Anti-IgLON5 disease: a novel topic beyond neuroimmunology

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

IgLON5 autoimmunity in a patient with Creutzfeldt-Jakob disease: case report and review of literature

Objective

We present the case of a patient with clinical and imaging features of sporadic Creutzfeldt-Jakob disease (sCJD) and positive IgLON5 antibodies (Abs) in the serum and CSF.

Case report

A 66-year-old Chinese man presented to the hospital with a stroke-like episode, followed by rapidly progressive cognitive decline, mutism, and parkinsonism. The MRI results showed a cortical ribboning sign in diffusion-weighted MRI, periodic triphasic waves with a slow background in EEG, and positive protein 14-3-3 in CSF. There were matching IgLON5 Abs in the serum and CSF. A literature review showed positive autoimmune encephalitis Abs or autoimmune inflammatory disease between 0.5 and 8.6% among patients with clinical suspicion of CJD, most commonly anti-voltage-gated potassium channel (VGKC) complex and anti-N-methyl-D-aspartate receptor (NMDAR) Abs; however, IgLON5 autoimmunity in CJD has been rarely reported. This is an intriguing association as both conditions have been associated with brain deposits of phosphorylated tau protein.

Conclusion

IgLON5 Abs may be observed in patients with a diagnosis of CJD; it is unknown whether a synergistic effect of IgLON5 Abs with CJD exists, increasing neurodegenerative changes.

Coexistence of anti-NMDAR and anti-IgLON5 antibodies in an autoimmune encephalitis patient: The first case report

Background

The coexistence of autoimmune encephalitis (AE) with multiple neural auto-antibodies is of great clinical significance because overlying antibodies may cause superposition or variation of clinical syndrome, which increases the difficulty of diagnosis and treatment of the disease. To the best of our knowledge, the coexistence of anti-N-methyl d-aspartate Receptor (NMDAR) and anti-IgLON5 antibodies in AE has not been published previously.

Case presentation

A 38-year-old female patient presented to our hospital due to headache and abnormal psychiatric behavior. Based on her clinical manifestations (psychiatric and behavioral abnormalities, involuntary limb movements, and sleep disorders) and laboratory assessment results (positive human leukocyte antigen (HLA)-DQB1*05:01 haplotype, anti-NMDAR, and anti-IgLON5 antibodies), she was diagnosed as AE with coexisting anti-NMDAR and anti-IgLON5 antibodies. After treatment with intravenous methylprednisolone and immunoglobulin, as well as plasmapheresis, her symptoms gradually improved with exception for the sleep disorders. Although oral prednisone acetate and mycophenolate mofetil were continued after discharge, her symptoms of sleep disorders did not improve at 6-month follow-up.

Conclusion

This is the first case of AE co-existing with anti-NMDAR and anti-IgLON5 antibodies. Co-existence of neural auto-antibodies should be considered when patients present with overlapping or atypical symptoms. Special attention should be paid to the treatment of these patients as some anti-IgLON5 encephalitis patients may not benefit from immunotherapy treatment.

A Case Report and Literature Review on Positivity for Multiple Antibodies: Autoimmune Encephalitis in Focus

Autoimmune encephalitis (AE) is a group of neuropsychiatric disorders caused by antibodies that target the neuronal surface, synaptic, or intracellular antigens, impairing brain function. Although AE can affect people of different age groups, the occurrence of AE within specific age brackets depends on the specific type of AE and the antibodies produced. While AE is frequently considered a paraneoplastic syndrome linked to cancer, it is essential to acknowledge that the intensity of this association can vary depending on the specific antibody, leading to diverse relationships with paraneoplastic syndromes. Numerous cases have been recorded where AE manifests without an underlying malignancy. The diagnostic criteria for AE are characterized by a subacute deterioration of cognition, altered mental status, or psychiatric symptoms. Immunotherapy is recommended as a treatment for the condition, and the prognosis varies depending on the subtype. In this case, we present the case of an elderly woman who showed acute mental status changes, psychiatric symptoms, EEG alterations, and positive antibody results in both serum and CSF. Our case breaks new ground as the first documented instance of a female with positive serum anti-LGI 1, anti-AMPAR2, anti-Ri, and anti-CENP-A/B antibodies.

Purified Serum IgG from a Patient with Anti-IgLON5 Antibody Cause Long-Term Movement Disorders with Impaired Dopaminergic Pathways in Mice

Background: Anti-IgLON5 disease is a rare autoimmune disease of the central nervous system. It typically manifests as a chronic condition, characterized by cognitive impairments, movement disorders, and sleep disorders. The mechanisms underlying movement disorders in this disease remain poorly understood due to a lack of research. Furthermore, this disease exhibits both neuroimmune and neurodegenerative characteristics. The objective of this study is to explore the underlying mechanisms of movement disorders caused by anti-IgLON5 antibodies for the first time. Methods: Antibodies were purified from the serum of a confirmed patient of anti-IgLON5 disease. The passive transfer animal models were employed, where antibodies were continuously injected into the substantia nigra pars compacta (SNc) of the mouse midbrain using stereotactic injection to explore the mechanism of movement disorder. The effects of anti-IgLON5 antibodies on dopaminergic neurons in the SNc and neurodegeneration were examined through immunohistochemistry. Changes in neurotransmitter levels in the basal ganglia were assessed using high-performance liquid chromatography. Additionally, RNA-seq was employed to identify the differentially expressed genes associated with the short-term and long-term effects of anti-IgLON5 antibody on the SNc. Results: Mice injected with anti-IgLON5 antibodies in the SNc exhibited persistent movement impairments for up to 3 months. One week after antibody injection, the number of TH neurons significantly decreased compared to the control group, accompanied by reduced projection fibers in the basal ganglia and decreased dopamine levels. After 3 months of antibody injection, an increase in phosphorylated Tau was observed in the SNc of the midbrain. Additionally, long-term sustained activation of microglia was detected in the SNc. The differentially expressed genes of long-term effects of IgLON5 antibodies were different from their short-term effects on the SNc. Conclusion: Purified serum IgG from a patient with anti-IgLON5 antibodies can cause long-term movement disorder in mice. The movement disorders appear to be linked to the impaired dopaminergic pathway, and the increased p-Tau showed neurodegenerative changes induced by the anti-IgLON5 antibody.

Functional changes in neuronal circuits due to antibody-driven autoimmune response

Autoimmune-mediated encephalitis syndromes are increasingly being recognized as important clinical entities. They need to be thought of as differential diagnosis in any patient presenting with fast-onset psychosis or psychiatric problems, memory deficits or other cognitive problems, including aphasias, as well as seizures or motor automatisms, but also rigidity, paresis, ataxia or dystonic / parkinsonian symptoms. Diagnosis including imaging and CSF search for antibodies needs to be fast, as progression of these inflammatory processes is often causing scarring of brain tissue, with hypergliosis and atrophy. As these symptoms show, the autoantibodies present in these cases appear to act within the CNS. Several of such antibodies have by now been identified such as IgG directed against NMDA-receptors, AMPA receptors, GABA_A and GABA_B receptors, and voltage gated potassium channels and proteins of the potassium channel complex (i.e. LGI1 and CASPR2). These are neuropil / surface antigens where antibody interaction can well be envisaged to cause dysfunction of the target protein, including internalization. Others, such as antibodies directed against GAD65 (an intracellular enzyme responsible for GABA-synthesis from glutamate), are discussed to constitute epiphenomena, but not causal agents in disease progression. This review will focus on the current knowledge of antibody interaction mechanisms, especially discussing cellular excitability changes and synaptic interactions in hippocampal and other brain networks. One challenge in this context is to find viable hypotheses for the emergence of both, hyperexcitability and seizures, and presumably reduced synaptic plasticity and underlying cognitive dysfunction.