Genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes.

PURPOSE OF REVIEW: We summarize the recent discoveries on genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes (PNS), emphasizing clinical and pathophysiological implications. RECENT FINDINGS: The human leukocyte antigen (HLA) is the most studied genetic factor in autoimmune encephalitis and PNS. The HLA haplotype 8.1, which is widely known to be related to systemic autoimmunity, has been only weakly associated with a few types of autoimmune encephalitis and PNS. However, the strongest and most specific associations have been reported in a subgroup of autoimmune encephalitis that comprises antileucine-rich glioma-inactivated 1 (LGI1) limbic encephalitis, associated with DRB1∗07 : 01 , anticontactin-associated protein-like 2 (CASPR2) limbic encephalitis, associated with DRB1∗11 : 01 , and anti-IgLON5 disease, associated with DRB1∗10 : 01∼DQA1∗01∼DQB1∗05 . Non-HLA genes have been poorly investigated so far in autoimmune encephalitis, mainly in those lacking HLA associations such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, with only a few genome-wide association studies (GWAS) reporting equivocal results principally limited by small sample size. SUMMARY: Genetic predisposition seems to be driven mostly by HLA in a group of autoimmune encephalitis characterized by being nonparaneoplastic and having predominantly IgG4 autoantibodies. The contribution of non-HLA genes, especially in those diseases lacking known or strong HLA associations, will require large cohorts enabling GWAS to be powerful enough to render meaningful results.

Different Genetic Signatures of Small-Cell Lung Cancer Characterize Anti-GABAB R and Anti-Hu Paraneoplastic Neurological Syndromes.

OBJECTIVE: Small-cell lung cancer (SCLC) is the malignancy most frequently associated with paraneoplastic neurological syndromes (PNS) and can trigger different antibody responses against intracellular (Hu) or neuronal surface (GABAB R) antigens. Our aim was to clarify whether the genomic and transcriptomic features of SCLC are different in patients with anti-GABAB R or anti-Hu PNS compared with SCLC without PNS. METHODS: A total of 76 SCLC tumor samples were collected: 34 anti-Hu, 14 anti-GABAB R, and 28 SCLC without PNS. The study consisted of 4 steps: (1) pathological confirmation; (2) next generation sequencing using a panel of 98 genes, including those encoding the autoantibodies targets ELAVL1-4, GABBR1-2, and KCTD16; (3) genome-wide copy number variation (CNV); and (4) whole-transcriptome RNA sequencing. RESULTS: CNV analysis revealed that patients with anti-GABAB R PNS commonly have a gain in chromosome 5q, which contains KCTD16, whereas anti-Hu and control patients often harbor a loss. No significantly different number of mutations regarding any onconeural genes was observed. Conversely, the transcriptomic profile of SCLC was different, and the differentially expressed genes allowed effective clustering of the samples into 3 groups, reflecting the antibody-based classification, with an overexpression of KCTD16 specific to anti-GABAB R PNS. Pathway analysis revealed that tumors of patients with anti-GABAB R encephalitis were enriched in B-cell signatures, as opposed to those of patients with anti-Hu, in which T-cell- and interferon-γ-related signatures were overexpressed. INTERPRETATION: SCLC genetic and transcriptomic features differentiate anti-GABAB R, anti-Hu, and non-PNS tumors. The role of KCTD16 appears to be pivotal in the tumor immune tolerance breakdown of anti-GABAB R PNS. ANN NEUROL 2023;94:1102-1115.

Disruption of RNA Metabolism in Neurological Diseases and Emerging Therapeutic Interventions.

RNA binding proteins are critical to the maintenance of the transcriptome via controlled regulation of RNA processing and transport. Alterations of these proteins impact multiple steps of the RNA life cycle resulting in various molecular phenotypes such as aberrant RNA splicing, transport, and stability. Disruption of RNA binding proteins and widespread RNA processing defects are increasingly recognized as critical determinants of neurological diseases. Here, we describe distinct mechanisms by which the homeostasis of RNA binding proteins is compromised in neurological disorders through their reduced expression level, increased propensity to aggregate or sequestration by abnormal RNAs. These mechanisms all converge toward altered neuronal function highlighting the susceptibility of neurons to deleterious changes in RNA expression and the central role of RNA binding proteins in preserving neuronal integrity. Emerging therapeutic approaches to mitigate or reverse alterations of RNA binding proteins in neurological diseases are discussed.

Mutated cancer autoantigen implicated cause of paraneoplastic myasthenia gravis.

INTRODUCTION: Antitumor immune responses are postulated to initiate paraneoplastic neurological disorders when proteins that are normally restricted to neural cells are expressed as oncoproteins. Mutated oncopeptides could bypass self-tolerant T cells to activate cytotoxic effector T lymphocytes and requisite helper T lymphocytes to stimulate autoantibody production by B lymphocytes. METHODS: We investigated muscle-type nicotinic acetylcholine receptor (AChR) antigen expression at transcriptional and protein levels in a small-cell lung cancer line (SCLC) established from a patient with AChR-immunoglobulin G (IgG)-positive myasthenia gravis. RESULTS: We identified messenger RNA transcripts encoding the 2 AChR α1-subunit isoforms and 7 alternative-splicing products, 3 of which yielded premature stop codons. Despite detecting native muscle-type AChR pentamers in the tumor, we did not identify mutant α1-peptides. However, we found α1-subunit-derived peptides bound to tumor major histocompatibility complex (MHC)1-protein. In a control SCLC from an antineuronal nuclear autoantibody, type 1 (anti-Hu)-IgG-positive patient, we identified MHC1-complexed Hu protein-derived peptides but not AChR peptides. DISCUSSION: Our findings support onconeural protein products as pertinent immunogens initiating paraneoplastic neurological autoimmunity. Muscle Nerve 58: 600-604, 2018.

Clinicopathological case: progressive somnolence and dementia in an accountant: when the shine rubs off the gold standard.

A 63-year-old accountant developed progressive somnolence, cognitive decline, gait disturbance and cerebellar dysfunction with autonomic features. This report documents the clinicopathological conference at the 39th Edinburgh Advanced Neurology Course 2017.

A case of acute paraneoplastic neurological syndrome in BRAF mutant metastatic melanoma.

A 58-year-old man with indolent metastatic BRAF mutant melanoma presented with several days' history of progressive ataxia and dysdiadochokinesia. His PET/computed tomography restaging scan indicated two new fluorine-18-fluorodeoxyglucose-avid mesenteric lymph nodes. Meanwhile, his MRI brain and whole spine were within normal limits. A lumbar puncture indicated an elevated protein level with a normal cell count and negative paraneoplastic antibodies. Because of the lack of an alternative differential, the diagnosis of paraneoplastic syndrome was made. He was started on high-dose corticosteroids as well as dabrafenib and trametinib. Despite this, his neurological symptoms continued to progress. Consequently, he was trialed on a course of intravenous immunoglobulin, which stabilized his symptoms. He continued to improve over several weeks, with near-complete resolution of all his neurological symptoms, and showed a complete radiological response of his disease. To our knowledge, this is the first reported case of paraneoplastic neurological syndrome with mixed neurology associated with BRAF mutant cutaneous melanoma that responded to BRAF targeted therapy.

Autoimmune channelopathies in paraneoplastic neurological syndromes.

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Paraneoplastic neuromyelitis optica spectrum disorder associated with metastatic carcinoid expressing aquaporin-4.

IMPORTANCE: Reports of neuromyelitis optica spectrum disorder (NMOSD) occurring in the setting of neoplasia suggest that aquaporin-4 autoimmunity may in some cases have a paraneoplastic basis. OBSERVATIONS: In this case report, we describe a patient with NMOSD whose test results were seropositive for aquaporin-4 IgG and who had a hepatic metastasis from a small-bowel neuroendocrine tumor. The tumor cells expressed aquaporin-4 immunoreactivity. She presented to the Neurology Department at Wayne State University with bilateral leg weakness, ascending paresthesias, and decreased sensation. CONCLUSIONS AND RELEVANCE: This case extends the context of NMOSD as a paraneoplastic disorder.

Paraneoplastic disorders of the central and peripheral nervous systems.

Paraneoplatic neurologic syndromes (PNS) have been seminally defined as acute or subacute neurological syndromes resulting from nervous system dysfunction that is remote from the site of a malignant neoplasm or its metastases. However, in respect to our current understanding of their pathogenesis we may redefine these disorders as cancer-related dysimmune neurologic syndromes. We first deal with the epidemiology and the pathogenesis of PNS, then the different classic PNS are reviewed with clinical features according to the associated onconeuronal antibodies. Finally, therapeutic approaches are discussed.

Human epidermal growth factor receptor 2 overexpression in breast cancer of patients with anti-Yo--associated paraneoplastic cerebellar degeneration.

Isolated case reports suggest that breast tumors from patients with paraneoplastic cerebellar degeneration (PCD) and Yo antibodies overexpress human epidermal growth factor receptor 2 (HER2). HER2 overexpression is present in 15%-25% of breast cancers and is associated with poor prognosis. We retrospectively analyzed the status of HER2 in breast tumors of 27 patients with anti-Yo-associated PCD to evaluate whether HER2 overexpression in this group of patients is higher than expected. In addition, we analyzed HER2 status of 19 breast tumors from patients with paraneoplastic neurological syndromes and Ri antibodies to see whether HER2 was specifically related to anti-Yo-associated PCD. We also assessed cdr2 expression (the onconeural antigen recognized by Yo antibodies) in 21 HER2-positive breast tumors from patients without paraneoplastic neurological syndromes. HER2 was overexpressed in 26 patients (96.3%) with anti-Yo-associated PCD but only in 2 patients (10.5%) with paraneoplastic neurological syndromes associated with Ri antibodies (P< .0001). Only 5 (23.8%) of the 21 HER2-positive breast tumors showed cdr2 immunoreactivity. This study shows a very high frequency of HER2 overexpression in breast cancers in patients with anti-Yo-associated PCD but not in those from patients with Ri antibodies. Although the expression of cdr2 onconeural antigen is not high in HER2-positive breast cancers, HER2 overexpression seems to be an important requirement to develop an anti-Yo-associated PCD.

Thymoma and paraneoplastic myasthenia gravis.

Paraneoplastic autoimmune diseases associate occasionally with small cell lung cancers and gynecologic tumors. However, myasthenia gravis (MG) occurs in at least 30% of all patients with thymomas (usually present at MG diagnosis). These epithelial neoplasms almost always have numerous admixed maturing polyclonal T cells (thymocytes). This thymopoiesis-and export of mature CD4(+)T cells-particularly associates with MG, though there are rare/puzzling exceptions in apparently pure epithelial WHO type A thymomas. Other features potentially leading to inefficient self-tolerance induction include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules in thymomas, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signaling. However, the strong focus on MG/neuromuscular targets remains unexplained and suggests some biased autoantigen expression, T-cell selection, or autoimmunization within thymomas. There must be further clues in the intriguing serological and cellular parallels in some patients with late-onset MG but without thymomas-and in others with AIRE mutations-and in the contrasts with early-onset MG, as discussed here.

Peptides derived from the onconeural HuD protein can elicit cytotoxic responses in HHD mouse and human.

Anti-Hu syndrome is a paraneoplastic neurologic disease seemingly associated with an efficient antitumoral immune response against HuD protein expressed by both small cell lung cancer (SCLC) and neurons. Since anti-Hu antibodies are not pathogenic, and oligoclonal CD8(+) T cells infiltrate neoplastic and nervous tissues, we examined MHC class I-restricted immunogenicity of human HuD. Among 14 HuD-derived peptides potentially immunogenic in HLA-A*0201 restriction, 10 had actual in vitro binding capacity to the HLA molecule, 8 elicited specific cytotoxic T lymphocytes (CTLs) in a humanized murine model after peptidic vaccination, 2 also elicited specific CTLs in healthy humans, and 1 was naturally processed and presented to the immune system.

Cell-specific RNA-binding proteins in human disease.

Cell-specific RNA-binding proteins (RBPs) are involved in a variety of processes that are critical for appropriate protein expression (e.g., alternative splicing of messenger RNAs and translational control). Perturbation of the normal functions of RBPs has been implicated in a number of clinical disorders. Disease-related RBPs include the CELF proteins, which are believed to play roles in normal heart and skeletal muscle development and in the pathology of myotonic dystrophy; the Nova autoimmune antigens, which are neuron-specific proteins involved in the pathogenesis of the neurodegenerative syndrome paraneoplastic opsoclonus-myoclonus ataxia; and the alphaCP proteins, which were originally discovered by virtue of their connection to alpha thalassemia. These proteins are representative of a potentially large repertoire of cell-specific RBPs that, together, help to distinguish among the various cell types. Structure/function studies of these RBPs have begun to yield important insights into how they help to shape the protein expression programs unique to heart, skeletal muscle, brain, and other tissues.

Neuroblastic tumors associated with opsoclonus-myoclonus syndrome: histological, immunohistochemical and molecular features of 15 Italian cases.

The aim of this study was to investigate the histological, immunohistochemical and molecular features of a series of children with neuroblastic tumors (NTs) and opsoclonus-myoclonus syndrome (OMS). Of 1187 children (age 0-15 years) with previously untreated NTs registered between 1979 and 1995, 15 (1.3%) had OMS at presentation. The majority of patients showed favorable biological characteristics, such as lack of amplification of the neuroblastoma-associated avian myelocytomatosis homolog MYCN oncogene and aneuploid nuclear DNA content. Tumor histology was reviewed according to the International Neuroblastoma Pathology Classification. Histology of the 15 cases of NTs with OMS was ganglioneuroblastoma, intermixed, in 10 patients; ganglioneuroma, maturing, in 1; and neuroblastoma in 4. Of 15 tumors, 12 (10 ganglioneuroblastomas, 2 neuroblastomas) showed abundant interstitial or perivascular lymphoid infiltrates, the latter often organized in secondary lymphoid follicles. The three remaining cases had only minimal infiltrates. A review of 91 cases of age- and stage-matched neuroblastic tumors not associated with OMS tested as controls showed that the degree of lymphoid infiltration was significantly lower than that detected in OMS-related tumors. Furthermore, lymphoid follicles were always present in the latter tumors, whereas they were detected only in a few ganglioneuroma, intermixed tumors from the control group. In conclusion, ganglioneuroblastoma, intermixed subtype, lack of MYCN amplification, aneuploid DNA content and presence of lymphoid infiltrates may contribute to favorable prognosis in NTs associated with OMS.

Autoantigen diversity in the opsoclonus-myoclonus syndrome.

Despite circumstantial evidence that opsoclonus-myoclonus (OM) is often immune mediated, no specific autoantigen has been identified. Using sera of 21 patients with several types of OM (idiopathic, associated to small cell lung cancer, and associated to neuroblastoma), we probed a brainstem cDNA library to isolate target neuronal antigens. Thirty-seven clones coding for 25 proteins were isolated, with two groups of autoantigens emerging: (1) proteins of the postsynaptic density, among them the adenomatous polyposis coli, and 2) proteins with expression or function restricted to neurons, including RNA or DNA-binding proteins and zinc-finger proteins. Usually, each patient's serum recognized a different autoantigen, except for adenomatous polyposis coli that was recognized by sera of two patients with idiopathic OM and two control patients with nystagmus, diplopia, and paraneoplastic brainstem dysfunction. Overall, in the indicated types of OM, (1) we found frequent and heterogeneous immunity to neuronal autoantigens without a single specific antibody marker of OM, (2) the occasional detection of antibodies to known onconeuronal antigens (ie, Hu proteins) probably is related to cancer-induced immunity rather than to OM, and (3) the postsynaptic density is a frequent source of novel autoantigens, with several proteins of this complex targeted by antibodies of OM patients.

[Cloning, expression and purification of neural specific HuD cDNA].

OBJECTIVE: To prokaryoticly express and purify HuD protein and its RNA recognition motifs. METHODS: HuD protein was prokaryoticly expressed and purified by molecular cloning technology. Its biologic activity was testified by Western Blot. RESULTS: Purified HuD protein and its RNA recognized motifs were observed. CONCLUSIONS: The result might aid for basic research and clinical application.

Phenotypic and neuropathologic heterogeneity of anti-Hu antibody-related paraneoplastic syndrome presenting with progressive dysautonomia: report of two cases.

The anti-Hu antibody (HuAb) is directed against RNA-associated neuronal proteins and is known to cause paraneoplastic encephalomyelitis/sensory neuronopathy syndrome mostly when associated with small cell lung cancer (SCLC). Paraneoplastic encephalomyelitis/sensory neuronopathy syndrome with concurrent autonomic neuropathy has been reported to occur in paraneoplastic syndromes, although its occurrence concomitant with acute pandysautonomia is less frequent. The authors describe the clinical, neuropathologic, and serologic features of two cases with an anti-Hu-related paraneoplastic syndrome presenting with progressive autonomic neuropathy. Both patients showed features of dysautonomia, including postural dizziness, abdominal pain, and diarrhea, and symptoms of sensory neuropathy. Investigations disclosed severe sensory and autonomic neuropathy and positive HuAb titers. The disease of patient 1 had a very rapid progression, and the patient died of cardiac arrest within 2 months of the onset of symptoms. The autopsy revealed SCLC. In contrast, the disease of patient 2 had a less aggressive course. An extensive tumor search disclosed SCLC only 28 months after onset of symptoms, and the patient died 1 month later of cardiorespiratory arrest. Autopsies in both cases showed inflammation involving the intermediolateral columns and the dorsal root ganglia. These two cases illustrate the association of early dysautonomia with HuAb-related paraneoplastic syndrome and the variations of clinical, neuropathologic, and serologic findings in these types of cases.

[Paraneoplastic neurological syndromes: from the diagnosis of exclusion to the use of immunological and molecular markers]. / Síndromes neurológicos paraneoplásicos: desde el diagnóstico de exclusión a la utilización de marcadores inmunológicos y moleculares.

For many years paraneoplastic neurological syndromes have been identified through the exclusion of other neurological complications in patients with cancer. The discovery that many paraneoplastic syndromes are associated with immunological reactions allows a specific and comprehensive definition of these disorders, which often can be promptly recognized by the serological detection of antineuronal antibodies. In a significant number of paraneoplastic syndromes the genes coding for the target onconeuronal antigens have been cloned and their functions are being elucidated. This study reviews the pathogenic mechanisms of paraneoplastic neurological syndromes and addresses the most frequently asked questions regarding their diagnosis and treatment.