Damato, Valentina

The 2 main subgroups of autoimmune myasthenia gravis, a neuromuscular junction disorder associated with muscle weakness, are early- and late-onset forms, defined by onset before or after 50 years of age. Both carry acetylcholine-receptor autoantibodies but differ in sex ratios, genetics, and occurrence of disease-specific thymus inflammation. To distinguish the 2 forms by cellular immune phenotyping, we applied multimodal techniques, including deep spectral cytometric phenotyping and single-cell sequencing. Analysis of 2 independent cohorts identified immunological differences driven by 3 main lymphocyte populations. Lower frequencies of mucosa-associated invariant T cells and naive CD8 + T cells were observed in late-onset myasthenia, suggesting enhanced immune senescence. A highly differentiated, canonical NK cell population was reduced in early-onset myasthenia and negatively correlated with the degree of thymic hyperplasia. Using only the frequency of these 3 populations, correct myasthenia subgroup assignment could be predicted with 90% accuracy. These distinct immunocellular endophenotypes for early- and late-onset disease suggest differences in immunopathogenic processes. Along with demographic factors and other disease subgroup–specific features, the frequency of the identified cell subpopulations may improve clinical classification.

Abstract Objective Autoimmune encephalitis is a cause of brain inflammation characterized by auto‐antibodies, which target cell surface neuronal proteins and lead to neuronal dysfunction. The most common form is associated with auto‐antibodies to leucine‐rich glioma‐inactivated 1 (LGI1) protein, the presentation of which includes frequent focal seizures. The exact cause of these auto‐antibodies remains unknown, but established predispositions include overrepresented human leukocyte antigen ( HLA ) alleles. Yet, these HLA alleles are themselves common in the healthy ancestry‐matched population. One potential etiological hypothesis is that an environmental trigger, such as the gut microbiome, interacts with a genetically predisposed individual. Methods To investigate this, we studied 42 patients with LGI1‐antibody encephalitis (LGI1‐Ab‐E) and 27 familial/environmentally matched controls, and performed metagenomic shotgun sequencing, to describe the compositional and functional differences in the gut microbiome. Results We observed that LGI1‐Ab‐E gut microbiomes exhibited a significant reduction in the ratio of Firmicutes (or Bacillota) and Bacteroidetes phyla, which is associated with the dosage of HLA susceptibility allele count in patients with LGI1‐Ab‐E. Furthermore, we identified differences in functional gene profiles in the gut microbiome that led to a reduction of neuroinflammatory protective short‐chain fatty acids (SCFAs) in LGI1‐Ab‐E patients. Significance Taken together, our results suggest that a compositional shift in the gut microbiome of LGI1‐Ab‐E associates with a neuroinflammatory state, possibly through the reduction of SCFA production. Our study highlights the potential of the gut microbiome to explain some of the complex condition and unravel etiological questions. Validation studies with greater sample sizes are recommended.

AbstractBackground and purposeThis study was undertaken to assess the long‐term outcome of patients with paraneoplastic and non paraneoplastic autoimmune cerebellar ataxia (ACA) using the Scale for the Assessment and Rating of Ataxia (SARA).MethodsPatients with subacute cerebellar ataxia admitted to our institution between September 2012 and April 2020 were prospectively recruited. Serum and/or cerebrospinal fluid was tested for neural autoantibodies by indirect immunofluorescence on mouse brain, cell‐based assays, and radioimmunoassay. SARA and modified Rankin Scale (mRS) score were employed to assess patients’ outcome.ResultsFifty‐five patients were recruited, of whom 23 (42%) met the criteria for cerebellar ataxia of autoimmune etiology. Neural autoantibodies were detected in 22 of 23 patients (Yo–immunoglobulin G [IgG], n = 6; glutamic acid decarboxylase 65–IgG, n = 3; metabotropic glutamate receptor 1–IgG, n = 2; voltage‐gated calcium channel P/Q type–IgG, n = 2; Hu‐IgG, n = 1; glial fibrillary acidic protein–IgG, n = 1; IgG‐binding unclassified antigens, n = 7). Thirteen patients were diagnosed with paraneoplastic cerebellar syndrome (PCS) and 10 with idiopathic ACA. All patients received immunotherapy. Median SARA score was higher in the PCS group at all time points (p = 0.0002), while it decreased significantly within the ACA group (p = 0.049) after immunotherapy. Patients with good outcome (mRS ≤ 2) had less neurological disability (SARA < 15) at disease nadir (p = 0.039) and presented less frequently with paraneoplastic neurological syndrome (p = 0.0028). The univariate linear regression model revealed a good correlation between mRS and SARA score both at disease onset (p < 0.0001) and at last follow‐up (p < 0.0001). SARA score < 11 identified patients with good outcome.ConclusionsPatients with idiopathic ACA significantly improved after immunotherapy. SARA score accurately reflects patients’ clinical status and may be a suitable outcome measure for patients with ACA.