Link found between childhood asthma and adolescent ADHD
Catarina Almqvist Malmros has shown in a population-based twin study published in the scientific journal Allergy that there is an association between asthma in childhood and an increased risk of ADHD in adolescence. The results of the study also indicate that some of the association has a genetic cause.
It has long been suspected that there is an association between pulmonary diseases such as asthma and neuropsychiatric diseases such as ADHD (Attention Deficit Hyperactivity Disorder) in children and adolescents. However, the temporal relation or whether there are common hereditary and environmental risk factors has remained unstudied. The purpose of the present study was therefore to investigate the longitudinal link between asthma and symptoms of ADHD, and the effect of genetic and environmental factors.
Twins share prenatal environmental factors in the womb and often an external environment when growing up. Identical (monozygotic) twins also share 100 per cent of their DNA and non-identical (dizygotic) twins 50 per cent of the segregating genes. 1,812 twins at the age of 8-9 were recruited to the TCHAD (Twin study of CHild and Adolescent Development) study, through the Swedish Twin Registry at Karolinska Institutet.
The study involved a survey of the children and their parents, who were invited to answer questions on asthma and ADHD symptoms as well as background factors such as socio-economic parameters, birth weights, sex, zygosity and asthma medication. The questionnaire was repeated when the twins were between 13 and 14 years old. Based on personal identification numbers and the survey, data on birth weight was sourced from the Medical Birth Register.
Correlational analyses between asthma and symptoms of ADHD, adjusted for background factors and zygosity, showed that children with asthma at the age of 8-9 had a two-fold greater risk of developing ADHD at the age of 13-14 than children without asthma. Twin analyses indicated that 68 per cent of the association between asthma and ADHD symptoms had genetic causes. The results were independent of asthma medication.
Asthma is one of the most common childhood diseases, with a prevalence of 6-8 per cent. ADHD is also relatively common, with a prevalence of 3-5 per cent. Early strategies to identify children at risk of being diagnosed with neuropsychiatric disease can reduce the disease burden.