McKeon, Andrew

Gephyrin is a postsynaptic scaffold protein essential for inhibitory neurotransmission. Gephyrin‐immunoglobulin G (IgG) was reported, decades ago, in a single case of paraneoplastic stiff‐person‐like syndrome, but its broader clinical relevance remains unknown. While investigating unclassified synaptic IgGs mimicking amphiphysin‐IgG, we identified gephyrin‐IgG in 3 patients using human protein microarray. Gephyrin specificity was confirmed using confocal tissue‐based immunofluorescence assay, cell‐based assay, and Western blot. The 3 patients, all female, had: encephalitis (2) and myeloneuropathy and breast cancer (1). All had inflammatory cerebrospinal fluid and abnormal magnetic resonance imaging, and improved following immunotherapy. Gephyrin‐IgG is associated with a treatable autoimmune neurological disease, sometimes paraneoplastic. ANN NEUROL 2026

Abstract Severe neuropathies with predominant involvement of motor fibres can resemble lower motor neuron disease (LMND) phenotypes. Given the fatal prognosis of LMND, identifying underlying autoimmune syndromes is crucial to provide treatment options to patients. We investigated a novel autoantibody binding pattern observed on murine teased sciatic nerve fibres. Target antigens were identified using immunoprecipitation combined with mass spectrometry. Target specificity of these autoantibodies was validated in cell-based assays, neutralization assays and knock-out models. A retrospective study cohort consisting of different neuropathies (chronic inflammatory demyelinating polyradiculopathy n = 86, Guillain–Barré syndrome n = 37, multifocal motor neuropathy n = 18, diabetic neuropathy n = 30, other inflammatory neuropathies n = 10), amyotrophic lateral sclerosis (n = 50), multiple sclerosis (n = 50) and healthy controls (n = 50) was negative for septin multimer autoantibodies. Histopathological analysis of skin and the sural nerve including electron microscopy was performed in one seropositive patient, and autoantibody binding was characterized in vitro. Extensive immunotherapy was initiated in one patient, with clinical and serological follow-up over 4 years. Among 3543 total samples tested, three patients (two male, one female)—diagnosed with the LMND variant of amyotrophic lateral sclerosis (aged 65, 72 and 79 years, respectively)—showed a novel and distinct autoantibody binding pattern of indirect immunofluorescence staining on peripheral nerves, targeting Schmidt–Lanterman incisures (SLIs), paranodes and the abaxonal myelin. Target identification and validation revealed septin multimers as autoantibody epitopes. Despite the primarily intracellular location of septins, autoantibody binding was evident in living myelinated dorsal root ganglia, primarily at SLIs (‘incisuropathy’). Septin multimer autoantibodies further initiated complement deposition on fixed and permeabilized cell-based assays. Sural nerve and skin biopsies showed inflammation, myelin and axonal pathology. Extensive immunotherapy in one patient was followed by disease stabilization over 3 years. The other two patients died of rapid disease progression: one of them received no immunotherapy while the other had ineffective treatments with single administrations of intravenous immunoglobulin and rituximab. Our data suggest that septin multimer autoimmunity occurs in severe motor-predominant neuropathies which can clinically resemble a neurodegenerative LMND. Screening for septin multimer autoantibodies should be considered in patients presenting with this phenotype. Follow-up studies need to determine the direct pathogenicity of septin multimer autoantibodies, their potential as a biomarker of an autoimmune syndrome and responses to immunotherapy in larger cohorts.

ABSTRACT Background Long‐term outcome data for stiff person spectrum disorder (SPSD) remain limited and sustained response to treatment varies. Methods In this retrospective cohort study, we included patients with probable or definite SPSD (Mayo Clinic criteria), evaluated at Mayo Clinic (12/1995‐07/2024) with ≥ 5 years of follow‐up after diagnosis. Primary outcome measures included the modified Rankin scale (mRS) and use of gait aids. Results Fifty‐four patients were included, 41 (76%) were female; median age at onset was 45 years (16–78). Most were antibody‐positive (51 [94%]), with high‐titer (serum, ≥ 20 nmol/L) GAD65‐IgG in 45 (83%). Nine patients had a stiff‐limb presentation (17%). The median interval from onset to diagnosis was 2 years (0–34), and median follow‐up was 9 years (5–26). Most patients (46 [85%]) received immune therapy; 37 (82%) reported improvement. All patients had significant impairment (mRS ≥ 2) at nadir, with 31 (57%) losing functional independence (mRS ≥ 3) and 40 (75%) requiring bilateral gait assistance. The median time from onset to nadir was 6 years (0–39). At last follow‐up, most (37 [69%]) were functionally independent (mRS ≤ 2), including 8 (15%) with minimal restrictions (mRS ≤ 1). Bilateral gait assistance was needed in 22 (41%). Among 40 patients with ≥ 10 years of follow‐up, 22 (56%) had an mRS ≤ 2 and 25 (63%) required a gait aid at last follow‐up. Poor outcome in this population was associated with bilateral gait assistance at nadir and older age ( p < 0.05). Conclusions Although over half of SPSD patients lose functional independence at disease nadir, many regain independence and achieve well‐controlled symptoms.

Autoimmune diseases arise when B and T lymphocytes lose tolerance to self. Yet in most disorders, the underlying molecular determinants, including autoantibodies, epitopes and lymphocyte clones that drive tissue injury remain undefined. Rapid-onset obesity with hypothalamic dysfunction, hypoventilation and autonomic dysregulation (ROHHAD) is a rare and often fatal pediatric neuroendocrine syndrome with strong evidence of antigen-driven paraneoplastic autoimmunity, including association with the intracellular autoantigen ZSCAN1. However, the effector immune circuit and the epitope-level determinants operating within the hypothalamus and brainstem have remained unknown. To address this challenge in ROHHAD and more broadly in autoimmune disease, we developed the Autoimmune Epitope and immunoGlobulin/Immune-receptor identification System (AEGIS), an integrated framework that links immune repertoires to their cognate self-epitopes. AEGIS combines B cell and T cell receptor profiling from sites of tissue injury with high-resolution epitope mapping, direct sequencing of antigen-specific autoantibodies, in silico antibody-antigen folding, selection, and T cell antigen discovery. Applied to a deeply phenotyped child with ROHHAD, AEGIS revealed a compartmentalized, clonally restricted immune response in which brain-deposited IgG and expanded cerebrospinal fluid B cell and CD4 T cell clonotypes converged on shared ZSCAN1 epitopes, resolved to minimal determinants and peptide-MHC ligands. These findings provide a clone- and epitope-linked mechanistic map of ROHHAD autoimmunity and establish a generalizable framework for identifying candidate pathogenic clones and antigens across diverse autoimmune diseases.

ABSTRACT Objective To (1) validate GAD65‐ELISA detection and quantification for type 1 diabetes mellitus and autoimmune neurological diagnoses, (2) correlate ELISA results (reference range < 5 IU/mL) with established radioimmunoprecipitation assay (RIA; ≤ 0.02 nmol/L), and (3) define ELISA clinical utility and pitfalls. Methods Serum performance for diabetes (FDA‐cleared, undiluted) was verified, and neurological laboratory‐developed serum and CSF dilution protocols were validated to extend the reportable range beyond > 250 IU/mL. ELISA and RIA values were correlated, including established neurological RIA cut‐offs (serum ≥ 20 nmol/L; CSF any positive). Results ELISA met analytical criteria (precision, accuracy, sensitivity, specificity, reference range) in serum and CSF and was clinically equivalent to RIA for autoimmune diabetes. Neurological ELISA cut‐offs were established at 10,000 IU/mL (serum) and 100 IU/mL (CSF). Precision was better below 10,000 IU/mL (CVs < 20%) than above (CVs 30.8% serum; 26.5% CSF). ELISA–RIA correlation and agreement was stronger below the neurological cut‐off (R 2 = 0.89) than above (R 2 = 0.36). Positive agreement for RIA‐defined neurological disease was 100% in serum and CSF; all serums were > 10,000 IU/mL. Clinical specificity was 97.5% in serum and 100% in CSF, exceeding reported RIA specificity. Screen results > 250 IU/mL spanned a wide range of dilution values; many were below the neurological cut‐off. Most patients with paired serum/CSF positivity showed elevated GAD65 IgG indices. Interpretation GAD65 ELISA and RIA have equivalent sensitivity for autoimmune diabetes and neurological testing, with higher specificity for ELISA. A serum cut‐off of 10,000 IU/mL is informative but requires clinical context, and dilution of screen > 250 IU/mL samples is essential for neurological interpretation.