Association between the adrenoreceptor β2 gene and pediatric asthma severity – a study of the PACMAN cohort

"Pharmacogenetics of Asthma medication in Children: Medication with Anti-Inflammatory effects" (PACMAN) is an observational retrospective pharmacy-based study carried out in 2009, in the Netherlands, aiming to investigate the effects of genetic variation on treatment response to asthma medication in children and to identify (profiles of) SNPs that characterize response phenotypes. Data on respiratory symptoms and medication use, including medication type and amount, was collected from pharmaceutical records of asthmatic children and data on the children’s sex, age, genetic traits, and ethnicity. We aimed to assess the association between asthma severity and the Arg16Glu polymorphism of the β2 adrenoreceptor gene (ADRB2). This gene is expressed in bronchial muscle cells, which is involved in the physiological response of the airway response and has been associated with clinical drug response and asthma exacerbations. We used the PACMAN data and considered the dispensing of oral corticosteroid prescriptions as a proxy of the disease severity since corticoids are commonly used in uncontrolled asthmatic states (exacerbations). We considered two different genetic models – additive and genotypic, which can be translated for analysis purposes into a numeric format, corresponding to the number of copies of the minor allele, and categorical (each genotype representing a category), respectively. We used models of the class of the Generalized Linear Mixed Models for count data with excess of zeros, namely zero-inflated and hurdle models, considering a Negative Binomial distribution to account for overdispersion. Both models included the polymorphism in the zero and count components and were adjusted for children’s baseline characteristics. In both approaches to deal with the excess of zeros, a significant effect of the polymorphism was found only in the binary component of the models. In the count component, only sex and age showed a significant effect. This points towards the existence of an effect of the polymorphism in ...