The association between asthma and ADHD in children and adolescents: An observational study and a meta-analysis of Mendelian randomization studies

Observational epidemiological analysis and a meta-analysis of Mendelian randomization (MR) were used to investigate the association between attention-deficit/hyperactivity disorder (ADHD) and asthma in children and adolescents. Based on data from the 1999 to 2004 National Health and Nutrition Examination Survey (NHANES), an analysis was conducted to evaluate the association between ADHD and asthma in children and adolescents aged between 4 and 19 years. ADHD and asthma were defined based on self- or parent/guardian proxy-reported physician/health-professional diagnoses from the NHANES Medical Conditions Questionnaire. After analyzing ADHD genome-wide association study data from the Psychiatric Genomics Consortium as instrumental variables, we performed two-sample MR analyses based on genome-wide association study data from 5 studies to examine the causal relationship between genetically predicted ADHD liabilities. In addition, we summarized the results of the inverse-variance weighted method using a random-effects meta-analysis. Asthma prevalence was higher among participants with ADHD than those without ADHD (10.2% vs 5.9%). ADHD was associated with higher odds of asthma (odds ratio = 1.64, 95% confidence interval = 1.36-1.98), and the pattern of results was broadly consistent across subgroups. In contrast, the MR meta-analysis did not support a causal effect of genetically predicted ADHD liability on childhood asthma (odds ratio = 0.94, 95% confidence interval = 0.84-1.05, P > .05). According to data from the NHANES, ADHD and asthma are significantly associated in children and adolescents. A meta-analysis of the MR data did not reveal a causal connection between genetically predicted ADHD liability and childhood asthma. This paradoxical finding illustrates the complex interplay of genetic and nongenetic mechanisms in the ADHD-asthma association.