Cognitive dysfunction is a common feature of autoimmune encephalitis. Pathogenic neuronal surface antibodies are thought to mediate distinct profiles of cognitive impairment in both the acute and chronic phases of encephalitis. In this review, we describe the cognitive impairment associated with each antibody-mediated syndrome and, using evidence from imaging and animal studies, examine how the nature of the impairment relates to the underlying neuroimmunological and receptor-based mechanisms. Neuronal surface antibodies, particularly serum NMDA receptor antibodies, are also found outside of encephalitis although the clinical significance of this has yet to be fully determined. We discuss evidence highlighting their prevalence, and association with cognitive outcomes, in a number of common disorders including cancer and schizophrenia. We consider mechanisms, including blood-brain barrier dysfunction, which could determine the impact of these antibodies outside encephalitis and account for much of the clinical heterogeneity observed.

Introduction Neuronal antibodies can cause encephalopathy syndromes often presenting with subacute cognitive impairment, sometimes resembling neurodegenerative dementias. Methods We searched Medline and Embase for studies reporting associations between neuronal surface antibodies in allcause dementia versus controls. Random-effects meta-analysis was used to pool adjusted estimates across studies. Results Six studies were included, all reporting frequency of serum NMDAR antibodies in dementia with four also reporting frequency in atypical dementias. Both IgG [OR = 8.09 (1.51; 56.85), p = 0.036] and IgA/IgM NMDAR antibodies [OR = 42.48 (11.39; 158.52), p < 0.001] were associated with atypical dementia, but neither were associated with all-cause dementia. Discussion In the first meta-analysis to explore this literature, serum IgG and IgA/IgM NMDAR antibodies were significantly more common in atypical dementias. However, methodological issues and small-sample sizes necessitate caution interpreting this result. Further studies measuring both serum and CSF antibodies are needed to investigate the role of neuronal antibodies in dementia, since evidence of pathogenicity in even a subset of patients could pave the way for novel treatment options. Keywords Autoimmune dementia • Atypical dementia • NMDAR antibody • Antibodies in dementia Abbreviations NMDAR N-Methyl-d-aspartate receptor LGI1 Leucine-rich glioma inactivated 1 CASPR2 Contactin-associated protein 2 AMPAR α-Amino-3-hydroxy-5-methyl-4isoxazolepropionic acid receptor GABA Gamma-aminobutyric acid GAD Glutamic acid decarboxylase

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Background Trimethylamine N-oxide (TMAO), a metabolite from red meat and fish consumption, plays a role in promoting cardiovascular events. However, data regarding TMAO and its impact on clinical outcomes are inconclusive, possibly due to its undetermined dietary source. Objective We hypothesized circulating TMAO derived from fish intake might cause less harm compared to red meat source by examining the concomitant level of 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), a known biomarker of fish intake, and investigated the association between TMAO, CMPF and outcomes. Design Patients were recruited from the European QUALity study on treatment in advanced CKD (EQUAL) among individuals ≥65 years whose eGFR had dropped for the first time to ≤20mL/min/1.73m2 during last 6 months. The association between TMAO, CMPF and outcomes including all-cause mortality and kidney replacement therapy (KRT) was assessed among 737 patients. Patients were further stratified by median cut-offs of TMAO and CMPF, suggesting high/low red meat and fish intake. Results During a median of 39 months’ follow-up, 232 patients died. Higher TMAO was independently associated with an increased risk of all-cause mortality (multivariable-hazard ratio (HR) 1.46, 95% confidence interval (CI) 1.17, 1.83). Higher CMPF was associated with a reduced risk of both all-cause mortality (HR 0.79, 95%CI 0.71, 0.89) and KRT (HR 0.80, 95%CI 0.71, 0.90), independent of TMAO and other clinically relevant confounders. In comparison to patients with low TMAO and CMPF, patients with low TMAO and high CMPF had reduced risk of all-cause mortality (adjusted HR 0.49, 95% CI 0.31, 0.73), whereas those with high TMAO and high CMPF showed no association across adjusted models. Conclusions High CMPF conferred an independent role in health benefits and might even counteract the unfavorable association between TMAO and outcomes. Whether higher circulating CMPF are due to fish consumption, and/or CMPF is a protective factor remains to be verified.