title: Risk factors and markers of asthma control differ between asthma subtypes in children.
abstract: BACKGROUND
  There is limited understanding about risk factors for asthma, and few studies have presented an overall picture of factors associated with asthma subtypes in schoolchildren. The aim of this study was to evaluate risk factors and markers of asthma control associated with asthma subtypes up to preadolescence.
  
  
  METHODS
  A Swedish birth cohort of 3015 children was followed for 12 yr using repeated parental questionnaires. At 8 yr, clinical investigation was performed, specifically evaluating lung function, allergic sensitization (IgE > 0.35 kUA /l), and body mass index (BMI). Children were categorized into three subtypes: transient asthma - asthma at 4 and 8, but not at 12 yr (n = 71), late-onset asthma - asthma at 12 yr, but not earlier (n = 103), and persistent asthma - asthma at 4, 8 and 12 yr (n = 125).
  
  
  RESULTS
  At 8 yr of age, high BMI (>85th percentile), sensitization, and rhinitis were significantly associated with late-onset asthma (p < 0.05). Prominent risk factors at birth associated with persistent, but not late-onset asthma, were male sex, tobacco exposure and, heredity for atopy (p < 0.05). Children with persistent asthma were also found to have significantly reduced lung function at 8 yr of age, more eczema/rhinitis, and were more atopic than non-asthmatics (p < 0.05). For persistent asthma, symptoms changed from 8 to 12 yr, with fewer nocturnal symptoms, less healthcare utilization, and less frequent wheeze at 12 yr (p < 0.05).
  
  
  CONCLUSIONS
  Risk factors differ between asthma subtypes and markers of asthma control vary with age up to preadolescence.
authors.affiliation: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden; Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Nordlund
authors.forename: Erik
authors.initials: E
authors.lastname: Melén
authors.forename: Erica S
authors.initials: ES
authors.lastname: Schultz
authors.forename: Hans
authors.initials: H
authors.lastname: Grönlund
authors.forename: Gunilla
authors.initials: G
authors.lastname: Hedlin
authors.forename: Inger
authors.initials: I
authors.lastname: Kull
mesh_terms: D001249:Asthma / Q000145:classification / Q000175:diagnosis* / Q000453:epidemiology; D015415:Biomarkers / Q000378:metabolism; D002648:Child; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood; D008297:Male; D011153:Population; D012129:Respiratory Function Tests; D012307:Risk Factors; D012737:Sex Factors; D013548:Sweden
chemical_list: D015415:Biomarkers; D007073:Immunoglobulin E
keywords: allergy asthma; asthma control; birth cohort; body-mass-index; children; population-based design; rhinitis; risk factors; symptoms