PHARMACOGENOMICS OF INHALED CORTICOSTEROID RESPONSIVENESS IN PATIENTS WITH ASTHMA

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DESCRIPTION (provided by applicant): Inhaled corticosteroids (ICS) are considered first-line therapy for the management and control of patients with persistent asthma. Use of inhaled steroids has been associated with reduced airway responsiveness, improved lung function, diminished symptoms, and fewer exacerbations. However studies show considerable inter-subject variability in ICS response with only 33 per cent to 50 per cent of patients demonstrating substantial improvement in forced expiratory volume in 1 second (FEV1) following therapy. It has also been estimated that corticosteroid resistance accounts for half of all asthma-related health care costs. Therefore understanding the factors that contribute to corticosteroid resistance is both clinical and economically important. African-American patients, in particular, appear less likely to respond to corticosteroid therapy when compared with white patients. However, it is not currently known whether this difference results from genetic or environmental factors, or whether differences exist in inhaled steroid responsiveness (i.e., the recommended route of therapy). This question is of particular importance, since African-American patients suffer disproportionately from asthma-related complications. To date there have been studies examining potential mechanisms of corticosteroid responsiveness, but none have addressed inhaled corticosteroid responsiveness, nor were these studies designed to identify potentially causative genetic factors at a population-level. Therefore in this application we first plan to assess differences in inhaled corticosteroid responsiveness (i.e., improvement in FEV1) between African-American and white patients with asthma following 6 weeks of inhaled beclomethasone diproprionate (BD) treatment. Second, we will seek to identify genetic loci associated with ICS responsiveness in this cohort treated with BD for 6 weeks. The diversity of our cohort is a distinct advantage, as it allows us to use both association analysis and admixture mapping to jointly identify loci associated with steroid response. Next, we will take advantage of our ability to assess ICS exposure and clinical outcomes longitudinally in our patient population so as to assess for pharmacogenomic interactions on asthma exacerbations (i.e., asthma-related emergency department visits, asthma-related hospitalizations, and oral steroid bursts) in this same group. Lastly, we will validate observed drug x gene interactions on asthma exacerbations in a separate, larger cohort of patients with asthma. This latter group will also come from our screened asthma population and will comprise those for whom we have both DNA and clinical data (i.e., historic ICS exposure measures and clinical outcomes). Therefore, in this application we plan to identify a set of genetic polymorphisms associated with ICS responsiveness as defined by both an improvement in pulmonary function and an alteration in exacerbation-related clinical outcomes.