title: Association between IgA deficiency & other autoimmune conditions: a population-based matched cohort study.
abstract: OBJECTIVE
  To examine autoimmune disorders in patients with IgA deficiency compared with the general population.
  
  
  METHODS
  Nationwide prospective population-based cohort study. Through six university hospitals in Sweden we identified 2100 individuals with IgA deficiency (IgA levels < .07 g/L) diagnosed between 1980 and 2011. Each patient with IgA deficiency was matched on age, sex, place of residence, and year of diagnosis with up to 10 general population controls (n = 18,653). Data on nine autoimmune disorders were retrieved from the Swedish National Patient Register (including inpatient and non-primary outpatient care). Autoimmune disorders were defined as having at least two visits listing the relevant international classification of disease (ICD) code as main diagnosis. Prevalences and prevalence ratios (PRs) were calculated.
  
  
  RESULTS
  Individuals with IgA deficiency more often had celiac disease (6.7 % vs. 0.19 % in controls) and type 1 diabetes (5.9 % vs. 0.57 %) corresponding to a 35-fold higher PR for celiac disease and 10-fold higher for type 1 diabetes. Also for the other autoimmune diseases did we see statistically significantly elevated prevalences and PRs (juvenile idiopathic arthritis (0.76 % vs. 0.09 % in controls, PR = 8.9), systemic lupus erythematosus (0.57 % vs. 0.06 %; PR = 8.9), inflammatory bowel disease (3.9 % vs. 0.81 %; PR = 5.0; specifically Crohn's disease (2.4 % vs. 0.42 %; PR = 5.7) and ulcerative colitis (1.7 % vs. 0.46 %; PR = 3.9)), hypothyreosis (0.76 % vs. 0.16 %; PR = 4.6), rheumatoid arthritis (2.2 % vs. 0.50 %; PR = 4.5), and hyperthyreosis (1.7 % vs. 0.43 %; PR = 3.9), but not with myasthenia gravis (0.05 % vs. 0.02 %; PR = 3.0).
  
  
  CONCLUSIONS
  Individuals with IgA deficiency have a higher prevalence of several other autoimmune disorders.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, jonasludvigsson@yahoo.com.
authors.forename: Jonas F
authors.initials: JF
authors.lastname: Ludvigsson
authors.forename: Martin
authors.initials: M
authors.lastname: Neovius
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarström
mesh_terms: D000293:Adolescent; D000328:Adult; D001327:Autoimmune Diseases / Q000150:complications / Q000453:epidemiology* / Q000276:immunology / Q000473:pathology; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D017098:IgA Deficiency / Q000150:complications / Q000453:epidemiology* / Q000276:immunology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries; D013548:Sweden / Q000453:epidemiology