PURPOSE OF THE STUDY.
Previous research has supported an association between asthma and attention-deficit/hyperactivity disorder (ADHD). The goals of this study were to assess (1) whether asthma is associated with inattentive or hyperactive/impulsive symptoms of ADHD, (2) the impact of asthma severity and asthma medications on ADHD, and (3) the contributions of shared genetic and environmental risk factors on the asthma-ADHD relationship.
Data were obtained from the Child and Adolescent Twin Study in Sweden (CATSS) and 3 Swedish national registers, which contained information on maternal and child diagnoses and prescribed drug dispensation. The population used in this study included all children born between 1992 and 2002 whose parents were interviewed between August 2003 and August 2011.
Diagnoses and severity of asthma wase based on responses to questions derived from the International Study of Asthma and Allergies in Childhood and codes from the National Patient Register. Similarly, data about ADHD was retrieved from parental reports, responses to the ADHD and other Comorbidities Inventory and National Patient Register codes. Statistical analyses adjusted for the child’s gender, age, birth weight, gestational age, and maternal socioeconomic variables. The classic twin design was used to assess the relative impact of genetic and environmental factors, both shared and nonshared.
The final study population of 20 072 was restricted to twins with complete answers to the main questions on asthma and ADHD. The overall incidences of asthma and ADHD were 14.0% and ∼2%, respectively. Asthma was associated with a nearly twofold increased risk of ADHD, of both subtypes, a link that increased with asthma severity. The overlap of genetic factors was weak. Asthma medications did not affect the risk factors.
Children with asthma had an increased risk of ADHD, the magnitude of which increased with asthma severity.
This study is unique in combining parental reports with national registers among twins in a large population. Limitations include lack of controls for comorbid mental illnesses and lack of information on school performance and ADHD impairment. Asthma and asthma severity, but not asthma medications, were associated with the diagnosis of ADHD.
- Copyright © 2015 by the American Academy of Pediatrics