Neurofascin-155 IgG4 in chronic inflammatory demyelinating polyneuropathy

Painful trigeminal neuropathy associated with anti-Plexin D1 antibody

OBJECTIVE

To determine whether anti-Plexin D1 antibody (Plexin D1-immunoglobulin G [IgG]), which is associated with limb and trunk neuropathic pain (NP) and binds to pain-conducting small unmyelinated dorsal root ganglion (DRG) neurons, exists in patients with idiopathic painful trigeminal neuropathy (IPTN) and whether Plexin D1-IgG binds to trigeminal ganglion (TG) neurons.

METHODS

We enrolled 21 consecutive patients with IPTN and 35 age- and sex-matched controls without NP (25 healthy persons and 10 with neurodegenerative diseases). We measured serum Plexin D1-IgG using a mouse DRG tissue-based indirect immunofluorescence assay (IFA) and by Western blotting (WB) using a recombinant human Plexin D1 (rhPlexin D1) accompanied by immunoadsorption tests with rhPlexin D1. The reactivity of Plexin D1-IgG toward mouse TG, brain, heart, and kidney was assessed by tissue-based IFAs.

RESULTS

Serum Plexin D1-IgG was detected more frequently in IPTN than in controls by both IFA and WB (14.3% vs 0%, p = 0.048). Three Plexin D1-IgG-positive patients also had limb or trunk NP and commonly showed tongue pain. In tissue-based IFAs, IgG from 2 Plexin D1-IgG-positive patients immunostained small TG neurons, which was prevented by preincubation with rhPlexin D1. Moreover, Plexin D1-IgG immunostaining mostly colocalized with isolectin B4-positive pain-conducting unmyelinated TG neurons. IFAs of other tissues with the same IgG revealed weak immunoreactivity only in endothelial cells, which was prevented by preincubation with rhPlexin D1.

CONCLUSIONS

Plexin D1-IgG, which binds to pain-conducting small TG neurons in addition to DRG neurons, can be present in IPTN as well as limb and trunk NP.

The Misdiagnosis of CIDP: A Review

There is a growing realization that many patients are incorrectly diagnosed with chronic inflammatory demyelinating polyneuropathy (CIDP), with at least half of patients that carry a diagnosis of CIDP in the USA possibly having a different explanation for their neuropathy or having no neuropathy at all. Many misdiagnosed patients go on to receive costly and potentially harmful treatments for a disease that they do not have, while at the same time missing an opportunity to treat their true ailment. The cost of misdiagnosis on patients and society is not trivial. Many factors contribute to misdiagnosis. Particular points of vulnerability include the evaluation of "atypical" CIDP, interpretation of equivocal nerve conduction studies, over-reliance on elevations in cerebrospinal fluid protein concentration in indeterminate ranges, and placing excessive diagnostic weight on subjective changes following the initiation of immunotherapy. In addition to heighted awareness of the challenges, adherence to CIDP diagnostic guidelines, utilization of objective metrics to document clinical change, and referrals to CIDP centers of excellence are strategies that may improve diagnostic accuracy.

Longitudinal study on nerve ultrasound and corneal confocal microscopy in NF155 paranodopathy

We report the case of a 27‐year‐old patient with subacute anti‐neurofascin‐155 neuropathy with bifacial palsy, who showed excellent response to rituximab. We provide longitudinal data of established clinical scores, nerve conduction studies, antibody titers, and novel imaging methods (nerve ultrasonography and corneal confocal microscopy). Clinical and electrophysiological improvement followed the reduction of serum antibody titer and correlated with a reduction of corneal inflammatory cellular infiltrates whereas the increase in the cross‐sectional area of the peripheral nerves remained 12 months after first manifestation. Our findings suggest that novel techniques provide useful follow‐up parameters in paranodopathies.

Zebrafish brain RNA sequencing reveals that cell adhesion molecules are critical in brain aging

Brain aging is a complex process, which involves multiple pathways including various components from cellular to molecular. This study aimed to investigate the gene expression changes in zebrafish brains through young-adult to adult, and adult to old age. RNA sequencing was performed on isolated neuronal cells from zebrafish brains. The cells were enriched in progenitor cell markers, which are known to diminish throughout the aging process. We found 176 statistically significant, differentially expressed genes among the groups, and identified a group of genes based on gene ontology descriptions, which were classified as cell adhesion molecules. The relevance of these genes was further tested in another set of zebrafish brains, human healthy, and Alzheimer's disease brain samples, as well as in Allen Brain Atlas data. We observed that the expression change of 2 genes, GJC2 and ALCAM, during the aging process was consistent in all experimental sets. Our findings provide a new set of markers for healthy brain aging and suggest new targets for therapeutic approaches to neurodegenerative diseases.

An Atypical and Multifactorial Acute Immune Polyradiculopathy: A Case Report

Clinical diagnosis often focuses on identifying the single cause of a patient's symptoms but it is becoming increasingly recognized that a subset of patients exist where 2 pathological entities coexist. These patients present a particular diagnostic challenge because the first "positive" diagnostic test is not the definitive stopping point in their evaluation. Here, we present the case of a 47-year-old woman with multiple cranial neuropathies and a polyradiculopathy. A significant pleocytosis in the cerebrospinal fluid sparked a broad evaluation which revealed pathologic evidence of sarcoidosis and molecular evidence of neurofascin (NF)-155 and NF-140 antibodies. The pathogenic contribution of these 2 pathologic entities, or interaction, to this patient's case is not clear. Nevertheless, the patient responded robustly to steroids and symptoms significantly improved. This case is a demonstration of the balance between Occam's razor and Hickam's dictum in clinical practice.

Distinguish CIDP with autoantibody from that without autoantibody: pathogenesis, histopathology, and clinical features

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is considered to be an immune-mediated heterogeneous disease involving cellular and humoral immunity. In recent years, autoantibodies against nodal/paranodal protein neurofascin155 (NF155), neurofascin186 (NF186), contactin-1 (CNTN1), and contactin-associated protein 1 (CASPR1) have been identified in a small subset of patients with CIDP, which disrupt axo-glial interactions at nodes/paranodes. Although CIDP electrodiagnosis was made in patients with anti-nodal/paranodal component autoantibodies, macrophage-induced demyelination, the characteristic of typical CIDP, was not observed. Apart from specific histopathology, the pathogenic mechanisms and clinical manifestations of CIDP with autoantibody are also distinct. We herein compared pathogenesis, histopathology, clinical manifestations, and therapeutic response in CIDP with autoantibody vs. CIDP without autoantibody. CIDP with autoantibodies should be considered as an independent disease entity, not a subtype of CIDP due to many differences. They possibly should be classified as CIDP-like chronic nodo-paranodopathy, which can better characterize these disorders, help diagnose and make the most effective therapeutic decisions.

Efficacy and Safety of Rituximab in Refractory CIDP With or Without IgG4 Autoantibodies (RECIPE): Protocol for a Double-Blind, Randomized, Placebo-Controlled Clinical Trial

BACKGROUND

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an immune-mediated peripheral neuropathy that is currently classified into several clinical subtypes, which are presumed to have different pathogenic mechanisms. Recently, studies identified a subgroup of patients with CIDP who were positive for IgG4 autoantibodies against paranodal proteins, such as neurofascin-155 and contactin-1, who respond poorly to first-line therapies for typical CIDP, including intravenous immunoglobulin therapy.

OBJECTIVE

This study aims to evaluate the efficacy and safety of intravenous rituximab according to IgG4 autoantibody status in patients with refractory CIDP.

METHODS

The Evaluation of the Efficacy and Safety of Rituximab in Refractory CIDP Patients with IgG4 Autoantibodies in the Exploratory Clinical (RECIPE) trial consists of 2 cohorts: a multicenter, placebo-controlled, randomized study cohort of 15 patients with IgG4 autoantibody-positive CIDP (rituximab:placebo = 2:1) and an open-label trial cohort of 10 patients with antibody-negative CIDP. The primary endpoint is improvement in functional outcome assessed using the adjusted Inflammatory Neuropathy Cause and Treatment Disability Scale score at 26, 38, or 52 weeks after the start of treatment with rituximab in patients with CIDP and anti-paranodal protein antibodies. Secondary outcome measures include grip strength, manual muscle testing sum scores, results of nerve conduction studies, and other functional scales.

RESULTS

We plan to enroll 25 cases for the full analysis set. Recruitment is ongoing, with 14 patients enrolled as of January 2020. Enrollment will close in September 2020, and the study is planned to end in December 2021.

CONCLUSIONS

This randomized controlled trial will determine if rituximab is safe and effective in patients with anti-paranodal antibodies. An open-label study will provide additional data on the effects of rituximab in patients with antibody-negative CIDP. The results of the RECIPE trial are expected to provide evidence for the positioning of rituximab as a pathogenesis-based therapeutic for refractory CIDP.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03864185, https://clinicaltrials.gov/ct2/show/NCT03864185 ; The Japan Registry of Clinical Trials jRCT2041180037, https://jrct.niph.go.jp/en-latest-detail/jRCT2041180037.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/17117.

Molecular organization and function of vertebrate septate-like junctions

Septate-like junctions display characteristic ladder-like ultrastructure reminiscent of the invertebrate epithelial septate junctions and are present at the paranodes of myelinated axons. The paranodal junctions where the myelin loops attach to the axon at the borders of the node of Ranvier provide both a paracellular barrier to ion diffusion and a lateral fence along the axonal membrane. The septate-like junctions constrain the proper distribution of nodal Na⁺ channels and juxtaparanodal K⁺ channels, which are required for the safe propagation of the nerve influx and rapid saltatory conduction. The paranodal cell adhesion molecules have been identified as target antigens in peripheral demyelinating autoimmune diseases and the pathogenic mechanisms described. This review aims at presenting the recent knowledge on the molecular and structural organization of septate-like junctions, their formation and stabilization during development, and how they are involved in demyelinating diseases.

Pain and the immune system: emerging concepts of IgG-mediated autoimmune pain and immunotherapies

The immune system has long been recognised important in pain regulation through inflammatory cytokine modulation of peripheral nociceptive fibres. Recently, cytokine interactions in brain and spinal cord glia as well as dorsal root ganglia satellite glia have been identified important- in pain modulation. The result of these interactions is central and peripheral sensitisation of nociceptive processing. Additionally, new insights and the term 'autoimmune pain' have emerged through discovery of specific IgGs targeting the extracellular domains of antigens at nodal and synaptic structures, causing pain directly without inflammation by enhancing neuronal excitability. Other discovered IgGs heighten pain indirectly by T-cell-mediated inflammation or destruction of targets within the nociceptive pathways. Notable identified IgGs in pain include those against the components of channels and receptors involved in inhibitory or excitatory somatosensory synapses or their pathways: nodal and paranodal proteins (LGI1, CASPR1, CASPR2); glutamate detection (AMPA-R); GABA regulation and release (GAD65, amphiphysin); glycine receptors (GLY-R); water channels (AQP4). These disorders have other neurological manifestations of central/peripheral hyperexcitabability including seizures, encephalopathy, myoclonus, tremor and spasticity, with immunotherapy responsiveness. Other pain disorders, like complex regional pain disorder, have been associated with IgGs against β2-adrenergic receptor, muscarinic-2 receptors, AChR-nicotinic ganglionic α-3 receptors and calcium channels (N and P/Q types), but less consistently with immune treatment response. Here, we outline how the immune system contributes to development and regulation of pain, review specific IgG-mediated pain disorders and summarise recent development in therapy approaches. Biological agents to treat pain (anti-calcitonin gene-related peptide and anti-nerve growth factor) are also discussed.

Associations between HLA and autoimmune neurological diseases with autoantibodies

Recently, several autoimmune neurological diseases have been defined by the presence of autoantibodies against different antigens of the nervous system. These autoantibodies have been demonstrated to be specific and useful biomarkers, and most of them are also pathogenic. These aspects have increased the value of autoantibodies in neurological practice, as they enable to establish more accurate diagnosis and to better understand the underlying mechanisms of the autoimmune neurological diseases when they are compared to those lacking them. Nevertheless, the exact mechanisms leading to the autoimmune response are still obscure. Genetic predisposition is likely to play a role in autoimmunity, HLA being the most reported genetic factor. Herein, we review the current knowledge about associations between HLA and autoimmune neurological diseases with autoantibodies. We report the main alleles and haplotypes, and discuss the clinical and pathogenic implications of these findings.

Inflammatory polyradiculoneuropathies: Clinical and immunological aspects, current therapies, and future perspectives

Inflammatory polyradiculoneuropathies are heterogeneous disorders characterized by immune-mediated leukocyte infiltration of peripheral nerves and nerve roots leading to demyelination or axonal degeneration or both. Inflammatory polyradiculoneuropathies can be divided into acute and chronic: Guillain–Barré syndrome and chronic inflammatory demyelinating polyneuropathy and their variants. Despite major advances in immunology and molecular biology have been made in the last years, the pathogenesis of these disorders is not completely understood. This review summarizes the current literature of the clinical features and pathogenic mechanisms of inflammatory polyradiculoneuropathies and focuses on current therapies and new potential treatment for the future.

Antibodies to neurofascin, contactin-1, and contactin-associated protein 1 in CIDP: Clinical relevance of IgG isotype

OBJECTIVE

To assess the prevalence and isotypes of anti-nodal/paranodal antibodies to nodal/paranodal proteins in a large chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) cohort, compare clinical features in seronegative vs seropositive patients, and gather evidence of their isotype-specific pathogenic role.

METHODS

Antibodies to neurofascin-155 (Nfasc155), neurofascin-140/186 (Nfasc140/186), contactin-1 (CNTN1), and contactin-associated protein 1 (Caspr1) were detected with ELISA and/or cell-based assay. Antibody pathogenicity was tested by immunohistochemistry on skin biopsy, intraneural injection, and cell aggregation assay.

RESULTS

Of 342 patients with CIDP, 19 (5.5%) had antibodies against Nfasc155 (n = 9), Nfasc140/186 and Nfasc155 (n = 1), CNTN1 (n = 3), and Caspr1 (n = 6). Antibodies were absent from healthy and disease controls, including neuropathies of different causes, and were mostly detected in patients with European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS) definite CIDP (n = 18). Predominant antibody isotypes were immunoglobulin G (IgG)4 (n = 13), IgG3 (n = 2), IgG1 (n = 2), or undetectable (n = 2). IgG4 antibody-associated phenotypes included onset before 30 years, severe neuropathy, subacute onset, tremor, sensory ataxia, and poor response to intravenous immunoglobulin (IVIG). Immunosuppressive treatments, including rituximab, cyclophosphamide, and methotrexate, proved effective if started early in IVIG-resistant IgG4-seropositive cases. Five patients with an IgG1, IgG3, or undetectable isotype showed clinical features indistinguishable from seronegative patients, including good response to IVIG. IgG4 autoantibodies were associated with morphological changes at paranodes in patients' skin biopsies. We also provided preliminary evidence from a single patient about the pathogenicity of anti-Caspr1 IgG4, showing their ability to penetrate paranodal regions and disrupt the integrity of the Nfasc155/CNTN1/Caspr1 complex.

CONCLUSIONS

Our findings confirm previous data on the tight clinico-serological correlation between antibodies to nodal/paranodal proteins and CIDP. Despite the low prevalence, testing for their presence and isotype could ultimately be part of the diagnostic workup in suspected inflammatory demyelinating neuropathy to improve diagnostic accuracy and guide treatment.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that antibodies to nodal/paranodal proteins identify patients with CIDP (sensitivity 6%, specificity 100%).

Progress in Hematopoietic Stem Cell Transplantation for CIDP

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a kind of autoimmune-mediated inflammation and demyelinating disease. The etiology is mainly related to autoimmune dysfunction. The conventional treatments of CIDP have relied on immunomodulation and inhibition therapies such as adrenal cortex hormone, intravenous immunoglobulin (IVIg) and plasma exchange. Hematopoietic stem cell transplantation (HSCT) is known as a novel therapy for autoimmune disorders, which provides the chance to cure CIDP. More than 70 patients with refractory CIDP have received HSCT. The clinical symptoms and electrophysiological examination results of most patients have been improved. However, the treatment still has risks. This review describes the pathogenesis of CIDP and the current conventional treatments, and highlights the application of HSCT in CIDP, including its efficacy and safety.

Behind the pathology of macrophage-associated demyelination in inflammatory neuropathies: demyelinating Schwann cells

In inflammatory peripheral demyelinating disorders, demyelination represents segmental demyelination in which the myelin sheath of a myelinating Schwann cell (SC) is completely removed by macrophages or a partial myelin degeneration in the paranode occurring due to autoantibodies attacking the node/paranode. For the segmental demyelination from living myelin-forming SCs, macrophages infiltrate within the endoneurium and insinuate between myelin lamellae and the cytoplasm of SCs, and the myelin is then removed via phagocytosis. During the macrophage invasion into the SC cytoplasm from the node of Ranvier and internodal areas, the attacked SCs do not remain quiescent but transdifferentiate into inflammatory demyelinating SCs (iDSCs), which exhibit unique demyelination pathologies, such as myelin uncompaction from Schmidt-Lanterman incisures with myelin lamellae degeneration. The longitudinal extension of this self-myelin clearance process of iDSCs into the nodal region is associated with the degeneration of nodal microvilli and paranodal loops, which provides a potential locus for macrophage infiltration. In addition to the nodal intrusion, macrophages appear to be able to invade fenestrated internodal plasma membrane or the degenerated outer mesaxon of iDSC. These SC demyelination morphologies indicate that the SC reprogramming to iDSCs may be a prerequisite for macrophage-mediated inflammatory demyelination. In contrast, paranodal demyelination caused by autoantibodies to nodal/paranodal antigens does not result in iDSC-dependent macrophage infiltration and subsequent segmental demyelination. In the context of inflammatory demyelination, the novel perspective of iDSCs provides an important viewpoint to understand the pathophysiology of demyelinating peripheral neuropathies and establish diagnostic and therapeutic strategies.

Antibody- and macrophage-mediated segmental demyelination in chronic inflammatory demyelinating polyneuropathy: clinical, electrophysiological, immunological and pathological correlates

BACKGROUND AND PURPOSE

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a heterogeneous autoimmune disorder critically lacking diagnostic biomarkers. Autoantibodies to nodal and paranodal components have recently been described in a small subset of patients. Here, the diagnostic value of immune reactivity toward the myelin compartment was investigated.

METHODS

Ninety-four French CIDP patients were retrospectively studied. The reactivity toward the peripheral nerve was investigated. Sural nerve biopsies were examined by electron microscopy and immunofluorescence.

RESULTS

Twenty-one patients (22%) and three patients (3%) presented with a strong immunoglobulin G or immunoglobulin M reactivity respectively against the myelin compartment. The clinical, electrophysiological and morphological features were examined in nine of these patients for whom sural nerve biopsies were available. Seven patients were electrodiagnosed with definite CIDP, one with possible CIDP and one was unclassifiable but sural nerve biopsy argued for CIDP diagnosis. Electron microscopy of sural nerve biopsies demonstrated the presence of macrophage-mediated demyelination restricted to the internode in all nine patients. Immunolabelling for voltage-gated sodium channels, myelin and axonal markers confirmed the presence of segmental demyelination and of remyelination. The nodal and paranodal regions, however, were unaffected in these patients. Nerve conduction studies corroborated the multifocal and segmental profile, and seven patients showed increased duration of proximal (1.5-5.1 times) and/or distal (1.2-3.4 times) compound muscle action potential in at least two nerves.

CONCLUSION

Antibody- and macrophage-mediated demyelination appears responsible for conduction alterations in CIDP patients and nerve immunostaining assays may serve as a supportive diagnostic biomarker.

Unique HLA haplotype associations in IgG4 anti-neurofascin 155 antibody-positive chronic inflammatory demyelinating polyneuropathy

To clarify the immunogenetic background of patients with immunoglobulin G (IgG)4 anti-neurofascin 155 (NF155) antibody-positive chronic inflammatory demyelinating polyneuropathy (CIDP), we genotyped the extended human leukocyte antigen (HLA) haplotypes in 22 Japanese patients with this disorder and compared them with those of healthy Japanese controls. All IgG4 anti-NF155 antibody-positive CIDP patients exclusively carried either HLA-DRB1*15:01-DRB5*01:01-DQA1*01:02-DQB1*06:02 or -(A*24:02)-B*52:01-C*12:02-DRB1*15:02-DRB5*01:02-DQA1*01:03-DQB1*06:01, resulting in significantly increased HLA-DRB1*15, -DRB1*15:01, -DQB1*06:01/06:02, -DQB1*06:02, and -DRB1*15:01-DQB1*06:02 frequencies compared with healthy Japanese controls. These findings indicate the involvement of specific HLA class II molecules in the pathomechanisms of IgG4 anti-NF155 antibody-positive CIDP.

Acute-onset chronic inflammatory demyelinating polyneuropathy with anti-neurofascin-155 antibodies and bilateral facial nerve enhancement

A 26-year-old female presented with acute onset distal paraparesis, upper limb tremor and bilateral facial palsy. Neurophysiology revealed a sensorimotor demyelinating polyneuropathy and lumbar puncture revealed an albuminocytologic dissociation. Neuroaxis MRI revealed bilateral facial nerve and cauda equina enhancement. Initially diagnosed as Guillain-Barré Syndrome, poor response to intravenous immunoglobulin, persistent deterioration, anti-neurofascin-155 antibodies and clinical response to steroid therapy led to diagnosis of acute-onset chronic inflammatory demyelinating polyneuropathy (CIDP). CIDP patients with anti-neurofascin-155 antibodies are younger, with distal predominant weakness, tremor, and poor response to intravenous immunoglobulin. Up to 16% can present acutely, however bilateral facial weakness is rare.

Autoantibodies in immune-mediated inflammatory neuropathies

Inflammatory neuropathies are a rare and heterogeneous group of diseases of the nervous system characterized by the dysfunction and damage of different structures of the peripheral nerves. This group includes Guillain-Barré syndrome, chronic demyelinating inflammatory polyradiculoneuropathy, multifocal motor neuropathy or neuropathies associated with monoclonal gammopathy. The aetiology of these diseases is unknown, but B cells and autoantibodies play a key role in their pathogenesis. Autoantibodies against peripheral nerve molecules such as gangliosides, proteins of the Ranvier node or myelin-associated glycoprotein have been described, allowing the identification of subgroups of patients with specific clinical phenotypes. For all these reasons, these antibodies are useful in clinical practice. This review focuses on the diagnostic and therapeutic relevance of autoantibodies in inflammatory neuropathies.

[Chronic inflammatory demyelinating polyneuropathy: Diagnosis and therapeutic update]

Chronic inflammatory demyelinating polyradiculoneuropathies are acquired demyelinating neuropathies belonging to the group of autoimmune neuropathies. Since specific biological markers are present in less than 10% of cases, the diagnosis is based on the clinical and electrophysiological analysis of each patient. Furthermore, a decision-making algorithm ranking all other available paraclinical tools will guide the physician to the diagnosis of atypical forms. In nearly 80% of cases, these dysimmune neuropathies are responsive to first-line treatments, namely intravenous immunoglobulins, corticosteroids and plasma exchanges. A second line treatment may be proposed in case of no response, intolerance or inaccessibility to the three reference treatments. While some immunosuppressants or monoclonal antibodies can sometimes be very effective, there is currently no predictive marker or recommendation available to determine which treatment will be most appropriate for which patient.

Intrathecal cytokine profile in neuropathy with anti-neurofascin 155 antibody

Objective

To characterize the CSF cytokine profile in chronic inflammatory demyelinating polyneuropathy (CIDP) patients with IgG4 anti‐neurofascin 155 (NF155) antibodies (NF155⁺ CIDP) or those lacking anti‐NF155 antibodies (NF155⁻ CIDP).

Methods

Twenty‐eight CSF cytokines/chemokines/growth factors were measured by multiplexed fluorescent immunoassay in 35 patients with NF155⁺ CIDP, 36 with NF155⁻ CIDP, and 28 with non‐inflammatory neurological disease (NIND).

Results

CSF CXCL8/IL‐8, IL‐13, TNF‐α, CCL11/eotaxin, CCL2/MCP‐1, and IFN‐γ were significantly higher, while IL‐1β, IL‐1ra, and G‐CSF were lower, in NF155⁺ CIDP than in NIND. Compared with NF155⁻ CIDP, CXCL8/IL‐8 and IL‐13 were significantly higher, and IL‐1β, IL‐1ra, and IL‐6 were lower, in NF155⁺ CIDP. CXCL8/IL‐8, IL‐13, CCL11/eotaxin, CXCL10/IP‐10, CCL3/MIP‐1α, CCL4/MIP‐1β, and TNF‐α levels were positively correlated with markedly elevated CSF protein, while IL‐13, CCL11/eotaxin, and IL‐17 levels were positively correlated with increased CSF cell counts. IL‐13, CXCL8/IL‐8, CCL4/MIP‐1β, CCL3/MIP‐1α, and CCL5/RANTES were decreased by combined immunotherapies in nine NF155⁺ CIDP patients examined longitudinally. By contrast, NF155⁻ CIDP had significantly increased IFN‐γ compared with NIND, and exhibited positive correlations of IFN‐γ, CXCL10/IP‐10, and CXCL8/IL‐8 with CSF protein. Canonical discriminant analysis of cytokines/chemokines revealed that NF155⁺ and NF155⁻ CIDP were separable, and that IL‐4, IL‐10, and IL‐13 were the three most significant discriminators.

Interpretation

Intrathecal upregulation of type 2 helper T (Th2) cell cytokines is characteristic of IgG4 NF155⁺ CIDP, while type 1 helper T cell cytokines are increased in CIDP regardless of the presence or absence of anti‐NF155 antibodies, suggesting that overproduction of Th2 cell cytokines is unique to NF155⁺ CIDP.

Chronic inflammatory demyelinating polyneuropathy with anti-NF155 IgG4 in China

Patients with chronic inflammatory demyelinating polyneuropathy (CIDP) seropositive for autoantibodies against nodal and paranodal proteins display distinct clinical presentations. We herein tested for autoantibodies against neurofascin (NF) 155, NF186, contactin-associated protein 1 and contactin-1 and investigated the autoantibody-related clinical features in 29 patients with CIDP from China. Six patients with anti-NF155 IgG4 antibodies displayed younger age of onset and poor response to intravenous immunoglobulin than seronegative patients. One patient had anti-NF186 IgG antibody and no patients had anti-contactin-associated protein 1 or anti-contactin-1 antibodies. Clinical features of CIDP patients with anti-NF155 antibodies in China were similar to those reported in other countries.

Biallelic mutations in neurofascin cause neurodevelopmental impairment and peripheral demyelination

Axon pathfinding and synapse formation are essential processes for nervous system development and function. The assembly of myelinated fibres and nodes of Ranvier is mediated by a number of cell adhesion molecules of the immunoglobulin superfamily including neurofascin, encoded by the NFASC gene, and its alternative isoforms Nfasc186 and Nfasc140 (located in the axonal membrane at the node of Ranvier) and Nfasc155 (a glial component of the paranodal axoglial junction). We identified 10 individuals from six unrelated families, exhibiting a neurodevelopmental disorder characterized with a spectrum of central (intellectual disability, developmental delay, motor impairment, speech difficulties) and peripheral (early onset demyelinating neuropathy) neurological involvement, who were found by exome or genome sequencing to carry one frameshift and four different homozygous non-synonymous variants in NFASC. Expression studies using immunostaining-based techniques identified absent expression of the Nfasc155 isoform as a consequence of the frameshift variant and a significant reduction of expression was also observed in association with two non-synonymous variants affecting the fibronectin type III domain. Cell aggregation studies revealed a severely impaired Nfasc155-CNTN1/CASPR1 complex interaction as a result of the identified variants. Immunofluorescence staining of myelinated fibres from two affected individuals showed a severe loss of myelinated fibres and abnormalities in the paranodal junction morphology. Our results establish that recessive variants affecting the Nfasc155 isoform can affect the formation of paranodal axoglial junctions at the nodes of Ranvier. The genetic disease caused by biallelic NFASC variants includes neurodevelopmental impairment and a spectrum of central and peripheral demyelination as part of its core clinical phenotype. Our findings support possible overlapping molecular mechanisms of paranodal damage at peripheral nerves in both the immune-mediated and the genetic disease, but the observation of prominent central neurological involvement in NFASC biallelic variant carriers highlights the importance of this gene in human brain development and function.

Chronic inflammatory demyelinating polyneuropathy: update on diagnosis, immunopathogenesis and treatment

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated neuropathy typically characterised by symmetrical involvement, and proximal as well as distal muscle weakness (typical CIDP). However, there are several 'atypical' subtypes, such as multifocal acquired demyelinating sensory and motor neuropathy (Lewis-Sumner syndrome) and 'distal acquired demyelinating symmetric neuropathy', possibly having different immunopathogenesis and treatment responses. In the absence of diagnostic and pathogenetic biomarkers, diagnosis and treatment may be difficult, but recent progress has been made in the application of neuroimaging tools demonstrating nerve hypertrophy and in identifying subgroups of patients who harbour antibodies against nodal proteins such as neurofascin and contactin-1. Despite its relative rarity, CIDP represents a significant economic burden, mostly due to costly treatment with immunoglobulin. Recent studies have demonstrated the efficacy of subcutaneous as well as intravenous immunoglobulin as maintenance therapy, and newer immunomodulating drugs can be used in refractory cases. This review provides an overview focusing on advances over the past several years.

Simulating perinodal changes observed in immune-mediated neuropathies: impact on conduction in a model of myelinated motor and sensory axons

Immune-mediated neuropathies affect myelinated axons, resulting in conduction slowing or block that may affect motor and sensory axons differently. The underlying mechanisms of these neuropathies are not well understood. Using a myelinated axon model, we studied the impact of perinodal changes on conduction. We extended a longitudinal axon model (41 nodes of Ranvier) with biophysical properties unique to human myelinated motor and sensory axons. We simulated effects of temperature and axonal diameter on conduction and strength-duration properties. We then studied effects of impaired nodal sodium channel conductance and paranodal myelin detachment by reducing periaxonal resistance, as well as their interaction, on conduction in the 9 middle nodes and enclosed paranodes. Finally, we assessed the impact of reducing the affected region (5 nodes) and adding nodal widening. Physiological motor and sensory conduction velocities and changes to axonal diameter and temperature were observed. The sensory axon had a longer strength-duration time constant. Reducing sodium channel conductance and paranodal periaxonal resistance induced progressive conduction slowing. In motor axons, conduction block occurred with a 4-fold drop in sodium channel conductance or a 7.7-fold drop in periaxonal resistance. In sensory axons, block arose with a 4.8-fold drop in sodium channel conductance or a 9-fold drop in periaxonal resistance. This indicated that motor axons are more vulnerable to developing block. A boundary of block emerged when the two mechanisms interacted. This boundary shifted in opposite directions for a smaller affected region and nodal widening. These differences may contribute to the predominance of motor deficits observed in some immune-mediated neuropathies.NEW & NOTEWORTHY Immune-mediated neuropathies may affect myelinated motor and sensory axons differently. By the development of a computational model, we quantitatively studied the impact of perinodal changes on conduction in motor and sensory axons. Simulations of increasing nodal sodium channel dysfunction and paranodal myelin detachment induced progressive conduction slowing. Sensory axons were more resistant to block than motor axons. This could explain the greater predisposition of motor axons to functional deficits observed in some immune-mediated neuropathies.

Anti-pan-neurofascin IgG3 as a marker of fulminant autoimmune neuropathy

Objective

To identify and characterize patients with autoantibodies against different neurofascin (NF) isoforms.

Methods

Screening of a large cohort of patient sera for anti-NF autoantibodies by ELISA and further characterization by cell-based assays, epitope mapping, and complement binding assays.

Results

Two different clinical phenotypes became apparent in this study: The well-known clinical picture of subacute-onset severe sensorimotor neuropathy with tremor that is known to be associated with IgG4 autoantibodies against the paranodal isoform NF-155 was found in 2 patients. The second phenotype with a dramatic course of disease with tetraplegia and almost locked-in syndrome was associated with IgG3 autoantibodies against nodal and paranodal isoforms of NF in 3 patients. The epitope against which these autoantibodies were directed in this second phenotype was the common Ig domain found in all 3 NF isoforms. In contrast, anti–NF-155 IgG4 were directed against the NF-155–specific Fn3Fn4 domain. The description of a second phenotype of anti–NF-associated neuropathy is in line with some case reports of similar patients that were published in the last year.

Conclusions

Our results indicate that anti–pan-NF-associated neuropathy differs from anti–NF-155-associated neuropathy, and epitope and subclass play a major role in the pathogenesis and severity of anti–NF-associated neuropathy and should be determined to correctly classify patients, also in respect to possible differences in therapeutic response.

Electrodiagnostic data-driven clustering identifies a prognostically different subgroup of patients with chronic inflammatory demyelinating polyneuropathy

OBJECTIVE

This study aimed to explore the correlations between electrodiagnostic (EDX) features in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and to investigate whether EDX data-driven clustering can identify a distinct subgroup regarding clinical phenotype and treatment response.

METHODS

We reviewed clinical and EDX data of 56 patients with definite CIDP fulfilling the 2010 European Federation of Neurological Societies and Peripheral Nerve Society criteria at two teaching hospitals. A hierarchical agglomerative clustering algorithm with complete linkage was used to partition the patients into subgroups with similar EDX features. A stepwise logistic regression analysis was performed to evaluate predictors of the long-term outcome.

RESULTS

EDX data-driven clustering partitioned the patients into two clusters, identifying a distinct subgroup characterised by coexistence of prominent conduction slowing and markedly reduced distally evoked compound muscle action potential (CMAP) amplitudes. This cluster of patients was significantly over-represented by an atypical subtype (distal acquired demyelinating symmetric polyneuropathy) compared with the other cluster (70% vs 26.1%, p=0.042). Furthermore, patients in this cluster invariably showed favourable long-term treatment outcome (100% vs 63%, p=0.023). In logistic regression analyses, the initial disability (OR 6.1, 95% CI 2.4 to 25.4), F-wave latency (OR 0.93, 95% CI 0.86 to 0.98) and distal CMAP duration (OR 0.96, 95% CI 0.91 to 0.99) were significant predictors of the poor long-term outcome.

CONCLUSION

Our results show that EDX data-driven clustering could differentiate a pattern of EDX features with prognostic implication in patients with CIDP. Reduced distally evoked CMAPs may not necessarily predict poor responses to treatment, and active treatment is warranted when prominent slowing of conduction is accompanied in the distal segments.

Clinical and laboratory features of anti-MAG neuropathy without monoclonal gammopathy

Antibodies against myelin-associated glycoprotein (MAG) almost invariably appear in the context of an IgM monoclonal gammopathy associated neuropathy. Very few cases of anti-MAG neuropathy lacking IgM-monoclonal gammopathy have been reported. We investigated the presence of anti-MAG antibodies in 69 patients fulfilling diagnostic criteria for CIDP. Anti-MAG antibodies were tested by ELISA and confirmed by immunohistochemistry. We identified four (5.8%) anti-MAG positive patients without detectable IgM-monoclonal gammopathy. In two of them, IgM-monoclonal gammopathy was detected at 3 and 4-year follow-up coinciding with an increase in anti-MAG antibodies titers. In conclusion, anti-MAG antibody testing should be considered in chronic demyelinating neuropathies, even if IgM-monoclonal gammopathy is not detectable.

Peripheral Demyelinating Diseases: From Biology to Translational Medicine

Demyelinating diseases represent a spectrum of disorders that impose significant burden on global economy and society. Generally, the prognosis of these diseases is poor and there is no available cure. In recent decades, research has shed some light on the biology and physiology of Schwann cells and its neuroprotective effects in the peripheral nervous system (PNS). Insults to the PNS by various infectious agents, genetic predisposition and immune-related mechanisms jeopardize Schwann cell functions and cause demyelination. To date, there are no effective and reliable biomarkers for PNS-related diseases. Here, we aim to review the following: pathogenesis of various types of peripheral demyelinating diseases such as Guillain-Barre syndrome, Chronic Inflammatory Demyelinating Polyradiculoneuropathy, Anti-Myelin Associated Glycoprotein Neuropathy, POEMS syndrome, and Charcot-Marie-Tooth disease; emerging novel biomarkers for peripheral demyelinating diseases, and Schwann cell associated markers for demyelination.

Anti-Neurofascin-155 IgG4 antibodies prevent paranodal complex formation in vivo

Neurofascin-155 (Nfasc155) is an essential glial cell adhesion molecule expressed in paranodal septate-like junctions of peripheral and central myelinated axons. The genetic deletion of Nfasc155 results in the loss of septate-like junctions and in conduction slowing. In humans, IgG4 antibodies against Nfasc155 are implicated in the pathogenesis of chronic inflammatory demyelinating polyneuropathy (CIDP). These antibodies are associated with an aggressive onset, a refractoriness to intravenous immunoglobulin, and tremor of possible cerebellar origin. Here, we examined the pathogenic effects of patient-derived anti-Nfasc155 IgG4. These antibodies did not inhibit the ability of Nfasc155 to complex with its axonal partners contactin-1/CASPR1 or induce target internalization. Passive transfer experiments revealed that IgG4 antibodies target Nfasc155 on Schwann cell surface, and diminished Nfasc155 protein levels and prevented paranodal complex formation in neonatal animals. In adult animals, chronic intrathecal infusions of antibodies also induced the loss of Nfasc155 and of paranodal specialization and resulted in conduction alterations in motor nerves. These results indicate that anti-Nfasc155 IgG4 perturb conduction in absence of demyelination, validating the existence of paranodopathy. These results also shed light on the mechanisms regulating protein insertion at paranodes.

Completing the Immunological Fingerprint by Refractory Proteins: Autoantibody Screening via an Improved Immunoblotting Technique

PURPOSE

Identifying autoantigens of serological autoantibodies requires expensive methods, such as protein microarrays or IP+MS. Thus, sera are commonly pre-screened for interesting immunopatterns via immunocytochemistry/immunohistochemistry. However, distinguishing immunopatterns can be difficult and intracellular antigens are less accessible. Therefore, a simple and cheap immunoblot screening able to distinguish immunopatterns and to detect refractory proteins is presented.

EXPERIMENTAL DESIGN

Five steps of immunoblotting-based autoantigen screening are revised: (1) choice of protein source, (2) protein extraction, (3) protein separation, (4) protein transfer, (5) antigen detection. Thereafter, 52 patients' sera with chronic inflammatory demyelinating polyneuropathy (CIDP) and 45 controls were screened.

RESULTS

The protein source impacts the detected antigen set. Steps 2-4 can be adapted for refractory proteins. Furthermore, longitudinal cutting of protein lanes saves ≥75% of time and material and allows for exact comparison of band patterns. As the latter are individually specific and temporarily constant, we call them "immunological fingerprints". In a proof-of-principle, a 155 kDa immunoband was detected with two anti-neurofascin-155-positive CIDP sera and two further immunobands (120/220 kDa) specific to a subgroup of 3-6 of 52 CIDP patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Adapted immunoblotting is a cheap and simple method for accurate serum screening including refractory and intracellular antigens.

Neurofascin (NFASC) gene mutation causes autosomal recessive ataxia with demyelinating neuropathy

INTRODUCTION

Neurofascin, encoded by NFASC, is a transmembrane protein that plays an essential role in nervous system development and node of Ranvier function. Anti-Neurofascin autoantibodies cause a specific type of chronic inflammatory demyelinating polyneuropathy (CIDP) often characterized by cerebellar ataxia and tremor. Recently, homozygous NFASC mutations were recently associated with a neurodevelopmental disorder in two families.

METHODS

A combined approach of linkage analysis and whole-exome sequencing was performed to find the genetic cause of early-onset cerebellar ataxia and demyelinating neuropathy in two siblings from a consanguineous Italian family. Functional studies were conducted on neurons from induced pluripotent stem cells (iPSCs) generated from the patients.

RESULTS

Genetic analysis revealed a homozygous p.V1122E mutation in NFASC. This mutation, affecting a highly conserved hydrophobic transmembrane domain residue, led to significant loss of Neurofascin protein in the iPSC-derived neurons of affected siblings.

CONCLUSIONS

The identification of NFASC mutations paves the way for genetic research in the developing field of nodopathies, an emerging pathological entity involving the nodes of Ranvier, which are associated for the first time with a hereditary ataxia syndrome with neuropathy.

Measuring disease activity and predicting response to intravenous immunoglobulin in chronic inflammatory demyelinating polyneuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) is characterised by significant clinical heterogeneity and as such reliable biomarkers are required to measure disease activity and assess treatment response. Recent advances in our understanding of disease pathogenesis and the discovery of novel serum-based, electrophysiologic and imaging biomarkers allow clinicians to make more informed decisions regarding individualised treatment regimes.

As a chronic immune-mediated process typified by relapse following withdrawal of immunomodulatory therapy, a substantial proportion of patients with CIDP require long term treatment with intravenous immunoglobulin (IVIg), a scarce and expensive donor-derived resource. The required duration and intensity of immunoglobulin treatment vary widely between individuals, highlighting both the heterogeneous nature of the underlying disease process as well as the variable pharmacologic properties of IVIg.

This review outlines the use of multimodal biomarkers in the longitudinal evaluation of nerve injury and how recent developments have impacted our ability to predict both response to immunoglobulin administration and its withdrawal.

Tongue tremor in neurofascin-155 IgG4 seropositive chronic inflammatory polyradiculoneuropathy

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) with anti-neurofascin-155 antibodies is a subgroup of CIDP with tremor and poor response to intravenous immunoglobulins. A 23-year-old male presented with a 6-month history ataxic-stepping gait, stocking tactile hypoesthesia, areflexia, tremor at limbs and tongue. Neurophysiology and cerebrospinal fluid analysis supported the diagnosis of CIDP. Tongue EMG was negative. Serum was positive for neurofascin-155 IgG4. His symptoms improved with intravenous methylprednisolone and then immunoglobulins, but not the tremor. Neurofascin-155 antibodies binding to cerebellar neurons suggests its central origin. This is the first neurofascin-155 antibody-seropositive patient with also tongue tremor, who is candidate to rituximab.

Anti-neurofascin autoantibody and demyelination

Demyelination diseases involving the central and peripheral nervous systems are etiologically heterogeneous with both cell-mediated and humoral immunities playing pathogenic roles. Recently, autoantibodies against nodal and paranodal proteins, such as neurofascin186 (NF186), neurofascin155 (NF155), contactin-1 (CNTN1), contactin-associated protein 1 (CASPR1) and gliomedin, have been discovered in not only chronic demyelinating conditions, such as multiple sclerosis (MS) and chronic inflammatory demyelinating polyradiculoneuropathy, but also in acute demyelinating conditions, such as Guillain-Barré syndrome. Only a minority of these patients harbor anti-nodal/paranodal protein antibodies; however, these autoantibodies, especially IgG4 subclass autoantibodies to paranodal proteins, are associated with unique features and these conditions are collectively termed nodopathy or paranodopathy. Establishing a concept of IgG4-related nodopathy/paranodopathy contributes to diagnosis and treatment strategy because IgG4 autoantibody-related neurological diseases are often refractory to conventional immunotherapies. IgG4 does not fix complements, or internalize the target antigens, because IgG4 exists in a monovalent bispecific form in vivo. IgG4 autoantibodies can bock protein-protein interaction. Thus, the primary role of IgG4 anti-paranodal protein antibodies may be blockade of interactions between NF155 and CNTN1/CASPR1, leading to conduction failure, which is consistent with the sural nerve pathology presenting paranodal terminal loop detachment from axons with intact internodes in the absence of inflammation. However, it still remains to be elucidated how these autoantibodies belonging to the same IgG4 subclass can cause each IgG4 autoantibody-specific manifestation. Another important issue is to clarify the mechanism by which IgG4 antibodies to nodal/paranodal proteins emerge. IgG4 antibodies develop on chronic antigenic stimulation and can block antibodies that alleviate allergic inflammation by interfering with the binding of allergen-specific IgE to allergens. Thus, environmental antigens cross-reacting with nodal and paranodal proteins may warrant future study.

Tremor Associated with Chronic Inflammatory Demyelinating Polyneuropathy and Anti-Neurofascin-155 Antibodies

Background

Tremor is an underrecognized feature in certain neuropathy subtypes.

Phenomenology shown

We show a patient with a disabling neuropathic tremor and mild cerebellar syndrome associated with chronic inflammatory demyelinating polyneuropathy (CIDP) and anti-neurofascin-155 (NF155) antibodies.

Educational value

Anti-NF155 testing should be considered in patients with CIDP and disabling tremor because of therapeutic implications.

Ultrastructural mechanisms of macrophage-induced demyelination in CIDP

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a form of chronic neuropathy that is presumably caused by heterogeneous immune-mediated processes. Recent advances in the search for autoantibodies against components expressed at nodal regions, such as the nodes of Ranvier and paranodes, have substantially contributed to clarifying the pathogenesis of CIDP in a subpopulation of patients. In particular, immunoglobulin G4 (IgG4) antibodies to paranodal junction proteins, including neurofascin-155 and contactin-1, have attracted the attention of researchers. Paranodal dissection resulting from the attachment of IgG4 at paranodal junctions and the absence of macrophage-induced demyelination are characteristic pathologic features in patients who have these antibodies. By contrast, the mechanisms of neuropathy in cases with classical macrophage-induced demyelination remain unclear despite the long-standing recognition of this process in CIDP. In addition to complement-dependent damage provoked by autoantibodies, recent studies have shed light on antibody-dependent phagocytosis by macrophages without participation of complements. However, a direct association between specific autoantibodies and macrophage-induced demyelination has not been reported. Electron microscopic examination of longitudinal sections of sural nerve biopsy specimens suggested that macrophages recognize specific sites of myelinated fibers as the initial target of demyelination. The site that macrophages select to initiate myelin breakdown is located around the nodal regions in some patients and internode in others. Hence, it seems that the components that distinguish between the nodal regions and internode play a pivotal role in the behavior of macrophages that initiate phagocytosis of myelin. Further studies are needed to elucidate the mechanisms underlying macrophage-induced demyelination from this perspective.

Neurofascin-155 IgM autoantibodies in patients with inflammatory neuropathies

OBJECTIVES

Recently, IgG autoantibodies against different paranodal proteins have been detected and this has led to important advances in the management of inflammatory neuropathies. In contrast, not much is known on IgM autoantibodies against paranodal proteins.

METHODS

In the present study, we screened a large cohort of patients (n=140) with inflammatory neuropathies for IgM autoantibodies against neurofascin-155, neurofascin-186 or contactin-1.

RESULTS

IgM autoantibodies against neurofascin-155 were detected by ELISA in five patients, four with inflammatory demyelinating polyradiculoneuropathy (CIDP) and one with Guillain-Barré syndrome (GBS), and were confirmed by ELISA-based preabsorption experiments and Western blot. Titres ranged from 1:100 to 1:400. We did not detect IgM anti-neurofascin-186 or anti-contactin-1 antibodies in this cohort. All patients presented with distally accentuated tetraparesis and hypesthesia. Remarkably, tremor was present in three of the patients with CIDP and occurred in the patients with GBS after the acute phase of disease. Nerve conduction studies revealed prolonged distal motor latencies and F wave latencies. Nerve biopsies showed signs of secondary axonal damage in three of the patients, demyelinating features in one patient. Teased fibre preparations did not demonstrate paranodal damage.

CONCLUSION

In summary, IgM neurofascin-155 autoantibodies may be worth testing in patients with inflammatory neuropathies. Their pathogenic role needs to be determined in future experiments.

Homozygous mutation in the Neurofascin gene affecting the glial isoform of Neurofascin causes severe neurodevelopment disorder with hypotonia, amimia and areflexia

The Neurofascins (NFASCs) are a family of proteins encoded by alternative transcripts of NFASC that cooperate in the assembly of the node of Ranvier in myelinated nerves. Differential expression of NFASC in neurons and glia presents a remarkable example of cell-type specific expression of protein isoforms with a common overall function. In mice there are three NFASC isoforms: Nfasc186 and Nfasc140, located in the axonal membrane at the node of Ranvier, and Nfasc155, a glial component of the paranodal axoglial junction. Nfasc186 and Nfasc155 are the major isoforms at mature nodes and paranodes, respectively. Conditional deletion of the glial isoform Nfasc155 in mice causes severe motor coordination defects and death at 16-17 days after birth. We describe a proband with severe congenital hypotonia, contractures of fingers and toes, and no reaction to touch or pain. Whole exome sequencing revealed a homozygous NFASC variant chr1:204953187-C>T (rs755160624). The variant creates a premature stop codon in 3 out of four NFASC human transcripts and is predicted to specifically eliminate Nfasc155 leaving neuronal Neurofascin intact. The selective absence of Nfasc155 and disruption of the paranodal junction was confirmed by an immunofluorescent study of skin biopsies from the patient versus control. We propose that the disease in our proband is the first reported example of genetic deficiency of glial Neurofascin isoforms in humans and that the severity of the condition reflects the importance of the Nfasc155 in forming paranodal axoglial junctions and in determining the structure and function of the node of Ranvier.

Immune-mediated neuropathies

Since the discovery of an acute monophasic paralysis, later coined Guillain-Barré syndrome, almost 100 years ago, and the discovery of chronic, steroid-responsive polyneuropathy 50 years ago, the spectrum of immune-mediated polyneuropathies has broadened, with various subtypes continuing to be identified, including chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN). In general, these disorders are speculated to be caused by autoimmunity to proteins located at the node of Ranvier or components of myelin of peripheral nerves, although disease-associated autoantibodies have not been identified for all disorders. Owing to the numerous subtypes of the immune-mediated neuropathies, making the right diagnosis in daily clinical practice is complicated. Moreover, treating these disorders, particularly their chronic variants, such as CIDP and MMN, poses a challenge. In general, management of these disorders includes immunotherapies, such as corticosteroids, intravenous immunoglobulin or plasma exchange. Improvements in clinical criteria and the emergence of more disease-specific immunotherapies should broaden the therapeutic options for these disabling diseases.

Detection Methods for Autoantibodies in Suspected Autoimmune Encephalitis

This review provides an overview on different antibody test methods that can be applied in cases of suspected paraneoplastic neurological syndromes (PNS) and anti-neuronal autoimmune encephalitis (AIE) in order to explain their diagnostic value, describe potential pitfalls and limitations, and discuss novel approaches aimed at discovering further autoantibodies. Onconeuronal antibodies are well-established biomarkers for PNS and may serve as specific tumor markers. The recommended procedure to detect onconeuronal antibodies is a combination of indirect immunohistochemistry on fixed rodent cerebellum and confirmation of the specificity by line assays. Simplification of this approach by only using line assays with recombinant proteins bears the risk to miss antibody-positive samples. Anti-neuronal surface antibodies are sensitive and specific biomarkers for AIE. Their identification requires the use of test methods that allow the recognition of conformation dependent epitopes. These commonly include cell-based assays and tissue based assays with unfixed rodent brain tissue. Tissue based assays can detect most of the currently known neuronal surface antibodies and thus enable broad screening of biological samples. A complementary testing on live neuronal cell cultures may confirm that the antibody recognizes a surface epitope. In patients with peripheral neuropathy, the screening may be expanded to teased nerve fibers to identify antibodies against the node of Ranvier. This method helps to identify a novel subgroup of peripheral autoimmune neuropathies, resulting in improved immunotherapy of these patients. Tissue based assays are useful to discover additional autoantibody targets that play a role in diverse autoimmune neurological syndromes. Antibody screening assays represent promising avenues of research to improve the diagnostic yield of current assays for antibody-associated autoimmune encephalitis.

Association of neurofascin IgG4 and atypical chronic inflammatory demyelinating polyneuropathy: A systematic review and meta-analysis

BACKGROUND

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is the most commonly observed phenotype among chronic acquired demyelinating polyneuropathies and is clinically variable. The aim of this meta-analysis was to evaluate the diagnostic value and characteristics of CIDP targeting neurofascin 155 (NF155).

METHODS

A systematic literature search was performed on March 2018, and two reviewers independently extracted data and assessed the risk of bias on MEDLINE, EMBASE, the Web of Science, and the Cochrane Library to identify relevant articles.

RESULTS

Ten articles for the NF155 protein test with 1,161 patients and 1,636 controls were identified. The results showed that the pooled sensitivity was 0.09 (95% CI: 0.06-015), and specificity was 1.00 (95% CI: 0.98-1.00) of the NF155 for CIDP. The meta-analysis revealed that the sensory ataxic occurrence rate (OR: 10.79, 95% CI: 5.24-22.22) and tremor occurrence rate (OR: 6.71, 95% CI: 3.37-13.39) were higher among patients positive for NF155 compared with NF155-negative CIDP patients. However, the rate of good treatment response to intravenous immunoglobulin (IVIg) (OR: 0.09, 95% CI: 0.02-0.42) was lower in NF155-positive CIDP patients.

CONCLUSIONS

NF155 is a specific protein marker for CIDP, but its diagnostic value has been questioned due to low sensitivity. However, as an antibody against paranodal antigens, NF155 seems more valuable in defining clinical subsets of CIDP.