and frameshift mutations, and one with a homozygous frameshift mutation. We mapped PRX to 19q13.13-13.2, a region recently associated with a severe autosomal recessive demyelinating neuropathy in a Lebanese family (Delague et al. 2000) and syntenic to the location of Prx on murine chromosome 7 (Gillespie et al. 1997).

The Absence of Myelin P0 Protein Produces a Novel Molecular Phenotype in Schwann Cell.

In order to better understand the pathogenesis of demyelination in P0 knockout (P0-/-) mice, we analyzed the myelin gene expression and the localization of myelin proteins in P0 null mouse sciatic nerve. We have demonstrated that the severe demyelinating neuropathy of P0-knockout mouse is associated with changes in the program of myelin gene expression. Some changes in myelin gene expression occur early, others occur during adulthood. We also provide evidence that the absence of P0 is associated with changes in the localization of specific paranodal proteins in the peripheral nerve. These data suggest that P0 plays an important role, either directly or indirectly, in the program of Schwann cell gene expression and in the specific distribution of peripheral myelin proteins. Furthermore, myelin gene dysregulation and improper localization of paranodal proteins may account, in part, for the pathogenesis of demyelination in P0-knockout mice, as well as in human demyelinating peripheral neuropathy associated with mutations in the P0 gene.

Distal axonopathy in peripheral nerves of PMP22-mutant mice

A partial duplication of chromosome 17 is associated with Charcot-Marie-Tooth disease type 1A (CMT1A), a demyelinating peripheral neuropathy that causes progressive distal muscle atrophy and sensory impairment. Trisomic expression of peripheral myelin protein 22 (PMP22) whose gene is contained within the duplicated region is considered to be responsible for the disease. By using recombinant gene technology in rodents, we had demonstrated previously that PMP22 is sensitive to gene dosage. Homozygous PMP22 knockout (PMP22(0/0)) mice and transgenic animals carrying additional copies of the PMP22 gene develop distinct peripheral polyneuropathies. We have now performed a detailed morphometrical analysis of the L3 roots, quadriceps and saphenous nerves of these PMP22-mutant mice to study whether the myelin and potential axonal deficits are evenly distributed. The L3 roots and the peripheral nerves were chosen as representatives of the proximal and distal segments of the peripheral nervous system. When the roots were compared with the peripheral nerves, myelin deficiencies appeared more severe at the radicular levels, in particular the ventral roots. Decreased numbers of large calibre axons were a prominent feature in the motor branches of both strains of PMP22-mutant mice, and these axonal deficits were more severe distally. Active axonal damage was only observed in the nerves of PMP22(0/0) mice. Despite the distinct effects on myelination and the Schwann cell phenotype that characterize the neuropathies of PMP22-mutant mice, both strains develop a distally accentuated axonopathy as a common disease mechanism which is likely to be responsible for the neurological deficits.

Multiple connexin expression in peripheral nerve, Schwann cells, and Schwannoma cells

Myelinating Schwann cells express the gap junction protein, connexin (Cx)32, which is present at the nodes of Ranvier and Schmidt-Lantermann incisures (Bergoffen et al. [1993] Science (Wash.) 262:2039–2042). Following peripheral nerve injury, other members of the connexin gene family are also expressed (Chandross et al. [1996a] Mol. Cell. Neurosci. 7:501–518). This study surveys the connexin(s) expressed by rat sciatic nerve, cultured Schwann cells, and a mouse Schwannoma (TR6 Bc1) cell line. Reverse transcriptase-polymerase chain reaction (RT-PCR) amplification revealed a constitutive expression of mRNA encoding Cx32 and 43 but not Cx26, 37, 40, 45, and 46 in sciatic nerve. Mitogenic stimulation of cultured Schwann cells expressing Cx32 also resulted in the appearance of Cx43 mRNA. Schwannoma cells expressed exclusively Cx43 mRNA. These results were confirmed by Northern blot analysis. Functional gap junctions in cultured Schwann and Schwannoma cells were shown by analysis of the intercellular transfer of Lucifer yellow, although the coupling between primary Schwann cells was weak or undetectable. Treatment of primary Schwann cells with mitogens resulted in extensive dye coupling. An immunohistochemical study of adult sciatic nerve sections demonstrated Cx32 immunoreactivity at the nodes of Ranvier and in Schwann cell bodies. Lower intensity staining of Cx43 along the myelin sheath and Schwann cell bodies was also observed. Indirect immunofluorescent studies of Schwann cells treated with mitogens showed characteristic punctate cell surface staining of Cx43; Cx32 staining was detected mainly intracellularly. These results lead to the conclusion that in addition to the expression of Cx32 by normal adult sciatic nerve, low amounts of Cx43 protein are also present. The implications of the expression of two connexins by Schwann cells in Charcot-Marie-Tooth X-linked disease, a demyelinating peripheral neuropathy, are discussed. J. Neurosci. Res. 57:166–175, 1999. © 1999 Wiley-Liss, Inc.

Multiple connexin expression in peripheral nerve, Schwann cells, and Schwannoma cells.

Myelinating Schwann cells express the gap junction protein, connexin (Cx)32, which is present at the nodes of Ranvier and Schmidt-Lantermann incisures (Bergoffen et al. [1993] Science (Wash. ) 262:2039-2042). Following peripheral nerve injury, other members of the connexin gene family are also expressed (Chandross et al. [1996a] Mol. Cell. Neurosci. 7:501-518). This study surveys the connexin(s) expressed by rat sciatic nerve, cultured Schwann cells, and a mouse Schwannoma (TR6 Bc1) cell line. Reverse transcriptase-polymerase chain reaction (RT-PCR) amplification revealed a constitutive expression of mRNA encoding Cx32 and 43 but not Cx26, 37, 40, 45, and 46 in sciatic nerve. Mitogenic stimulation of cultured Schwann cells expressing Cx32 also resulted in the appearance of Cx43 mRNA. Schwannoma cells expressed exclusively Cx43 mRNA. These results were confirmed by Northern blot analysis. Functional gap junctions in cultured Schwann and Schwannoma cells were shown by analysis of the intercellular transfer of Lucifer yellow, although the coupling between primary Schwann cells was weak or undetectable. Treatment of primary Schwann cells with mitogens resulted in extensive dye coupling. An immunohistochemical study of adult sciatic nerve sections demonstrated Cx32 immunoreactivity at the nodes of Ranvier and in Schwann cell bodies. Lower intensity staining of Cx43 along the myelin sheath and Schwann cell bodies was also observed. Indirect immunofluorescent studies of Schwann cells treated with mitogens showed characteristic punctate cell surface staining of Cx43; Cx32 staining was detected mainly intracellularly. These results lead to the conclusion that in addition to the expression of Cx32 by normal adult sciatic nerve, low amounts of Cx43 protein are also present. The implications of the expression of two connexins by Schwann cells in Charcot-Marie-Tooth X-linked disease, a demyelinating peripheral neuropathy, are discussed.

Gap junctions in health and disease

Gap junctions are communicating junctions that consist of hexameric proteins called connexins and mediate the exchange of low molecular weight metabolites and ions between cells in contact. It has long been hypothesized that gap junctional intercellular communication plays a crucial role in the maintenance of homeostasis, morphogenesis, cell differentiation, and growth control in multicellular organisms. Recent discoveries of human genetic disorders associated with mutations in connexin genes and experimental data on connexin knockout mice have provided direct evidence of this. Connexin 32 mutations cause X-linked Charcot-Marie-Tooth disease, an inherited peripheral demyelinating neuropathy. Connexin 26 mutations have been found in hereditary nonsyndromic sensorineural deafness. Connexin 43 knockout mice die shortly after delivery because of cardiac malformation. Connexin 32 knockout mice show high incidences of spontaneous and chemically induced liver tumors, and develop a late-onset progressive peripheral neuropathy analogous to human Charcot-Marie-Tooth disease. Female connexin 37 knockout mice are infertile as the result of abnormalities in ovarian follicular growth, control of luteinization, and oocyte maturation. Connexin 46 knockout mice develop nuclear cataracts. Further identification of connexin mutations in other human diseases and generation of mice with modified connexin genes will aid our understanding of the biology of gap junctions.

Campylobacter jejuni strains from patients with Guillain-Barré syndrome.

Guillain-Barré syndrome (GBS), an acute demyelinating peripheral neuropathy, may be triggered by an acute infectious illness; infection with Campylobacter jejuni is the most frequently reported antecedent event. In Japan, O:19 is the most common serotype among GBS-associated C. jejuni strains. To determine whether serotype O:19 occurs among GBS-associated strains in the United States and Europe, we serotyped seven such strains and found that two (29%) of seven GBS-associated strains from patients in the United States and Germany were serotype O:19. To determine whether GBS-associated strains may be resistant to killing by normal human serum (NHS), we studied the serum susceptibility of 17 GBS- and 27 enteritis-associated strains (including many O:19 and non-O:19 strains) using C. jejuni antibody positive (pool 1) or negative (pool 2) human serum. Using pool 1 serum we found that one (6%) of 18 serotype O:19 strains compared with 11 (42%) of 26 non-O:19 strains were killed; results using pool 2 serum were nearly identical. Finally, 8 O:19 and 8 non-O:19 strains were not significantly different in their ability to bind complement component C3. Serotype O:19 C. jejuni strains were overrepresented among GBS-associated strains in the United States and Germany and were significantly more serum-resistant than non-O:19 strains. The mechanism of this resistance appears unrelated to C3 binding.

2-31-27 Multiple sclerosis associated with peripheral demyelinating neuropathy improves after intravenous IGG treatment

2-31-27 Multiple sclerosis associated with peripheral demyelinating neuropathy improves after intravenous IGG treatment

Proteolipid Protein Is Necessary in Peripheral as Well as Central Myelin

Alternative products of the proteolipid protein gene ( PLP), proteolipid protein (PLP) and DM20, are ma- jor components of compact myelin in the central nervous system, but quantitatively minor constituents of Schwann cells. A family with a null allele of PLP has a less severe CNS phenotype than those with other types of PLP mutations. Moreover, individuals with PLP null mutations have a demyelinating peripheral neuropathy, not seen with other PLP mutations of humans or animals. Direct analysis of normal peripheral nerve demonstrates that PLP is localized to compact myelin. This and the clinical and pathologic observations of the PLP null phenotype indicate that PLP/DM20 is necessary for proper myelin function both in the central and peripheral nervous systems.

Pathological findings in a patient with amyotrophic lateral sclerosis and multifocal motor neuropathy with conduction block

We studied a 53-year-old woman with progressive weakness of the left arm, gradually spreading to the other limbs. Neurological examination revealed a motor neuron syndrome with paresis, fasciculations and atrophy. Electrophysiological studies showed multiple motor conduction blocks. The anti-GM1 IgM titer was elevated. The patient was thought to have a multifocal motor neuropathy. Despite intravenous cyclophosphamide treatment, however, she died with respiratory insufficiency. On postmortem examination, the brachial plexus showed patches of demyelination underlying different areas of motor conduction block. The spinal cord, however, revealed severe neuronal loss in the ventral horn and axonal loss in the corticospinal tract, indicative of amyotrophic lateral sclerosis. Demyelination of peripheral nerves could have been responsible for the other conduction blocks in this patient. The prominent degeneration of motor neurons, however, must also have played a role in the clinical picture. Some patients with the syndrome of a multifocal motor neuropathy may have MND rather than, or in addition to, a demyelinating peripheral motor neuropathy.

Demyelinating Peripheral Neuropathy in Merosin-Deficient Congenital Muscular Dystrophy

It has recently been shown that merosin, a laminin variant, is deficient in a proportion of patients with congenital muscular dystrophy. Merosin is a heterotrimer composed of the alpha 2, beta 1, and gamma 1 subunits, and further studies have shown that it is the alpha 2 subunit that is deficient in these patients. Because the alpha 2 subunit is also expressed in S-merosin, found in Schwann cells, we have investigated whether peripheral nerve function is also affected in these patients. Motor nerve conduction velocities and sensory distal latencies were examined in 25 cases of congenital muscular dystrophy and the results correlated with the merosin expression in their muscle biopsies. All but two of the 10 merosin-deficient cases had reduced motor nerve conduction, whereas all the merosin-positive cases had normal results. Analysis of the biopsies of these two cases showed that they produced merosin in reduced amounts, in contrast to all other merosin-deficient patients that produced no or only traces of merosin. Sensory nerve studies showed no difference between the two groups. These results indicate that a peripheral demyelinating neuropathy is a feature of merosin-deficient congenital muscular dystrophy. The fact that the alpha 2 subunits is also expressed in Schwann cells supports the idea that the alpha 2 gene, located on chromosome 6, is the candidate gene for merosin-deficient congenital muscular dystrophy.

New functions for gap junctions

The most significant finding of the past year in gap junction research has been the association of connexin defects with human diseases. Connexin32 mutations cause X-linked Charcot-Marie-Tooth disease, a demyelinating peripheral neuropathy. Mutations in connexin43 may underlie cardiac malformations in visceroatrial heterotaxia syndromes. Genetic approaches and gene targeting have provided new insights, but also raise new questions concerning connexin function, the significance of connexin diversity and the regulation of intercellular communication.

The natural history of chronic demyelinating neuropathy associated with benign IgM paraproteinaemia. A clinical and neurophysiological study.

Eighteen patients are described, all of whom had chronic demyelinating peripheral neuropathy and benign IgM paraproteinaemia. All patients had serum antibodies against peripheral nerve myelin or myelin-associated glycoprotein. Seventeen were followed up clinically and electrophysiologically for between 1 and 14 years (mean 7.4 years). The presenting symptoms and signs were almost always those of a distal sensory disturbance in the limbs followed by distal weakness. All patients developed tremor or ataxia in the arms, and gait ataxia. The severity of the neuropathy varied greatly between patients at similar stages. Some had a predominantly sensory deficit and others a predominantly motor deficit. All patients eventually developed both motor and sensory signs. The neuropathy became slowly worse over the first 2-5 years and then appeared to stabilize, although long-term follow-up did reveal a very slow progression in the group as a whole. No patient developed evidence of haematological malignancy but two patients died of malignancy involving other systems. On reviewing 75 patients from the literature, non-haematological malignancy was found to be the commonest cause of death.

Horner's syndrome and demyelinating peripheral neuropathy caused by high‐dose cytosine arabinoside

High-dose cytosine arabinoside may benefit patients with refractory acute leukemia. Peripheral nervous system disturbances caused by cytosine arabinoside have rarely been reported. We describe a patient with acute leukemia who developed Horner's syndrome and a severe demyelinating peripheral neuropathy leading to death after receiving high-dose cytosine arabinoside. Peripheral nerve dysfunction is a potentially serious complication of high-dose cytosine arabinoside.