Epidemiological studies of asthma and neurodevelopmental disorders in children

Asthma and neurodevelopmental disorders including autism spectrum disorders (ASD) and attention deficit hyperactivity disorders (ADHD) are common diseases starting in early childhood. The prevalence of both diseases is rising and little is known about the potential genetic and environmental risk factors. Therefore, the overall aim of this thesis was to investigate the early life risk factors associated with the subsequent development of asthma and neurodevelopmental disorders, especially ASD using population- and family-based designs.

In Study I, we investigated the association between parental socioeconomic status (measured by income and education), risk of asthma, and patterns of medication dispenses in a large population-based cohort of preschool children. We found an age-varying effect on the risk of asthma, but no effect on the pattern of medication dispenses by parental income. Parental education, however, was negatively associated with asthma regardless of age and positively associated with controller medication dispenses.

In Studies II and III, we evaluated the association between exposure to traffic-related air pollution and neurodevelopmental disorders among children born in Stockholm during 1992- 2007. In contrast to previous findings, there was no clear association between air pollution during pregnancy or early infancy and subsequent risk of ASD and ADHD. Residual confounding from parental socioeconomic status and psychiatric diagnoses can partly explain the findings and the differences observed in some subgroups.

In Study IV, we assessed the association between parental asthma, use of asthma medication during pregnancy and the risk of ASD in offspring by comparing cases and controls in the general population and within families. Maternal, but not paternal, asthma, was associated with a slightly increased risk of ASD, which was neither confounded by familial factors shared among half-siblings and cousins nor mediated through use of asthma medications during pregnancy.

In conclusion, these collective studies shed light on the relationship between many early life risk factors and subsequent risk of asthma and neurodevelopmental disorders. The higher risk of incident asthma and lower rate of controller medication dispenses among young children with lower parental socioeconomic background warrants clinical attention. Traffic-related air pollution, despite being a major concern to the general public, was not associated with ASD and ADHD in the Swedish urban setting. Furthermore, the association between maternal asthma and offspring ASD appeared to be persistent, suggesting the importance of future investigation into potential biological mechanisms.

List of scientific papers

I. Gong T, Lundholm C, Rejno G, Mood C, Langstrom N, Almqvist C. Parental socioeconomic status, childhood asthma and medication use - a populationbased study. PLoS One. 2014;9(9):e106579.
https://doi.org/10.1371/journal.pone.0106579

II. Gong T, Almqvist C, Bolte S, Lichtenstein P, Anckarsater H, Lind T, Lundholm C, Pershagen G. Exposure to air pollution from traffic and neurodevelopmental disorders in Swedish twins. Twin Res Hum Genet. 2014;17(6):553-62.
https://doi.org/10.1017/thg.2014.58

III. Gong T, Dalman C, Wicks S, Dal H, Magnusson C, Lundholm C, Almqvist C, Pershagen G. Perinatal exposure to traffic-related air pollution and autism spectrum disorders. [Submitted]

IV. Gong T, Lundholm C, Rejnö G, Bölte S, Larsson H, D’Onofrio B, Lichtenstein P, Almqvist C. Parental asthma and maternal asthma medication during pregnancy and risk of offspring autism spectrum disorder. [Submitted]