There is a slight association between maternal asthma and autism spectrum disorder in children, according to a study published in Clinical and Experimental Allergy. The association between paternal asthma and offspring autism spectrum disorder, however, appeared to be confounded by familial factors.

This observational study included 1,579,263 Swedish children born between 1992 and 2007. Using a nested case-control design, individuals with autism spectrum disorder were compared in a 1:10 ratio with biologically unrelated controls matched for sex, county, and age. These controls were selected using incidence density sampling. Additionally, children in the autism group were compared with half- and full-cousins and half- and full-siblings. Data were drawn from the National Patient Register. Odds ratios (ORs) for autism spectrum disorder in children with exposure to prenatal asthma treatment or parental asthma were estimated using conditional logistic regression. Possible mediators and confounding factors were identified using a directed acyclic graph.

There were 22,894 cases of autism spectrum disorder matched with 228,940 controls in the study population. An increased risk for autism spectrum disorder in offspring was weakly associated with paternal asthma (OR, 1.17; 95% CI, 1.11-1.23), while a stronger association existed with maternal asthma (OR, 1.43; 95% CI, 1.38-1.49). Adjustments for shared familial factors with paternal half-siblings revealed similar results for the relationship between offspring autism spectrum disorder and mothers with asthma (OR, 1.20; 95% CI, 0.80-1.81), as did shared familial factors with half- (OR, 1.30; 95% CI, 1.10-1.54) and full-cousins (OR, 1.28; 95% CI, 1.16-1.41). There was no association between offspring autism spectrum disorder and prenatal maternal use of asthma medications.

Limitations to this study included incomplete follow-up coverage of certain registers, the observational study design that led to an inability to draw firm conclusions about causal relationships and biological mechanisms, the potential for reverse causality, a lack of trimester-specific use of medications, and potential misclassifications.

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“[W]e found an association between parental asthma and offspring [autism spectrum disorder], which might be crucial for the understanding of the [autism spectrum disorder] etiology in a subgroup of cases,” the researchers wrote. ”For pregnant women with asthma, use of asthma medications during pregnancy did not seem to increase the risk of offspring [autism spectrum disorder], which further highlights the importance of surveillance and monitoring of asthma in pregnancy.”

Reference

Gong T, Lundholm C, Rejnö G, et al. Parental asthma and risk of autism spectrum disorder in offspring: a population and family based case-control study [published online February 11, 2019]. Clin Exp Allergy. doi:10.1111/cea.13353