Citations

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.

Abstract The discovery of pathogenic neuroglial surface-directed autoantibodies (NGSAbs) has fundamentally transformed clinical neurology, by enabling molecular-level diagnoses in potentially treatable, yet previously unrecognized, diseases. Annual descriptions of novel CNS-targeting antibodies create a continuous stream of new conditions in which to evaluate distinct phenotypes, specific tumour associations and immunotherapy responses. Alongside this clinical growth, increasing basic knowledge has highlighted origins and mechanisms underlying disease causation, most comprehensively interrogated in the well-established autoantibody-mediated conditions of autoimmune encephalitis (AE), neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD). The corresponding most common ‘big six’ autoantigens are LGI1, the N-methyl-D-aspartate (NMDA) receptor, CASPR2, IgLON5, in forms of AE, AQP4 and MOG. Each of these autoantigens associates with a homogenous set of basic clinical features, across age, sex, tumour associations and ethnicities, coupled with partly distinctive profiles of triggers and predispositions, paradigms of immune tolerance escape in the periphery, how cells and autoantibodies gain access to the CNS, and discrete mechanisms by which the CNS autoantibodies induce neuroglial dysfunction. These observations lead us to reconstruct a proposed chronological series of events as the ‘cascade to pathogenicity’, which together culminate in a rare CNS disease. By extension, we hypothesize elucidating the underlying biology of each condition will present differing precision medicine approaches to optimize patient care. Despite distinctions, there are also clinical and biological overlaps between these diseases, collectively creating opportunities to compare and contrast their individual features. Here, in each condition, we review current knowledge regarding the similarities and differences between the triggering events, underlying immunological processes and pathogenic mechanisms of autoantibodies. In some instances, we identify scientific clues that drive hypothetical pathways of pathogenesis and, for others, highlight striking observations that aim to generate hypothesis-driven next steps. Our aim is to construct a model across the major autoantibody-mediated CNS diseases to highlight distinct components of cascades to pathogenicity, which may offer targeted therapeutic approaches to improve patient outcomes, and identify key areas and questions for future research.

Background Psychiatric comorbidities are increasingly recognised in demyelinating diseases, yet their frequency and timing in myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are not well defined. We aimed to characterise the spectrum and temporal pattern of psychiatric illness in MOGAD and compare to multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) with aquaporin-4 antibody (AQP4-IgG). Methods We conducted a cross-sectional study of patients with MOGAD (n=388), age-matched and sex-matched MS (n=257) and AQP4-IgG-positive NMOSD (n=58) evaluated at Mayo Clinic (1991–2025). Psychiatric diagnoses, timing relative to the first attack and patient-reported outcomes were extracted from electronic health records (EHRs). Complementary analyses were conducted using the NeuroBlu real-world EHR database. Results Among 388 patients with MOGAD, 54.8% had ≥1 psychiatric disorder, most commonly anxiety (47.7%), depression (36.6%) and attention-deficit/hyperactivity disorder (ADHD, 9%). After the first attack, 33.3% of patients with MOGAD developed a new psychiatric disorder, often within the first year. MOGAD showed a lower frequency of depression versus MS (36.6% vs 47.5%, p=0.02) but similar rates of anxiety and ADHD. Temporal patterns differed: psychiatric disorders often appeared years before onset in MS but clustered shortly after onset in MOGAD. NeuroBlu analyses supported high rates of psychiatric disorders across the three conditions. Conclusion Psychiatric comorbidities are common in MOGAD, particularly depression and anxiety, typically emerging close after onset, whereas in MS they often preceded onset by years. These findings underscore the need for routine psychiatric screening in MOGAD and highlight unresolved questions regarding whether, and to what extent, MOG-IgG-mediated inflammatory demyelination contributes to psychiatric vulnerability.

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.