As corticosteroids inhibit and downregulate the expression of cyclooxygenase (COX)2 and subsequent PGD2 production20–22, we hypothesized that the continuation of standard-of-care corticosteroid treatment, as occurred in the majority of trials, may have decreased the effectiveness of DP2 antagonism in the treatment of asthma. This evidence concerns the gene HPGDS and asthma.