title: Impact of asthma medication and familial factors on the association between childhood asthma and attention-deficit/hyperactivity disorder: a combined twin- and register-based study: Epidemiology of Allergic Disease.
abstract: BACKGROUND
  Asthma and attention-deficit/hyperactivity disorder (ADHD) are prevalent in childhood and may cause functional impairment and stress in families. Previous research supports an association between asthma and ADHD in children, but several aspects of this relationship are unclear.
  
  
  OBJECTIVE
  Our aim was to study whether the association between asthma and ADHD is restricted to either the inattentive or the hyperactive/impulsive symptoms of ADHD, to explore the impact of asthma severity and asthma medication and the contribution of shared genetic and environmental risk factors on the asthma-ADHD relationship.
  
  
  METHODS
  Data on asthma, ADHD, zygosity and possible confounders were collected from parental questionnaires at 9 or 12 years on 20 072 twins through the Swedish Twin Register, linked to the Swedish Medical Birth Register, the National Patient Register and the Prescribed Drug Register. The association between asthma and ADHD, the impact of asthma severity and medication, was assessed by generalized estimating equations. Cross-twin-cross-trait correlations (CTCT) were estimated to explore the relative importance of genes and environment for the association.
  
  
  RESULTS
  Asthmatic children had a higher risk of also having ADHD [odds ratio (OR) 1.53, 95% confidence interval (CI): 1.16-2.02]. The association was not restricted to either of the two dimensions of ADHD. The magnitude of the association increased with asthma severity (OR 2.84, 95% CI: 1.86-4.35) for ≥ 4 asthma attacks in the last 12 months and was not affected by asthma treatment. The CTCTs possibly indicate that the genetic component in overlap of the disorders is weak.
  
  
  CONCLUSIONS
  Childhood asthma, especially severe asthma, is associated with ADHD. Asthma medication seems not to increase the risk of ADHD. Clinicians should be aware of the potential of ADHD in asthma. Optimal asthma care needs to be integrated with effective evaluation and treatment of ADHD in children with co-existing disorders.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.|Neuropediatric unit, Sachs' Children and Youth Hospital, South General Hospital, Stockholm, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Holmberg
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Lundholm
authors.affiliation: Institute of Neuroscience and Physiology, Forensic Psychiatry, University of Gothenburg, Gothenburg, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Anckarsäter
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Larsson
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.|Lung and allergy unit, Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Almqvist
mesh_terms: D001249:Asthma / Q000150:complications* / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D001289:Attention Deficit Disorder with Hyperactivity / Q000150:complications* / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D003430:Cross-Sectional Studies; D005190:Family; D005260:Female; D006801:Humans; D008297:Male; D016017:Odds Ratio; D011159:Population Surveillance; D012042:Registries; D012307:Risk Factors; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D014427:Twins
keywords: anti-asthmatic agents; asthma; attention-deficit/hyperactivity disorder (ADHD); epidemiology; twins