CYSLTR1 and asthma: Even though the gold standard of long-term asthma care is inhaled corticosteroid (ICS); LTRAs have their advantage of easy oral dose, and reducing long-term side effects of ICS.5 Current Global Initiative for Asthma (GINA) guidelines recommend LTRAs as a monotherapy in mild persistent asthma, as an add-on or alternative to increasing dose of ICS or adding a long-acting β2-agonist.6 Montelukast inhibits the actions of leukotriene D4 (LTD4) by reversibly binding on the cysteinyl leukotriene receptor CysLT1 in the lungs and bronchial tubes.