Complement activation profiles in anti-acetylcholine receptor positive myasthenia gravis.

BACKGROUND AND PURPOSE: Complement component 5 (C5) targeting therapies are clinically beneficial in patients with acetylcholine receptor antibody+ (AChR-Ab+ ) generalized myasthenia gravis (MG). That clearly implicates antibody-mediated complement activation in MG pathogenesis. Here, classical and alternative complement pathways were profiled in patients from different MG subgroups. METHODS: In a case-control study, concentrations of C3a, C5a and sC5b9 were simultaneously quantified, indicating general activation of the complement system, whether via the classical and lectin pathways (C4a) or the alternative pathway (factors Ba and Bb) in MG patients with AChR or muscle-specific kinase antibodies (MuSK-Abs) or seronegative MG compared to healthy donors. RESULTS: Treatment-naïve patients with AChR-Ab+ MG showed substantially increased plasma levels of cleaved complement components, indicating activation of the classical and alternative as well as the terminal complement pathways. These increases were still present in a validation cohort of AChR-Ab+ patients under standard immunosuppressive therapies; notably, they were not evident in patients with MuSK-Abs or seronegative MG. Neither clinical severity parameters (at the time of sampling or 1 year later) nor anti-AChR titres correlated significantly with activated complement levels. CONCLUSIONS: Markers indicative of complement activation are prominently increased in patients with AChR-Ab MG despite standard immunosuppressive therapies. Complement inhibition proximal to C5 cleavage should be explored for its potential therapeutic benefits in AChR-Ab+ MG.

A Prospective Study of the Incidence of Myasthenia Gravis in the East Midlands of England.

OBJECTIVES: A number of worldwide studies have highlighted a rising incidence of myasthenia gravis (MG) over the past few decades. This is largely due to an increase in numbers in older patients. To establish whether this was a consistent finding in the United Kingdom, we conducted a large, 4-year prospective cohort study of all known patients with new-onset MG in the East Midlands of the United Kingdom. METHODS: Between 2014 and 2018, all 120 patients with a new diagnosis of MG who were residing in the East Midlands were enrolled. RESULTS: Median age at disease onset was 63 years (78% aged over 50 years) and most patients (57%) were male. The average annual incidence rate (IR) was 17.6/1,000,000 (95% CI 10.7-28.6). IRs remained stable between 2014 and 2018 except for rising IRs in patients over 65 years of age (p value for trend, <0.001). CONCLUSIONS: Twenty years after the last comprehensive prospective incidence survey of MG in the east of England, we have demonstrated a rising incidence. The greatest increases seen were in patients over 65 years. Given the rigorous study methods employed, future replicate prospective studies from the same region will establish whether these rising figures are due to biological factors, independent of improved case ascertainment.

False-positive acetylcholine receptor antibody results in patients without myasthenia gravis.

Acetylcholine receptor antibodies are very specific for myasthenia. During a large prospective cohort study of myasthenia, we encountered five patients, positive for acetylcholine receptor (AChR) antibodies by radioimmunoprecipitation assay (RIA), whose clinical course revealed diagnoses other than myasthenia. Two patients had transiently raised AChR antibodies associated with Guillain-Barré syndrome. Antibodies to clustered AChRs, in a live cell-based assay, were negative in all five patients, suggesting that results from the RIAs were false-positives. It is possible that the AChR antibodies detected by RIA in these cases were non-pathogenic, and directed to intracellular epitopes of the AChR.

Circulating microRNA miR-21-5p, miR-150-5p and miR-30e-5p correlate with clinical status in late onset myasthenia gravis.

There are no biomarkers for late onset myasthenia gravis (LOMG; onset >50 years). We evaluated circulating microRNA in a discovery cohort of 4 LOMG patients and 4 healthy controls and in a prospective diagnostic validation cohort of 73 LOMG patients (48 male) with longitudinal follow-up samples. In immunosuppression naïve patients, levels of miRNAs miR-150-5p, miR-21-5p and miR-30e-5p decreased in parallel with clinical improvement after initiation of immunosuppression and their levels positively correlated with the clinical MG composite score. Levels of miR-150-5p and miR-21-5p were lower in patients with ocular compared to generalized LOMG. Circulating miR-150-5p, miR-21-5p and miR-30e-5p correlate with the clinical course in LOMG.