OBJECTIVES: To determine the prevalence of myasthenia gravis (MG), and the rate of concurrent autoimmune diseases in patients with MG.
DESIGN AND SETTING: Using the Swedish health and population registers, during the period 2005-2010 we conducted a nested case-control study of MG patients (n = 2045) with five age- and sex-matched population-based controls per case. Register-based MG diagnosis was validated against the Stockholm MG Cohort. Similar nested case-control studies were conducted in patients with multiple sclerosis (MS), as a neuroinflammatory disease control, and siblings of MG patients.
MAIN OUTCOME MEASURE: Odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated as a measure of the association between MG and other autoimmune diseases.
RESULTS: The prevalence of MG was 24.8/100 000 and MG patients had an increased risk of another autoimmune disease compared to controls (22.0% vs. 8.9%; OR: 2.82, 95% CI: 2.49-3.20); this risk was stronger among younger persons and women. Polymyositis/dermatomyositis, systemic lupus erythematosus and Addison's disease, three conditions regulated by the HLA-B8-DR3 haplotype, were most strongly associated with MG, especially early-onset disease. HLA typing in the Stockholm MG Cohort showed that early-onset MG was indeed dominated by HLA-B8-DR3. The risk of another autoimmune disease was increased in both MS patients and siblings of MG patients, compared to their respective controls, but to a lesser extent than in MG patients.
CONCLUSIONS: Our results suggest that MG shares risk factors with other autoimmune diseases, to a greater degree than MS, with a particular role of the HLA-B8-DR3 haplotype, especially among younger and female patients. This article is protected by copyright. All rights reserved.
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